Toe Of Slope Research Articles

Source and Accumulation of Soil Carbon along Catena Toposequences over 12,000 Years in Three Semi-Natural Miscanthus sinensis Grasslands in Japan

Miscanthus-dominated semi-natural grasslands in Japan appear to store considerable amounts of soil C. To estimate the long-term effect of Miscanthus vegetation on the accumulation of soil carbon by soil biota degradation in its native range, we measured total soil C from the surface to a 1.2 m depth along a catena toposequence in three annually burned grasslands in Japan: Kawatabi, Soni, and Aso. Soil C stock was estimated using a radiocarbon age and depth model, resulting in a net soil C accumulation rate in the soil. C4-plant contribution to soil C accumulation was further estimated by δ13C of soil C. The range of total soil C varied among the sites (i.e., Kawatabi: 379–638 Mg, Soni: 249–484, and Aso: 372–408 Mg C ha−1). Catena position was a significant factor at Kawatabi and Soni, where the toe slope soil C accumulation exceeded that of the summit. The soil C accumulation rate of the whole horizon in the grasslands, derived C mainly from C4 plant species, was 0.05 ± 0.02 (Average ± SE), 0.04 ± 0.00, and 0.24 ± 0.04 Mg C ha−1 yr−1 in Kawatabi, Soni, and Aso, respectively. Potential exists for long-term sequestration of C under M. sinensis, but the difference in the C accumulation rate can be influenced by the catena position and the amount of vegetation.

Geometrical profile of cohesive-frictional soil slopes for optimal stability

: In this study, finite element method with strength reduction technique is employed to study the stability of slopes with non-straight line profiles comprises three segments. According to this method, the strength parameters are reduced until the slope becomes on the verge of failure. A software called (Optum G2) is used to analyze the geometrical and mechanical parameters. The effect of the geometrical shape of the slope with specific limitations on the factor of safety (FOS) has been investigated to find the corresponding profile configuration that provides maximum stability. The profile (slope face geometry) has been divided into three straight lines (segments) with different lengths. The study involved the soil cohesion (c), angel of internal friction (∅) and the angle of the imaginary straight line linking the slope toe with slope crest (β) called herein slope inclination. The main results showed that using the three segments facing profile can increase the factor of safety (FOS) by up to 15% in comparison with the corresponding slopes of straight line profile. Design charts has been introduced to be utilized by engineers and practitioners to obtain the geometrical parameters for the optimal profile as well as the expected improvement percentage in factor of safety.

Studies on the Genesis of Soils in Jong River Basin in the Northern Province of Sierra Leone

The soil resources of Sierra Leone remain an integral part of sustainable agricultural development but knowledge of the suitability of soils and their management requirements for a variety of land uses is still lacking to a greater extent. In this view, a detailed soil survey of three chiefdoms in Northern Sierra Leone was undertaken to evaluate the genesis of soils and interpret soil-landscape properties and their relationships using the toposequence and free style approach of soil survey. Three major soil types, viz, gravelly, gravel-free over gravel and gravel-free soils, formed either directly or indirectly from weathered and disintegrated parent materials of two geologic origins namely Rokel River Series (comprising of sandstone, shale and mudstone), and Granite and Acid Gneiss were identified. The gravelly soils are formed from sandstone and sandy shales of the Rokel River Series, which upon weathering released iron and hydrated oxides that hardened into plinthite upon drying. The gravel-free over gravel soils are formed from acid gneiss containing acid and intermediate igneous and metamorphic rocks, which upon weathering produced sandy clay textured soils whereas the gravel-free soils are derived from sedimentary rocks (shales and mudstones) of Rokel River Series, which upon weathering and action of organisms produced sandy clay loam and sandy clay textured soils. The gravel-free over gravel soils are mostly located in the summit and back slopes and show dark brown to dark yellowish-brown hue and moderate chroma, weak to moderate structure and absence of coarse fragments in the 0 - 40 cm layer, and a strong brown hue and high chroma, very weak fine angular blocky structure having abundance of coarse fragments from 40 cm and above. In these soils, the compactness of ironstone and sandstone gravels increases with depth. The gravel-free soils are found on three landscape positions, viz, back slopes, foot slopes and toe slopes. On the back and foot slopes, the soils are characterized by very dark brown to dark yellowish-brown hue and high chroma, sandy loam to sandy clay texture, coarse angular to moderate sub-angular blocky structure and absence of coarse fragments throughout the horizon. In these soils, the clay content and sand grain sizes were observed to increase with depth. On the toe slopes, the soils show black to greyish-brown hue and low chroma, silty loam to sandy loam, structureless and high water holding capacity.

