Cohesive Soils Research Articles

Three-dimensional strength reduction and two-dimensional limit equilibrium methods of slope stability analysis

Landslides caused tremendous damage to the life and properties of society. In this study, cut slopes were analyzed using the two-dimensional (2D) limit equilibrium method (LEM) by slope/w software and a three-dimensional (3D) strength reduction method (SRM) by using Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D), which is a finite difference method (FDM) numerical software. Analysis of the slope is done by representative soil samples collected and transported to the laboratory to determine input parameters like unit weight (γ), shear strength parameters (c,φ), and the water level position. Strength parameters were determined from direct shear tests for cohesionless soil and consolidated undrained (CU) triaxial tests for cohesive soils. For 2D analysis, the factor of safety (FOS) was calculated for the condition of dry and maximum water levels using Morgenstern-price methods, and the analysis gave FOS 0.743 and 0.614 for the dry and maximum water level conditions, respectively; for SRM, the input parameters of bulk and shear modulus (B, G) which were determined from the empirical equation using modulus of elasticity(E) and Poisson's ratio(ʋ).Moreover, ʋ were adjusted according to the principle of φ-v inequality. For 2D analysis, FOS were 0.743 and 0.614 for dry and maximum water levels using Morgenstern-price methods, whereas 3D analysis gave FOS 0.34 and 0.31 for dry and maximum water levels, respectively. From the analysis, it is concluded that 2D LEM is given higher FOS than 3D FDM. Moreover, the 3D analysis showed that velocity and displacement in the lateral Y direction were minimal and maximum in the horizontal X direction. The maximum horizontal velocity for the respective dry and maximum water level conditions gave 6.64*10−4 m/step and 6.04*10−4 m/step and maximum horizontal displacement 7.36 m and 6.06 m for dry and maximum water levels, respectively.

Calculation of Rock Pressure in Loess Tunnels Based on Limit Equilibrium Theory and Analysis of Influencing Factors

The research on the calculation method of tunnel envelope pressure is a key issue in the design of tunnel engineering support structure. Based on the limit equilibrium theory, this paper proposes a method to calculate the surrounding rock pressure in shallow buried loess tunnels. Firstly, based on the investigation of the damage mode of the loess tunnel surrounding rock and the field measurement results of the surrounding rock pressure, the damage mode of the loess tunnel is proposed, and then a method of calculating the surrounding rock pressure applicable to the shallow buried loess tunnel is derived according to the limit equilibrium condition of the tunnel square soil body and the side wedge; the basic mechanical parameters are known in this method, so only the rupture angle β needs to be determined, and the rupture angle calculation model in the shallow buried loess tunnel is proposed Three assumptions are made in the rupture angle calculation model, and the rupture angle calculation formula is derived according to the stress state on the slip surface of the surrounding rock; the pressure of the surrounding rock in the loess tunnel obtained by this method is compared with four methods, namely, the pressure theory of the surrounding rock in the existing loose body of Taishaki, the pressure formula of the deeply buried surrounding rock in the railroad tunnel design code, the Beer Baumann method, and the Xie Jiayi method, in order to verify the correctness and validity of the calculation method used, and to analyze the influence of different parameters on the surrounding rock pressure. The innovation of this paper lies in the derivation of a method for calculating the pressure in the surrounding rock of a shallow buried loess tunnel using the limit equilibrium theory, and also further proposes a formula for calculating the rupture angle. The pressure of surrounding rock decreases with the increase of static earth pressure coefficient, lateral pressure coefficient, friction angle and cohesion in soil, but the static earth pressure coefficient has a greater influence on the surrounding rock pressure. With the increase of sagittal span ratio, tunnel burial depth and soil weight, the surrounding rock pressure peaked with the increase of tunnel burial depth, and the surrounding rock pressure curve increased first and then decreased.

