Soil Internal Friction Research Articles

Analysis of the Shear Strength of Iron Oxide-Kaolinite Cementing Materials in Granite Red Soil

Shear strength is the key index to determine the stability of a soil slope, and cementation between iron oxide and clay minerals is one of the internal factors affecting soil shear strength; however, the effects of the form of iron oxide on the shear strength of granite-weathered red soil are still unclear. Kaolinite, which is the main clay mineral of granite red soil, was selected as the research object, and the effects of three different forms of iron oxide (hematite: HT, goethite: GT, and amorphous iron oxide: AIO) on the soil microstructure, microscopic quantitative parameters, cohesion, internal friction angle, and shear strength were analyzed by scanning electron microscopy, X-ray diffraction, and the shear strength test. The results revealed that the iron oxide promoted the cementation of soil particles, and the cementation characteristics differed with the different forms of iron oxide. Hematite mainly showed flocculent cementation, poor cementation, and simple soil microstructures. Goethite mainly exhibited acicular cementation and the best cementation effect. The degree of aggregation of the soil particles was increased by the coatings, thus forming larger aggregate particles. The cementation effect of amorphous iron oxide was between those of hematite and goethite but included both the flocculation cementation of hematite and acicular cementation of goethite. Amorphous iron oxide and goethite effectively increased the contact area and friction degree between soil particles, while hematite had the opposite effect. The addition of three kinds of ferric oxide reduced the fractal dimension of soil, increased the apparent porosity, and promoted the irregularity of particles to a certain extent, among which hematite had the most significant growth on the long and short axes of the particles. At a content of 10 g kg−1, the addition of AIO and GT increased the soil cohesion and internal friction angle, and therefore increased the soil shear strength, and it was mainly determined by the soil microstructure: the contact area, apparent porosity, and particle short axis. These results indicated that GT and AIO are the main cementing materials affecting soil mechanical properties, and the transformation of iron oxide should be paid attention to when predicting soil slope stability.

Study of Asymmetric Face Failure and Limit Support Pressure During Curved Tunnels Excavation in Sandy Soils

ABSTRACTWith the continuous urban development, tunnels are increasingly designed with curved alignments to avoid existing structures and to make better use of the underground space. However, these tunnels are usually subjected to complex forces, and current research on the curved tunnels face stability remains incomplete. This paper presents a detailed face stability analysis of curved tunnels, both analytically and numerically. Initially, a series of 3‐D numerical simulations are performed to investigate the spatially asymmetric failure pattern of the soil ahead of the curved tunnel face and the stress transfer mechanism of the soil arching effect during the excavation process is explored. Subsequently, based on traditional limit equilibrium methods and the results from numerical simulations, an improved wedge‐prism model and corresponding theoretical calculation formulas for the limit support pressure are proposed. The validity of the improved model is confirmed through illustrative analyses, while sensitivity analyses are conducted on the impacts of soil internal friction angle, structural depth ratio, and tunnel curvature radius on the limit support pressure. This study can aid in the calculation of the stability of the tunnel face and the limit support pressure in curved tunnel excavation.

Effects of electrokinetic stabilization combined with addition of calcium ions on soil shear strength characteristics in the hilly granitic region of southern China

Enhancing soil shear strength is of great importance in preventing soil collapse and erosion in the hilly granitic region of southern China. However, limited studies have been conducted on improving soil shear strength in collapsing gullies. Electrokinetic stabilization (EKS) involves applying an electrical current through a soil mass to promote the migration of chemicals from injection points, thereby altering the chemical composition of the treated soil to improve its physical properties. In this study, the effects of calcium chloride (CaCl 2 ) addition and EKS techniques on the soil shear characteristics (shear strength, and its two components: cohesion and internal friction angle) of three different soil layers in collapsing gullies were investigated. The results showed that the EKS techniques significantly increased the migration of calcium ions from the anode to the cathode region of the power supply device used in the soils. Using EKS process alone did not increase or even decrease the soil shear strength, but combining EKS with CaCl 2 injection (Ca-EKS) increased the soil shear strength, and this increase was mainly due to the increasing the soil cohesion. The soil cohesion after Ca-EKS treatment increased on average by 49.84%, 83.11%, and 100.36% compared with the soil without treatments (CK) for the red soil, sandy soil, and detritus, respectively. However, soil amended by sole CaCl 2 addition, Water-EKS or Ca-EKS all can not increase soil internal friction angles compared with the CK. These results demonstrated that the application of Ca-EKS can be applied to improve the soil shear strength and stability of gully walls in hilly granitic regions.