Variations in Soil Physico-Chemical Properties as Influenced by Landuse in a Toposequence

Soil, water and air work interchangeably for optimum growth and productivity. Soil as a resource provides crops with essential nutrients necessary for growth and human consumption. With the insurgence of high population growth leading to pressure on lands, poor land management etc., this tendency of the soil as a nutrient pool is seen to be dwindling. It is therefore prudent to investigate and understand the dynamism of soil properties to inform proper management. Understanding topography effects and assessing soil properties on different slope positions is a first-hand step in ensuring proper soil management practices. This paper considers the assessment of physico-chemical properties of soils located on different slope gradients and land use types on the Wamaso research site in Ghana made principally of cape coast granite. In all, eighteen samples were collected from identified horizons of five distinctive subsections of the slope were delineated as follows, summit (PP1), shoulder (PP2), middle (PP3), foot slope (PP4) and toe slope (PP5) respectively. Remarkable variations were observed within PP1 to PP3 and then PP5. Pearson’s correlation index revealed that the associations between most of the soil physico-chemical were not consistent across the identified slope positions. The biplot of the first two principal components together is 68.3% of the total variation and might be interpreted as change in Cation exchange capacity, sodium, sand and clay. On the first axis highlights the influence of sand and clay on soil fertility, also the relationship between pH and Na. Organic carbon derived from organic matter contributes to the availability of the basic soil cations and therefore enhances ECEC of the soils and hence the relationship obtained from the biplot. In sum, this research achieved the objective which sought to substantiate indeed the impact topography has on soil physico-chemical properties thereby serving as a reference for the classification of the soils identified.

Field Application of Mulberry Straw Arch in Ecological Bank Revetment

With the growing level of awareness and increasing demand for environmental protection, timber pile revetments with significant ecological effects have experienced increasingly wide application in China. The current timber pile revetment system has two problems: continuous dense piles have high construction costs and require large timber consumptions, while the discrete pile-bamboo fence systems have poor retaining effects. Considering these problems, an original revetment structure form is proposed: a discrete pile-mulberry straw arch structure. To investigate the mechanical properties of the mulberry straw, some mechanical tests are conducted on mulberry straw and its arch structure. It is found that the average compressive strength of mulberry straw is 2.30 MPa, the bending strength is 20.08 MPa and the shear strength is 2.99 MPa; considering the structural characteristics of arches, mulberry straw arches have a high bending strength, which affords immense potential for their application in revetment structures. Furthermore, by doing field study of the discrete timber pile-mulberry straw arch structure for bank revetment, it is found that the arch height of the mulberry straw arch changes 1.4–1.6 cm after 489 d observation. The soil settlement before the straw arch is 0.13–0.18 cm and the settlement of the pile is 0.66– 0.72 mm. Compared with bamboo fence structure, the cost of using mulberry straw arch structure as revetment material can save up to 27.07%. Therefore, the discrete timber pile-mulberry straw arch has a rational and stable structure that provides effective support for protecting the riverbank and the toe of gentle slopes and effectively prevents the collapse of bank slopes in the rear. The new revetment structure proposed in this paper has signifi- cant ecological and economic effects, is easy to construct and feasible for standard production, and consequently has great application potential.

Deformation Characteristics and Safety Evaluation of the Throw Filling Soft Clay Cofferdam under Super‐Historical Flood Conditions

Affected by super‐historical flood, the surface deformation of throw filling soft clay cofferdam is obvious and the stability of the cofferdam slope is difficult to ensure. Relying on the cofferdam project of Jiangxi Xinjiang Shuanggang navigation power junction and according to the data of filed investigation and automatic monitoring, the Plaxis infinite element software is used to analyze the deformation characteristics and stabilities of cofferdam during the super‐historical flood period, and the effective emergency reinforcement measures are presented. The results show that (1) the stability of cofferdam is controlled by downstream face slope of cofferdam during the super‐historical flood period, and there is a most dangerous slide surface interpenetrating through the top to the toe of downstream face slope; (2) the stability of upstream face slope is influenced significantly by the water level fluctuation and it is reduced sharply during the water level decline process; and (3) real‐time remote monitoring can effectively reflect the deformation and failure characteristics of cofferdam under the condition of super‐historical flood level and provide early warning and prediction in time. The results and analyzing methods can be applied to analyze the similar projects excellently.

