Clay Slopes Research Articles

Reliability analysis of excavated slopes in undrained clay

Reliability analysis of excavated slopes in undrained clay

A systematic review of clay shale research development for slope construction

The issue of stability controlling cutting slopes is particularly important in clay-shale slopes, a typical expanding sedimentary layer with poor engineering geological conditions and mechanical characteristics. Therefore, research on the causes of failure and remedies for clay-shale cutting slopes is required to serve as an overview for handling and preserving clay-shale slopes in identical conditions. However, the trusted information about the need for further related clay shale research and clay shale in slope stability has yet to be specifically presented. This review study summarizes the published research for clay shale beginning in 1980, presents a bibliometric analysis to examine the published research based on year and country, and provides various study trends in cluster diagram using the VOSviewer program. The analysis also summarized some key goals, effective methodology, and significant findings from the most recent studies to extract information from them that would benefit future research. In conclusion, the results show the need for developing research to fill the knowledge gap regarding clay shale, landslide, and clay mineralogy. In addition, the clay shale slope analysis has revealed the need for additional research into dynamic force and its deformation.

A new p – y curve criterion for piles in proximity to undrained clay slopes

In this paper, a systematic study of the soil – pile interaction of a laterally loaded pile in proximity to undrained clay slope is conducted. The emphasis is on a modified actual displacement of the induced soil resistance in the p – y curve criterion by considering the displacement of the slope surface. On the above basic, the effect of slope on the ultimate soil resistance is also considered. A new p – y curve criterion, which divides the p – y curves in front of the pile into three cases, is proposed. Finally, the accuracy of the new model is verified through a pile test and two hyperbolic p - y curve criterions. The new criterion not only automatically reduces the stiffness of the p - y curve, but also reasonably reveals the effect of slope on the soil-pile interaction.

Effects of construction waste clay bricks on growth of pepper and improvement of clay properties

Pot experiment, indoor detection and triaxial experiment were carried out to study the effects of construction waste clay bricks on the growth of pepper and improvement of clay nutrient and strength properties. The clay from southern Shaanxi was rolled and screened by 2mm, and the construction waste clay bricks were ground to 0-2, 2-5 and 5-7 mm. Construction waste with different particle sizes was mixed with clay in a mass ratio of 0:1 (CK), 1:1, 1:2, and 1:3. Construction waste accounted for 0, 50, 33 and 25% in the four mixed matrices, respectively. About 33~50% construction waste clay bricks with particle size of 5~7mm mixed with pure clay showed higher nutrient levels than that of pure clay. The plant height and yield of cultured pepper were the highest in construction waste clay bricks of 33~50%, with particle size of 5~7mm mixed with pure clay and the soil strength 33.2% higher than that of pure clay. This treatment provides sufficient nutrient conditions for plant growth. This not only provides sufficient nutrient conditions for pepper growth, but also meets the corresponding shear strength and suitability for clay area soil improvement, especially for clay slope stability improvement. The application value and prospect of using construction waste in land engineering construction and soil organic reconstruction and identified a new way of utilizing construction waste as a resource were explored. Bangladesh J. Bot. 52(2): 503-514, 2023 (June) Special

Effects of construction waste clay bricks on growth of pepper and improvement of clay properties

Pot experiment, indoor detection and triaxial experiment were carried out to study the effects of construction waste clay bricks on the growth of pepper and improvement of clay nutrient and strength properties. The clay from southern Shaanxi was rolled and screened by 2mm, and the construction waste clay bricks were ground to 0-2, 2-5 and 5-7 mm. Construction waste with different particle sizes was mixed with clay in a mass ratio of 0:1 (CK), 1:1, 1:2, and 1:3. Construction waste accounted for 0, 50, 33 and 25% in the four mixed matrices, respectively. About 33~50% construction waste clay bricks with particle size of 5~7mm mixed with pure clay showed higher nutrient levels than that of pure clay. The plant height and yield of cultured pepper were the highest in construction waste clay bricks of 33~50%, with particle size of 5~7mm mixed with pure clay and the soil strength 33.2% higher than that of pure clay. This treatment provides sufficient nutrient conditions for plant growth. This not only provides sufficient nutrient conditions for pepper growth, but also meets the corresponding shear strength and suitability for clay area soil improvement, especially for clay slope stability improvement. The application value and prospect of using construction waste in land engineering construction and soil organic reconstruction and identified a new way of utilizing construction waste as a resource were explored. Bangladesh J. Bot. 52(2): 503-514, 2023 (June) Special

