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Relationship between seepage water volume and total suspended solids of landslide dam failure caused by seepage: an experimental investigation

Relationship between seepage water volume and total suspended solids of landslide dam failure... Background: Landslide dams inevitably demonstrate the potential for catastrophic failure with high-risk damage to life and property at the downstream site. Hence, knowledge of the internal stability of dam materials is a key to predicting the seepage failure of landslide dams. In this study, experiments were conducted to examine the relationship between seepage volume and total suspended solids (TSS) of seepage water based on hydro mechanical constrains. Understanding the relationship between the seepage volume and TSS with hydro-mechanical constraints supports the prediction of the seepage failure of landslide dams at the field level. Result: Experiments were conducted with a mixed sample of silica sands. Seepage water was collected from a flume tank with the facility to measure the hydraulic gradient, vertical displacement, and seepage water volume. Grain size affected the life span of the dam. The seepage volume increased with the increase in the percentage of silica sand S4, whereas TSS increased with the increase in the percentage of silica sand S8. With the increase in the dam height, the dam life decreases for low coeficient of uniformity of the grain size distribution. With the increase in the reservoir size, TSS decreased, and the total seepage volume increased. Conclusion: Dam failure depends on the particle size, dam geometry, inflow rates, reservoir size, hydraulic gradient, and seepage water volume, and TSS of seepage water. The results indicated that with the increase in fine particles, the life span decreases, and TSS increases. With the increase in the flow rate, the dam life span decreases, and the TSS and seepage volume rate increase.The dam height leads to an increase seepage volume with low TSS, where the life span of the dam also depends on the particle size distribution With the increase in the reservoir size, the seepage water volume decreases with low TSS. Keywords: Landslide dam, Seepage volume, Hydraulic gradient, Total suspended solids (TSS), Inflow rate, Dam height Introduction it may contain debris and loose soils. Hence, a landslide Formation and failure of landslide dams in mountain- dam is composed of heterogeneous or poorly consoli- ous areas constitute a significant natural hazard. A dated material with debris. A landslide dam differs from majority of landslides that block rivers are either caused a constructed embankment dam as it exhibits no con- by heavy rainfall or earthquakes (Schuster and Costa, trol structure for seepage and drainage (Uhlir, 1998; 1986; Canuti et al., 1988; Costa and Schuster, 1988; Awal et al., 2007). A better understanding of premoni- Korup, 2004; Evans et al., 2011; Peng and Zhan, 2012; tory factors, which can easily be measured or observed Casagli et al. 2003; Tacconi et al., 2018). As the land- in actual landslide dams that are at high risk of failure, slide mass shifts from its original position to the river, is crucial for disaster reduction (Wang et al., 2018). In real fields, due to the high risk of failure, limited pa- rameters such as seepage quantity, turbidity of down- * Correspondence: civildhungana@gmail.com stream seepage, vertical displacement of the dam crest, Department of Earth Science, Shimane University, 1060 Nishikawatsu-Cho, Matsue, Shimane 690-8504, Japan © The Author(s). 2020 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 2 of 11 reservoir level, and impounded area can be monitored the development of internal erosion in earth dams and (Dhungana and Wang, 2019). landslide dams (Wit et al., 1981; Brauns, 1985; Maknoon The inflow rate into the reservoir and reservoir and Mahdi, 2010; Wang et al., 2018; Okeke et al., 2016a, volume, dam size, and dam material are important fac- 2016b). Hanson et al. (2010) analyzed the variation in tors that affect the failure of a landslide dam (Schuster the erodibility of different soil materials due to the in- and Costa, 1988). Some authors already reported the ternal erosion of dams by large-scale outdoor model statistics of landslide dams and their failure in various tests. They observed that the rate of erosion in different regions worldwide. They have summarized the import- soil materials varies in order of magnitude. ant characteristics of landslide dams including their Chang et al. (2011) conducted field erodibility tests classification, cause and type of failure, life span, and on two landslide dams triggered by the 12 May 2008, some other important parameters (Costa and Schuster, Ms. 8.0 Wenchuan earthquake in the Sichuan 1991;Korup, 2004; Stefanelli et al., 2015;Xuet al., Province of China and revealed that an increase in 2009; Casagli and Ermini, 1999;Chai et al., 1995; the bulk density is inversely proportional to the coef- Clague and Evans, 1994). ficient of erodibility with depth. Furthermore, Hanson Overtopping, piping, and seepage failure constitute et al. (2010) conducted large-scale physical tests to the typical failures of landslide dams. Dams compris- investigate the impact of erosion resistance on in- ing homogeneous soil mostly undergo failure by ternal erosion in embankment dams and revealed that seepage and downstream slope saturation (Dunning erosion resistance for the same embankment material et al., 2006), whereas piping holes are formed in dams increases with the increase in the compactive effort that are built with mixed soil, depending on the and water content. percentage of the fine content and the interlocking Many studies have been conducted on different land- bond between soil particles. slide dam failures, possibly overtopping, piping, and seep- Failure sequence of a dam was reportedly categorized age (Awal et al., 2007, 2011; Wang et al., 2018). However, into four periods: 1) emergence of seepage water and a majority of these studies highlighted failure patterns, front wetting, 2) hyper-concentrated flow discharge, 3) while only limited studies focused on the seepage failure emergence and development of a dam crest, and 4) and internal erosion. In addition, effects on the turbidity, failure of a dam crest with a sharp increase in its sub- seepage volume, and failure mechanism with different sidence (Wang et al., 2018). Dhungana and Wang parameters of landslide dams were not examined. (2019) described the conditions for the failure and Hence, this study aimed to highlight the relation- stability of the landslide dam for seepage failure, where ship between the seepage volume and TSS of land- trends of total suspended solids (TSS) and the slide dams during failure. In this case, the hydraulic hydraulic gradient were compared under failure and gradient was measured using pore-water pressure sen- stable conditions. sors; vertical displacement was measured using a laser Internal instability is a failure mode of soil subjected sensor at the dam crest; seepage water was collected, to seepage. The seepage failure mode is characterized by and seepage volume was monitored using a pore- the erosion of fine particles through the pore matrix of water pressure sensor. A seepage water sample was the coarse fraction of the soil (Richards and Reddy, collected, and TSS was measured. 2007). Due to the erosion of fine particles, the flow path undergoes expansion, leading to the resistance strength Methods loss of the external load (Ahlinhan et al., 2016). Experimental setup In addition, TSS supports the understanding of the In the laboratory, a flume tank with 0.45 m height × dam material erosion. Turbidity and TSS are identical 0.45 m width × 2.0 m length was prepared for the experi- premonitory factors that can be measured under field ment. On the downstream side of the flume tank, the and laboratory settings (Rugner et al., 2013; Stubblefield flow of seepage water was stopped and diverted into a et al., 2007). Fine particles, which are among coarser tank using holes at a distance of 0.75 m from the dam grains, are almost free from effective overburden and it center (Fig. 1). Experimental studies of the flume tank can migrate under an extremely-low-velocity seepage were performed for the selection of a dam size, including flow (Takaji et al., 2008). Such eroded particles can be the 1 m × 0.6 m × 0.45 m model used by Sidle et al. measured as TSS in the laboratory and in the field (1995), 5 m × 0.3 m × 0.5 m model used by Awal et al. (Dhungana and Wang, 2019). (2007), 1.5 m × 1 m model used by Wilson (2009), 1.4 Several studies (Rinaldi and Casagli, 1999; Lobkovsky m × 1 m model used by Wilson (2011), and 0.5 m × 0.5 et al., 2004; Wilson et al., 2007; Fox et al., 2007) reported m × 0.5 m model used by Fox et al. (2014). In this study, detailed research on seepage erosion for slope failures. the dam heights were 0.2 m and 0.25 m, and upstream Numerous experimental methods were used to simulate and downstream slopes were 45° and 35°, respectively. Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 3 of 11 Fig. 1 Experimental setup of the flume tank. a 3D view; b cross-section; and c longitudinal section The dam height was increased from 0.2 m to 0.25 m monitored at two fixed points by laser sensors. A whereas the downstream and upstream slopes were half-cut polyvinyl chloride (PVC) pipe was fixed constant, and the dam volume was also increased due below the holes with a gentle slope to collect seepage to height increase. Similarly, in the flume tank, the water. The collected seepage water volume was moni- position of the dam was shifted downstream side by tored by the Pwp4 sensor. 0.1 m to increase the reservoir size. The width of dam crest was 0.1 m. On the floor of the flume tank, Material and method adouble-sidedtapewas used,and dry silicasand6 Typically, landslide dams comprise fragmented materials was poured over it to maintain the roughness be- with a wide range of sediment sizes (Costa and Schuster, tween the dam material and flume tank floor. The 1988; Schuster, 1995). It is challenging to scale down ac- flume tank was built using Plexiglas, permitting visi- tual landslide dam material to the laboratory scale. From bility into the flume. The flume bed slope was main- laboratory practice, three mixtures of artificial silica sand tained constant at 1:20 during all experiments. Four were selected for the experiment for seepage failure. Dif- pore-water pressure sensors, with a rated capacity of ferent proportions of a combination of silica sands S4, 50 kPa, were used—hereafter referred to as Pwp1, S5, S6, and S8 were used (Table 1). The main part of the Pwp2, Pwp3, and Pwp4—for the downstream and up- sample was silica sands S5 and S6. Silica sands S4 and stream sides of the dam body and at the reservoir S8 were considered as coarser and finer particles, re- and seepage water collection tank, respectively. Sen- spectively, and mixed with silica sands S5 and S6. Three sors Pwp1, Pwp2, and Pwp3 were connected to the samples, i.e., S456, S4568, and S568, respectively, were flume tank from the base of the flume tank facing prepared in the presence and absence of silica sands S4 upwards. Pwp1 and Pwp2 were covered by the filter and S8. The grain size distributions of the samples are material to control the flow of sand over it. The shown in Fig. 2. Pwp4 sensor was connected to the tank base, where A mixing machine was used for mixing dam materials. seepage water was collected. Multi-function analog Initially, the mixing machine was used for dry mixing, laser sensors (CMOS) were used to measure the verti- followed by mixing with water for affording the desired cal displacement from the top of the flume tank using shape of the dam. Before creating the dam in the flume a wooden frame—hereafterknown as Vdrand Vdl, tank, a sample was collected to estimate its initial water for the right and left sides, respectively. The vertical content. In addition, sensors were placed in their re- displacement of the dam crest was continuously spective positions, and the dam was prepared by layer- Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 4 of 11 Table 1 Mixed ratios and mechanical properties of samples Sample number SS 4 (kg) SS 5 (kg) SS 6 (kg) SS 8 (kg) Water (kg) Total (kg) D C C 50 u c (mm) S456 1 5 5 – 0.5 11.5 0.394 3.075 1.375 S4568 0.5 5 5 0.5 0.5 11.5 0.565 2.185 1.098 S568 – 5 5 1 0.5 11.5 0.557 2.264 1.065 D = median grain size; C = coefficient of uniformity; C = coefficient of curvature 50 u c to-layer compaction, divided into four and six parts for understand the effect of the dam height, reservoir size, dam heights of 0.2 m and 0.25m, respectively. Each layer and inflow rate into the reservoir on hydraulic gradient, comprised ~ 9 kg of sample, and 1–2 kg of sample was vertical displacement, TSS, seepage water volume, and used to obtain the final shape of the dam. Real-time data longevity of the dam for three soil samples prepared by were collected using universal recorders (KYOWA PCD the mix of silica sands S4, S5, S6, and S8. Table 2 sum- 330B and PCD 400). Sampling frequency was two of marizes the experimental details. data per second. A stopwatch was used during the col- Time of landslide dam failure is key factor to reducing lection of a seepage water sample for TSS. After collect- natural disasters. In this study as well, dams failed at ing a sample for TSS, the volume was measured, varying periods under different conditions. The time fac- followed by oven-drying at 105 °C. The dried sample tor plays roles in soil saturation and shear strength re- weight was measured, and the TSS value was calculated. duction. From experiments, the higher the percentage of Seepage water was directly collected into a tank using silica sand S8 in the dam material, the shorter the life the half-cut PVC pipe, and Pwp4 was used to measure span of the dam. Higher the percentage of silica sand S4 the volume. The hydraulic gradient was calculated using in the dam material, the longer the life span of the dam. the pressure head of two sensors, i.e., Pwp1 and Pwp2, Despite this observation, a longer time was taken for the respectively, and the flume tank slope. Pwp1 and Pwp2 seepage water to drain out from the dam body for a were fixed below the dam crest edge downstream and sample containing silica sand S8. The density of the dam upstream of the dam, respectively. The seepage vol- controlled the time for the initial peak hydraulic gradi- ume was calculated using porewater pressure Pwp4 ent, whereas density exhibited a lower effect for the total and tank diameter. life span in contrast to the initial peak hydraulic gradient (Fig. 3). Results and discussion General characteristics of the experiments Effect of inflow rate on dam failure Dam failure leads to flash floods on the downstream Experiments were conducted with three samples, i.e., side. Hence, it is crucial to understand the failure pattern S456, S4568, and S568, respectively, for inflow rates of − 5 3 − 5 3 of landslide dams to minimize natural hazards caused by 1.1 × 10 m /s and 1.667 × 10 m /s. The inflow rates floods. In this study, experiments were conducted to were selected based on practice on these samples to get Fig. 2 Grain size distribution curves of samples used in experiments Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 5 of 11 Table 2 Outline of all experiments under different testing conditions 3 3 Exp. No Sample type Inflow rate (m /s) Dam height (m) Reservoir size Dry density (kg/m ) Initial moisture content (%) −5 Exp1 S568 1.1*10 0.2 1294 2.7 − 5 Exp2 1.67*10 1251 2.7 Exp3 0.25 R1 1269 2.8 Exp4 R2 1223 3.2 −5 Exp5 S4568 1.1*10 0.2 1334 2.7 −5 Exp6 1.67*10 1301 2.9 Exp7 0.25 R1 1234 2.8 Exp8 R2 1241 2.7 −5 Exp9 S456 1.1*10 0.2 − 5 Exp10 1.67*10 1302 2.5 Exp11 0.25 R1 1275 2.8 Exp12 R2 1202 3.0 seepage failures. If we increase inflow rate, the dam fail- the high TSS and dam crest settlement. The rapid in- ure type changed to overflow and if we decrease the in- crease in the hydraulic gradient supported the erosion of flow rate, the dam crest will not failed. Experimental soil particles from the dam body, while the seepage vol- results revealed a time lag between the peak hydraulic ume was comparatively low. gradient (which is responsible for the start of seepage) For the S4568 sample, the initial peak hydraulic and seepage flow out time (referred as TSS starting time gradients were 0.26 and 0.27 for low and high inflow in figures). Inflow rates into the reservoir created varia- rates, respectively, and at the time of failure, the cor- tions in the hydraulic process for different soil types. For responding values were 0.39 and 0.38 (Fig. 5). For the the S568 sample, the initial peak hydraulic gradient that high inflow rate, the total volume of seepage water started seepage was varied from 0.29 to 0.39 (Fig. 4). In was lower, and the TSS value was high, related to the case of the higher inflow rate, the hydraulic gradient was higher rate of seepage water released from the dam decreased from its peak value of 0.39 to 0.23, and again body. With the increase in the percentage of silica started to increase, and the dam crest underwent failure sand S4, the TSS value decreased for both inflow when it reached 0.28. For the low inflow rate, the hy- rates; however, the time taken for failure increased draulic gradient decreased from its peak value of 0.29 to with the increase in the percentage of silica sand S4. 