Stability Analysis of Loess High Slope under Dynamic Compaction Based on Matrix Discrete Element Method

In order to investigate the safety and stability of loess high slope under dynamic ramming, the MatDem software was used to simulate the process of heavy rammer compacting the spot which was 11 m away from the toe of loess high slope. The rammer was applied with different energies of 10000 kN·m, 8000 kN·m, and 6000 kN·m. In this way, the safety and stability of slope under the action of different dynamic tamping energies can be determined. The results show that the loess high slope presented circular landslide damage by dynamic compaction. Under the same ramming times, with the decrease of ramming energy, the damage degree of loess high slope gradually reduced. According to the displacement value of different monitoring points, the large horizontal and vertical displacement points in landslide were obtained. When the ramming energy was 10000 kN·m and 8000 kN·m, the maximum horizontal displacements were 15.45 m and 10.72 m, and the maximum vertical displacements were 17.43 m and 11.91 m. When the ramming energy was 6000 kN·m, the soil at the bottom of slope would produce slight vibration. Considering the actual project, when the ramming energy was 10000 kN·m and 8000 kN·m, the minimum safe distance was recommended to be 25 m and 20 m. When the ramming energy was 6000 KN·m, the slope remained stable as a whole, and the minimum safe distance suggested should not be less than 11 m. A safety distance of collapse of loess high slope under dynamic compaction was determined, which provided a strong safety guidance for loess high slope construction under dynamic compaction.

Seismic Behavior Analysis of the Bank Slope Considering the Effect of Earthquake-Induced Excess Pore Water Pressure

Soil slopes, located near rivers or the sea, often get damaged dramatically under seismic action due to the high groundwater level. To determine the failure mechanism, this study proposed an analytical method for a composite critical slip surface of a multi-layer slope considering the effects of the excess pore water pressure using the Newmark’s method and variational principle. Based on this, a method for evaluating the effects of the excess pore water pressure on the permanent displacement of the slope under seismic action was established, and influence mechanisms of the excess pore water pressure on failure modes of the multi-layer bank slope at different groundwater levels were studied. The research results show that slip surfaces basically have same shapes at different groundwater levels; however, with the rise of the groundwater level, soil above a seepage line is not affected by the excess pore water pressure, and its sliding scale slightly changes. For soil below the seepage line influenced by the excess pore water pressure, the slip surface constantly extends to the interior of the slope, resulting in the increase in the sliding scale. Due to the cumulative increase in the excess pore water pressure, the bank slope at different groundwater levels is generally manifested as shear sliding at the slope toe and tensile fracture at the top. Finally, based on the shaking table test, the proposed method was verified to be reasonable and accurate. This research provides a simple and reliable method for slope engineering technicians to evaluate the stability of water-rich soil slopes.

Study on the Influence of Various Rainfall Types on the Stability of High and Steep Slopes

Taking the high and steep slope of a ski resort as the background, in order to ensure the structural safety of the slope in the subsequent complex rainfall environment, the calculation principle of unsaturated soil slope stability is summarized, and the parameter interaction analysis is proposed. The numerical simulation method is used to study the influence of various rainfall types on slope stability; combined with a multiparameter combination, the slope stability is analyzed. The results show that different types of rainfall have a significant impact on the safety factor of the slope, the safety factor of the slope under the front rainfall type is the smallest, the minimum value is 1.38, and the front rainfall mostly occurs in the late summer, so it is necessary to avoid construction in the late summer or do a good job of safety monitoring in the late summer. Through setting monitoring points, it is found that the pore water pressure of the three positions from small to large is in the order of slope toe<slope middle<slope top, and the pore water pressure at the slope toe is basically 0 kPa. At this time, the matric suction at the slope toe is the minimum, so the protection should be strengthened. In the combination analysis of the four parameters, the direct effect and coupling effect of C15 are at a small level, which indicates that when the four parameters fluctuate together, the mutual coupling is not the effect of a single parameter, which provides a theoretical reference for the follow-up related research.