Bank erosion under the impacts of fluvial erosion, frost heaving/freeze-thaw process of rivers in seasonal frozen regions

Bank erosion is a key feature of channel evolution in alluvial rivers, and will occur under the combined effect of hydraulic erosion and frost heave/freeze-thaw process of rivers in seasonal frozen regions. However, most research on bank erosion modeling has seldom considered the impact of the frost heave/freeze-thaw process. Therefore, the variation in the mechanical characteristics of riverbank soil under the freeze-thaw cycle was investigated firstly in the current research and then used in the modeling of bank erosion processes at typical sections of the Songhua River. Additionally, a sensitivity analysis of riverbank stability was conducted using orthogonal experiments. The results indicate that after 7 freeze-thaw cycles, the soil cohesion and internal friction angle of bank soil decreased by about 10%–47 % and 9%–19 %, respectively. Unlike lowland rivers, bank erosion of rivers in seasonal frozen regions is more likely to occur during the rising water period. The frost heaving/freeze-thaw process will make the bank stability safety coefficient Fs more quickly decrease to the unstable critical value. As compared with the case without considering the frost heaving/freeze-thaw process, the mass failure occurred in advance when the frost heaving/freeze-thaw process was considered, and the calculated bank erosion volume was increased by 11%–51 %, agreeing better with the measured value. The sensitivity ranking of the four influencing factors on riverbank stability under freezing-thawing conditions is as follows: river stage > groundwater level > cohesion > internal friction angle. The current study can provide a reference for research on bank erosion and channel evolution of rivers in seasonal frozen regions.

Analytical solution of overlying pressure for shallowly buried underwater box tunnel: A case study of box jacking in Suzhou, China

Accurately predicting the overlying pressure is crucial for determining an appropriate cover depth of underwater box tunnels to avoid the uplifting failure. Based on the project of box jacking crossing the Beijing-Hangzhou Grand Canal in Suzhou, the characteristics of overlying pressure variation during tunneling are investigated. The monitoring results reveal that the fluctuation of overlying pressure is weakened during the rapid tunneling process. A modified analytical model for vertical earth pressure is conceived, in which the active and passive limit states for multi-layered soils are both considered. The probable range of overlying pressure obtained by the proposed model is suitable to cover the actual values. The anti-floating behavior of underwater box tunnels for two different working conditions is discussed by calculating the minimum cover depth. Using the calibrated analytical models, a parametric study is conducted to explore the influence of injection pressure, hardened slurry unit weight, soil internal friction angle, soil cohesion, and tunnel geometry. It is found that the injection pressure during the construction process is crucial for determining the necessary cover depth, and the change of box tunnel height makes it easier to trigger the variation of minimum cover depth.

A GSD‐driven approach to deriving stochastic soil strength parameters under hybrid machine learning models