0.21 and again started to increase and undergo failure For the S456 sample, no failure was observed at an − 5 3 when it reached 0.39. The rapid increment in the hy- inflow rate of 1.11 × 10 m /s. The pore water pres- draulic gradient initiated the high seepage gradient, lead- sure at Pwp2 and Pwp3 became constant after 8000 s, ing to the early flow of seepage and shear strength and hence considered as the stable case, whereas for − 5 3 reduction of the dam material. This result in turn led to an inflow rate of 1.67 × 10 m /s, failure was Fig. 3 Effects of density on (a) time for initial peak hydraulic gradient and (b) time for failure of dam crest Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 6 of 11 Fig. 4 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S568 at a low inflow rate (LI) of − 5 3 − 5 3 1.1 × 10 m /s and high inflow rate (HI) 1.67 × 10 m /s. a Hydraulic gradient and vertical displacement; b Seepage volume and TSS observed within 3700 s. The seepage water flow at the instability. For the soil slope instability, downstream lower inflow rate became extremely high, leading to a slope angles and the soil layer gradient are major factors stable dam crest, whereas the TSS and vertical dis- that control the critical hydraulic gradient (Iverson and placement were constant as reported by Dhungana Major, 1986; Budhu and Gobin, 1996). The landslide and Wang (2019). At a high inflow rate, the lowest dam height is a key parameter for examining the stability initial peak hydraulic gradient was observed through- of the natural dam. The increase in the dam height re- out the study, and the vertical displacement sharply duces the stability of the dam crest (Okeke and Wang, increased before failure. At a low inflow rate, the ver- 2016b). Experiments were conducted to understand the tical displacement increased due to cracks in the dam effect of the dam height on the stability, TSS, and seep- crest after that horizontal movement occurred and age water volume. For the S4568 sample (Fig. 6), con- dam crest failed. taining a higher percentage of coarser sand particles and increase in dam height decrease the longevity of dam, Effect of dam height on dam failure which also was in agreement with the results reported A statistical approach proposed a dimensionless break- by Okeke and Wang (2018), which may be possibly re- ing index (DBI) to investigate the stability of the dam lated to the mass block failure in the downstream site (Ermini and Casagli, 2003). This empirical relation pre- and increased percentage of coarser particles and sample dicted the dam stability by using the dam geometry, S4568 has lowest value of coefficient of uniformity. As where the reservoir volumes and dam heights are key the initial peak hydraulic gradient of the higher dam was parameters. The landslide dam size is the major factor greater than that of the lower dam, the instability of the that contributes to the seepage erosion and slope internal structure increased, leading to higher TSS on Fig. 5 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S4568 at a low inflow rate (LI) of − 5 3 − 5 3 1.1 × 10 m /s and high inflow rate (HI) 1.67 × 10 m /s. a Hydraulic gradient and vertical displacement; b Seepage volume and TSS Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 7 of 11 Fig. 6 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S4568 at a Low dam height (LD) (200 mm) and High dam height (HD) (250 mm). a Hydraulic gradient and vertical displacement; b Seepage volume and TSS seepage water. The seepage water volume on the down- increase the time for filling up the entire reservoir, stream side increased with the dam height for all three which will play a role in the stability of the dam body. samples. For the lower dam height, the total seepage The reservoir size was longitudinally increased by 0.1 m, volume was limited in comparison to that for the which increased the reservoir area by 0.043 m . The total higher dam height within the same period. All three time for the failure of the dam crest increased with the samples in this study revealed that the height be- increase in the reservoir size for all three samples. The tween the reservoir water level and dam crest at the maximum hydraulic gradient for the experiment with time of failure increases with the dam height; simi- the S456 sample was increased in comparison to those larly, it increased with the percentage of silica sand with the S4568 and S568 samples. Notably, the times for S4; however, significant settlement in the dam crest the initial peak hydraulic gradient for the S456, S4568, for both cases was observed. The dam crest exhib- and S568 samples were nearly the same, whereas for a ited cracks during the test for a higher dam, and the small reservoir, time for the initial hydraulic gradient crack size increased with the increase in the percent- increased from S456 to S568. age of silica sand S4. For the S568 sample, for the small reservoir, the hy- draulic gradient was greater at the time of failure than Effect of reservoir size on dam failure the initial peak hydraulic gradient, and for the large res- Reservoir area is a leading factor in statistical analysis ervoir, the initial peak hydraulic gradient was greater for proposing DBI. The static pressure caused by the than the failure hydraulic gradient (Fig. 7). Compared to river gradient to the dam body increases if the reservoir the small reservoir, a small amount of hydraulic force size increases. The increase in the reservoir level will was observed at the initiation time of internal instability Fig. 7 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S568 at a small reservoir (SR) and large reservoir (LR). a Hydraulic gradient and vertical displacement; b Seepage volume and TSS Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 8 of 11 Fig. 8 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S4568 at a small reservoir (SR) and large reservoir (LR). a Hydraulic gradient and vertical displacement; b Seepage water volume and TSS for the large reservoir due to which a longer life span hydraulic gradient at the time of failure compared to was recorded. The TSS has increased abruptly before the that observed for a large-sized reservoir. failure of dam crest for both small and large reservoirs. For the S456 sample, TSS was nearly constant for the The vertical displacement was high for the large reser- large reservoir and rapidly increased at the time of failure, voir case, where the seepage water volume was also high, whereas for the small reservoir, TSS slowly increased with and the failure for half part of the dam crest was noticed fluctuation (Fig. 9). The hydraulic gradient for the small for the large reservoir case. reservoir was less than that for the large reservoir, which For the S4568 sample, the TSS value was greater in was different from other experiments with the S568 sam- case of the small-sized reservoir, due to which the ple. Similarly, for the large reservoir, failure hydraulic gra- vertical displacement was also high, and the failure of dient was highest throughout this study, which may be dam crest was observed earlier than in the case of the effect of the reservoir size. Takaji and Yusuke (2008) the large-sized reservoir (Fig. 8). The initial rate of reported that physical parameters such as particle density, seepage water volume for the small reservoir was hydraulic conductivity, and gravel content affect the seep- greater, and the cumulative total seepage water vol- age development in landslide dams and soil slopes, which ume before the dam failure was greater for the large- can be used in this experiment. The seepage rate was sized reservoir. For the small reservoir, due to the nearly the same for large- and small-sized reservoirs, but higher TSS, internal erosion occurred, and the shear the total seepage volume was greater for the large-sized strength of the soil decreased, leading to a low reservoir. Horizontal displacement was noticed for a Fig. 9 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S456 at a small reservoir (SR) and large reservoir (LR). a Hydraulic gradient and vertical displacement; b Seepage volume and TSS Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 9 of 11 Fig. 10 Time taken for failure of dam crest for different conditions small reservoir after the failure of the half part of the dam 1. Experiments conducted on three samples prepared crest; hence, the vertical displacement decreases. by mixing the silica sand revealed that the time of failure of experiments increases depending on the Conclusion changes in the percentages of fine and coarser sand. A series of experiments were performed to investigate Samples with finer particles exhibited a short dam the effects of particle size, inflow rate into the reservoir, life span (Fig. 10) dam height, and reservoir size on the seepage volume, 2. At a low inflow rate into the reservoir, the time of failure, and TSS of for seepage-induced failure of hydraulic gradient to initiate the seepage was less landslide dams using a flume tank. Limit values of hy- than that at the time of failure (Fig. 4 and Fig. 5). draulic gradients were determined under different The internal structure was more stable due to the hydro-mechanical and geometrical conditions. Based on low hydraulic gradient, leading to low TSS and the experimental results, the following conclusions are negligible vertical displacement; however, the total drawn. seepage volume was high Fig. 11 Maximum hydraulic gradient for low inflow rate (LI), high inflow rate (HI), low dam (LD), high dam (HD), small reservoir (SR) and large reservoir (LR) of three samples Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 10 of 11 3. For the sample comprising coarser particles and Managing hydro- geological disaster in a vulnerable environment. Grifo Publishers, Perugia, pp 189–202 small coefficient of uniformity may reduce the Casagli N, Ermini L (1999) Geomorphic analysis of landslide dams in the northern life span of dam, possibly