An image recognition method for the deformation area of open-pit rock slopes under variable rainfall

Due to human mining action, relatively fragile open-pit mine rock slopes are prone to instability induced by heavy rain. Accurately identifying the information and area of deformation features on rock slopes is a key step for landslide disaster warning and prevention. This study simulates the deformation process of a large and steep rock slope in Dexing City, Jiangxi Province, China, under a variable rainfall event. The test results show that 1) the increased deformation region has positive relationships with increasing pore water pressure and water content values for the open-pit mine rock slope affected by heavy rainfall. 2) The infiltration of variable rainfall on the rock slope softens the weak interlayers and leads to failure of the slope toe first. Due to the action of gravity, the middle and upper parts slide and fail in sequence. In addition, an improved region growing segmentation method (IRGSM) is proposed based on the combination of multipixel seed points and point cloud coordinates for the image recognition of the deformation area of open-pit mine rock slopes. An error comparison with the original region growing segmentation method (ORGSM) shows that the average identification error in the X and Y directions by the method is reduced significantly (6.56% and 5.32% in IRGSM; 13.37% and 11.29% in ORGSM). This method may be applied to identify rock slope deformation in complex scenes with high precision.

Analysis of an excavation-induced landslide in stiff clay using the material point method

The results of an analysis concerning a landslide occurred in Calabria (Southern Italy) in 2014 are presented. This landslide was triggered by some excavations carried out at the slope toe to allow the construction of a power plant. Failure developed mainly within a thick layer of stiff clay that experienced a pronounced strain-softening behaviour during the laboratory tests. The landslide involved some gabion walls and a sheet-pile wall, which were severely damaged. The paper focuses on the triggering mechanism of the landslide and on its evolution after the slope failure (run-out process). To simulate the occurred deformation processes, the material point method (MPM) is used along with a strain-softening Mohr–Coulomb constitutive model in which the soil strength reduces with increasing deviatoric plastic strain. In this connection, an analytical and simple to use methodology is proposed to reduce the mesh influence on the numerical results. The study shows that a progressive failure occurred in the slope owing to the excavations. Location of the failure surface, displacement magnitude and final configuration of the landslide body resulting from the numerical simulation are in good agreement with the observed ones. Some kinematical aspects of the landslide are also discussed.

Effect of Different Reinforced Load Transfer Platforms on Geosynthetic-Reinforced Pile-Supported Embankment: Centrifuge Model Test

Geosynthetic-reinforced pile-supported (GRPS) embankment has been widely utilized in the railways and highways subgrade of soft clay area. The load transfer platform (LTP), consisting of sand layers and one or more layers of geosynthetic, is constantly used at the base of embankment to increase the load transfer to piles and reduce the differential settlement of embankment surface. However, the effect of different reinforced LTPs on the performances of GRPS embankment has not been fully understood. Eight centrifuge model tests were conducted to investigate the effect of five influence factors on deformation and load transfer of embankment, and tensile force of geogrid: placing geogrid or not, the number of geogrid layers, geogrid reinforced position, geogrid stiffness, wrapped-back geogrid setting in LTP. The results showed that the wrapped-back geogrid setting in the LTP was equivalent to anchoring the geogrid at the slope toe of embankment, which strengthened the reinforcement-soil interaction and restricted the pull-out displacement of geogrid to enhance the stiffness for LTP. The LTP reinforced with stiffer geogrid or multi-layer geogrid contributed to increase the stability and load transfer of embankment due to the increase of the integrity stiffness for LTP. When the geogrid was set at the middle of LTP, the performances of the GRPS embankment was enhanced due to the more interfaces between the geogrid and soil to improve the integrity stiffness of the LTP. The two-layer geogrid reinforced in the LTP could be the best choice to enhance the performance of the GRPS embankment under the comprehensive consideration of the performance and economy. The five setting ways of the reinforcement in LTP increased the integrity stiffness of LTP, which provided more methods to enhance the performances of the GRPS embankment.