Meningkatkan Stabilitas Lereng Berdasarkan Pengujian Karakteristik Tanah

Kediri Regency has diverse potential and wealth, including natural resources, culture, and tourism. One example is the Dolo waterfall located in Jugo Village. In January 2023 there was an avalanche caused by heavy rainfall in the mountainous area of Jugo Village, Mojo District, Kediri. The landslide disrupted road access to tourist attractions, infrastructure and also affected the economy. Several studies have revealed that soil type, shear strength, and soil consistency properties are important in influencing a slope’s stability level. However, the discussion of landslide prevention efforts regarding soil and slope characteristics is still limited. This study aims to determine soil type, consistency properties, shear angle, soil cohesion, and slope safety factors in Jugo Village, Mojo District, Kediri Regency. Research begins with a survey and sampling, then testing is carried out in the laboratory and calculated the slope safety factor (Fs). The results revealed that the characteristics of the soil in Jugo Village influenced the landslides that occurred. Both the type of soil, the consistency limit, and the shear strength of the soil indicate that the slope is unstable, this is also indicated by the calculation value of Fs <1. The results of this study can be used as a reference in planning and carrying out slope stability at that location so as to prevent landslides in the future. The effort that can be done is to change the slope to 35° so that the slope becomes stable.

Evolution and Influencing Mechanisms of the Yili Loess Mechanical Properties under Combined Wetting-Drying and Freeze-Thaw Cycling.

Landslides frequently occur in the loess-rich Yili region of Xinjiang, China, due to the combined effects of wetting-drying and freeze-thaw (WD-FT) cycles, which cause changes in the soil/loess internal structure and shear strength. This paper explores the combined effect of WD-FT cycles on the shear strength evolution of Yili loess through cyclic and triaxial shear tests. The micromechanism of the effect of WD-FT cycles on the loess properties is studied through scanning electron microscopy tests. Finally, the gray correlation analysis method assesses the correlation between relevant macro and micro parameters. The results show that: (1) With the increase in WD-FT cycles, the cohesion of loess decreases first and then gradually stabilizes, while the internal friction angle first grows and then drops before stabilizing. This indicates that the WD-FT cycles cause different degrees of decline in the soil's internal friction angle and cohesion. (2) As the number of WD-FT cycles increases, the average abundance and directional probability entropy fluctuate slightly, gradually decreasing and stabilizing. In contrast, the particle size dimensionality gradually decreases and stabilizes, and the pore area ratio first increases and then gradually stabilizes. (3) Six microstructural parameters (average diameter, average abundance, particle size dimensionality, directional probability entropy, particle roundness, and pore area) are selected for correlation analysis with the shear strength index of loess. The results show that the particle size dimensionality closely correlates with macroscopic internal friction angle under coupled cycling, while the pore area closely correlates with macroscopic cohesion. These findings are instrumental in preventing and controlling loess landslides caused by WD-FT cycles in the Yili region of Xinjiang, China, and similar loess-rich regions.

Experimental study on predicting head-cut migration rate of check dams

Head-cut erosion is the primary mechanism causing overtopping-induced breaches of check dams. Furthermore, the dam fill soil properties directly influence the head-cut migration rate. Although the fill materials of most flume model tests are cohesive soils, there are no experimental studies on loess materials with low erosion resistance. Accordingly, this study conducted 26 groups of flume model tests on the check dam head-cut migration mechanisms. Furthermore, it comprehensively analyzed the factors influencing the characteristics of head-cut migration in check dams, namely compactness, water content, inflow, and head-cut height, from the macro-and micro-viewpoints. The head-cut erosion rate models of compacted loess were developed considering multiple factors. A nonlinear multiple head-cut migration coefficient regression model was developed using the energy dissipation theory, the findings from the head-cut erosion tests, and experimental results from other studies, while considering the water content, compactness, clay content, inflow, and head-cut height as inputs. Seven sets of measured data with different erosion resistances were selected to verify the rationality and accuracy of the proposed model. In general, the sensitivity analysis results showed that the model could be used for cohesive soil with strong erosion resistance and silty sand and loess with weak erosion resistance. Its generalization and prediction accuracy have been further improved compared to other models of the same type.