related to the change Apennine. Trans Jpn Geomorphol Union 20(3):219–249 in the permeability and effect of the critical Casagli N, Ermini L, Rosati G (2003) Determining grain size distribution of material composing landslide dams in the northern Apennines: sampling and hydraulic gradient to initiate the seepage or processing methods. Eng Geol 69(1):83–89 internal instability Chai HJ, Liu HC, Zhang ZY (1995) The catalog of Chinese landslide dam events. J 4. With the increase in reservoir volume, the Geol Hazards Environ Preservation 6(4):1–9 Chang DS, Zhang LM, Xu Y, Huang RQ (2011) Field testing of erodibility of two maximum hydraulic gradient exhibited differently landslide dams triggered by the 12 may Wenchuan earthquake. Landslides as that observed in case of inflow rates and dam 8(3):321–332 height (Fig. 11), and the seepage water volume Clague JJ, Evans SG (1994) Formation and failure of natural dams in the Canadian cordillera. Geol Survey Canada Bull 464:1–35 increased, and TSS decreased with the increase in Costa JE, Schuster RL (1988) The formation and failure of natural dams. Geol Soc the reservoir volume. Am Bull 100:1054–1068 5. Although there was a continuous process of the Costa JE, Schuster RL (1991) Documented historical landslide dams from around the world. Bull US Geol Surv:1–486. https://pubs.er.usgs.gov/publication/ hydraulic gradient and seepage and erosion, the ofr91239. hydraulic gradient was predominantly affected by Dhungana P, Wang F (2019) The relationship among the premonitory factors of the inflow rate and dam geometry, whereas the landslide dam failure caused by seepage: an experimental study. Geoenviron Disasters. https://doi.org/10.1186/s40677-019-0135-7 total seepage volume, seepage rate, and TSS Dunning SA, Rosser NJ, Petley DN, Massey CR (2006) Formation and failure of the depended on the particle size of the dam material Tsatichhu landslide dam, Bhutan. Landslides 3:107–113 and reservoir size. Ermini L, Casagli N (2003) Prediction of the behavior of landslide dam using a geomorphological dimensionless index. Earth Surf Proc Land 28(1):31–47 Abbreviations Evans SG, Delaney KB, Hermanns RL, Strom A, Scarascia-Mugnozza G (2011) The TSS: Total suspended solids; PVC: polyvinyl chloride. formation and behavior of natural and artificial rockslide dams; implications for engineering performance and hazard management. In: Evans SG, Acknowledgments Hermanns RL, Strom A (eds) Scarascia-Mugnozza G Natural and artificial The first author would like to express warm gratitude to the Rotary rockslide dams. Springer, Berlin Heidelberg, pp 1–75 Yoneyama Memorial Foundation and the Izumo South Rotary Club for Fox GA, Felice RG, Midgley TL, Wilson GV, Al-Madhhachi AS (2014) Laboratory soil providing a scholarship for the first author. The authors would also like to piping and internal erosion experiments: evaluation of a soil-piping model thank the anonymous reviewers for reviewing the manuscript. for low-compacted soils. Earth Surf Proc Land 39(9):1137–1145 Fox GA, Wilson GV, Simon A, Langendoen EJ, Akay O, Fuchs JW (2007) Measuring Authors’ contributions streambank erosion due to groundwater seepage: correlation to bank pore DP conducted the laboratory work with close coordination with FW. FW water pressure, precipitation and stream stage. Earth Surf Proc Land 32(10): provided guidance and support for data analysis and presentation. DP 1558–1573 drafted the manuscript, and both authors read and approved the Hanson GJ, Tejral RD, Hunt SL, Temple DM. (2010) Internal erosion and impact of manuscript. erosion resistance. In Proceedings of the 30th U.S. Society on Dams Annual Meeting and Conference, April 12-16, 2010, Sacramento, California. p. 773– Funding 784. None. Iverson RM, Major JJ (1986) Groundwater seepage vectors and the potential for hillslope failure and debris flow mobilization. Water Resour Res 22(11):1543– Availability of data and materials 1548 The data sets used and analysed during the current study are available from Korup O (2004) Geomorphometric characteristics of New Zealand landslide dams. the corresponding author on reasonable request. All data used in this study Eng Geol 73(1):13–35 were produced in the department of Earth science laboratory of Shimane Lobkovsky AE, Jensen B, Kudrolli A, Rothman DH (2004) Threshold phenomena in University. erosion driven by subsurface flow. J Geophys Res Earth Surf 109:F04010. https://doi.org/10.1029/2004JF000172 Maknoon M, Mahdi TF (2010) Experimental investigation into embankment Competing interests external suffusion. Nat Hazards 54(3):749–763 The authors declare that they have no competing interests. Okeke ACU, Wang F (2016a) Critical hydraulic gradients for seepage induced Received: 14 November 2019 Accepted: 27 January 2020 failure of landslide dams. Geoenviron Dis. https://doi.org/10.1186/s40677-016- 0043-z Okeke ACU, Wang F (2016b) Hydromechanical constraints on the piping failure of landslide dams: an experimental investigation. Geoenviron Dis. https://doi. References org/10.1186/s40677-016-0038-9 Ahlinhan MF, Koube MB, Adjovi CE (2016) Assessment of the internal instability Peng M, Zhan LM (2012) Breaching parameters of landslide dam. Landslides 9: for granular soils subjected to seepage. J Geosci Environ Protect 4:46–55 13–31. https://doi.org/10.1007/s10346-011-0271-y Awal R, Nakagawa H, Baba Y, Sharma RH (2007) Numerical and experimental Richards KS, Reddy KR (2007) Critical appraisal of piping phenomena in earth study on landslide dam failure by sliding. Annual J Hydraul Eng JSCE 51:7–12 dams. Bull Eng Geol Environ 66(4):381–402 Awal R, Nakagawa H, Fujita M, Kawaike K, Baba Y, Zhang H (2011) Study on the Rinaldi M, Casagli N (1999) Stability of streambanks formed in partially saturated piping failure of a natural dam. Ann Dis Prev Res Institute Kyoto Univ 54: soils and effects of negative pore-water pressures: the Sieve River (Italy). 539–547 Geomorphology 26(4):253–277 Brauns J (1985) Stability of layered granular soil under horizontal groundwater flow. In: Proceedings of the 15th international congress on large dams, Rügner H, Schwientek M, Beckingham B, Kuch B, Grathwohl P (2013) Turbidity as Lausanne 1985 a proxy for total suspended solids (TSS) and particle facilitated transport in Budhu M, Gobin R (1996) Slope instability from ground-water seepage. J Hydraul catchments. Environ Earth Sci 69(2):373–380 Eng 122(7):415–417 Schuster RL (1995) Landslide dams-a worldwide phenomenon. In: Proceedings of Canuti P, Casagli N, Ermini L (1988) Inventory of landslide dam in the northern the annual symposium of the Japanese landslide society. Kansai Branch, Apennine as a model for induced flood hazard forecasting. In: Andah K (ed) Osaka, pp 1–23 Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 11 of 11 Schuster RL, Costa JE (1986) A perspective on landslide dam. In: Shuster RL (ed) Landslide dams: Processes, risk, and mitigation. Proceedings of a session in conjunction with the ASCE convention. ASCE (Geotechnical Special Publ no. 3), New York, pp 1–20 Sidle RC, Kitahara H, Terajima T, Nakai Y (1995) Experimental studies on the effects of pipe flow on through flow partitioning. J Hydrol 165(1):207–219 Stefanelli CT, Catani F, Casagli N (2015) Geomorphological investigations on landslide dams. Geoenviron Dis 2(1):21 Stubblefield AP, Reuter JE, Dahlgren RA, Goldman CR (2007) Use of turbidometry to characterize suspended sediment and phosphorus fluxes in the Lake Tahoe basin, California, USA. Hydrol Process 21:281–291. https://doi.org/10. 1002/hyp.6234 Tacconi C, Vilímek V, Emmer A, Catani F (2018) Morphological analysis and features of the landslide dams in the cordillera Blanca. Landslides 15(3):507– Takaji K, Yusuke F (2008) Effect of particle gradation on seepage failure in granular soils. In: Sekiguchi H (ed) Proceedings of the 4th international conference on scour and Erosion (ICSE-4), November 5–7, 2008. The Japanese Geotechnical Society, Tokyo, pp 497–504 Uhlir CF (1998) Landslide-dammed lakes: a case study of the Lamabagr and Chanurikharka landslide deposits, Dolakha and Solukhumbu districts, eastern Nepal. J Nepal Geol Soc 18:329–334 Wang F, Dai Z, Okeke CAU, Mitani Y, Yang H (2018) Experimental study to identify premonitory factors of landslide dam failures. Eng Geol 232:123–134 Wilson G (2011) Understanding soil-pipe flow and its role in ephemeral gully erosion. Hydrol Process 25(15):2354–2364 Wilson GV (2009) Mechanisms of ephemeral gully erosion caused by constant flow through a continuous soil-pipe. Earth Surf Proc Land 34(14):1858–1866 Wilson GV, Periketi RK, Fox GA, Dabney SM, Shields FD, Cullum RF (2007) Soil properties controlling seepage erosion contributions to streambank failure. Earth Surf Proc Land 32(3):447–459 Wit JD, Sellmeijer JB, Penning A (1981) Laboratory testing on piping, 517–520. Tenth International Conference on Soil Mechanics and Foundation Engineering, In Xu Q, Fan XM, Huang RQ, Westen CV (2009) Landslide dams triggered by the Wenchuan earthquake, Sichuan Province, Southwest China. Bull Eng Geol Environ 68(3):373–386 Publisher’sNote Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geoenvironmental Disasters Springer Journals