Environmental Implications of Municipal Dump Site on Soil Nitrogen in Calabar Metropolis, Nigeria

Organic matter exhibit strong variations in nitrogen retention and transformation cycle in soil. However, nitrogen could be altered by seasonal variations, leading us to hypothesize that the open municipal waste dump site in Calabar exposed to dry and wet season could alter nitrogen dynamics in that soil. A total of sixty (60) composite soil samples were collected at different landscape positions (summit crest, shoulder slope, toe slope, interfluve slope, valley floor) of a municipal dump site and a control (no refuse area) during the dry and wet seasons in Calabar and analyzed to ascertain the effects on forms and status of soil nitrogen. The soils were loamy sand across the study location with pH values of 4.50, 7.00, 6.70, 7.30, 5.00, 7.30 (dry season) and 5.00. 7.30, 7.00, 7.40, 5.90, 7.40 (wet season) for the control, summit crest, shoulder slope, toe slope, interfluve slope and valley floor accordingly. Values obtained for total nitrogen (N) from the study site were generally low (<0.21 %), with values for dry season slightly higher than the wet season. NH4+ recorded higher content in wet than in dry season with values ranging between 12.11-14.11 mg/kg (control), 14.60 - 15.90 mg/kg (Summit crest); 18.25 - 20.05 mg/kg (Shoulder slope), 18.30 - 20.20 mg/kg (Toe slope), 12.30 - 14.00 mg/kg (Interfluve slope) and 9.24 -11.07 mg/kg (Valley floor). The Shoulder and toe slopes recorded the highest NH4+ concentration in the wet season. N02- contents documented for the control site were within the ranges of 2.78- 3.20 and 3.22-3.62 mg/kg while the dumpsite had values between 2.49-3.45 and 2.98 -3.22 mg/kg was observed for the shoulder position, the toe slope contained between 2.30-2.75 and 2.70 -2.82 mg/kg, the inter fluve slope had similar ranges of 2.32-2.90 and 2.70-3.08 mg/kg, and the valley floor 2.45-2.60 and 2.78-2.98 mg/kg. N02- values were higher for the wet than dry season. NO3- nitrogen was observed to be excessive across the dumpsite with the highest values > 80 mg/kg obtained at the valley floor. The NO3- values were higher in dry season across the all the landscape positions than in the wet season. The values were equally higher for the dumpsite than the control. It was observed that the dumpsite soils contend excessive NO3- which could be converted to nitrous oxide (N2O) thus contributing to green house (GHG) emissions. It was also noted that seasonal variation did not significantly affect the N content at the different landscape positions of the municipal dumpsite in Calabar. It is highly recommended that municipal waste be sorted and the organic materials composted to harness the rich NO3- content as observed in this research.
 
 Received: 22 September 2021 / Accepted: 25 October 2021 / Published: 5 November 2021

Movement characteristics of a creeping slope influenced by river erosion and aggradation: Study of Xinwulü River in southeastern Taiwan

The average surface displacement rate of 0.1 m/year of the studied slope adjacent to the Xinwulü River has been measured over the past three decades. Damage to the retaining structures of a highway and tunnel through the slope has frequently been reported. Maintenance and reconstruction have been required at intervals of several to ten years. In this study, multi-temporal remote sensing images, site investigations, and ground and tunnel monitoring are interpreted to clarify the movement characteristics of the slope and the factors that affect them. The results of this study reveal that riverbed erosion and aggradation of the adjacent river dominate the movement characteristics of the slope. When the riverbed is low, the direction of slope movement ranges between that of the maximum slope gradient and the dip direction of foliation. Gravitational deformation, which is associated with a deep slip surface, is the main cause of movement; it is facilitated by gullies that develop upward from the sides of the Xinwulü River and the surrounding sliding masses. When the riverbed is high as a result of the aggradation of debris from upstream, the slope moves in the direction of the maximum gradient. Water washes out the slope toe, which has a relatively low strength because it has previously been displaced. Slope collapses occur frequently along the river bank, and gullies actively grow upward, stimulating the movement of the sliding masses with a shallow slip surface. Furthermore, the cyclic erosion and aggradation of the river account for the formation of shallow and deep slip surfaces of 33 m and 90 m, respectively. The results of this study demonstrate the effects of riverbed erosion and aggradation on the creeping deformation and stability of the adjacent slope in the Xinwulü River region; this is valuable for formulating countermeasures to protect the study site and maintain the existing tunnel.