Development of new rotation pile technology mirai pile ® and preliminary study in Vietnam on construction

In recent years sustainability and environmental impacts have been highlighted as an important issue in design and construction particularly in urban area in construction of buildings and bridges. Mirai piler (M-pile) is new rotating pile technology, which was developed in 2020, is highly appreciated for its environmentally friendly functions such as: rapid construction, low noise; low vibration; no waste soil during construction; no ground water contamination. In this study, construction sequence and prediction of axial bearing capacity of M-pile on cohesive soil were introduced. M-pile analysis used with outer diameter of 318.5mm and thickness of 12.7mm. The analysis results show that the ultimate bearing capacity prediction of M-pilein soft clay soil considerablyincrease compared with bored and cast-in-place piles with the same diameter and depth thanks to multipleblades welded along the pile shaft.

Laboratory analysis for coconut coir fiber to improve compressibility characteristics of cohesive nature soil

Laboratory analysis for coconut coir fiber to improve compressibility characteristics of cohesive nature soil

Effects of moisture content on strength and compression properties of foundation soils of cultural relics in areas flooded by the Yellow River

This study investigated the effects of soil moisture content on the strength and deformation properties of the foundation soils of cultural relics. Our goal is to inform the formulation and implementation of the repair scheme for cultural relics above the foundation soils and help protect cultural relics. Soil samples with five different moisture contents were prepared and used in unconfined compression, triaxial, and consolidation tests. Several mechanical parameters were determined under different soil moisture contents: failure morphology, compressive strength, compressive modulus, and compressibility coefficient. Based on the test results, the soil cohesion and angle of internal friction were obtained using Mohr’s circle. Regions where the mechanical parameters were particularly sensitive to moisture content were located during the consolidation test. These were also the regions where the soil’s compressive modulus declined rapidly, which was detrimental to the overall stability and safety of overlying structures. The internal structure and particle size distribution of the foundation soils supporting cultural relics were determined by scanning electron microscopy. Constitutive parameters of soils were determined by the triaxial test and consolidation test. It was also found that when the soil moisture content exceeded the optimal level, the foundation soils were very likely to pose a risk to the safety of the overlying cultural relics. The moisture content of foundation soils supporting cultural relics deserves special attention in engineering practice.

Time dependent analysis of lateral bearing capacity of reinforced concrete piles combined with corrosion and scour

This study investigates the effect of chlorine corrosion and flow scour on the lateral bearing capacity of piles. A chloride diffusion model was established to obtain the initial corrosion time of reinforcement based on Fick's second law. The degradation of stiffness after corrosion is represented by a reduction coefficient. The finite difference method is used to solve the deflection differential equation of laterally loaded piles. The maximum scouring depth of piles in cohesive soil and the variation of scouring depth with time are calculated by empirical model. The calculated results from the analytical solution revealed that the pile stiffness decreases with the exposure time. As the time increase, the lateral displacement and shear force decrease on the other hand the bending moment increases. The increase of flow velocity and pile diameter results in the increase of the maximum scour depth around the pile. The bending moment, shear force, and lateral displacement of piles after scour increase significantly compared to the lateral bearing performance of piles before scour.

Performance and mechanism of a novel biopolymer binder for clayey soil stabilization: Mechanical properties and microstructure characteristics

In this study, a novel stabilization approach using locust bean gum (LBG) was proposed to enhance the strength properties of natural soil. A series of laboratory tests were first performed on specimens using various biopolymer contents and curing durations. Subsequently, scanning electron microscopy and X-ray diffractometry were used to assess the intrinsic mechanism and microstructure. The LBG treatment considerably improved the mechanical strength of the natural soil, and the compressive, shear, and tensile strength increased with increasing biopolymer content. The increment in soil cohesion with increasing biopolymer content was more apparent than that in the internal friction angle. Sol–gel film sticking to soil particles significantly alters the macrofailure characteristic, which increases the failure path and ruptures plane unevenness, resulting in the failure of plane tortuosity. The increased curing duration prolonged interparticle interaction and strengthened biopolymer bonds, leading to improved mechanical properties. The enhanced effect of the LBG binder on soil can be explained by the formation of large stable aggregates with widely structured bonding groups. The entire biopolymer-soil matrix structures an integral matrix phase with a network system for strength enhancement.