Relationship between seepage water volume and total suspended solids of landslide dam failure caused by seepage: an experimental investigation

Geoenvironmental Disasters , Volume 7 (1) – Apr 28, 2020

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Abstract

Background: Landslide dams inevitably demonstrate the potential for catastrophic failure with high-risk damage to life and property at the downstream site. Hence, knowledge of the internal stability of dam materials is a key to predicting the seepage failure of landslide dams. In this study, experiments were conducted to examine the relationship between seepage volume and total suspended solids (TSS) of seepage water based on hydro mechanical constrains. Understanding the relationship between the seepage volume and TSS with hydro-mechanical constraints supports the prediction of the seepage failure of landslide dams at the field level. Result: Experiments were conducted with a mixed sample of silica sands. Seepage water was collected from a flume tank with the facility to measure the hydraulic gradient, vertical displacement, and seepage water volume. Grain size affected the life span of the dam. The seepage volume increased with the increase in the percentage of silica sand S4, whereas TSS increased with the increase in the percentage of silica sand S8. With the increase in the dam height, the dam life decreases for low coeficient of uniformity of the grain size distribution. With the increase in the reservoir size, TSS decreased, and the total seepage volume increased. Conclusion: Dam failure depends on the particle size, dam geometry, inflow rates, reservoir size, hydraulic gradient, and seepage water volume, and TSS of seepage water. The results indicated that with the increase in fine particles, the life span decreases, and TSS increases. With the increase in the flow rate, the dam life span decreases, and the TSS and seepage volume rate increase.The dam height leads to an increase seepage volume with low TSS, where the life span of the dam also depends on the particle size distribution With the increase in the reservoir size, the seepage water volume decreases with low TSS. Keywords: Landslide dam, Seepage volume, Hydraulic gradient, Total suspended solids (TSS), Inflow rate, Dam height Introduction it may contain debris and loose soils. Hence, a landslide Formation and failure of landslide dams in mountain- dam is composed of heterogeneous or poorly consoli- ous areas constitute a significant natural hazard. A dated material with debris. A landslide dam differs from majority of landslides that block rivers are either caused a constructed embankment dam as it exhibits no con- by heavy rainfall or earthquakes (Schuster and Costa, trol structure for seepage and drainage (Uhlir, 1998; 1986; Canuti et al., 1988; Costa and Schuster, 1988; Awal et al., 2007). A better understanding of premoni- Korup, 2004; Evans et al., 2011; Peng and Zhan, 2012; tory factors, which can easily be measured or observed Casagli et al. 2003; Tacconi et al., 2018). As the land- in actual landslide dams that are at high risk of failure, slide mass shifts from its original position to the river, is crucial for disaster reduction (Wang et al., 2018). In real fields, due to the high risk of failure, limited pa- rameters such as seepage quantity, turbidity of down- * Correspondence: civildhungana@gmail.com stream seepage, vertical displacement of the dam crest, Department of Earth Science, Shimane University, 1060 Nishikawatsu-Cho, Matsue, Shimane 690-8504, Japan © The Author(s). 2020 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 2 of 11 reservoir level, and impounded area can be monitored the development of internal erosion in earth dams and (Dhungana and Wang, 2019). landslide dams (Wit et al., 1981; Brauns, 1985; Maknoon The inflow rate into the reservoir and reservoir and Mahdi, 2010; Wang et al., 2018; Okeke et al., 2016a, volume, dam size, and dam material are important fac- 2016b). Hanson et al. (2010) analyzed the variation in tors that affect the failure of a landslide dam (Schuster the erodibility of different soil materials due to the in- and Costa, 1988). Some authors already reported the ternal erosion of dams by large-scale outdoor model statistics of landslide dams and their failure in various tests. They observed that the rate of erosion in different regions worldwide. They have summarized the import- soil materials varies in order of magnitude. ant characteristics of landslide dams including their Chang et al. (2011) conducted field erodibility tests classification, cause and type of failure, life span, and on two landslide dams triggered by the 12 May 2008, some other important parameters (Costa and Schuster, Ms. 8.0 Wenchuan earthquake in the Sichuan 1991;Korup, 2004; Stefanelli et al., 2015;Xuet al., Province of China and revealed that an increase in 2009; Casagli and Ermini, 1999;Chai et al., 1995; the bulk density is inversely proportional to the coef- Clague and Evans, 1994). ficient of erodibility with depth. Furthermore, Hanson Overtopping, piping, and seepage failure constitute et al. (2010) conducted large-scale physical tests to the typical failures of landslide dams. Dams compris- investigate the impact of erosion resistance on in- ing homogeneous soil mostly undergo failure by ternal erosion in embankment dams and revealed that seepage and downstream slope saturation (Dunning erosion resistance for the same embankment material et al., 2006), whereas piping holes are formed in dams increases with the increase in the compactive effort that are built with mixed soil, depending on the and water content. percentage of the fine content and the interlocking Many studies have been conducted on different land- bond between soil particles. slide dam failures, possibly overtopping, piping, and seep- Failure sequence of a dam was reportedly categorized age (Awal et al., 2007, 2011; Wang et al., 2018). However, into four periods: 1) emergence of seepage water and a majority of these studies highlighted failure patterns, front wetting, 2) hyper-concentrated flow discharge, 3) while only limited studies focused on the seepage failure emergence and development of a dam crest, and 4) and internal erosion. In addition, effects on the turbidity, failure of a dam crest with a sharp increase in its sub- seepage volume, and failure mechanism with different sidence (Wang et al., 2018). Dhungana and Wang parameters of landslide dams were not examined. (2019) described the conditions for the failure and Hence, this study aimed to highlight the relation- stability of the landslide dam for seepage failure, where ship between the seepage volume and TSS of land- trends of total suspended solids (TSS) and the slide dams during failure. In this case, the hydraulic hydraulic gradient were compared under failure and gradient was measured using pore-water pressure sen- stable conditions. sors; vertical displacement was measured using a laser Internal instability is a failure mode of soil subjected sensor at the dam crest; seepage water was collected, to seepage. The seepage failure mode is characterized by and seepage volume was monitored using a pore- the erosion of fine particles through the pore matrix of water pressure sensor. A seepage water sample was the coarse fraction of the soil (Richards and Reddy, collected, and TSS was measured. 2007). Due to the erosion of fine particles, the flow path undergoes expansion, leading to the resistance strength Methods loss of the external load (Ahlinhan et al., 2016). Experimental setup In addition, TSS supports the understanding of the In the laboratory, a flume tank with 0.45 m height × dam material erosion. Turbidity and TSS are identical 0.45 m width × 2.0 m length was prepared for the experi- premonitory factors that can be measured under field ment. On the downstream side of the flume tank, the and laboratory settings (Rugner et al., 2013; Stubblefield flow of seepage water was stopped and diverted into a et al., 2007). Fine particles, which are among coarser tank using holes at a distance of 0.75 m from the dam grains, are almost free from effective overburden and it center (Fig. 1). Experimental studies of the flume tank can migrate under an extremely-low-velocity seepage were performed for the selection of a dam size, including flow (Takaji et al., 2008). Such eroded particles can be the 1 m × 0.6 m × 0.45 m model used by Sidle et al. measured as TSS in the laboratory and in the field (1995), 5 m × 0.3 m × 0.5 m model used by Awal et al. (Dhungana and Wang, 2019). (2007), 1.5 m × 1 m model used by Wilson (2009), 1.4 Several studies (Rinaldi and Casagli, 1999; Lobkovsky m × 1 m model used by Wilson (2011), and 0.5 m × 0.5 et al., 2004; Wilson et al., 2007; Fox et al., 2007) reported m × 0.5 m model used by Fox et al. (2014). In this study, detailed research on seepage erosion for slope failures. the dam heights were 0.2 m and 0.25 m, and upstream Numerous experimental methods were used to simulate and downstream slopes were 45° and 35°, respectively. Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 3 of 11 Fig. 1 Experimental setup of the flume tank. a 3D view; b cross-section; and c longitudinal section The dam height was increased from 0.2 m to 0.25 m monitored at two fixed points by laser sensors. A whereas the downstream and upstream slopes were half-cut polyvinyl chloride (PVC) pipe was fixed constant, and the dam volume was also increased due below the holes with a gentle slope to collect seepage to height increase. Similarly, in the flume tank, the water. The collected seepage water volume was moni- position of the dam was shifted downstream side by tored by the Pwp4 sensor. 0.1 m to increase the reservoir size. The width of dam crest was 0.1 m. On the floor of the flume tank, Material and method adouble-sidedtapewas used,and dry silicasand6 Typically, landslide dams comprise fragmented materials was poured over it to maintain the roughness be- with a wide range of sediment sizes (Costa and Schuster, tween the dam material and flume tank floor. The 1988; Schuster, 1995). It is challenging to scale down ac- flume tank was built using Plexiglas, permitting visi- tual landslide dam material to the laboratory scale. From bility into the flume. The flume bed slope was main- laboratory practice, three mixtures of artificial silica sand tained constant at 1:20 during all experiments. Four were selected for the experiment for seepage failure. Dif- pore-water pressure sensors, with a rated capacity of ferent proportions of a combination of silica sands S4, 50 kPa, were used—hereafter referred to as Pwp1, S5, S6, and S8 were used (Table 1). The main part of the Pwp2, Pwp3, and Pwp4—for the downstream and up- sample was silica sands S5 and S6. Silica sands S4 and stream sides of the dam body and at the reservoir S8 were considered as coarser and finer particles, re- and seepage water collection tank, respectively. Sen- spectively, and mixed with silica sands S5 and S6. Three sors Pwp1, Pwp2, and Pwp3 were connected to the samples, i.e., S456, S4568, and S568, respectively, were flume tank from the base of the flume tank facing prepared in the presence and absence of silica sands S4 upwards. Pwp1 and Pwp2 were covered by the filter and S8. The grain size distributions of the samples are material to control the flow of sand over it. The shown in Fig. 2. Pwp4 sensor was connected to the tank base, where A mixing machine was used for mixing dam materials. seepage water was collected. Multi-function analog Initially, the mixing machine was used for dry mixing, laser sensors (CMOS) were used to measure the verti- followed by mixing with water for affording the desired cal displacement from the top of the flume tank using shape of the dam. Before creating the dam in the flume a wooden frame—hereafterknown as Vdrand Vdl, tank, a sample was collected to estimate its initial water for the right and left sides, respectively. The vertical content. In addition, sensors were placed in their re- displacement of the dam crest was continuously spective positions, and the dam was prepared by layer- Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 4 of 11 Table 1 Mixed ratios and mechanical properties of samples Sample number SS 4 (kg) SS 5 (kg) SS 6 (kg) SS 8 (kg) Water (kg) Total (kg) D C C 50 u c (mm) S456 1 5 5 – 0.5 11.5 0.394 3.075 1.375 S4568 0.5 5 5 0.5 0.5 11.5 0.565 2.185 1.098 S568 – 5 5 1 0.5 11.5 0.557 2.264 1.065 D = median grain size; C = coefficient of uniformity; C = coefficient of curvature 50 u c to-layer compaction, divided into four and six parts for understand the effect of the dam height, reservoir size, dam heights of 0.2 m and 0.25m, respectively. Each layer and inflow rate into the reservoir on hydraulic gradient, comprised ~ 9 kg of sample, and 1–2 kg of sample was vertical displacement, TSS, seepage water volume, and used to obtain the final shape of the dam. Real-time data longevity of the dam for three soil samples prepared by were collected using universal recorders (KYOWA PCD the mix of silica sands S4, S5, S6, and S8. Table 2 sum- 330B and PCD 400). Sampling frequency was two of marizes the experimental details. data per second. A stopwatch was used during the col- Time of landslide dam failure is key factor to reducing lection of a seepage water sample for TSS. After collect- natural disasters. In this study as well, dams failed at ing a sample for TSS, the volume was measured, varying periods under different conditions. The time fac- followed by oven-drying at 105 °C. The dried sample tor plays roles in soil saturation and shear strength re- weight was measured, and the TSS value was calculated. duction. From experiments, the higher the percentage of Seepage water was directly collected into a tank using silica sand S8 in the dam material, the shorter the life the half-cut PVC pipe, and Pwp4 was used to measure span of the dam. Higher the percentage of silica sand S4 the volume. The hydraulic gradient was calculated using in the dam material, the longer the life span of the dam. the pressure head of two sensors, i.e., Pwp1 and Pwp2, Despite this observation, a longer time was taken for the respectively, and the flume tank slope. Pwp1 and Pwp2 seepage water to drain out from the dam body for a were fixed below the dam crest edge downstream and sample containing silica sand S8. The density of the dam upstream of the dam, respectively. The seepage vol- controlled the time for the initial peak hydraulic gradi- ume was calculated using porewater pressure Pwp4 ent, whereas density exhibited a lower effect for the total and tank diameter. life span in contrast to the initial peak hydraulic gradient (Fig. 3). Results and discussion General characteristics of the experiments Effect of inflow rate on dam failure Dam failure leads to flash floods on the downstream Experiments were conducted with three samples, i.e., side. Hence, it is crucial to understand the failure pattern S456, S4568, and S568, respectively, for inflow rates of − 5 3 − 5 3 of landslide dams to minimize natural hazards caused by 1.1 × 10 m /s and 1.667 × 10 m /s. The inflow rates floods. In this study, experiments were conducted to were selected based on practice on these samples to get Fig. 2 Grain size distribution curves of samples used in experiments Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 5 of 11 Table 2 Outline of all experiments under different testing conditions 3 3 Exp. No Sample type Inflow rate (m /s) Dam height (m) Reservoir size Dry density (kg/m ) Initial moisture content (%) −5 Exp1 S568 1.1*10 0.2 1294 2.7 − 5 Exp2 1.67*10 1251 2.7 Exp3 0.25 R1 1269 2.8 Exp4 R2 1223 3.2 −5 Exp5 S4568 1.1*10 0.2 1334 2.7 −5 Exp6 1.67*10 1301 2.9 Exp7 0.25 R1 1234 2.8 Exp8 R2 1241 2.7 −5 Exp9 S456 1.1*10 0.2 − 5 Exp10 1.67*10 1302 2.5 Exp11 0.25 R1 1275 2.8 Exp12 R2 1202 3.0 seepage failures. If we increase inflow rate, the dam fail- the high TSS and dam crest settlement. The rapid in- ure type changed to overflow and if we decrease the in- crease in the hydraulic gradient supported the erosion of flow rate, the dam crest will not failed. Experimental soil particles from the dam body, while the seepage vol- results revealed a time lag between the peak hydraulic ume was comparatively low. gradient (which is responsible for the start of seepage) For the S4568 sample, the initial peak hydraulic and seepage flow out time (referred as TSS starting time gradients were 0.26 and 0.27 for low and high inflow in figures). Inflow rates into the reservoir created varia- rates, respectively, and at the time of failure, the cor- tions in the hydraulic process for different soil types. For responding values were 0.39 and 0.38 (Fig. 5). For the the S568 sample, the initial peak hydraulic gradient that high inflow rate, the total volume of seepage water started seepage was varied from 0.29 to 0.39 (Fig. 4). In was lower, and the TSS value was high, related to the case of the higher inflow rate, the hydraulic gradient was higher rate of seepage water released from the dam decreased from its peak value of 0.39 to 0.23, and again body. With the increase in the percentage of silica started to increase, and the dam crest underwent failure sand S4, the TSS value decreased for both inflow when it reached 0.28. For the low inflow rate, the hy- rates; however, the time taken for failure increased draulic gradient decreased from its peak value of 0.29 to with the increase in the percentage of silica sand S4. 