AbstractThe quantification of soil strength parameters is a crucial prerequisite for constructing physical models related to hydro‐geophysical processes. However, due to ignoring soil spatial variability at different scales, traditional parameter assignment strategies, such as assigning values depending on land use classification or other classification systems, as well as those extrapolation and interpolation methods, are insufficient for physical process modelling. This work addressed this deficiency by proposing a method to derive stochastic soil strength parameters under hybrid machine learning (ML) models, taking into account the grain‐size distribution (GSD) of soil with scaling invariance. The nonlinear connection between GSD parameters (derived from GSD curves, such as μ and Dc), moisture content, and soil shear strength parameters was fitted by the suggested hybrid ML model. An analysis of a case study revealed that: (i) the Multi‐layer Perceptron optimized by the African Vulture Optimization Algorithm (AVOA) algorithm performs the best and can estimate the shear strength parameters of soil mass on vegetated slopes; (ii) all the selected ML models showed significant improvements in predictive performance after optimization with the AVOA, with R2 scores increasing by 24.72% for Support Vector Regressor, 34.04% for eXtreme Gradient Boosting, and 35.53% for Multi‐layer Perceptron; and (iii) soil cohesion has an increasing relationship with the GSD parameter μ, while soil internal friction angle has a negative correlation with the grain‐size parameter Dc. The proposed methodology can give predictions of soil shear strength distribution parameters, providing parameter support for the physical modelling of surface process dynamics.

Geotechnical Evaluation of Landslide in Nanggerang Village

Landslides are significant geological events that can cause extensive damage to infrastructure, disrupt communities, and pose serious safety hazards. Understanding the mechanisms behind slope failures is crucial for effective risk mitigation and the development of engineering solutions to improve slope stability. According to data from the National Disaster Management Agency (BNPB), Indonesia experienced 83 landslide events from January to February 2024. A notable landslide occurred in Nanggerang Village, Sukasari Sub-district, Sumedang Regency, West Java Province, on February 3, 2024. This landslide happened in a terraced rice field area following heavy rainfall earlier in the day. This study focuses on evaluating the failed slope to understand its condition just before failure and the material properties that influence the landslide event. The research methodology includes field data collection, soil testing, and slope stability analysis using the Limit Equilibrium Method (LEM) with a probabilistic approach via Slide 2 software. The analysis revealed that the failed slope had an average safety factor (FS) of 0.968 and a landslide probability of 58.897%. Sensitivity analysis showed that the cohesion parameter in the soil layer (CWZ) significantly impacts the safety factor of the slope. The study concludes that the reduction in soil cohesion and internal friction angle due to excessive moisture was the primary cause of the landslide, and the cohesion parameter of the soil layer is the most sensitive factor affecting slope stability.

FELA evaluated bearing capacity factors for circular, planar, and interfering cutting edges of open caisson

ABSTRACT In the study, a thorough analysis of the drained bearing capacity factors of cutting edges of open caissons with and without interference has been carried out which helps in planning the controlled sinking of caissons. Five different conditions are analysed in this study: single circular, single planar, V-shape planar, interfering planar, and interfering V-shape planar cutting edges. Implementing upper and lower bound finite element limit analysis (FELA) in accordance with Terzaghi's conventional bearing capacity equation, the bearing capacity factors of the cutting edge of open caissons are evaluated. The design charts for the bearing capacity of cutting edges are determined by accounting for the effects of the radii ratio of the circular caisson, distance ratio of planar cutting edges, cutting angle of cutting edge, soil internal friction angle, and spacing between the cutting edges. The soil failure planes corresponding to the aforementioned aspects of the cutting edges are also evaluated.

Reliability and sensitivity analyses of monopile supported offshore wind turbines based on probability density evolution method with pre-screening of controlling parameters

To reasonably investigate the influence of pile-soil interaction on the dynamic reliability of monopile supported offshore wind turbines (OWTs), a framework with high efficiency and good accuracy is proposed for reliability and sensitivity analyses of monopile supported OWTs. This proposed framework combines the grey relational analysis (GRA), the probability density evolution method (PDEM), and the interval mathematical analysis method (IM). Firstly, the GRA is applied to identify the main controlling parameters influencing the stochastic dynamic response of a monopile supported OWT, considering various factors such as pile elasticity modulus, soil internal friction angle and soil unit weight. Secondly, combining the probability density evolution theory, a complete sample probability set is established to obtain the dynamic reliability of the monopile supported OWT under wind and wave loads. Finally, the effect of each controlling parameter on the dynamic reliability of the monopile supported OWT is systematically analyzed by combining the IM and the change of probability measure. The proposed GRA-PDEM-IM-based framework for reliability analyses of monopile supported OWTs can effectively reduce the number of samples for probability density evolution calculations and provide reasonable and accurate reliability analyses results which can serve as a reference for design and construction of monopile supported OWTs.

