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Use of RCC pile, anchor bolt and geogrid for building construction on theunstable slope

Use of RCC pile, anchor bolt and geogrid for building construction on theunstable slope Rapid construction of buildings in urban area is creating lack of space available for new construction. This problem enforced to construct building on slope in hilly regions. However, the engineers and designers are concerned with the stability analysis of structures built on soil slopes, as it is difficult to achieve a uniform structural level on moun- tainous terrain. Also, it cannot be reduced to the same level of structural forms and part of base member may not be bound by an identical horizontal plane. The fundamental stability of the structure built on hill slope depends upon on its slope stability. Slope failure has been identified as one of the frequent devastating natural disasters that have claimed huge loss of property and lives. Therefore, in this research, “Phase 2 (2002)”, a Rocscience Finite Element (FE) program and “Slide”, a Rocscience limit equilibrium program were used to simulate and analyze a complex multi- staged model with RCC pile, Anchor Bolt and Geogrid for the stability analysis of slope. Bishop’s method was used to evaluate and analyze the factor of safety. Analysis of the two section (Section 1-1 and 2-2) of slope was taken into consideration for slope stability analysis. As per the analysis using the limit equilibrium approach, the factor of safety for existing slope at Section 1-1 and Section 1-1 was found to be 0.579 and 0.70 respectively. Moreover, it was found that the factor of safety of slope was increased significantly from 0.579 to 1.593 in Sections 1-1 and 0.70 to 1.319 in Section 2-2. In addition, the factor of safety of slope with strength reduction method is 1.408 and 1.05 for Sections 1 and 2 respectively after slope stabilization work in seismic condition. This shows that, the construction of buildings in slope terrain is possible, but it needs specialized excavation and slope protection work. RCC pile with anchor bolt and geogrid is one of the sustainable solutions for construction of structure in slope area. Keywords Slope stability, Strength reduction method, Limit equilibrium method, Factor of safety, RCC pile, Anchor bolt, Geogrid of settlement demands the use of slope terrain where Introduction we can construct safe structures after proper design and Considering the increased urbanization and hilly terrain structural analysis. The buildings on mountainous slopes of Nepal, there is a need to use modified methods in the cannot have same structural foundation and base as that field of engineering and use them to counter the growing of plain areas. Although the topography and structure of problem of settlement. In context of Nepal this problem the building in slope are distinctive, it is crucial to adapt to the mountainous terrain that is paramount. While *Correspondence: accompanied by irregularities in vertical and horizontal Sanjaya Kumar Jain planes, adjustment is tough. Thus, this emphasizes the gsgroup.sanju@gmail.com Department of Civil Engineering, Lincoln University College, Petaling intricate nature of seismic design and the uniqueness of Jaya, Malaysia the seismic response of such structures. Department of Civil Engineering and Architecture, Wuhan University Few research work are carried out in the field of build - of Technology, Wuhan, China Department of Civil Engineering, Institute of Engineering, Western ing’s seismic design in slope land area due to the limita- Region Campus, Pokhara, Nepal tion to comprehend the investigation parameters and © The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 2 of 19 Hill Hill slope slope (a) (b) Fig. 1 Building on flat ground (modified after Paul and Kumar 1997) Hill Hill slope slope Natural slope Natural slope Fig. 2 Building on slope ground (modified after Paul and Kumar 1997) earthquake damage assessment of such structures. There seismic condition in order to determine the suitability is a lack of organized or proper mechanism for con- of various construction configurations. Stability analysis ducting fundamental research on structural design and was conducted to calculate the factor of safety against unique issues with structures in mountain areas (Gör sliding failure, several building configurations on flat ter - et al. 2022, Parkash 2019). Even though there are no spe- rain and sloped ground are used (Paul and Kumar 1997); cific codes which helps an engineer design a structure on that are listed below: slope land, it provides great value once completed. Lack (i) Building on a flat ground e.g. regular framed build - of specific codes has led to various research works that ings, setback framed buildings as shown in Fig. 1 addresses different methods for slope stability which can (ii) Building on sloping ground e.g. stepback framed be adopted for the safe and sound construction of struc- buildings, stepback and setback framed buildings tures, executed with proper design/ analysis and use of as shown in Fig. 2 advancements engineering has achieved over this time (Kumar et al. 2021). The stability of the slope is the main factor that deter - Most building structures constructed in mountain mines the safety of the building constructed in slope area. areas require retaining structures (Wang et  al. 2021). A In unstable slope even structurally sound buildings can specific cognitive process is required to comprehend collapse. Therefore, it is imperative to do stability analysis the relationship between the retaining structure and the of the slope with surcharge loads under both static and building structure. Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 3 of 19 Fig. 3 Location map of the study area Slope failure is one of the most common natural hills/slope land areas, human settlement, and other disasters that can cause significant property loss and development initiatives has greatly contributed to human casualties. Several external factors, such as geo- an increase in slope failures in the mountain regions logical forces, weathering and erosion mechanisms, over time. Stabilization of a slope may depend on a and exacerbated anthropogenic activities contribute number of factors such as; its geometry, surface and to slope failure. The construction of road networks in groundwater condition, strength of materials and the Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 4 of 19 reason for stabilization. A number of techniques have Study area been developed to stabilize slopes considering differ - The study area is located in the Seti watershed ent above mentioned factors (Abramson et  al. 2001). of the Pokhara valley. The area has a longitude Pile have been used successfully in many situations to of 83º57′18.30’’E to 83º57′19.8’’ E and latitude of stabilize slopes (ANAGOSTOPOULOS et  al. 1992; 28 13′28.99’’ N to 28º13′26.81’’N and an elevation of Chen and Poulos 1997; Ito and Matsui 1975; Popescu 857–842  m. The watershed lies in the Pokhara Munic - 1991; Poulos 1995; Won et  al. 2005). Pile and anchor ipality, Kaski district of Gandaki Province, Nepal rods are considered to be effective solution for slopes (Fig.  3). The area is surrounded by High mountains in as they are easy to build, quick, require fewer projects the north and middle-range mountains in the south (Seyhan 2009). They are usually applied during protec - (Rimal et al. 2015). tion works for landslides and other geo hazards (Zhang et  al. 2016). Similarly, geogrids are also widely used for Geology soil reinforcement in slopes and embankments. (Mesut The Pokhara valley is a famous intermontane basin of et  al.). Therefore, the main objective of this research is Nepal [Bhandari et  al. 2021]. Diversely oriented ter- the slope stabilization using reinforced pile, anchor rod races, deep and narrow gorges with disappearing white and geogrid and construction of building in that stabi- rivers, immense cliffs, and blue lakes are the main con - lized slope. The study is focused on the construction of stituents of the basin landscape. The Pokhara valley building on a steep slope with three steps of cutting. lies in the core of Pokhara-Gorkha- Trishuli anticline. This type of research can give a useful suggestion for It has soft lacustrine sediment in its central part sur- construction on slopes in seismic zone like Nepal. rounded by hard rock geology. The central part of the Fig. 4 Geology of Pokhara valley (modified from Dhital 2015 and Bhandari et al. 2021) Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 5 of 19 Fig. 5 a Foundation plan (Sectional view of block building). b Construction at Section 1-1. c Construction at Section 1-1 Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 6 of 19 Fig. 6 Topographic map of survey contour boundary line Table 1 Soil parameters for analysis of slope stability Soil type Depth Soil unit weight (KN/m2) Cohesion, c (kPa) Angle of internal friction, ɸ (degree) Red soil with phylite gravel mix 3.0 18.25 0.43 36 Phylite rock 6.0 19.5 0.00 45 Brown fracture phylite rock > 6.5 19.00 Infinite strength valley has a lacustrine deposit of huge ‘paleo-pokhara The area of interest in this research belongs to the lake’ and several lakes deposit containing peat, sand, Kuncha Formation in the hill range (Fig.  4). Kuncha carbonaceous clay, sand gravel and boulders (Hagen Formation bedrock is covered with a residual and/ 1969). The Pokhara basin is divided into nine groups: or colluvial deposit. The Kuncha Formation basement Alluvial Deposit, Colluvial Pokhara Formation, Phewa rock is highly to moderately weathered phyllites vary- Formation, Ghachok Formation, Indi Khola Formation, ing from from few millimeters to several centimeters Tallakot Formation, Kuncha Formation (Koirala et  al. and medium to thickly bedded gritty quartzites varying 1996) Yamanaka et  al. (1982) as shown in the figure. from 5 cm to about 1 m. The direction of bedrock dips The Pleistocene deposits of Pokhara valley overlie the southwest facing slopes as in Kaon hill and the bedrock phyllites, meta sandstones, quartzites, and slates. is covered by around 1–3 m thick blanket (Koirala and Rimal 1996). Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 7 of 19 Site characteristics First the numerical analysis of slope without any stabil- The specific site research area is a construction site of ity measures and then with stability measures of anchor Hotel Barahi in Pokhara valley. The site has a Casino bolt, RCC bore pile and geogrid was performed. In this block building of Barahi Hotel with Mat Foundation. research, “Phase 2 (2002)”, a Rocscience Finite Element The study site is located on a steep slope with sur - program and “Slide”, a Rocscience Limit Equilibrium rounding hills. The sectional view of the building is programs were used to understand and simulate multi- shown in Fig. 5. staged model for stability analysis of slope of the study site. Materials and methods A direct way for determining a stress reduction fac- Topographic mapping, field survey and geotechnical tor (SRF) or factor of safety  that drives a slope to the investigation of soil sample of the project area was done point of absolute failure is the shear strength reduction for this research work. The sample were then tested (SSR) methodology of the Finite Element (FE) method in laboratory and according to lab test report and site for stability analysis of slope. The SSR methodology topography, slope stability analysis was performed by ensures that the slope’s materials have Mohr–Cou- Rocscience software (Phase 2 and Slide). lomb strength. The most commonly used failure crite - The topographical map prepared based on field survey rion in geotechnical engineering is the Mohr–Coulomb is shown in Fig. 6. strength envelope. This linear failure model differs from The laboratory tested geotechnical properties of both others in that it can be represented directly and con- soil and rock sample for slope stability analysis are tabu- cisely in both principal (s1-s3) and shear-normal (t-sn) lated in Table 1. stress spaces. The Mohr–Coulomb criterion’s popular - Using the field and laboratory test data, slope stabil - ity can be attributed to its simplicity, explicit repre- ity analysis is done. Limit Equilibrium method using sentation in both main and shear-normal stress space, Slide software and Finite Element Method using Phase 2 appropriate description of strength behavior for a software are used for the analysis of stability of the area. variety of materials, and simple to get parameters. The Fig. 7 Schematic diagram of Slope for FEM based simulation Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 8 of 19 equation below can be used to calculate the factored or Table 2 Material properties for anchor bolt decreased shear strength for Mohr–Coulomb material: Material Fe525/575 ′ ′ t c tan f Tensile strength, Mpa 525 = + (1) F F F Shear strength, Mpa 210 Diameter of Anchor, mm 25 It can also be written as: Cross section area, mm2 490.874 Tensile force, KN 257.709 = c ∗+tanf ∗ (2) where F = factor of safety; c’ = effective parameter of cohesion; t’ = effective shear strength; f’ = effective tan f internal frictional angle c∗= and f ∗= arc tan F F .   The following steps can be used to methodically seek for critical safety value F that pushes a once stable slope (F ≥ 1) to the brink of failure: Step 1: Developing an FE model of a slope, using the appropriate materials deformation and strength properties. Computing the model and recording overall deformation at maximum. Step 2: Increasing the value of F (or SRF) and calcu- lating factored Mohr Coulomb material parameters as described above. The slope model is updated after the new strength properties are entered. The overall Fig. 8 Uniaxial geogrid used in construction deformation at maximum is being noted. Step 3: Continuously reducing strength of the mate- rial until slope collapses by repeating step 2 with the center of the circular slip surfaces are satisfied, but the precise F increases until the Finite element model horizontal force equilibrium is not considered. that does not really yield to a conclusion. The factor The simplified analysis is as follows: of safety of slope will be the critical F value just past which failure occurs. ′ ′ ′ τ = c + σ tan φ (3) The process is same for a slope with less than 1 factor To find σ resolve forces on a vertical axis to obtain: of safety value, with an exception that fractional F values will be gradually dropped (resulting in increases in the 1 ′ ′ ′ ′ W − c + σ tan φ �X tan α − σ + u �X = 0 factored strength parameters) until the slope stabilizes. (4) The main benefit of SSR methodology is that it works with any FE analysis program currently available because it 1 ′ W − u�X − c �X tan α ′ F uses factored strength values as data into models (Fig.  7). ∴ σ = (5) �X(1 + (tan φ tan α)/F) Calculating the factored Mohr Coulomb strength param- eters is all that is necessary for the approach to be used in a Now, F = sum (maximum resisting forces around arc)/ slope analysis. sum (moving forces around arc) The simplified Bishop technique (Bishop 1955) is rec- ′ ′ ′ (c + σ tan φ )�X sec α ognized as an outstanding limit equilibrium approach for (6) computing the factors of safety of circular slip surfaces and W sin α has been applied extensively in slope stability analysis. In this method, the inter-slice forces are assumed to be hori- ′ ′ 1 c �X + (W − u�X) tan φ zontal, or vertical inter-slice forces are neglected, the ver- (7) tical force equilibrium and the moment equilibrium about W sin α Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 9 of 19 Table 3 Properties of geogrid material approach that takes into account the forces acting on slices’ sides. Property Units Value Bishop (1955), suggested that for the calculation of Raw material Polypropylene slope’s factor of safety, whole slope is divided into vertical Initial strength (ISO 10319) MD KN/m 200 slices and each of them is individually analyzed using cir- Initial Strength (ISO 10319) CD KN/m 50 cular failure analysis to get the individual slice safety fac- Initial strength at 5% strain (ISO 10319) MD KN/m 100 tor and summarized for overall factor of safety of slope. Strain at initial strength MD % 10 Stability measures RCC Pile sin αtanφ where, M = cos α + .τ = shear strength, The RCC bored pile is used for its load carrying capacity σ’ = normal stress, φ’ = angle of friction, W = Weight of in terms of lateral as well as axial load for heavy struc- slice, ∆X = width of slice and u = pore pressure ture on unstable slope. The bored pile has medium to To facilitate the analysis of slope stability for a large large diameter and it may be easy or difficult to trans - number of potential failure surfaces and a variety of con- port. For installation, high skilled manpower and sophis- ditions, computer programs are used. When compared ticated machine grade of concrete M25 and slump to the results of an ordinary method of slices, the Bishop 150–180  mm (IS 2911 Part1/Sec 1) and Reinforcement Method produces more realistic safety factors. The as per (IS1786:2008) is required. The cage reinforcement Bishop Method is a simplified approach that produces was done on the drilled hole and trimmer method was results for factor of  safety that are near to the correct used for concreting. solution, according to analysis using a more sophisticated Fig. 9 a Steep slope of construction Site, b Study area after cutting, c Ongoing construction on site, d Another view of ongoing construction of site Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 10 of 19 Table 4 Material properties for modelling Abdel-Mohti (2014), explained how RCC pile react and axial and lateral load interaction with soil. Seyhan (2009), Modeling Parameters Red soil with phylite gravel mix has explained about the method and process of RCC bore Elastic modulus 50000 Kpa piling technique. Poisson”s ratio 0.4 In this study, like any other civil engineering work, at Tensile strength 4 Kpa first the site was made accessible and was cleared, neces - Friction angle 36 sary cutting of the natural slope was done as per design Cohesion 0.43 to meet construction needs. Then, the work was com - Constitutive model Mohr coulomb failure criterion menced from the section one (as seen in Fig.  5a), where concrete piles of varying depth and diameter from 600 to 800 mm and 12 m to 20 m depth were bored into the ground. In total 52 nos of concrete