Effect of Bi-modulus characteristic on the Brazilian disc test: Insights from numerical study

The materials with different elastic behavior under tension and compression are called bi-modulus materials, and this type of materials widely exists in nature, such as rock, concrete, and cohesive soil. However, due to the lack of a constitutive model that is suitable for bi-modulus materials, the bi-modulus property of materials was often ignored in previous studies. In this study, the uncoupled strain-driven constitutive model for bi-modulus materials proposed by Latorre and Montáns1 is firstly embedded into the finite element software FssiCAS. Then the distribution characteristics of stress, strain, and displacement in Brazilian disc are systematically compared under the two conditions, i.e., considering the bi-modulus property and ignoring them. Besides, the constitutive model is used to verify the reliability of the measurement methods proposed by Ye et al.2,3 for the tensile elastic modulus. The results show that the bi-modulus property of materials has a significant effect on the magnitude, and the distribution of stress, strain, and displacement in Brazilian disc. The measurement methods proposed by Ye et al.2,3 own acceptable reliability only under certain conditions.

Developing interpretable machine learning-Shapley additive explanations model for unconfined compressive strength of cohesive soils stabilized with geopolymer.

This paper seeks to develop an interpretable Machine Learning (ML) model for predicting the unconfined compressive strength (UCS) of cohesive soils stabilized with geopolymer at 28 days. Four models including Random Forest (RF), Artificial Neuron Network (ANN), Extreme Gradient Boosting (XGB), and Gradient Boosting (GB) are built. The database consists of 282 samples collected from the literature with three different types of cohesive soil stabilized with three geopolymer categories including Slag-based geopolymer cement, alkali-activated fly ash geopolymer and slag/fly ash-based geopolymer cement. The optimal model is selected by comparing their performances with each other. The values of hyperparameters are tuned by Particle Swarm Optimization (PSO) algorithm and K-Fold Cross Validation. Statistical indicators show the superior performance of the ANN model with three metrics performance such as coefficient of determination R2 = 0.9808, Root Mean Square Error RMSE = 0.8808 MPa and Mean Absolute Error MAE = 0.6344 MPa. In addition, a sensitivity analysis was performed to determine the influence of different input parameters on the UCS of cohesive soils stabilized with geopolymer. The order of feature effect can be ordered in descending order using the Shapley additive explanations (SHAP) value as follows: Ground granulated blast slag content (GGBFS) > Liquid limit (LL) > Alkali/Binder ratio (A/B) > Molarity (M) > Fly ash content (FA) > Na/Al > Si/Al. The ANN model can obtain the best accuracy using these seven inputs. LL has a negative correlation with the growth of unconfined compressive strength, whereas GGBFS has a positive correlation.

Sediment penetration performance of a portable underwater robot for core sampling

AbstractAs described in this paper, we investigate the sediment penetration performance of a portable underwater robot with a helical screw pipe using marine thrusters with limited force. First, we derive a mathematical model based on an empirical and simple method using the undrained shear strength of cohesive soil to provide a rough estimate of maximum penetration depths. Then, we perform numerical analysis for estimating the maximum depth of sediment penetration and for designing a sampling pipe. Additionally, we use experimentation to investigate the relation between the penetration depth of the helical screw pipe and the force of marine thrusters mounted on the portable underwater robot. After testing the penetration performance in a water tank, we conduct a field experiment at Lake Biwa and obtain results of the penetration depths. The maximum penetration into the lake sediment is at least 0.30 m. The results demonstrated the possibility of using the derived mathematical model to make a rough estimation of the maximum penetration depth for clay sediments. Additionally, we can use non‐powerful thrusters equipped with small autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs) for sediment sampling. The proposed method is also applicable for the installation of underwater sensors using small AUVs and ROVs.