Crack Resistance and Strength Properties of Red Clay Modified with Lignocellulose and Guar Gum

Desiccation cracking is a common problem of red clay under wet and dry conditions. The presence of cracks could reduce soil strength properties, which is the major reason for shallow failure of red clay slopes. This study aims to propose some additives to improve the crack resistance as well as the strength of red clay. To this end, three natural fibers and three natural gels were primarily selected to modify red clay. Desiccation crack tests were conducted to identify the best fiber and gel in terms of crack resistance. Then, direct shear tests and uniaxial tensile tests were performed on the soil specimens modified by the best fiber and gel to determine the optimal dosages regarding strength improvements. The results demonstrated that natural gels reduced the crack resistance of red clay, while natural fibers could enhance the crack resistance. Lignocellulose was the best additive in improving the crack resistance of red clay, and the modified effect was positively correlated with the fiber dosage. Adding 1.5% lignocellulose into red clay could reduce the crack rate from 2.19% to 0.30%, with a reduction of 0.86 times. The tensile strength, shear strength and its parameters of lignocellulose-modified red clay showed a trend of increasing first and then decreasing with increasing lignocellulose dosage. At the optimal lignocellulose dosage of 0.75%, the shear strength and tensile strength were increased by 44.63% and 18.21%, respectively. The strength of red clay modified by both lignocellulose and guar gum was positively correlated with the dosage of guar gum, and the desirable dosage of guar gum was 1.0%. In engineering practice, the wet red clay mixed with 0.75% lignocellulose and grass seeds can be employed as planting soil and is sprayed uniformly onto the slope surface after excavation using a spraying planting machine. To further improve the strength of the planting soil, 1.0% guar gum solution can be sprayed on the soil surface. The findings could provide useful guidance for the protection of red clay slopes.

Evaluating the likelihood of slope failure in ageing earthworks using Bayesian updating

Earthwork assets, including cut slopes and embankments, are essential components of the infrastructure supporting road and rail transportation networks. Asset owners must assess the stability of these slopes as they deteriorate, to prevent unwanted slope failures. Assessing the stability of individual earthworks within a portfolio using slope stability analyses can be expensive and time consuming. Hence, a Bayesian logistic regression model was developed to evaluate the probability of slope failure, using training data from published case histories of slope failures. The Bayesian model was then used to assess the probability of failure for the more specific case of clay cut slopes within a railway earthwork asset portfolio owned by Network Rail (NR) in the UK. The portfolio includes earthworks at various stages of degraded strength and with different drainage conditions. The results from models with material properties that were equivalent to those for the deteriorated strength of clays compared most closely with clay cut slope failures within the NR data set. Steeper slopes (>35°) had the highest probability of failure, regardless of slope height, and drainage condition. However, for shallower slopes, poorly drained slopes had a ≈20% higher probability of failure than well-drained slopes.

Enzyme induced carbonate precipitation with fibers for the improvement of clay soil slopes against rainfall and surface runoff erosions

In order to improve the erosion resistance of the highway embankment slopes against rainfall and surface runoff erosions, the enzyme induced calcium carbonate precipitation (EICP) technology combined with different types of fibers, including steel, glass, and Polypropylene (PP) fibers, was studied for the treatment of the cohesive soil slope surface. The treatments were applied by a two-step method. In the first step, the treatment solutions were sprayed to the soil surface. In the second step, after the cracks were fully developed, quartz sand was filled into the cracks and another round of EICP spray treatment was applied in order to repair the cracks. Soil crack image analysis, crack repair test, rainfall and surface runoff erosion test, surface penetration resistance test, moisture content measurement, and soil microstructure analysis were carried out. The results show that the EICP technology can effectively cement the soil and improve the mechanical strength and erosion resistance of the cohesive soil slope. The average penetration resistance is about 10 times that of the untreated samples. The strength and erosion resistance of the fiber-added samples were further improved after EICP treatment with the addition of fibers. Both the glass fiber- and steel fiber-added samples exhibited excellent erosion resistance under rainfall and surface runoff erosion, with the amounts of eroded particles 35.78% and 1.89%, respectively, as compared with the sample treated with EICP only. The additions of fibers did not have any negative impact on the conversion efficiency of calcium. Meanwhile, the fibers could function together with calcium carbonate to form a net structure inside the soil so as to increase the strength and the durability, and reduce the water infiltration into soil. Therefore, the EICP treated samples with steel fibers and glass fibers have better treatment effects and are recommended for further applications.