piles were bored along Anchor bolt the Section 1 & 2 as seen in Fig.  5 with different lengths Anchor bolt is a device to transfer forces in given direc- from 12 to 20 m depth. The cut slope was stabilized using tion from structure to rock – medium. By anchoring, a rock anchor bolts of varying depth of 3  m to 4  m and compression force is delivered directly to the crucial joint surface dressing was done using high strength geogrid within the rock mass. The anchorage increases the inher - of 200/50 KNm. After that, the stabilization of Section 2 ent strength of the rock mass and helps in its ability to was completed in the same way. The construction work maintain itself against sliding by generating a compres- was commenced starting from bottom to top and simi- sive stress. lar work procedure was followed in Section  1 at 872  m Landslides, slips and rock-falls are some of the modes and Section  2 at 857  m as shown in Fig.  5b and c. The of movement of rocks beneath the gravitational influ - sequence of the state of construction site work in shown ence. The movement, sometimes can be extremely dam - in Fig.  9. The intact steep slope of project site can be aging or can even be disastrous. In highways, hydraulic seen in Fig. 9a. According to design, the slope was cut in engineering structures and foundations that rest on rock, desired slope shown in Fig. 9b. And ongoing construction it is imperative to assess the degree of stability of natural work with rcc pile, anchor bolt and geogrid was shown in slopes and also manmade slopes. Properties of Anchor Fig. 9c and d. bolt used in this project is below in Table 2. Analysis Geogrid The geotechnical properties of both soil and rock for Geogrid are engineered materials suitable for soil rein- slope stability analysis are taken from the laboratory test forcement for erosion control. Geogrid are manufactured data which is tabulated in Table 4. From the topographi- from polymer such as PET, Polyester Yarns (as per ASTM cal survey data, 2 critical sections are considered for the D2455, ASTM 4603 and ASTM D1248). There are dif - modeling of the slope. ferent apertures of various size and have strength in the The material properties of model are shown in Table  4. transverse and longitudinal direction. PET, HDPE and For vertical boundary, u = 0 and u is free and for hori- x y polyester geogrid maintain minimum UV resistance as zontal boundary; u = u = 0. Mohr–Coulomb failure cri- x y per ASTM D4355. The tensile and physical characteris - terion is used to simulate the model. The shear strength tics of the geogrid are improved by stretching in either reduction (SSR) methodology of Finite Element (FE) one, two or three directions. In this study, the uniaxial and the simplified Bishop method were used to analyze geogrid is used for surface protection with the properties the slope stability problem to gain insight into soil mass as below in Fig. 8 and Table 3. behavior, progressive failures and explicit modelling of discontinuities. In both approaches, the stability of cur- Sequence of construction method rent natural slope conditions was first assessed by analy - The construction methods with reinforced soil using cast sis and then, for cut slopes. in  situ bored RCC pile are well explained by Kocherz- We have numerically modelled the project site using henko and Suleymanova (2021) Zolotuchin et  al. (2018). FEM in static condition considering it as a continuum by Similarly, Kaewjuea et al. (2022) and Kocherzhenko et al. SSR approach. By determining the safety factor of natural (2021), has explained how RCC pile are tested and work slope (which demonstrated failure), post-disaster analysis on sloppy ground, increase the bearing capacity of rein- is carried out. While, by using FEM methodology, stress forced concrete piles by friction forces. Khodair and developed in the slope is determined to focus on probable Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 11 of 19 Fig. 10 Factor of safety of natural slope obtained from Bishops method for Section 1-1 failure. The Phase 2 analytical program was used to com - slope at Section  1-1 and Section  2-2 were obtained plete the task. FEM, a commonly used technique for respectively (as shown in Figs.  10 and 11). Then, the numerical modeling of slopes, operates on the tenet of cut slope was analyzed in which safety factor value was discretizing the entire design into a predetermined num- less than 1. After cutting slope, factor of safety of Sec- ber of components, allowing for continuous modification tion 1-1 and 2-2 is 0.539 and 0.799 (as shown in Figs. 12 in material properties. The slope design has been discre - and 13). Since Bishop’s method showed safety factor tized using three triangle shaped  plane strain elements value less than 1, the slope was prone to failure which in two dimensions. It has been decided to use the SSR was visible in the site. The existing soil was strength - technique using non-failure criteria. It is considered that ened using a combination of RCC pile, Anchor Bolt, the failure mechanism of the slope is closely linked to the and geogrid to increase the factor of safety and improve growth of shear strain since the rupture surface and the slope stability. Further, after protection work with RCC failure zone’s maximum shear strain coincide. pile, anchor bolt and geogrid were applied and stability was checked. Results and discussion It was found that the slope’s safety factor was increased The slope was evaluated for a factor of safety, analyzed from 0.579 to 1.593 in Section  1-1 and 0.70 to 1.319 in as per Bishop’s method, as mentioned in earlier sec- Section  2-2 obtained from limit equilibrium method tions. The safety factor of 0.579 and 0.70 for existing (Figs.  14 and 15). In addition, safety factor with strength Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 12 of 19 Fig. 11 Factor of safety of natural slope obtained from Bishops method for Section 2-2 reduction method is 1.408 and 1.05 for Sections 1-1 and depend on the number of factors such as; its geometry, 2-2 respectively, after slope stabilization work (Fig.  16 surface and ground water conditions, strength of mate- and 17). All these results are shown in tabular form in rials and reasons for stabilization. Therefore, number of Table 5. techniques are developed so far to stabilize slopes. The slope was analyzed with the combination of RCC In this research; the existing slope are known to have pile, anchor bolt and geogrid and it was observed that the the safety factor below the value 1 from Bishops method. factor of safety was improved and obtained to be greater Also, after maintaining slope, factor of slope was still than 1. less than 1 from all methods. And after structure load Failure of mass movements often result in significant and slope protection work with rcc pile, anchor bolt and loss of human lives and property. It is recognized that geogrid, safety factor was greater than 1 from both SSR maintaining the stability of both natural and artificial method in Phase and Bishops Method in Slide. slopes continues to be a basic problem in geotechnical There are various methods for slope protection for engineering. There is no universally accepted method for building construction in slope ground. In recent years, the prevention or correction of slope failures. Each fail- RCC pile combined with anchor bolt and geogrid ure is unique and should be considered based on unique are being used in various projects of structure con- inherent characteristics. Stabilization of slope may struction in slope ground. RCC piles are foundation Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 13 of 19 Fig. 12 Factor of safety of cutting plane obtained from Bishops method for Section 1-1 pile used for the building construction in mountain- Table 5 Factor of safety by the limit equilibrium method and by ous areas. And for slope protection, anchor bolt and the finite element analysis geogrid are widely used. In this research, concrete Factor of safety Section 1-1 Section 2-2 piles of varying depth and diameter from 600 to 800  mm and 12  m to 20  m depth were driven into the Bishop of existing slope 0.579 0.70 ground. In total, 52 concrete piles were driven with Bishop of cutting Slope 0.531 0.799 different lengths from 12 to 20 m depth. The cut slope Bishop of after slope stabilization 1.539 1.319 was stabilized using anchor bolts of varying depth of SSR of after slope stabilization 1.408 1.05 3  m to 4  m and surface dressing was done using high strength geogrid of 200/50 kNm. The construction work was commenced starting from bottom to top. This research finding suggest that RCC pile with This research has attempted to validate the solution anchor bolt and geogrid shows good results in con- for construction of building in slope ground. struction of building in slope ground as well as slope stabilization work. RCC pile was used to take lateral Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 14 of 19 Fig. 13 Factor of safety of cutting pane obtained from Bishops method for Section 2-2 and shear force of structure, anchor bolt and geogrid was not considered but for drainage system, semi was used for retaining structure as well as to increase perforated HDP pile of 6inch diameter was laid in soil strength  for shear. According to soil investigation 1:2 gradient over coarse aggregates and then pile was work performed in site, water table was not found, wrapped with geotextile and sand was filled over it in hence there are limitation in this study as in analysis each cut slope. Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 15 of 19 Fig. 14 Factor of safety after slope stabilization work Section 1-1 measures. The project one completed adds a great value Conclusion to the owner considering the terrain, especially in the Even though building a structure on a slope land has its context of Nepal. The owner will appreciate the scen - own challenges and difficulties, it is possible to execute ery, the geomorphology and landscapes, natural lighting, a project with safe design/ analysis and slope stability Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 16 of 19 Fig. 15 Factor of safety after slope stabilization work Section 2-2 privacy, and space. This illustrates why so many of the deeper excavation by specialized excavation process to world’s most desirable residences are constructed on ensure that the building is in accordance to code and safe slopes. However, it necessitates complicated foundation to inhabit. systems, which add to the cost and length of the con- The limit equilibrium method of analysis was widely struction process. The cost is often more than that of an used due to its clear physical meaning and simple cal- entire house on flat ground. It requires more concrete, culation. At present, with development in the finite element method, the strength reduction method is Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 17 of 19 Fig. 16 Verification with Shear strength reduction (SSR) method Section 1-1 gradually recognized to assess the safety factor of slope. can be one of the sustainable solutions among oth- In this paper, the safety factor of the slope is firstly cal - ers to address the issue. Following, the safety factor is culated by Bishop’s method, which is then compared increased using RCC pile, anchor pile and geogrid as with the safety factor obtained from the strength reduc- reinforcement. For construction of structure in moun- tion method by FEM. Thus, from LEM and FEM, factor tainous area like Nepal, a combination of RCC pile, of safety were found to be greater than 1. anchor bolt and geogrid can be an effective solution; The construction of building in slope ground is pos - are the concluding remarks can be drawn from this sible, but it needs specialized excavation and slope pro- work. tection work; RCC pile with anchor bolt and geogrid Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 18 of 19 Fig. 17 Verification with Shear strength reduction (SSR) method Section 2-2 Acknowledgements Bhandari C, Dahal RK, Timilsina M (2021) Disaster risk understanding of local The Authors are really thankful to Dr. Purosottam Dangol, Mr. Prakash Sing people after the 2015 Gorkha Earthquake in Pokhara City, Nepal. Geoen- Rawal and the Hotel Barahi for their help in this research work. Authors also viron Disast 8(1):1–19. https:// doi. org/ 10. 1186/ s40677- 020- 00173-9 want to appreciate every helping hand to complete this research work. Bishop AW (1955) The use of the slip circle in the stability analysis of slopes. Geotechnique 5(1):7–17 Author contributions Chen L, Poulos H (1997) Piles subjected to lateral soil movements. J Geotech SKJ was involved in the data collection in field, data analysis, simulations and Geoenviron Eng 123(9):802–811 writing the manuscript. And all other author contributed in data analysis, Dhital MR (2015) Geology of the Nepal Himalaya: regional perspective of simulations and writing the paper. All authors read and approved by the final the classic collided orogen. Springer, Berlin.https:// doi. org/ 10. 1007/ manuscript.978-3- 319- 02496-7 Hagen T (1969) Report on the geological survey of Nepal: preliminary Availability of data and materials reconnaissance. Denkschriften Der Schweizerischen Naturforschenden The most of the data is collected from field work and simulations. The pub - Gesellschaft Memoires De La Societe Helvetique Des Sciences lished studies that are referenced in the manuscript use some of the data that Naturelles 84(1):185 were created or examined throughout this research. Ito T, Matsui T (1975) Methods to estimate lateral force acting on stabilizing piles. Soils Found 15(4):43–59 Kaewjuea W, Shaingchin S, Khamtip W, Chompoorat T, Chaimahawan P Declarations (2022) Lateral loading test of reinforced concrete bored pile in stiff clay and near slope. Eng J 26(3):29–40 Competing interests Khodair Y, Abdel-Mohti A (2014) Numerical analysis of pile–soil interaction The authors declare no competing interests. under axial and lateral loads. Int J Concr Struct Mater 8(3):239–249 Koirala A, Rimal L (1996) Geological hazards in Pokhara valley, western Competing interest Nepal. J Nepal Geol Soc 14:99–108 The authors claim to have no conflicts of interest. Kumar JS, Nusari MS, Purushotam D, Prasad AI, Rajyaswori S (2021) Eec ff tive - ness of geocell wall, geogrid and micropile anchors for mitigation of unstable slopes. Geoenviron Disasters 8(1):1–15 Received: 10 February 2023 Accepted: 8 May 2023 Paul D, Kumar S (1997) Stability analysis of slope with building loads. Soil Dyn Earthq Eng 16(6):395–405 Poulos HG (1995) Design of reinforcing piles to increase slope stability. Can Geotech J 32(5):808–818 Rimal B, Baral H, Stork NE, Paudyal K, Rijal S (2015) Growing city and rapid References land use transition: assessing multiple hazards and risks in the Pokhara Abramson LW, Lee TS, Sharma S, Boyce GM (2001) Slope stability and stabiliza- valley. Nepal Land 4(4):957–978 tion methods. Wiley, USA Seyhan F (2009) Stability analysis of pile-slope system. Sci Res Essays 4(9):842–852 Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 19 of 19 Wang X, Shrestha R, Li X, Mandal AK (2021) Design theory and method of geo- synthetic reinforced soil retaining wall combined with a gravity retaining wall or full height rigid facing. Geotech Geol Eng 39(3):2075–2086 Won J, You K, Jeong S, Kim S (2005) Coupled effects in stability analysis of pile– slope systems. Comput Geotech 32(4):304–315 Yamanaka H, Yoshida M, Arrita K (1982) Terrace landforms and quaternary deposit arounf Pokhara valley, central Nepal. J Nepal Geol Soc 2:113–142 ANagostopoulos C, Hada M, Fukuoka M (1992) Piles as landslide countermeas- ures-model study. International symposium on landslides Kocherzhenko V, Suleymanova L & Kocherzhenko A (2021) Innovative pile technologies in modern foundation construction. IOP conference series: materials science and engineering Kocherzhenko V, & Suleymanova L (2021) Methods for the construction of lowered structures and pile foundations. E3S web of conferences Koirala A, Rimal L, Sikrikar S, Pradhananga U, Pradhan P, HAnisch S, Busch K (1996) Engineering and environmental geological map of Pokhara valley (1: 50000). Depart Mines Geol Cooperat BGR: Kathmandu, Nepal Gör M, Taher NR, Aksoy HS, Awlla HA (2022) Eec ff t of Geogrid Inclusion on the Slope Stability. In Proceedings of the 5th International European Conference on Interdisciplinary Scientific Research, Valencia, Spain, 28–29 January 2022; pp. 275–286 Parkash S (2019) Landslide preparedness guidelines for safety of buildings on slopes; published by national institute of disaster management. Ministry of home affairs, Government of India, New Delhi, 110001, India, 80 Popescu M (1991) Landslide control by means of a row of piles: Keynote paper. Slope stability engineering developments and applications: proceedings of the international conference on slope stability organized by the Insti- tution of Civil Engineers and held on the Isle of wight on 15–18 Apr 1991 Zhang R, Zhao J, & Wang G (2016) Stability analysis of anchored soil slope based on finite element limit equilibrium method. Mathemat Probl Eng Zolotuchin S, Novikova K, & Kim M (2018) New method for the construc- tion of pile foundations in low-rise constructions using micro-piles in the knocked-out wells. IOP conference series: materials science and engineering Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in pub- lished maps and institutional affiliations. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geoenvironmental Disasters Springer Journals

Use of RCC pile, anchor bolt and geogrid for building construction on theunstable slope

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Abstract