Analysis of Stability of Concealed Cataclinal Slopes with Talus Deposits Accumulated at Their Toes with Respect to Biplanar Failure

Talus deposits naturally form to a certain height in the toes of slopes because of the accumulation of collapsed material and small landslides. However, the stability of concealed cataclinal slopes with talus deposits accumulated at their toes (referred to as TDAT-CC slopes) with respect to biplanar failure is rarely studied. In this work, the typical geological profiles associated with TDAT-CC slopes are summarized and generalized and their failure modes are classified. A qualitative analysis of their stability is also carried out. The biplanar failure process is investigated by analyzing the development of plastic failure and displacement deformation using Universal Distinct Element Code. The analysis reveals the penetration process occurring in the biplanar sliding planes and clarifies the compression–shear failure processes taking place in such slopes. A new method for determining the stability of TDAT-CC slopes and predicting the failure surface formed is proposed based on limit-equilibrium theory and a model consisting of sliding mass blocks. Finally, the proposed method is used to calculate the stability of TDAT-CC slopes with deposits of different shapes and strengths and the results compared with the results of numerical simulations. The results obtained using the two methods are generally consistent. The talus deposits at the toe of the slope play the role of a toe buttress and help improve the slope’s stability. The safety factor of the slope increases as the inclination of the toe deposits becomes gentler; it also increases as the height of the toe deposits increases. The method proposed offers a sound basis for investigating biplanar failure in TDAT-CC slopes.

Seismic Analysis of a Limestone Rock Slope Through Numerical Modelling: Pseudo-Static vs. Non-Linear Dynamic Approach

In the present work, a seismic analysis was performed in advance on a limestone rock slope (height = 150 m) outcropping along the Tagliamento River valley, in the Friuli Venezia Giulia Region, north-eastern Italy. The analysed slope is characterised by strong rock mass damage, thus resulting in a critical stability condition (unstable volume = 110,000–200,000 m3). The seismic analysis was performed adopting the 2D finite difference method (FDM) and employing both a pseudo-static approach and a non-linear dynamic approach. Model outcomes demonstrate that the seismic motion induces internal, localised ruptures within the rock mass. Some important differences in the mechanical behaviour of the rock slope were highlighted, depending on the specific modelling approach assumed. When adopting a pseudo-static approach, the slope failure occurs for PGA values ranging between 0.056 g and 0.124 g, depending on the different initial static stability condition assumed for the slope (Strength Reduction Factor SRF = 1.00–1.15). According to the non-linear dynamic approach, the slope failure is achieved for PGA values varying between 0.056 g and 0.213 g. Pre-collapse slope displacements calculated with the pseudo-static approach (12–15 cm) are much more greater than those obtained through the non-linear dynamic approach (0.5–3 mm). The modelling results obtained through the non-linear dynamic analysis also testify that the seismic topographic amplification is 1.5 times the target acceleration at the slope face and 2.5 times the target acceleration at the slope toe.

Retraction Note: Slope rainfall environment characteristics based on target tracking algorithm and economic efficiency of green city

With the rapid development of China’s economic construction, large-scale infrastructure construction has been carried out in the slope area. However, due to the poor geological environment, concentrated rainfall, and limited land resources in the region, a large number of slope toe excavation and graded slope cutting are carried out in the process of engineering construction. The unreasonable excavation method destroys the original slope shape and affects the stability of the slope, which brings many geological disasters in the loess area. Therefore, it is of great significance to analyze the influence of rainfall and excavation on the deformation and stability of loess slope. Considering the practical application, this paper also considers the target tracking on FPGA. The target tracking algorithm on FPGA must be reliable, real-time, meet certain tracking accuracy, and have certain operability. The proposed target tracking algorithm combines Harris method and optical flow method. Firstly, Harris method is used to extract some target angle features, and then optical flow method is used to match angle features more accurately for subsequent video frames. When the target is rotated or twisted, the barycenter algorithm is used to calculate the barycenter of the matching features. Based on the above research, this paper draws the following conclusions: the overall level of green economy efficiency is unbalanced; There is a U-shaped relationship between urban economic development and environmental pollution; The main influencing factors of urban green development efficiency are industrial structure, economic development degree, opening degree, financial development level, and human capital.