0.21 and again started to increase and undergo failure For the S456 sample, no failure was observed at an − 5 3 when it reached 0.39. The rapid increment in the hy- inflow rate of 1.11 × 10 m /s. The pore water pres- draulic gradient initiated the high seepage gradient, lead- sure at Pwp2 and Pwp3 became constant after 8000 s, ing to the early flow of seepage and shear strength and hence considered as the stable case, whereas for − 5 3 reduction of the dam material. This result in turn led to an inflow rate of 1.67 × 10 m /s, failure was Fig. 3 Effects of density on (a) time for initial peak hydraulic gradient and (b) time for failure of dam crest Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 6 of 11 Fig. 4 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S568 at a low inflow rate (LI) of − 5 3 − 5 3 1.1 × 10 m /s and high inflow rate (HI) 1.67 × 10 m /s. a Hydraulic gradient and vertical displacement; b Seepage volume and TSS observed within 3700 s. The seepage water flow at the instability. For the soil slope instability, downstream lower inflow rate became extremely high, leading to a slope angles and the soil layer gradient are major factors stable dam crest, whereas the TSS and vertical dis- that control the critical hydraulic gradient (Iverson and placement were constant as reported by Dhungana Major, 1986; Budhu and Gobin, 1996). The landslide and Wang (2019). At a high inflow rate, the lowest dam height is a key parameter for examining the stability initial peak hydraulic gradient was observed through- of the natural dam. The increase in the dam height re- out the study, and the vertical displacement sharply duces the stability of the dam crest (Okeke and Wang, increased before failure. At a low inflow rate, the ver- 2016b). Experiments were conducted to understand the tical displacement increased due to cracks in the dam effect of the dam height on the stability, TSS, and seep- crest after that horizontal movement occurred and age water volume. For the S4568 sample (Fig. 6), con- dam crest failed. taining a higher percentage of coarser sand particles and increase in dam height decrease the longevity of dam, Effect of dam height on dam failure which also was in agreement with the results reported A statistical approach proposed a dimensionless break- by Okeke and Wang (2018), which may be possibly re- ing index (DBI) to investigate the stability of the dam lated to the mass block failure in the downstream site (Ermini and Casagli, 2003). This empirical relation pre- and increased percentage of coarser particles and sample dicted the dam stability by using the dam geometry, S4568 has lowest value of coefficient of uniformity. As where the reservoir volumes and dam heights are key the initial peak hydraulic gradient of the higher dam was parameters. The landslide dam size is the major factor greater than that of the lower dam, the instability of the that contributes to the seepage erosion and slope internal structure increased, leading to higher TSS on Fig. 5 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S4568 at a low inflow rate (LI) of − 5 3 − 5 3 1.1 × 10 m /s and high inflow rate (HI) 1.67 × 10 m /s. a Hydraulic gradient and vertical displacement; b Seepage volume and TSS Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 7 of 11 Fig. 6 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S4568 at a Low dam height (LD) (200 mm) and High dam height (HD) (250 mm). a Hydraulic gradient and vertical displacement; b Seepage volume and TSS seepage water. The seepage water volume on the down- increase the time for filling up the entire reservoir, stream side increased with the dam height for all three which will play a role in the stability of the dam body. samples. For the lower dam height, the total seepage The reservoir size was longitudinally increased by 0.1 m, volume was limited in comparison to that for the which increased the reservoir area by 0.043 m . The total higher dam height within the same period. All three time for the failure of the dam crest increased with the samples in this study revealed that the height be- increase in the reservoir size for all three samples. The tween the reservoir water level and dam crest at the maximum hydraulic gradient for the experiment with time of failure increases with the dam height; simi- the S456 sample was increased in comparison to those larly, it increased with the percentage of silica sand with the S4568 and S568 samples. Notably, the times for S4; however, significant settlement in the dam crest the initial peak hydraulic gradient for the S456, S4568, for both cases was observed. The dam crest exhib- and S568 samples were nearly the same, whereas for a ited cracks during the test for a higher dam, and the small reservoir, time for the initial hydraulic gradient crack size increased with the increase in the percent- increased from S456 to S568. age of silica sand S4. For the S568 sample, for the small reservoir, the hy- draulic gradient was greater at the time of failure than Effect of reservoir size on dam failure the initial peak hydraulic gradient, and for the large res- Reservoir area is a leading factor in statistical analysis ervoir, the initial peak hydraulic gradient was greater for proposing DBI. The static pressure caused by the than the failure hydraulic gradient (Fig. 7). Compared to river gradient to the dam body increases if the reservoir the small reservoir, a small amount of hydraulic force size increases. The increase in the reservoir level will was observed at the initiation time of internal instability Fig. 7 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S568 at a small reservoir (SR) and large reservoir (LR). a Hydraulic gradient and vertical displacement; b Seepage volume and TSS Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 8 of 11 Fig. 8 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S4568 at a small reservoir (SR) and large reservoir (LR). a Hydraulic gradient and vertical displacement; b Seepage water volume and TSS for the large reservoir due to which a longer life span hydraulic gradient at the time of failure compared to was recorded. The TSS has increased abruptly before the that observed for a large-sized reservoir. failure of dam crest for both small and large reservoirs. For the S456 sample, TSS was nearly constant for the The vertical displacement was high for the large reser- large reservoir and rapidly increased at the time of failure, voir case, where the seepage water volume was also high, whereas for the small reservoir, TSS slowly increased with and the failure for half part of the dam crest was noticed fluctuation (Fig. 9). The hydraulic gradient for the small for the large reservoir case. reservoir was less than that for the large reservoir, which For the S4568 sample, the TSS value was greater in was different from other experiments with the S568 sam- case of the small-sized reservoir, due to which the ple. Similarly, for the large reservoir, failure hydraulic gra- vertical displacement was also high, and the failure of dient was highest throughout this study, which may be dam crest was observed earlier than in the case of the effect of the reservoir size. Takaji and Yusuke (2008) the large-sized reservoir (Fig. 8). The initial rate of reported that physical parameters such as particle density, seepage water volume for the small reservoir was hydraulic conductivity, and gravel content affect the seep- greater, and the cumulative total seepage water vol- age development in landslide dams and soil slopes, which ume before the dam failure was greater for the large- can be used in this experiment. The seepage rate was sized reservoir. For the small reservoir, due to the nearly the same for large- and small-sized reservoirs, but higher TSS, internal erosion occurred, and the shear the total seepage volume was greater for the large-sized strength of the soil decreased, leading to a low reservoir. Horizontal displacement was noticed for a Fig. 9 Time series data of hydraulic gradient, vertical displacement, seepage volume and TSS for the sample S456 at a small reservoir (SR) and large reservoir (LR). a Hydraulic gradient and vertical displacement; b Seepage volume and TSS Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 9 of 11 Fig. 10 Time taken for failure of dam crest for different conditions small reservoir after the failure of the half part of the dam 1. Experiments conducted on three samples prepared crest; hence, the vertical displacement decreases. by mixing the silica sand revealed that the time of failure of experiments increases depending on the Conclusion changes in the percentages of fine and coarser sand. A series of experiments were performed to investigate Samples with finer particles exhibited a short dam the effects of particle size, inflow rate into the reservoir, life span (Fig. 10) dam height, and reservoir size on the seepage volume, 2. At a low inflow rate into the reservoir, the time of failure, and TSS of for seepage-induced failure of hydraulic gradient to initiate the seepage was less landslide dams using a flume tank. Limit values of hy- than that at the time of failure (Fig. 4 and Fig. 5). draulic gradients were determined under different The internal structure was more stable due to the hydro-mechanical and geometrical conditions. Based on low hydraulic gradient, leading to low TSS and the experimental results, the following conclusions are negligible vertical displacement; however, the total drawn. seepage volume was high Fig. 11 Maximum hydraulic gradient for low inflow rate (LI), high inflow rate (HI), low dam (LD), high dam (HD), small reservoir (SR) and large reservoir (LR) of three samples Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 10 of 11 3. For the sample comprising coarser particles and Managing hydro- geological disaster in a vulnerable environment. Grifo Publishers, Perugia, pp 189–202 small coefficient of uniformity may reduce the Casagli N, Ermini L (1999) Geomorphic analysis of landslide dams in the northern life span of dam, possibly