Geotechnical properties of cohesive soils used in the construction of subgrade for the development of the railways in the Azov-Black Sea region

This work is devoted to the determination and systematization of the properties of clay soils used in the construction of new railway tracks in order to develop the railway network in the Azov-Black Sea region of Russia. To this end, classification characteristics are determined by traditional laboratory methods, and the possibility of soil swelling under excessive moisture is estimated. In addition, the compressibility of soils is studied as the main factor ensuring the trouble-free operation of the subgrade of railways during their long-term operation. Soil samples for measurements were taken from open pits located near construction sites at an extended length of construction of 530 km. The new regression relations proposed in the work provide in some cases the accuracy of determining the soil characteristics close to the accuracy of laboratory tests. They may be in demand when monitoring the accuracy of laboratory tests of soil properties of other open pits and increasing the speed of pre-design surveys during further development of the railroad network in this region.

Application of plaxis 3D with the hardening soil and mohr coulomb model in simulation of diaphragm wall deflection

Diaphragm wall deflection is considered one of the reasons for soil instability around excavation, causing serious consequences for neighboring constructions. Therefore, in the design and calculation of deep excavation, analyzing and simulating the diaphragm wall deflection between phases of excavation construction becomes very important. However, selecting an appropriate mathematical model and determining its input parameters affect the accuracy of the calculation results and their deviation from reality. In this article, the Hardening Soil (HS) model and the Mohr Coulomb (MC) model were used to simulate deflection calculations of diaphragm wall using Plaxis 3D and compared with data obtained from a real project in Ho Chi Minh City. The results showed that the stiffness parameter Eref50 was taken according to the formula Eref50 = 1000N for sandy soil (N: number of SPT blows), Eref50 = 500Su for cohesive soil (Su: undrained soil resistance) in the HS model, resulting in analysis of deflection that was quite compatible with actual data. In addition, the deflection of diaphragm wall varied inversely with its thickness, but this change was relatively small.

Effect of compaction water on strength and hydraulic properties of bentonite-based liner

The abundance of pond ash and its resemblance to natural sand encourages its use as a substitute for sand in sand–bentonite (SB) liner material. Compaction water content influences the geoengineering properties of cohesive soil to a great extent. Accordingly, the compaction, strength, permeability and shrinkage characteristics of both pond ash–bentonite (PAB) and SB mixes are investigated at standard and modified Proctor compaction energies at various water contents to support the recommendation of the PAB mixture as an alternative landfill liner. At similar compaction conditions, the PAB mix exhibits higher unconfined compressive strength (UCS) and hydraulic conductivity than the SB mix. The UCS values of mixes compacted on the dry side of optimum are higher than those of mixes compacted on the wet side. Dry-side compacted mixes exhibit a reduction in hydraulic conductivity with permeation time, whereas no substantial reduction in hydraulic conductivity is noticed for wet-side compacted mixes. Furthermore, the volumetric shrinkage of both PAB and SB mixes is within the permissible value of 4%, for a wide range of water variation from the dry to the wet side of optimum. The observed mechanical properties are correlated to the shape of coarse fraction particles and the corresponding microstructural arrangements of the compacted specimens.

Study on the Drying Process and the Influencing Factors of Desiccation Cracking of Cohesive Soda Saline-Alkali Soil in the Songnen Plain, China

The surface of cohesive soda saline-alkali soil in the Songnen Plain of China exhibits obvious desiccation cracking phenomenon during water evaporation. Quantitative research on the process and influencing factors of desiccation cracking are significant for determining the mechanical properties of salt-affected soil, improving the salinization status and the local ecological environment. This study aims to conduct laboratory-controlled cracking experiments on soda saline-alkali soils, and to regularly measure the soil moisture and the cracking status of 40 soil samples. After processing the crack images uniformly, crack characteristics including crack length, crack area, contrast texture feature, and box-counting fractal dimension are extracted. The results indicate that the decrease in soil moisture can be divided into three stages such as fast evaporation stage, slow evaporation stage and stable evaporation stage, and that the evaporation rate shows a linear negative correlation with soil salinity. The measurements also indicate that crack length rapidly increases and reaches stability with a decrease in water content compared with the crack area. The high correlation between different crack characteristics and the soil total salinity (correlation coefficient from 0.44 to 0.95) shows that salt content is the dominant factor affecting the desiccation cracking of soda saline-alkali soil. A multiple linear regression prediction model was finally established based on crack characteristics for different salinity parameters with high prediction accuracy for Na+, EC and total salinity (R2 > 0.91 and RPD > 2.5) and also certain prediction accuracy for Cl− and CO32− (R2 > 0.66 and RPD > 1.5).