Measured Rainfall Infiltration and the Infiltration Interface Effect on Double-Layer Loess Slope

It is of great theoretical and engineering significance to carry out field rainfall tests and research on double-layer soil slopes in loess areas. Based on the developed rainfall simulation system with slow-moving injection, field rainfall tests were carried out on a natural double-layer loess slope. The characteristics of volumetric water content were monitored, and the rainfall infiltration characteristics and infiltration effect at the interface of the soil layer were analyzed by numerical simulation. The results showed the fastest infiltration at the top platform of the slope, followed by that at the upper surface of the slope, and the slowest infiltration at the lower surface of the slope during rainfall. Under various rainfall intensities, the erosion of the upper silty loess slope was greater than that of the lower clay loess slope, and the erosion patterns were quite different at the end of rainfall. During the infiltration process in the double-layer loess slope, a stagnant transition area was formed near the interface of the soil layer. The equipotential line of water content in the stagnant transition area of the upper region was roughly parallel to the slope surface, and the equipotential line in the lower region was roughly parallel to the interface of the soil layer. With an increase in rainfall intensity, the upper transition area at the interface of the soil layer continued to extend from the slope surface inward, showing the interface infiltration effect that became increasingly significant with the intensification of rainfall. The infiltration effect at the soil layer interface could provide an evaluation basis for rainfall infiltration analyses of multi-layer soil slopes.

Crack development in a physical model of undisturbed expansive soil slope and core sample under wet-dry cycles

Cyclic wetting and drying in expansive soil slopes results in the formation of desiccation cracks and irreversible structural changes which can cause substantial reduction in overall soil strength leading to slope instability. This study investigates the structural and crack development in a physical model of undisturbed expansive clay slope and small core sample subjected to five wet-dry cycles. The surface distribution and vertical extent of cracks in the slope model was measured during the various drying and drying cycles. The crack intensity factor, which quantifies surface cracks increased with increasing wet-dry cycles and became constant in the third cycle. Vertical cracks whose bases are connected by near horizontal cracks or cracks parallel to the slope developed to a maximum depth of 28 cm in the physical model. The shallow depth and orientation of these cracks along the slope may be a contributing factor for the shallow infinite slope failure in expansive soils. In addition, suction and water content measurements were made during various cycles. Changes in suction occurred to a depth of 28 cm, and the maximum suction increased with increasing cycle number. The results also demonstrate boundary and size effects on crack formation.

Optimal reconstruction of constrained janbu method with ADP and non-integral safety factor

Notwithstanding the rich research on the slicing method, it is still impossible to accomplish the limit equilibrium analysis of all phases before the evaluation of the safety factor. Bearing this dilemma in view, in this paper, the Janbu method is optimized and reformulated by introducing adaptive dynamic programming (ADP). The fractional average safety factor is no longer used; instead, a sequence of safety factors is used. The critical slip state is chosen as the equilibrium point, the nonlinearity of safety coefficients of adjacent blocks is approximated by the neural network, and the remaining variables and constraints of the system are added to assist in transforming the original redundant safety coefficient evaluation-finding optimal solution problem into a Janbu-qualified cost function. The action network and critic network of ADP accomplish the boundary trajectory solving and safety evaluation, respectively. The validity of the method is verified when the optimized and reorganized framework is applied to solve the critical slip surface of a clay slope.