A case study on soil slope landslide failure and parameter analysis of influencing factors for safety factor based on strength reduction method and orthogonal experimental design.

In civil engineering, stability analysis of slope is one of the main content of design. By using the finite element limit analysis software OptumG2, a landslide geological model is established to simulate the failure process of the landslide in Huadu District, Guangzhou City, China. The analysis focused on the deformation and failure characteristics, as well as the mechanical mechanism of landslide; the landslide mode of homogeneous soil is circular sliding. Additionally, investigating the influencing factors affecting slope stability is crucial in engineering implementation; in which the five influencing factors are considered as follow: slope height, slope gradient, soil cohesion, soil internal friction angle, and soil unit weight, respectively. A stability calculation model for a soil slope is established under 25 working conditions based on strength reduction method and orthogonal experimental design, in which the relationship between the safety factor and slope height, slope gradient, soil cohesion, soil internal friction angle, and soil unit weight is obtained. As the slope height increases from 5m to 45m, the safety factor of soil slope gradually decreases from 2.21 to 0.94; As the slope gradient increases from 20° to 60°, the safety factor of soil slope decreases approximately linearly from 1.80 to 0.95; As the cohesion of soil increases from 10kpa to 30kpa, the safety factor of soil slope increases approximately linearly from 1.04 to 1.60; As the internal friction angle of soil increases from 10° to 30°, the safety factor of soil slope increases approximately linearly from 1.00 to 1.81; As the unit weight of soil increases from 13kN/m3 to 21kN/m3, the safety factor of soil slope decreases approximately linearly from 1.50 to 1.21. The influencing factors affecting the safety factor of soil slope in descending order are slope height, slope angle, soil internal friction angle, soil cohesion, and soil unit weight. The research has reference significance for studying the stability and failure laws of soil slopes and conducting landslide control on soil slopes.

Analytical Method for the Deformation-Based Design of Retaining Walls in Asymmetric Excavation

Conventional methods for designing retaining structures are not applicable to asymmetric excavation or deformation-based designs. This study proposes a quadruple-line displacement-dependent earth pressure coefficient model. Based on the proposed model, an analytical solution was developed to facilitate the deformation-based design of the asymmetric length of retaining walls propped at the crest. Furthermore, the effects of the soil internal friction angle, strut stiffness, excavation asymmetry level, and deformation control value on the embedment ratio (Re) of retaining walls were investigated. The results showed that Re determined by the classical equivalent-beam method is unsafe due to its basis on the ultimate-state earth pressure theory. The Re value of the shallower side exhibited greater sensitivity to asymmetric excavation than that of the deeper side. The retaining structure’s required Re decreased with an increase in the excavation asymmetry level. The required Re on either side of the retaining structure decreased as the deformation control values increased. The controlled deformation had a more obvious effect on the Re value of the retaining structure on the deeper side. The proposed method can be used for the deformation-based design of asymmetric wall lengths of retaining structures propped at the crest, considering the different excavation depths on both sides.

An EPR model for predicting the bearing capacity of single and double-strip foundations near earth slope crests.

It is imperative to understand how foundations behave on earthen slopes to accurately predict their allowable carrying capacity in geotechnical engineering. A comprehensive finite element (FE) simulation with PLAXIS 2D was conducted to assess the effects of various parameters on the bearing capacity (BC) of single- and double-strip foundations placed near the earth's slope crest. The specified parameters include foundation width (B) and depth (Df/B); setback distance between the slope edge and foundation (b/B); soil internal friction (ϕ) and cohesion (c); slope inclination (β); and spacing between foundations (S/B). In addition, the numerically simulated database was used to develop simple mathematical expressions for predicting the capacities in both cases using evolutionary polynomial regression (EPR). The results revealed that the bearing capacity of single- and double-strip foundations increased with an increase in all studied parameters except slope inclination. For single-strip foundations, the outcomes demonstrated that slope inclination has no impact on BC when it is located 6B from the slope edge. However, under interference conditions, the critical center-to-center spacing between foundations is 3-4B, beyond which they behave as individual foundations. Additionally, EPR provides a robust method of predicting the BC of single- and double-strip foundations within slope crests based on the strong correlation of various statistical criteria between simulated and predicted results from training, validation, and testing. Finally, according to sensitivity analysis, in both single and double-strip foundations resting on an earthen slope crest, b/B, B, and ϕ are the most important input parameters that impact the output results.