Rapid construction of buildings in urban area is creating lack of space available for new construction. This problem enforced to construct building on slope in hilly regions. However, the engineers and designers are concerned with the stability analysis of structures built on soil slopes, as it is difficult to achieve a uniform structural level on moun- tainous terrain. Also, it cannot be reduced to the same level of structural forms and part of base member may not be bound by an identical horizontal plane. The fundamental stability of the structure built on hill slope depends upon on its slope stability. Slope failure has been identified as one of the frequent devastating natural disasters that have claimed huge loss of property and lives. Therefore, in this research, “Phase 2 (2002)”, a Rocscience Finite Element (FE) program and “Slide”, a Rocscience limit equilibrium program were used to simulate and analyze a complex multi- staged model with RCC pile, Anchor Bolt and Geogrid for the stability analysis of slope. Bishop’s method was used to evaluate and analyze the factor of safety. Analysis of the two section (Section 1-1 and 2-2) of slope was taken into consideration for slope stability analysis. As per the analysis using the limit equilibrium approach, the factor of safety for existing slope at Section 1-1 and Section 1-1 was found to be 0.579 and 0.70 respectively. Moreover, it was found that the factor of safety of slope was increased significantly from 0.579 to 1.593 in Sections 1-1 and 0.70 to 1.319 in Section 2-2. In addition, the factor of safety of slope with strength reduction method is 1.408 and 1.05 for Sections 1 and 2 respectively after slope stabilization work in seismic condition. This shows that, the construction of buildings in slope terrain is possible, but it needs specialized excavation and slope protection work. RCC pile with anchor bolt and geogrid is one of the sustainable solutions for construction of structure in slope area. Keywords Slope stability, Strength reduction method, Limit equilibrium method, Factor of safety, RCC pile, Anchor bolt, Geogrid of settlement demands the use of slope terrain where Introduction we can construct safe structures after proper design and Considering the increased urbanization and hilly terrain structural analysis. The buildings on mountainous slopes of Nepal, there is a need to use modified methods in the cannot have same structural foundation and base as that field of engineering and use them to counter the growing of plain areas. Although the topography and structure of problem of settlement. In context of Nepal this problem the building in slope are distinctive, it is crucial to adapt to the mountainous terrain that is paramount. While *Correspondence: accompanied by irregularities in vertical and horizontal Sanjaya Kumar Jain planes, adjustment is tough. Thus, this emphasizes the gsgroup.sanju@gmail.com Department of Civil Engineering, Lincoln University College, Petaling intricate nature of seismic design and the uniqueness of Jaya, Malaysia the seismic response of such structures. Department of Civil Engineering and Architecture, Wuhan University Few research work are carried out in the field of build - of Technology, Wuhan, China Department of Civil Engineering, Institute of Engineering, Western ing’s seismic design in slope land area due to the limita- Region Campus, Pokhara, Nepal tion to comprehend the investigation parameters and © The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 2 of 19 Hill Hill slope slope (a) (b) Fig. 1 Building on flat ground (modified after Paul and Kumar 1997) Hill Hill slope slope Natural slope Natural slope Fig. 2 Building on slope ground (modified after Paul and Kumar 1997) earthquake damage assessment of such structures. There seismic condition in order to determine the suitability is a lack of organized or proper mechanism for con- of various construction configurations. Stability analysis ducting fundamental research on structural design and was conducted to calculate the factor of safety against unique issues with structures in mountain areas (Gör sliding failure, several building configurations on flat ter - et al. 2022, Parkash 2019). Even though there are no spe- rain and sloped ground are used (Paul and Kumar 1997); cific codes which helps an engineer design a structure on that are listed below: slope land, it provides great value once completed. Lack (i) Building on a flat ground e.g. regular framed build - of specific codes has led to various research works that ings, setback framed buildings as shown in Fig. 1 addresses different methods for slope stability which can (ii) Building on sloping ground e.g. stepback framed be adopted for the safe and sound construction of struc- buildings, stepback and setback framed buildings tures, executed with proper design/ analysis and use of as shown in Fig. 2 advancements engineering has achieved over this time (Kumar et al. 2021). The stability of the slope is the main factor that deter - Most building structures constructed in mountain mines the safety of the building constructed in slope area. areas require retaining structures (Wang et  al. 2021). A In unstable slope even structurally sound buildings can specific cognitive process is required to comprehend collapse. Therefore, it is imperative to do stability analysis the relationship between the retaining structure and the of the slope with surcharge loads under both static and building structure. Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 3 of 19 Fig. 3 Location map of the study area Slope failure is one of the most common natural hills/slope land areas, human settlement, and other disasters that can cause significant property loss and development initiatives has greatly contributed to human casualties. Several external factors, such as geo- an increase in slope failures in the mountain regions logical forces, weathering and erosion mechanisms, over time. Stabilization of a slope may depend on a and exacerbated anthropogenic activities contribute number of factors such as; its geometry, surface and to slope failure. The construction of road networks in groundwater condition, strength of materials and the Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 4 of 19 reason for stabilization. A number of techniques have Study area been developed to stabilize slopes considering differ - The study area is located in the Seti watershed ent above mentioned factors (Abramson et  al. 2001). of the Pokhara valley. The area has a longitude Pile have been used successfully in many situations to of 83º57′18.30’’E to 83º57′19.8’’ E and latitude of stabilize slopes (ANAGOSTOPOULOS et  al. 1992; 28 13′28.99’’ N to 28º13′26.81’’N and an elevation of Chen and Poulos 1997; Ito and Matsui 1975; Popescu 857–842  m. The watershed lies in the Pokhara Munic - 1991; Poulos 1995; Won et  al. 2005). Pile and anchor ipality, Kaski district of Gandaki Province, Nepal rods are considered to be effective solution for slopes (Fig.  3). The area is surrounded by High mountains in as they are easy to build, quick, require fewer projects the north and middle-range mountains in the south (Seyhan 2009). They are usually applied during protec - (Rimal et al. 2015). tion works for landslides and other geo hazards (Zhang et  al. 2016). Similarly, geogrids are also widely used for Geology soil reinforcement in slopes and embankments. (Mesut The Pokhara valley is a famous intermontane basin of et  al.). Therefore, the main objective of this research is Nepal [Bhandari et  al. 2021]. Diversely oriented ter- the slope stabilization using reinforced pile, anchor rod races, deep and narrow gorges with disappearing white and geogrid and construction of building in that stabi- rivers, immense cliffs, and blue lakes are the main con - lized slope. The study is focused on the construction of stituents of the basin landscape. The Pokhara valley building on a steep slope with three steps of cutting. lies in the core of Pokhara-Gorkha- Trishuli anticline. This type of research can give a useful suggestion for It has soft lacustrine sediment in its central part sur- construction on slopes in seismic zone like Nepal. rounded by hard rock geology. The central part of the Fig. 4 Geology of Pokhara valley (modified from Dhital 2015 and Bhandari et al. 2021) Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 5 of 19 Fig. 5 a Foundation plan (Sectional view of block building). b Construction at Section 1-1. c Construction at Section 1-1 Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 6 of 19 Fig. 6 Topographic map of survey contour boundary line Table 1 Soil parameters for analysis of slope stability Soil type Depth Soil unit weight (KN/m2) Cohesion, c (kPa) Angle of internal friction, ɸ (degree) Red soil with phylite gravel mix 3.0 18.25 0.43 36 Phylite rock 6.0 19.5 0.00 45 Brown fracture phylite rock > 6.5 19.00 Infinite strength valley has a lacustrine deposit of huge ‘paleo-pokhara The area of interest in this research belongs to the lake’ and several lakes deposit containing peat, sand, Kuncha Formation in the hill range (Fig.  4). Kuncha carbonaceous clay, sand gravel and boulders (Hagen Formation bedrock is covered with a residual and/ 1969). The Pokhara basin is divided into nine groups: or colluvial deposit. The Kuncha Formation basement Alluvial Deposit, Colluvial Pokhara Formation, Phewa rock is highly to moderately weathered phyllites vary- Formation, Ghachok Formation, Indi Khola Formation, ing from from few millimeters to several centimeters Tallakot Formation, Kuncha Formation (Koirala et  al. and medium to thickly bedded gritty quartzites varying 1996) Yamanaka et  al. (1982) as shown in the figure. from 5 cm to about 1 m. The direction of bedrock dips The Pleistocene deposits of Pokhara valley overlie the southwest facing slopes as in Kaon hill and the bedrock phyllites, meta sandstones, quartzites, and slates. is covered by around 1–3 m thick blanket (Koirala and Rimal 1996). Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 7 of 19 Site characteristics First the numerical analysis of slope without any stabil- The specific site research area is a construction site of ity measures and then with stability measures of anchor Hotel Barahi in Pokhara valley. The site has a Casino bolt, RCC bore pile and geogrid was performed. In this block building of Barahi Hotel with Mat Foundation. research, “Phase 2 (2002)”, a Rocscience Finite Element The study site is located on a steep slope with sur - program and “Slide”, a Rocscience Limit Equilibrium rounding hills. The sectional view of the building is programs were used to understand and simulate multi- shown in Fig. 5. staged model for stability analysis of slope of the study site. Materials and methods A direct way for determining a stress reduction fac- Topographic mapping, field survey and geotechnical tor (SRF) or factor of safety  that drives a slope to the investigation of soil sample of the project area was done point of absolute failure is the shear strength reduction for this research work. The sample were then tested (SSR) methodology of the Finite Element (FE) method in laboratory and according to lab test report and site for stability analysis of slope. The SSR methodology topography, slope stability analysis was performed by ensures that the slope’s materials have Mohr–Cou- Rocscience software (Phase 2 and Slide). lomb strength. The most commonly used failure crite - The topographical map prepared based on field survey rion in geotechnical engineering is the Mohr–Coulomb is shown in Fig. 6. strength envelope. This linear failure model differs from The laboratory tested geotechnical properties of both others in that it can be represented directly and con- soil and rock sample for slope stability analysis are tabu- cisely in both principal (s1-s3) and shear-normal (t-sn) lated in Table 1. stress spaces. The Mohr–Coulomb criterion’s popular - Using the field and laboratory test data, slope stabil - ity can be attributed to its simplicity, explicit repre- ity analysis is done. Limit Equilibrium method using sentation in both main and shear-normal stress space, Slide software and Finite Element Method using Phase 2 appropriate description of strength behavior for a software are used for the analysis of stability of the area. variety of materials, and simple to get parameters. The Fig. 7 Schematic diagram of Slope for FEM based simulation Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 8 of 19 equation below can be used to calculate the factored or Table 2 Material properties for anchor bolt decreased shear strength for Mohr–Coulomb material: Material Fe525/575 ′ ′ t c tan f Tensile strength, Mpa 525 = + (1) F F F Shear strength, Mpa 210 Diameter of Anchor, mm 25 It can also be written as: Cross section area, mm2 490.874 Tensile force, KN 257.709 = c ∗+tanf ∗ (2) where F = factor of safety; c’ = effective parameter of cohesion; t’ = effective shear strength; f’ = effective tan f internal frictional angle c∗= and f ∗= arc tan F F .   The following steps can be used to methodically seek for critical safety value F that pushes a once stable slope (F ≥ 1) to the brink of failure: Step 1: Developing an FE model of a slope, using the appropriate materials deformation and strength properties. Computing the model and recording overall deformation at maximum. Step 2: Increasing the value of F (or SRF) and calcu- lating factored Mohr Coulomb material parameters as described above. The slope model is updated after the new strength properties are entered. The overall Fig. 8 Uniaxial geogrid used in construction deformation at maximum is being noted. Step 3: Continuously reducing strength of the mate- rial until slope collapses by repeating step 2 with the center of the circular slip surfaces are satisfied, but the precise F increases until the Finite element model horizontal force equilibrium is not considered. that does not really yield to a conclusion. The factor The simplified analysis is as follows: of safety of slope will be the critical F value just past which failure occurs. ′ ′ ′ τ = c + σ tan φ (3) The process is same for a slope with less than 1 factor To find σ resolve forces on a vertical axis to obtain: of safety value, with an exception that fractional F values will be gradually dropped (resulting in increases in the 1 ′ ′ ′ ′ W − c + σ tan φ �X tan α − σ + u �X = 0 factored strength parameters) until the slope stabilizes. (4) The main benefit of SSR methodology is that it works with any FE analysis program currently available because it 1 ′ W − u�X − c �X tan α ′ F uses factored strength values as data into models (Fig.  7). ∴ σ = (5) �X(1 + (tan φ tan α)/F) Calculating the factored Mohr Coulomb strength param- eters is all that is necessary for the approach to be used in a Now, F = sum (maximum resisting forces around arc)/ slope analysis. sum (moving forces around arc) The simplified Bishop technique (Bishop 1955) is rec- ′ ′ ′ (c + σ tan φ )�X sec α ognized as an outstanding limit equilibrium approach for (6) computing the factors of safety of circular slip surfaces and W sin α has been applied extensively in slope stability analysis. In this method, the inter-slice forces are assumed to be hori- ′ ′ 1 c �X + (W − u�X) tan φ zontal, or vertical inter-slice forces are neglected, the ver- (7) tical force equilibrium and the moment equilibrium about W sin α Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 9 of 19 Table 3 Properties of geogrid material approach that takes into account the forces acting on slices’ sides. Property Units Value Bishop (1955), suggested that for the calculation of Raw material Polypropylene slope’s factor of safety, whole slope is divided into vertical Initial strength (ISO 10319) MD KN/m 200 slices and each of them is individually analyzed using cir- Initial Strength (ISO 10319) CD KN/m 50 cular failure analysis to get the individual slice safety fac- Initial strength at 5% strain (ISO 10319) MD KN/m 100 tor and summarized for overall factor of safety of slope. Strain at initial strength MD % 10 Stability measures RCC Pile sin αtanφ where, M = cos α + .τ = shear strength, The RCC bored pile is used for its load carrying capacity σ’ = normal stress, φ’ = angle of friction, W = Weight of in terms of lateral as well as axial load for heavy struc- slice, ∆X = width of slice and u = pore pressure ture on unstable slope. The bored pile has medium to To facilitate the analysis of slope stability for a large large diameter and it may be easy or difficult to trans - number of potential failure surfaces and a variety of con- port. For installation, high skilled manpower and sophis- ditions, computer programs are used. When compared ticated machine grade of concrete M25 and slump to the results of an ordinary method of slices, the Bishop 150–180  mm (IS 2911 Part1/Sec 1) and Reinforcement Method produces more realistic safety factors. The as per (IS1786:2008) is required. The cage reinforcement Bishop Method is a simplified approach that produces was done on the drilled hole and trimmer method was results for factor of  safety that are near to the correct used for concreting. solution, according to analysis using a more sophisticated Fig. 9 a Steep slope of construction Site, b Study area after cutting, c Ongoing construction on site, d Another view of ongoing construction of site Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 10 of 19 Table 4 Material properties for modelling Abdel-Mohti (2014), explained how RCC pile react and axial and lateral load interaction with soil. Seyhan (2009), Modeling Parameters Red soil with phylite gravel mix has explained about the method and process of RCC bore Elastic modulus 50000 Kpa piling technique. Poisson”s ratio 0.4 In this study, like any other civil engineering work, at Tensile strength 4 Kpa first the site was made accessible and was cleared, neces - Friction angle 36 sary cutting of the natural slope was done as per design Cohesion 0.43 to meet construction needs. Then, the work was com - Constitutive model Mohr coulomb failure criterion menced from the section one (as seen in Fig.  5a), where concrete piles of varying depth and diameter from 600 to 800 mm and 12 m to 20 m depth were bored into the ground. In total 52 nos of concrete piles were bored along Anchor bolt the Section 1 & 2 as seen in Fig.  5 with different lengths Anchor bolt is a device to transfer forces in given direc- from 12 to 20 m depth. The cut slope was stabilized using tion from structure to rock – medium. By anchoring, a rock anchor bolts of varying depth of 3  m to 4  m and compression force is delivered directly to the crucial joint surface dressing was done using high strength geogrid within the rock mass. The anchorage increases the inher - of 200/50 KNm. After that, the stabilization of Section 2 ent strength of the rock mass and helps in its ability to was completed in the same way. The construction work maintain itself against sliding by generating a compres- was commenced starting from bottom to top and simi- sive stress. lar work procedure was followed in Section  1 at 872  m Landslides, slips and rock-falls are some of the modes and Section  2 at 857  m as shown in Fig.  5b and c. The of movement of rocks beneath the