3D Stability and Failure Mechanism of Undrained Clay Slopes Subjected to Seismic Load

3D Stability and Failure Mechanism of Undrained Clay Slopes Subjected to Seismic Load

Interpretation of Small-Scaled Model Test for Uniform Clay Slope Design

Abstract Small-scaled model tests under normal gravity are widely used to examine slope stabilities and failure mechanisms. Nevertheless, in practice, it is impossible to comply to all similarity principles, which could affect the modeled results in the prototype. This paper performs finite element analyses to investigate the behavior of uniform clay slopes as commonly performed in a 1g model test without following similarity principles. The numerical model is validated with previously published data. A parametric study is then carried out with varying slope scales, soil properties, etc. Based on extensive numerical modeling data, four formulas are established to correlate and interpolate the sliding surface and safety factor of a model slope in a 1g test. A framework is proposed to interpret 1g model-scale test results for applications in slope designs.

Theoretical Evaluation for Soil Thrust of Single-Track System over Clay Slope via Upper Bound Analysis

This study aimed to theoretically evaluate soil thrust on a clay slope as a reaction force associated with the motion of an off-road tracked vehicle. The existing concept of the potential failure modes of a clay block on flat ground has extended to determine the soil thrust of sloped clay ground. Based on the upper-bound limit analysis, the soil thrust under the most critical failure was derived for three potential failure modes: block, triangular-wedge, and trapezoidal-wedge failures. Specifically, the influence of the slope angle, the shear strength of clay, the weight of a vehicle, and the geometry of a track system on the soil thrust was investigated. Only the block and triangular wedge failure modes were able to occur, and the geometry of a single-track system could lead to different failure modes. Under the block failure mode, the soil thrust decreased as the slope became stiff, and the vehicle weight increased. On the other hand, the soil thrust decreased as the slope angle decreased under the triangular-wedge failure mode.

Failure Mechanism of a Rainfall-Triggered Landslide in Clay Slopes

In December 2013, a portion of a large and deep ancient landslide on the southern slope of the Montescaglioso town (Basilicata, Southern Italy) was abruptly reactivated, as a consequence of exceptional rainfall events, causing relevant damages to structures and infrastructures. The sliding surface is supposed to be located within a thick deposit of Pleistocene stiff clays overlain by dislocated blocks of calcarenites and cemented conglomerates. This paper discusses the research carried out to investigate the failure mechanism that occurred during the landslide event and the factors that controlled the reactivation. To this purpose, geological and geomorphological analyses were first proposed, followed by a back-analysis of the landslide process, performed via limit equilibrium calculations implementing time-dependent pore water pressure distributions derived from transient seepage finite element analyses. Furthermore, the overall landslide mechanism was investigated through a three-dimensional finite element analysis, built using the monitoring campaign carried out in the post-failure stage and calibrated according to the in situ failure mechanism evidence. Both the limit equilibrium and finite element analyses provide results in good agreement with the geomorphological evidence, further allowing us to recognize the effects of rainfall infiltration in the increase of pore water pressure along the sliding surface and the variation of the stress–strain state leading to failure occurrence.

Multivariate adaptive regression splines analysis for 3D slope stability in anisotropic and heterogenous clay

Little research can be found in relation to the stability of anisotropic and heterogenous soils in three dimensions. In this paper, we propose a study on the three-dimensional (3D) undrained slopes in anisotropic and heterogenous clay using advanced upper and lower bounds finite element limit analysis (FELA). The obtained stability solutions are normalized, and presented by a stability number that is a function of three geometrical ratios and two material ratios, i.e. depth ratio, length ratio, slope angle, shear strength gradient ratio and anisotropic strength ratio. Numerical results are compared with experimental data in the literature, and charts are presented to cover a wide range of design parameters. Using the multivariate adaptive regression splines (MARS) analysis, the respective influence and sensitivity of each design parameter on the stability number and the failure mechanism are investigated. An empirical equation is also developed to effectively estimate the stability number.

Vertical distribution differences of the understory herbs and their driving factors on shady and sunny slopes in high altitude mountainous areas