Experimental Study of Cationic-Modified Biopolymer for Increasing the Shear Strength of Sand

The application of biopolymers as a more environmentally friendly alternative to cement has emerged as an interesting research subject.The purpose is to enhance the shear strength of sandy soils. In this article, the selected biopolymer is cationic-modified starch. It is expected that cationic starch will have less water absorption properties since modified starch has cationic groups in place of the OH- groups found in the normal starch. This cationic-modified starch namely Amylofax. Five types of samples are created for this testing, including Sample A is prepared with the composition of (silica sand + 2% Amylofax T1100 (w/w) + 20% water (w/w))., Sample B consists of (silica sand + 2% Amylofax T2200 (w/w) + 20% water (w/w))., Sample C is comprised of (silica sand + 2% Amylofax T1100 (w/w) + 2% Glucomannan (w/w) + 20% water (w/w)), Sample D consists of (silica sand + 2% Amylofax T2200 (w/w) + 2% Glucomannan (w/w) + 20% water (w/w)), and Sample E includes (Ottawa sand + 2% cement (w/w) + 20% water (w/w)). The samples were tested using a direct shear test apparatus to determine the soil shear strength parameters (c) cohesion and (Ø) internal friction angle. After conducting the tests on the sand samples with the addition of modified starch biopolymer (cationic starch), it was found that the cohesion value was 961kPa, and the internal friction angle was 63°. These results indicate higher shear strength values compared to sand mixed with natural starch.

Advanced prediction of soil shear strength parameters using index properties and artificial neural network approach

This study embarks on developing predictive models for soil shear strength parameters, cohesion (c) and angle of internal friction (ϕ), in Bishoftu town, employing Artificial Neural Networks (ANN). It aims at offering a cost-effective and time-saving alternative to traditional, often expensive, and labor-intensive laboratory methods. The research utilizes soil index properties such as Sand %, Fines %, Liquid Limit, Plastic Limit, and Plasticity Index to construct separate ANN models for c and ϕ. These models use a multi-layer perceptron network with feed-forward back propagation, varying the number of hidden layers to optimize performance. The study's dataset comprises 316 soil test results, encompassing both primary and secondary data, conforming to ASTM Standards. Soil cohesion and internal friction angle were determined using the direct shear box method. The models demonstrated remarkable success in predicting shear strength parameters, evidenced by correlation values of approximately 0.99 for cohesion and 0.98 for internal friction angle, surpassing the capabilities of existing empirical methods. Further examination of the models included comparison with existing correlation techniques and cross-validation using primary soil test data. This validation process confirmed the ANN method's superior accuracy and fit for predicting shear strength parameters over selected empirical methods. This research substantiates the efficiency of ANN in geotechnical engineering, particularly for areas with limited resources for extensive soil testing. It establishes ANN as a powerful, efficient tool for estimating soil shear strength parameters, with significant implications for future planning, design, and construction projects in similar environments.