Field model experiments and numerical analysis of rainfall-induced shallow loess landslides

Shallow loess landslide induced by rainfall is a widespread form of slope failure on the Loess Plateau of China. The hydrological response, evolutionary mechanism and failure processes of unsaturated loess slopes under precipitation in a field scale are currently lacking. Three groups of full-scale field experiments with different rainfall intensities were conducted in Jingyang County, Northwest China. Instrumentations including soil moisture sensors, tensiometers and earth pressure cells were installed in the slope. This paper presents the results from three types of sensors to reveal the surface infiltration process and deformation characteristics of unsaturated loess slopes. In addition, SEEP/W and SLOPE/W were selected to quantify the effects of soil suction strength on the stability of the homogeneous loess slope. The results show that the maximum infiltration depth of homogeneous loess slope after two days of continuous heavy rainfall is about 0.6 m. The infiltration depth and seepage velocity on the slope crest and slope toe are faster than the middle of the slope; The decrease amplitude and decrease speed of matric suction increase with the increase of rainfall intensity. Moreover, it is found that the rainfall intensity only affect the development of slope deformation and failure in terms of the time scale, but has little influence on the failure mode; Tensile cracks at the slope shoulder develope more rapidly due to the creep deformation of slope, the deformation and failure at the slope shoulder are the key factors controlling the occurrence of loess landslides. In addition, the proportion of suction strength in shear strength is limited, and the finiteness of the suction strength determines that its attenuation will not determine the stability of homogeneous loess slope without preferential infiltration channels. However, the increase of positive pore water pressure at the potential slide surface may be the key factor to determine the slope failure.

Three-Dimensional Numerical Investigation on the Seepage Field and Stability of Soil Slope Subjected to Snowmelt Infiltration

Cutting slope failures occur frequently along the high-speed railways in Northeast China during the construction due to snowmelt infiltration. This study addresses this issue by applying a three-dimensional numerical model. The influence of the depth of accumulated snow (ds), daily temperature variation (ΔT), and freeze-thaw (F-T) cycles on the seepage field and stability of cutting slopes is discussed. The results demonstrate that water seepage due to snowmelt infiltration primarily extends through the ground surface by about 10 m. The deep-seated instability is likely to occur under a prolonged and highly accumulated infiltration, while shallow failure is associated with intense, short-duration snowmelt infiltration. The maximum degree of saturation (Sr) and pore-water pressure (PWP) values are observed at the slope toe. Increasing ds and ΔT increase the Sr and PWP due to snowmelt infiltration and thereby decreases cutting slope stability. Compared to the ds and ΔT, the F-T cycle is more likely to cause slope failure. In addition, the F-T cycle also induces the reduction of soil strength and the crack propagation. Overall, the conducted study provided useful help toward the process of safer design for cutting slope along the high-speed railway in seasonally cold regions.

Analysis and numerical simulation of toppling deformation and failure characteristics of anti-dipping rock slope under impoundment

High dam engineering is characterized by high water head, steep slope and complex geological conditions. Excavation or water storage will destroy the original equilibrium state of the bank slope and induce the deformation of the bank slope. Based on the monitoring data, this paper analyzes the spatio-temporal evolution of slope deformation during the impoundment of a reservoir bank in China. On this basis, considering the influence mechanism of water pressure, temperature, rainfall, seepage, rock mass rheology and other factors on slope deformation in the process of water impoundment, a statistical regression model of slope deformation is established, and the regression analysis of the deformation process of typical measuring points is carried out, and the main influencing factors of slope deformation are analyzed. Based on regression analysis, the slope deformation and failure process under impoundment are simulated and the influence degree of effective stress change and parameter weakening of rock mass on bank slope deformation and failure in the process of seepage field change is studied to reveal the main inducement of slope deformation under impoundment through the fractured rock mass seepage-stress-rheology coupling finite element analysis method. The results show that the slope deformation is the rheologic deformation triggered by the decrease of effective stress at slope toe caused by the rise of water level and the softening of rock mass, and the toppling form is the dominant one in space.