The vertical distribution understanding of undergrowth herbaceous plants in high altitude mountain areas is of great significance to reveal the environmental gradient change law of plant diversity. However, the species composition of herbaceous plants at different altitude gradients and the relationship between diversity and environmental factors is still vague. This study takes the Sejila Mountain in southeast Tibet at an altitude of 2,000–3,300 m as the study area to analyze the vertical distribution differences of the understory herbs and their driving factors on shady and sunny slopes. The results showed that: (1) The number of families, genera and species of herbaceous plants on sunny slope is greater than that on shady slope. Asteraceae on shady and sunny slopes has the largest number of species; (2) The α diversity index of the herbs on shady slope shows a U-shaped trend. The Cody heterogeneity index (βC) is negatively correlated with the β diversity index. The herb richness index (R) on sunny slope is unimodal. The β diversity index displays the same as that of shady slope; (3) Different environmental factors have different effects on herb diversity. The correlation between environmental factors and diversity indicators indicates that there is a certain degree of clustering among samples. The environmental factors of shady slope and sunny slope are separated; and (4) The difference of water and heat conditions caused by altitude and slope aspect is an important driving factor for the diversity of herbage species, followed by soil clay content, silt content and slope gradient. This study will help to understand the species diversity and ecosystem characteristics of the region, and provide a reference for the study of plant community structure and function and rational utilization of understory plant resources in high-altitude mountain areas.

Selecting the Safety and Cost Optimized Geo-Stabilization Technique for Soft Clay Slopes

Slope failure poses a serious threat to the built environment as it is currently one of the fundamental contributors to climate change fears across the world, and this threatens the environmental goals of the United Nations Sustainable Development Goals (UNSDGs) for the year 2050. In this research paper, an optimized geo-stabilization numerical model has been developed with a Plaxis 2D code under safety and cost optimization considerations for a 37 m high slope embankment located on a soft clay watershed with an infinite extension. The site was prepared with four monitoring wells installed at 2.5 m, 7.5 m, 12.5 m, and 21.5 m from the foot of the slope to measure the water level conditions, and samples were collected and tested in the laboratory to determine the hydraulic and shear strength and modulus of the soil. Seven (7) different simulation alternatives were considered in terms of the model solutions to be deployed under dry and wet states, which were slope steep (angle) reduction (Alt-1), dewatering (Alt-2), jet grouting (Alt-3), jet grouting/dewatering (Alt-4), slope reduction/jet grouting (Alt-5), slope reduction/dewatering (Alt-6), and slope reduction/jet grouting/dewatering (Alt-7). The finite element model implementation of the alternatives showed that Alt-2, Alt-3, and Alt-4 had FOS of less than 1.5 and were omitted because their stability considerations did not meet the requirements for the normal operating conditions of a slope and also the short-term and long-term stability conditions according to the literature. Alternatives 1, 5, 6, and 7 with FOS above 1.5 were selected for further optimization considerations. Economic and sustainability factors were selected and considered based on the cost in line with current average market prices, constructability, reliability, and the environmental impact needed to achieve the required earthwork, jet grouting, dewatering, and selected combinations. Finally, the Alt-1 (FOS = 1.505), though not the cheapest, was selected as the optimal choice in terms of reliability, constructability, and environmental impact. However, Alt-6 (FOS = 1.520) and Alt-7 (FOS = 1.508) are the most economical but ranked low in reliability and environmental impact considerations. Doi: 10.28991/CEJ-2023-09-02-015 Full Text: PDF

Stability charts for undrained clay slopes considering soil anisotropic characteristics

Stability charts for undrained clay slopes considering soil anisotropic characteristics

Predictive models for the run-out distance of clay slopes based on material point method

This paper aims to propose run-out distance predictive models for clay slopes using the material point method (MPM), which can simulate the progressive failure process of slopes considering the strain softening effect of soils. A suite of 100 ground motions is selected from the NGA-West2 database and then scaled for conducting the dynamic analysis of slopes. The permanent slope displacements (D) can be classified into two categories, namely the “un-failure” category with D smaller than 0.4 m and the “failure” category with D in the range of 10 m to 15 m. It is found that peak ground velocity (PGV) exhibits the highest correlation with D for the “un-failure” category, whereas all ground-motion intensity measures (e.g., PGV, peak ground acceleration) are less correlated with D for the “failure” category. Therefore, the run-out distance of collapsed clay slopes is more related to the failure model rather than the triggering shaking intensities. Moreover, thousands of slope models with various slope angles, slope heights (H), soil densities, and peak and residual strength parameters are developed based on MPM. The run-out distances for the slopes being collapsed are then collected. Predictive models for different slope angles are proposed, which predict the run-out distance as a function of H, unit weight, residual cohesion, and residual friction angle. The proposed models are applicable for clay slopes with slope angles in the range of 30° to 45° and H in the range of 10 m to 30 m.