Simplified solution for calculating active thrusts on retaining walls with a broken backslope

This paper reviewed Satyanarayana’s solution for calculating the active thrust on a retaining wall with a broken backslope. To improve Satyanarayana’s solution, a limit broken backslope height was proposed. A parametric study was conducted to investigate the influences of several key factors on the calculated active thrusts and their application point heights using the Satyanarayana solution. To simplify the calculation method, this paper proposes an equivalent infinite backslope angle based on the force equivalency between Satyanarayana’s and Coulomb’s solutions. This paper also proposes an empirical formula to estimate the equivalent infinite backslope angle and a simplified solution for calculating the active thrust. A numerical method was used to examine design examples of retaining walls with a broken backslope as compared with the Satyanarayana, Coulomb, and simplified solutions. The parametric study showed that the broken backslope height, the soil internal friction angle, the wall inclination angle, and the broken backslope angle had significant effects on active thrusts, while the wall-soil interface angle had a minor influence on the active thrust. The calculated equivalent infinite backslope angle using the proposed empirical formula well matched that calculated based on the force equilibrium. The design examples demonstrated that the simplified solution was easy and accurate for the design of retaining walls with a broken backslope.

Effects of different irrigation amounts and biochar application on soil physical and mechanical properties in the short term

AbstractBiochar application, as a kind of soil amendment, significantly influences soil physical and mechanical properties. This study revealed the effects of biochar application on the physical and mechanical properties of a clay‐type soil at different irrigation levels. Soil was treated with three levels of biochar application: B0 (0 t ha⁻¹), B1 (25 t ha⁻¹) and B2 (50 t ha⁻¹), and three levels of irrigation: T0 (1.2 pan evaporation Ep), T1 (1.0 Ep) and T2 (0.8 Ep). The results indicated that other treatments reduced the soil bulk density compared with the control treatment (CK) (B0T1). Compared to CK, the highest reduction in soil bulk density was 18%. Irrigation did not improve the soil bulk density and porosity at the same biochar application in the short term. Biochar enhanced the stability of the soil aggregates. Compared to CK, the largest MWD (mean weight diameter) was enhanced by 9%. The addition of biochar and decreasing irrigation could decrease soil cohesion. The addition of biochar and increasing irrigation could increase the soil internal friction angle. The soil cohesion first increased and then decreased as the soil water content increased. According to the fitting formula, the soil cohesion was found to be minimum at B2T2, which was a decrease of 39% compared to B0T1. At the same irrigation level, the soil internal friction angle decreased with increasing soil water content. Soil penetration resistance showed a decreasing trend with the application of biochar. The more irrigation there is, the larger the soil penetration resistance.

Effects of freeze-thaw on soil detachment capacity in the black soil region of Northeastern China

Soil detachment capacity (Dc) is an important parameter used to determine erosion intensity in physical-process-based erosion models. Freeze-thaw affects soil detachment processes by altering the mechanical properties of soil; however, due to the compound action of freeze-thaw and runoff on Dc, quantifying the impact of seasonal freeze-thaw on Dc remains challenging. A series of experiments with six freeze-thaw cycles (FTC), six initial soil moisture contents (SMC), three slope gradients, and five flow discharges were conducted to investigate the effect of freeze-thaw and hydrodynamic characteristics on Dc. The results showed that soil shear strength (τm), cohesion (Coh), and internal friction angle (φ) gradually tended to become stable with increasing FTC, indicating that repeated FTC had a cumulative impact on soil mechanical properties, and there was a critical FTC between 5 and 7. When FTC rose from 1 to 15, the reduction in τm, Coh, and φ was 0.03∼23.96%, 2.63∼75.21%, and − 5.70∼19.24%, respectively, which increased with an increasing SMC, suggesting that the deterioration effect of FTC on soil mechanical properties was promoted by increasing SMC. During alternating FTC, the relative range and variation coefficient of Dc were 2.21–2.43 and 67.87–75.72%, respectively, indicating that Dc was highly sensitive to FTC. Furthermore, Dc increased by 2.37–71.22% after 15 FTC. Alternating freeze-thaw weakened the soil resistance to detachment. Moreover, the promoting effect of FTC on Dc intensified with an increasing SMC, indicating that the variation in Dc was strongly affected by SMC during FTC. A prediction model (R2=0.955, RRMSE=14.99%) was established to quantify the influence of freeze-thaw and hydrodynamic characteristics on Dc. The explanation rate of variables in the Dc prediction equation was quantitated: the explanation rate of stream power (64.3%) was higher than that of FTC (10.02%) and SMC (3.92%), suggesting that the impact of freeze-thaw on Dc was covered by hydrodynamic characteristics. Further validation is required for the prediction equations when applied beyond the range of construction conditions.