gravitational influ - sequence of the state of construction site work in shown ence. The movement, sometimes can be extremely dam - in Fig.  9. The intact steep slope of project site can be aging or can even be disastrous. In highways, hydraulic seen in Fig. 9a. According to design, the slope was cut in engineering structures and foundations that rest on rock, desired slope shown in Fig. 9b. And ongoing construction it is imperative to assess the degree of stability of natural work with rcc pile, anchor bolt and geogrid was shown in slopes and also manmade slopes. Properties of Anchor Fig. 9c and d. bolt used in this project is below in Table 2. Analysis Geogrid The geotechnical properties of both soil and rock for Geogrid are engineered materials suitable for soil rein- slope stability analysis are taken from the laboratory test forcement for erosion control. Geogrid are manufactured data which is tabulated in Table 4. From the topographi- from polymer such as PET, Polyester Yarns (as per ASTM cal survey data, 2 critical sections are considered for the D2455, ASTM 4603 and ASTM D1248). There are dif - modeling of the slope. ferent apertures of various size and have strength in the The material properties of model are shown in Table  4. transverse and longitudinal direction. PET, HDPE and For vertical boundary, u = 0 and u is free and for hori- x y polyester geogrid maintain minimum UV resistance as zontal boundary; u = u = 0. Mohr–Coulomb failure cri- x y per ASTM D4355. The tensile and physical characteris - terion is used to simulate the model. The shear strength tics of the geogrid are improved by stretching in either reduction (SSR) methodology of Finite Element (FE) one, two or three directions. In this study, the uniaxial and the simplified Bishop method were used to analyze geogrid is used for surface protection with the properties the slope stability problem to gain insight into soil mass as below in Fig. 8 and Table 3. behavior, progressive failures and explicit modelling of discontinuities. In both approaches, the stability of cur- Sequence of construction method rent natural slope conditions was first assessed by analy - The construction methods with reinforced soil using cast sis and then, for cut slopes. in  situ bored RCC pile are well explained by Kocherz- We have numerically modelled the project site using henko and Suleymanova (2021) Zolotuchin et  al. (2018). FEM in static condition considering it as a continuum by Similarly, Kaewjuea et al. (2022) and Kocherzhenko et al. SSR approach. By determining the safety factor of natural (2021), has explained how RCC pile are tested and work slope (which demonstrated failure), post-disaster analysis on sloppy ground, increase the bearing capacity of rein- is carried out. While, by using FEM methodology, stress forced concrete piles by friction forces. Khodair and developed in the slope is determined to focus on probable Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 11 of 19 Fig. 10 Factor of safety of natural slope obtained from Bishops method for Section 1-1 failure. The Phase 2 analytical program was used to com - slope at Section  1-1 and Section  2-2 were obtained plete the task. FEM, a commonly used technique for respectively (as shown in Figs.  10 and 11). Then, the numerical modeling of slopes, operates on the tenet of cut slope was analyzed in which safety factor value was discretizing the entire design into a predetermined num- less than 1. After cutting slope, factor of safety of Sec- ber of components, allowing for continuous modification tion 1-1 and 2-2 is 0.539 and 0.799 (as shown in Figs. 12 in material properties. The slope design has been discre - and 13). Since Bishop’s method showed safety factor tized using three triangle shaped  plane strain elements value less than 1, the slope was prone to failure which in two dimensions. It has been decided to use the SSR was visible in the site. The existing soil was strength - technique using non-failure criteria. It is considered that ened using a combination of RCC pile, Anchor Bolt, the failure mechanism of the slope is closely linked to the and geogrid to increase the factor of safety and improve growth of shear strain since the rupture surface and the slope stability. Further, after protection work with RCC failure zone’s maximum shear strain coincide. pile, anchor bolt and geogrid were applied and stability was checked. Results and discussion It was found that the slope’s safety factor was increased The slope was evaluated for a factor of safety, analyzed from 0.579 to 1.593 in Section  1-1 and 0.70 to 1.319 in as per Bishop’s method, as mentioned in earlier sec- Section  2-2 obtained from limit equilibrium method tions. The safety factor of 0.579 and 0.70 for existing (Figs.  14 and 15). In addition, safety factor with strength Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 12 of 19 Fig. 11 Factor of safety of natural slope obtained from Bishops method for Section 2-2 reduction method is 1.408 and 1.05 for Sections 1-1 and depend on the number of factors such as; its geometry, 2-2 respectively, after slope stabilization work (Fig.  16 surface and ground water conditions, strength of mate- and 17). All these results are shown in tabular form in rials and reasons for stabilization. Therefore, number of Table 5. techniques are developed so far to stabilize slopes. The slope was analyzed with the combination of RCC In this research; the existing slope are known to have pile, anchor bolt and geogrid and it was observed that the the safety factor below the value 1 from Bishops method. factor of safety was improved and obtained to be greater Also, after maintaining slope, factor of slope was still than 1. less than 1 from all methods. And after structure load Failure of mass movements often result in significant and slope protection work with rcc pile, anchor bolt and loss of human lives and property. It is recognized that geogrid, safety factor was greater than 1 from both SSR maintaining the stability of both natural and artificial method in Phase and Bishops Method in Slide. slopes continues to be a basic problem in geotechnical There are various methods for slope protection for engineering. There is no universally accepted method for building construction in slope ground. In recent years, the prevention or correction of slope failures. Each fail- RCC pile combined with anchor bolt and geogrid ure is unique and should be considered based on unique are being used in various projects of structure con- inherent characteristics. Stabilization of slope may struction in slope ground. RCC piles are foundation Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 13 of 19 Fig. 12 Factor of safety of cutting plane obtained from Bishops method for Section 1-1 pile used for the building construction in mountain- Table 5 Factor of safety by the limit equilibrium method and by ous areas. And for slope protection, anchor bolt and the finite element analysis geogrid are widely used. In this research, concrete Factor of safety Section 1-1 Section 2-2 piles of varying depth and diameter from 600 to 800  mm and 12  m to 20  m depth were driven into the Bishop of existing slope 0.579 0.70 ground. In total, 52 concrete piles were driven with Bishop of cutting Slope 0.531 0.799 different lengths from 12 to 20 m depth. The cut slope Bishop of after slope stabilization 1.539 1.319 was stabilized using anchor bolts of varying depth of SSR of after slope stabilization 1.408 1.05 3  m to 4  m and surface dressing was done using high strength geogrid of 200/50 kNm. The construction work was commenced starting from bottom to top. This research finding suggest that RCC pile with This research has attempted to validate the solution anchor bolt and geogrid shows good results in con- for construction of building in slope ground. struction of building in slope ground as well as slope stabilization work. RCC pile was used to take lateral Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 14 of 19 Fig. 13 Factor of safety of cutting pane obtained from Bishops method for Section 2-2 and shear force of structure, anchor bolt and geogrid was not considered but for drainage system, semi was used for retaining structure as well as to increase perforated HDP pile of 6inch diameter was laid in soil strength  for shear. According to soil investigation 1:2 gradient over coarse aggregates and then pile was work performed in site, water table was not found, wrapped with geotextile and sand was filled over it in hence there are limitation in this study as in analysis each cut slope. Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 15 of 19 Fig. 14 Factor of safety after slope stabilization work Section 1-1 measures. The project one completed adds a great value Conclusion to the owner considering the terrain, especially in the Even though building a structure on a slope land has its context of Nepal. The owner will appreciate the scen - own challenges and difficulties, it is possible to execute ery, the geomorphology and landscapes, natural lighting, a project with safe design/ analysis and slope stability Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 16 of 19 Fig. 15 Factor of safety after slope stabilization work Section 2-2 privacy, and space. This illustrates why so many of the deeper excavation by specialized excavation process to world’s most desirable residences are constructed on ensure that the building is in accordance to code and safe slopes. However, it necessitates complicated foundation to inhabit. systems, which add to the cost and length of the con- The limit equilibrium method of analysis was widely struction process. The cost is often more than that of an used due to its clear physical meaning and simple cal- entire house on flat ground. It requires more concrete, culation. At present, with development in the finite element method, the strength reduction method is Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 17 of 19 Fig. 16 Verification with Shear strength reduction (SSR) method Section 1-1 gradually recognized to assess the safety factor of slope. can be one of the sustainable solutions among oth- In this paper, the safety factor of the slope is firstly cal - ers to address the issue. Following, the safety factor is culated by Bishop’s method, which is then compared increased using RCC pile, anchor pile and geogrid as with the safety factor obtained from the strength reduc- reinforcement. For construction of structure in moun- tion method by FEM. Thus, from LEM and FEM, factor tainous area like Nepal, a combination of RCC pile, of safety were found to be greater than 1. anchor bolt and geogrid can be an effective solution; The construction of building in slope ground is pos - are the concluding remarks can be drawn from this sible, but it needs specialized excavation and slope pro- work. tection work; RCC pile with anchor bolt and geogrid Jain et al. Geoenvironmental Disasters (2023) 10:13 Page 18 of 19 Fig. 17 Verification with Shear strength reduction (SSR) method Section 2-2 Acknowledgements Bhandari C, Dahal RK, Timilsina M (2021) Disaster risk understanding of local The Authors are really thankful to Dr. Purosottam Dangol, Mr. Prakash Sing people after the 2015 Gorkha Earthquake in Pokhara City, Nepal. Geoen- Rawal and the Hotel Barahi for their help in this research work. Authors also viron Disast 8(1):1–19. https:// doi. org/ 10. 1186/ s40677- 020- 00173-9 want to appreciate every helping hand to complete this research work. Bishop AW (1955) The use of the slip circle in the stability analysis of slopes. Geotechnique 5(1):7–17 Author contributions Chen L, Poulos H (1997) Piles subjected to lateral soil movements. J Geotech SKJ was involved in the data collection in field, data analysis, simulations and Geoenviron Eng 123(9):802–811 writing the manuscript. And all other author contributed in data analysis, Dhital MR (2015) Geology of the Nepal Himalaya: regional perspective of simulations and writing the paper. All authors read and approved by the final the classic collided orogen. Springer, Berlin.https:// doi. org/ 10. 1007/ manuscript.978-3- 319- 02496-7 Hagen T (1969) Report on the geological survey of Nepal: preliminary Availability of data and materials reconnaissance. Denkschriften Der Schweizerischen Naturforschenden The most of the data is collected from field work and simulations. The pub - Gesellschaft Memoires De La Societe Helvetique Des Sciences lished studies that are referenced in the manuscript use some of the data that Naturelles 84(1):185 were created or examined throughout this research. Ito T, Matsui T (1975) Methods to estimate lateral force acting on stabilizing piles. Soils Found 15(4):43–59 Kaewjuea W, Shaingchin S, Khamtip W, Chompoorat T, Chaimahawan P Declarations (2022) Lateral loading test of reinforced concrete bored pile in stiff clay and near slope. Eng J 26(3):29–40 Competing interests Khodair Y, Abdel-Mohti A (2014) Numerical analysis of pile–soil interaction The authors declare no competing interests. under axial and lateral loads. Int J Concr Struct Mater 8(3):239–249 Koirala A, Rimal L (1996) Geological hazards in Pokhara valley, western Competing interest Nepal. J Nepal Geol Soc 14:99–108 The authors claim to have no conflicts of interest. Kumar JS, Nusari MS, Purushotam D, Prasad AI, Rajyaswori S (2021) Eec ff tive - ness of geocell wall, geogrid and micropile anchors for mitigation of unstable slopes. Geoenviron Disasters 8(1):1–15 Received: 10 February 2023 Accepted: 8 May 2023 Paul D, Kumar S (1997) Stability analysis of slope with building loads. Soil Dyn Earthq Eng 16(6):395–405 Poulos HG (1995) Design of reinforcing piles to increase slope stability. Can Geotech J 32(5):808–818 Rimal B, Baral H, Stork NE, Paudyal K, Rijal S (2015) Growing city and rapid References land use transition: assessing multiple hazards and risks in the Pokhara Abramson LW, Lee TS, Sharma S, Boyce GM (2001) Slope stability and stabiliza- valley. Nepal Land 4(4):957–978 tion methods. Wiley, USA Seyhan F (2009) Stability analysis of pile-slope system. Sci Res Essays 4(9):842–852 Jain  et al. Geoenvironmental Disasters (2023) 10:13 Page 19 of 19 Wang X, Shrestha R, Li X, Mandal AK (2021) Design theory and method of geo- synthetic reinforced soil retaining wall combined with a gravity retaining wall or full height rigid facing. Geotech Geol Eng 39(3):2075–2086 Won J, You K, Jeong S, Kim S (2005) Coupled effects in stability analysis of pile– slope systems. Comput Geotech 32(4):304–315 Yamanaka H, Yoshida M, Arrita K (1982) Terrace landforms and quaternary deposit arounf Pokhara valley, central Nepal. J Nepal Geol Soc 2:113–142 ANagostopoulos C, Hada M, Fukuoka M (1992) Piles as landslide countermeas- ures-model study. International symposium on landslides Kocherzhenko V, Suleymanova L & Kocherzhenko A (2021) Innovative pile technologies in modern foundation construction. IOP conference series: materials science and engineering Kocherzhenko V, & Suleymanova L (2021) Methods for the construction of lowered structures and pile foundations. E3S web of conferences Koirala A, Rimal L, Sikrikar S, Pradhananga U, Pradhan P, HAnisch S, Busch K (1996) Engineering and environmental geological map of Pokhara valley (1: 50000). Depart Mines Geol Cooperat BGR: Kathmandu, Nepal Gör M, Taher NR, Aksoy HS, Awlla HA (2022) Eec ff t of Geogrid Inclusion on the Slope Stability. In Proceedings of the 5th International European Conference on Interdisciplinary Scientific Research, Valencia, Spain, 28–29 January 2022; pp. 275–286 Parkash S (2019) Landslide preparedness guidelines for safety of buildings on slopes; published by national institute of disaster management. Ministry of home affairs, Government of India, New Delhi, 110001, India, 80 Popescu M (1991) Landslide control by means of a row of piles: Keynote paper. Slope stability engineering developments and applications: proceedings of the international conference on slope stability organized by the Insti- tution of Civil Engineers and held on the Isle of wight on 15–18 Apr 1991 Zhang R, Zhao J, & Wang G (2016) Stability analysis of anchored soil slope based on finite element limit equilibrium method. Mathemat Probl Eng Zolotuchin S, Novikova K, & Kim M (2018) New method for the construc- tion of pile foundations in low-rise constructions using micro-piles in the knocked-out wells. IOP conference series: materials science and engineering Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in pub- lished maps and institutional affiliations.

Journal

Geoenvironmental Disasters – Springer Journals

Published: May 25, 2023

Keywords: Slope stability; Strength reduction method; Limit equilibrium method; Factor of safety; RCC pile; Anchor bolt; Geogrid

References

  • Disaster risk understanding of local people after the 2015 Gorkha Earthquake in Pokhara City, Nepal
    Bhandari, C; Dahal, RK; Timilsina, M
  • The use of the slip circle in the stability analysis of slopes
    Bishop, AW
  • Piles subjected to lateral soil movements
    Chen, L; Poulos, H
  • Report on the geological survey of Nepal: preliminary reconnaissance
    Hagen, T
  • Methods to estimate lateral force acting on stabilizing piles
    Ito, T; Matsui, T
  • Lateral loading test of reinforced concrete bored pile in stiff clay and near slope
    Kaewjuea, W; Shaingchin, S; Khamtip, W; Chompoorat, T; Chaimahawan, P
  • Numerical analysis of pile–soil interaction under axial and lateral loads
    Khodair, Y; Abdel-Mohti, A
  • Geological hazards in Pokhara valley, western Nepal
    Koirala, A; Rimal, L
  • Effectiveness of geocell wall, geogrid and micropile anchors for mitigation of unstable slopes
    Kumar, JS; Nusari, MS; Purushotam, D; Prasad, AI; Rajyaswori, S
  • Stability analysis of slope with building loads
    Paul, D; Kumar, S
  • Design of reinforcing piles to increase slope stability
    Poulos, HG
  • Growing city and rapid land use transition: assessing multiple hazards and risks in the Pokhara valley
    Rimal, B; Baral, H; Stork, NE; Paudyal, K; Rijal, S
  • Stability analysis of pile-slope system
    Seyhan, F
  • Design theory and method of geo-synthetic reinforced soil retaining wall combined with a gravity retaining wall or full height rigid facing
    Wang, X; Shrestha, R; Li, X; Mandal, AK
  • Coupled effects in stability analysis of pile–slope systems
    Won, J; You, K; Jeong, S; Kim, S
  • Terrace landforms and quaternary deposit arounf Pokhara valley, central Nepal
    Yamanaka, H; Yoshida, M; Arrita, K