related to the change Apennine. Trans Jpn Geomorphol Union 20(3):219–249 in the permeability and effect of the critical Casagli N, Ermini L, Rosati G (2003) Determining grain size distribution of material composing landslide dams in the northern Apennines: sampling and hydraulic gradient to initiate the seepage or processing methods. Eng Geol 69(1):83–89 internal instability Chai HJ, Liu HC, Zhang ZY (1995) The catalog of Chinese landslide dam events. J 4. With the increase in reservoir volume, the Geol Hazards Environ Preservation 6(4):1–9 Chang DS, Zhang LM, Xu Y, Huang RQ (2011) Field testing of erodibility of two maximum hydraulic gradient exhibited differently landslide dams triggered by the 12 may Wenchuan earthquake. Landslides as that observed in case of inflow rates and dam 8(3):321–332 height (Fig. 11), and the seepage water volume Clague JJ, Evans SG (1994) Formation and failure of natural dams in the Canadian cordillera. Geol Survey Canada Bull 464:1–35 increased, and TSS decreased with the increase in Costa JE, Schuster RL (1988) The formation and failure of natural dams. Geol Soc the reservoir volume. Am Bull 100:1054–1068 5. Although there was a continuous process of the Costa JE, Schuster RL (1991) Documented historical landslide dams from around the world. Bull US Geol Surv:1–486. https://pubs.er.usgs.gov/publication/ hydraulic gradient and seepage and erosion, the ofr91239. hydraulic gradient was predominantly affected by Dhungana P, Wang F (2019) The relationship among the premonitory factors of the inflow rate and dam geometry, whereas the landslide dam failure caused by seepage: an experimental study. Geoenviron Disasters. https://doi.org/10.1186/s40677-019-0135-7 total seepage volume, seepage rate, and TSS Dunning SA, Rosser NJ, Petley DN, Massey CR (2006) Formation and failure of the depended on the particle size of the dam material Tsatichhu landslide dam, Bhutan. Landslides 3:107–113 and reservoir size. Ermini L, Casagli N (2003) Prediction of the behavior of landslide dam using a geomorphological dimensionless index. Earth Surf Proc Land 28(1):31–47 Abbreviations Evans SG, Delaney KB, Hermanns RL, Strom A, Scarascia-Mugnozza G (2011) The TSS: Total suspended solids; PVC: polyvinyl chloride. formation and behavior of natural and artificial rockslide dams; implications for engineering performance and hazard management. In: Evans SG, Acknowledgments Hermanns RL, Strom A (eds) Scarascia-Mugnozza G Natural and artificial The first author would like to express warm gratitude to the Rotary rockslide dams. Springer, Berlin Heidelberg, pp 1–75 Yoneyama Memorial Foundation and the Izumo South Rotary Club for Fox GA, Felice RG, Midgley TL, Wilson GV, Al-Madhhachi AS (2014) Laboratory soil providing a scholarship for the first author. The authors would also like to piping and internal erosion experiments: evaluation of a soil-piping model thank the anonymous reviewers for reviewing the manuscript. for low-compacted soils. Earth Surf Proc Land 39(9):1137–1145 Fox GA, Wilson GV, Simon A, Langendoen EJ, Akay O, Fuchs JW (2007) Measuring Authors’ contributions streambank erosion due to groundwater seepage: correlation to bank pore DP conducted the laboratory work with close coordination with FW. FW water pressure, precipitation and stream stage. Earth Surf Proc Land 32(10): provided guidance and support for data analysis and presentation. DP 1558–1573 drafted the manuscript, and both authors read and approved the Hanson GJ, Tejral RD, Hunt SL, Temple DM. (2010) Internal erosion and impact of manuscript. erosion resistance. In Proceedings of the 30th U.S. Society on Dams Annual Meeting and Conference, April 12-16, 2010, Sacramento, California. p. 773– Funding 784. None. Iverson RM, Major JJ (1986) Groundwater seepage vectors and the potential for hillslope failure and debris flow mobilization. Water Resour Res 22(11):1543– Availability of data and materials 1548 The data sets used and analysed during the current study are available from Korup O (2004) Geomorphometric characteristics of New Zealand landslide dams. the corresponding author on reasonable request. All data used in this study Eng Geol 73(1):13–35 were produced in the department of Earth science laboratory of Shimane Lobkovsky AE, Jensen B, Kudrolli A, Rothman DH (2004) Threshold phenomena in University. erosion driven by subsurface flow. J Geophys Res Earth Surf 109:F04010. https://doi.org/10.1029/2004JF000172 Maknoon M, Mahdi TF (2010) Experimental investigation into embankment Competing interests external suffusion. Nat Hazards 54(3):749–763 The authors declare that they have no competing interests. Okeke ACU, Wang F (2016a) Critical hydraulic gradients for seepage induced Received: 14 November 2019 Accepted: 27 January 2020 failure of landslide dams. Geoenviron Dis. https://doi.org/10.1186/s40677-016- 0043-z Okeke ACU, Wang F (2016b) Hydromechanical constraints on the piping failure of landslide dams: an experimental investigation. Geoenviron Dis. https://doi. References org/10.1186/s40677-016-0038-9 Ahlinhan MF, Koube MB, Adjovi CE (2016) Assessment of the internal instability Peng M, Zhan LM (2012) Breaching parameters of landslide dam. Landslides 9: for granular soils subjected to seepage. J Geosci Environ Protect 4:46–55 13–31. https://doi.org/10.1007/s10346-011-0271-y Awal R, Nakagawa H, Baba Y, Sharma RH (2007) Numerical and experimental Richards KS, Reddy KR (2007) Critical appraisal of piping phenomena in earth study on landslide dam failure by sliding. Annual J Hydraul Eng JSCE 51:7–12 dams. Bull Eng Geol Environ 66(4):381–402 Awal R, Nakagawa H, Fujita M, Kawaike K, Baba Y, Zhang H (2011) Study on the Rinaldi M, Casagli N (1999) Stability of streambanks formed in partially saturated piping failure of a natural dam. Ann Dis Prev Res Institute Kyoto Univ 54: soils and effects of negative pore-water pressures: the Sieve River (Italy). 539–547 Geomorphology 26(4):253–277 Brauns J (1985) Stability of layered granular soil under horizontal groundwater flow. In: Proceedings of the 15th international congress on large dams, Rügner H, Schwientek M, Beckingham B, Kuch B, Grathwohl P (2013) Turbidity as Lausanne 1985 a proxy for total suspended solids (TSS) and particle facilitated transport in Budhu M, Gobin R (1996) Slope instability from ground-water seepage. J Hydraul catchments. Environ Earth Sci 69(2):373–380 Eng 122(7):415–417 Schuster RL (1995) Landslide dams-a worldwide phenomenon. In: Proceedings of Canuti P, Casagli N, Ermini L (1988) Inventory of landslide dam in the northern the annual symposium of the Japanese landslide society. Kansai Branch, Apennine as a model for induced flood hazard forecasting. In: Andah K (ed) Osaka, pp 1–23 Dhungana and Wang Geoenvironmental Disasters (2020) 7:13 Page 11 of 11 Schuster RL, Costa JE (1986) A perspective on landslide dam. In: Shuster RL (ed) Landslide dams: Processes, risk, and mitigation. Proceedings of a session in conjunction with the ASCE convention. ASCE (Geotechnical Special Publ no. 3), New York, pp 1–20 Sidle RC, Kitahara H, Terajima T, Nakai Y (1995) Experimental studies on the effects of pipe flow on through flow partitioning. J Hydrol 165(1):207–219 Stefanelli CT, Catani F, Casagli N (2015) Geomorphological investigations on landslide dams. Geoenviron Dis 2(1):21 Stubblefield AP, Reuter JE, Dahlgren RA, Goldman CR (2007) Use of turbidometry to characterize suspended sediment and phosphorus fluxes in the Lake Tahoe basin, California, USA. Hydrol Process 21:281–291. https://doi.org/10. 1002/hyp.6234 Tacconi C, Vilímek V, Emmer A, Catani F (2018) Morphological analysis and features of the landslide dams in the cordillera Blanca. Landslides 15(3):507– Takaji K, Yusuke F (2008) Effect of particle gradation on seepage failure in granular soils. In: Sekiguchi H (ed) Proceedings of the 4th international conference on scour and Erosion (ICSE-4), November 5–7, 2008. The Japanese Geotechnical Society, Tokyo, pp 497–504 Uhlir CF (1998) Landslide-dammed lakes: a case study of the Lamabagr and Chanurikharka landslide deposits, Dolakha and Solukhumbu districts, eastern Nepal. J Nepal Geol Soc 18:329–334 Wang F, Dai Z, Okeke CAU, Mitani Y, Yang H (2018) Experimental study to identify premonitory factors of landslide dam failures. Eng Geol 232:123–134 Wilson G (2011) Understanding soil-pipe flow and its role in ephemeral gully erosion. Hydrol Process 25(15):2354–2364 Wilson GV (2009) Mechanisms of ephemeral gully erosion caused by constant flow through a continuous soil-pipe. Earth Surf Proc Land 34(14):1858–1866 Wilson GV, Periketi RK, Fox GA, Dabney SM, Shields FD, Cullum RF (2007) Soil properties controlling seepage erosion contributions to streambank failure. Earth Surf Proc Land 32(3):447–459 Wit JD, Sellmeijer JB, Penning A (1981) Laboratory testing on piping, 517–520. Tenth International Conference on Soil Mechanics and Foundation Engineering, In Xu Q, Fan XM, Huang RQ, Westen CV (2009) Landslide dams triggered by the Wenchuan earthquake, Sichuan Province, Southwest China. Bull Eng Geol Environ 68(3):373–386 Publisher’sNote Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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