Clayey Soil Improvement with Polyethylene Terephthalate (PET) Waste

Population expansion and the development of technology have led to an increase in construction activities. In many cases, foundation grounds do not have a high enough bearing capacity and are not capable of ensuring the safe exploitation of the construction. A soil with poor mechanical characteristics must be improved using various methods, such as adding hydraulic binders (lime and cement), natural fibres, or more recently, plastic waste materials. This work aims to study the behaviour of plastic waste materials made from polyethylene terephthalate (PET) in soil improvement. Thus, the mechanical characteristics of a clay improved with shredded PET were studied. PET was added in relation to the dry mass of the clay, in percentages of 2%, 4% and 6%. The studied clay was collected from a construction site around Cluj-Napoca, Romania, from a depth of 1 ÷ 10 m. PET was provided by a local plastic waste repository. It comes from recycled water, beer and soda bottles and was cleaned using specific methods for cleaning and recycling plastic waste. PET was shredded into irregular shapes with sizes ranging from 3 mm to 12 mm and was randomly distributed in the test specimens. Compression and direct shear tests were carried out to study the compressibility and shear parameters of the improved soil (internal friction angle and cohesion). The experimental results showed an improvement in the mechanical characteristics of the clay even at a low PET addition of 2% and 4%. This method can contribute to solving two current problems of the modern world: reducing pollution by recycling plastic waste materials and using them to improve the mechanical characteristics of soil.

Underground storage tank blowout analysis: Stability prediction using an artificial neural network

Most geotechnical stability research is linked to “active” failures, in which soil instability occurs due to soil self-weight and external surcharge applications. In contrast, research on passive failure is not common, as it is predominately caused by external loads that act against the soil self-weight. An earlier active trapdoor stability investigation using the Terzaghi's three stability factor approach was shown to be a feasible method for evaluating cohesive-frictional soil stability. Therefore, this technical note aims to expand “active” trapdoor research to assess drained circular trapdoor passive stability (blowout condition) in cohesive-frictional soil under axisymmetric conditions. Using numerical finite element limit analysis (FELA) simulations, soil cohesion, surcharge, and soil unit weight effects are considered using three stability factors (Fc, Fs, and Fγ), which are all associated with the cover-depth ratio and soil internal friction angle. Both upper-bound (UB) and lower-bound (LB) results are presented in design charts and tables, and the large dataset is further studied using an artificial neural network (ANN) as a predictive model to produce accurate design equations. The proposed passive trapdoor problem under axisymmetric conditions is significant when considering soil blowout stability owing to faulty underground storage tanks or pipelines with high internal pressures.

Study of the Effect of Installation of Stone Columns on the Stability of Soil Slopes using Finite Element Method

There are several ways to mitigate the failure of a soil slope. The installation of stone columns for this purpose, is easy as well as economical. As their strength is greater than that of soil, they disrupt the slip surfaces. Also being more porous, they dissipate the pore pressure generated in the soil in the vicinity of the stone columns to a certain extent. This paper illustrates 2D finite element analyses carried out to simulate the behavior of stone columns in cohesive soil using the computer program PLAXIS. Parametric study was conducted to analyze the effect of number, length and diameter of the stone columns on the Factor of Safety of the soil slope. The F.O.S. of the soil slope was predicted using prediction models created using artificial neural networks (ANN) considering slope geometry like slope angle and height, material properties like cohesion and angle and internal friction of soil as well as granular material used in the columns, and the stone column parameters like the stone column’s number, length, diameter and the centre to centre (c/c) distance between two adjacent columns as input parameters. It was found that introduction of stone columns significantly improved the stability of the soil slopes. Further, it was seen that all the parameters considered in the study influenced the Factor of Safety of the soil slope.