Assessment of Slope Stability by the Fellenius Slice Method: Analytical and numerical approach

Slope stability is a topic of great importance in civil engineering, as slope failures can cause considerable damage to infrastructure and downstream properties. In this study, we applied the Fellenius slice method, using both the analytical method, as well as the numerical method, which was performed using the SLOPE/W module of the Geostudio software. The results obtained by both methods showed that the increase in soil cohesion improves the stability of the slope. The safety coefficients obtained by the analytical method vary between 0.534 and 1.086, while those obtained by the numerical method vary between 0.539 and 1.096, for cohesion values ranging from 4 kPa to 20 kPa. The safety coefficients obtained by the analytical and numerical methods follow straight lines of equation y=0.0344x+0.4092 and y=0.0345x+0.4169, respectively. The results of the analytical method show that a safety factor of 1.5 is achieved at a value of 32 kPa for the cohesion, while the numerical method shows a safety factor of 1.5 achieved at a value of 32 kPa for the cohesion. The difference between the two cohesions is explained by the smaller number of slices used in the analytical method. Nevertheless, the equation from the analytical method can be used as a general guide to evaluate the evolution of the safety coefficient of a slope with surcharge under long-term behavior with incremental cohesion, but this does not exclude verification by dedicated software based on the finite element method.

Three-dimensional DEM tillage simulation: Validation of a suitable contact model for a sweep tool operating in cohesion and adhesion soil

Discrete element modelling (DEM) is widely used to estimate soil-tool interaction and tillage forces. To run an accurate simulation, it is essential to determine the appropriate DEM contact model and parameters. Although previous work has been introduced to determine the DEM contact model and parameters, the accuracy of numerical simulation is not high because of the soil differences when tillage tools operate in cohesion and adhesion soil in the middle and lower reaches of the Yangtze River in China. In this paper a Hertz-Mindlin with JKR Cohesion contact model and Linear Cohesion contact model were used to predict soil disturbance area and draft forces. The DEM parameters were determined using cone penetration, and uniaxial unconfined compression as an assisted test. The field experiment using sweep tool was used to validate the simulation results. A good agreement has been showed between simulation results and experiment results. Using verified model, the relative error for the predicted soil disturbance area at speeds of 0.50, 0.75 and 1.00 m/s were 5.3, 3.6 and 7.1 %, respectively. The maximum and average relative errors between simulated and measured draft forces were 6.98 and 3.91%, respectively. The effect of tillage depth and speed at soil disturbance area and draft forces were found which can provide some guidance for the selection of parameters during actual operation.

Experimental Research on the Settlement Feature of Two Ground Deformation Modes Induced by Tunnelling

Two ground deformation modes, i.e., the arching mode and collapsing mode, may be caused by tunnel excavation. However, the development of the ground deformation corresponding to the two modes is unclear. A piece of a model test facility is designed to study the ground settlement induced by tunnel excavation. Tunnel excavation is realized by decreasing the area of the model tunnel. Two model tests with different soil cohesion are conducted, and the two ground deformation modes form in the two tests, respectively. The former mode is observed at higher soil cohesion while the latter is found to develop at lower soil cohesion. Whether the failure surface develops to the ground surface or not is the most significant difference between the two ground deformation modes. In the two modes, the failure surface occurs at the position where the ground settlement contours distribute densely, and the shape of the failure surface can be described by the semi-oval for both modes. Meanwhile, for both the arching mode and the collapsing mode, Gaussian curves can reasonably describe the ground settlement troughs before the ground surface settlement becomes stable or increases sharply, and distribution of the trough width parameter is similar.