Mohr-Coulomb Model Research Articles

3D Numerical Simulation of Landslides for the Full High Waste Dump Using SPH Method

Waste dump that is generally composed of a large number of loose geotechnical materials is prone to landslides under external loads. In this work, the smoothed particle hydrodynamics (SPH) method combined with the Mohr–Coulomb model is used to study the dynamic characteristics of the landslides that occurred in the waste dump during the failure process. A benchmark test is firstly conducted to verify the effectiveness of the SPH model. Then, taking the Nanfen full high waste dump with a vertical drop of 300 m in Benxi City, China, as an example, the most dangerous section is selected to establish the SPH numerical model for the waste dump landslides, and the overall dynamic process of the landslides is simulated. The simulation results show that the particles in the middle and upper of the slope have larger potential energy, and their sliding distance is larger. On the contrary, the sliding distance of particles in the lower of the slope is smaller. The particles' sliding distance decreases as the depth increases in the vertical direction of both shoulder and middle of the slope. The particles undergo a process of first acceleration and then deceleration. The sliding distance is in good agreement with the field survey result, and the landslides profile is basically consistent with the actual one. The sensitivity analysis of different particle numbers shows that the number of particles has little effect on the numerical results. The SPH method can vividly reproduce the dynamic process of the landslides in the full high waste dump. The evaluation of the sliding characteristics and risk impact range can provide the key parameters and basis for the prevention and control of the landslides in the full high waste dump and ensure the safety of the mine life cycle.

Numerical Analysis of Soil Deformation and Collapse Due to Hydrate Decomposition.

Natural gas hydrates are an ideal alternative clean energy source. Many countries are currently attempting the trial production of gas hydrates. Japan became the first country to achieve offshore hydrate trial production in 2013, and China conducted 60 days of continuous trial exploitation in 2017. This study analyzes the changes in the internal stress of the hydrate zone and hydrate saturation of the soil throughout the monitoring period and calculates the failure stress of the hydrate deposit layer. The Mohr–Coulomb model is used to simulate Japan’s test exploitation conditions to verify the feasibility of the method. Finally, the hydrate decomposition range, the difference in the soil dip angle in the test exploitation area, and the bearing capacity of the hydrate reservoir are numerically simulated to evaluate the stability of the soil. Through the sensitivity analysis of the hydrate decomposition range and the inclination angle of the hydrate sediment layer, it can be found that the hydrate decomposition range has the greatest impact on the deformation, and the soil around the decomposition area may be sheared and collapsed. Within 1 week of decompression and exploitation, the hydrate decomposition radius is approximately 3 m. When the inclination angle increases from 3° to 9°, the sediment deformation increases by 12 times. Therefore, it is necessary to pay attention to the critical value of the decomposition range during the exploitation process.

3-dimension stresses and new failure model to predict behavior of clay soils in various liquid limit ranges

Data analytics are becoming important to better characterize the material behavior. In this study, over 3000 data from the laboratory studies and literature for the field soils were analyzed to quantify the relationship between the density, natural moisture content, shear strength, deviatoric shear stress at failure (3-dimension stress) with the liquid limit (LL). With the increase in the construction of wells, tunnels, piles, and storage facilities, there is interest in determining the safety of soils under multiaxial loading. The range of liquid limit (LL) for the soil investigated varied from 20 to 60%. The ranges of the dry density (γd) and the natural moisture content (MC) for the soils varied from 1.2 to 2.6 g/cm3 and 13 to 56% respectively. The statistical distribution of the data collected varied from normal distribution to Weibull distribution. Vipulanandan correlation model correlated some of the physical properties of the soils. Vipulanandan failure model was used to the failure stresses for the soil and compared to the Mohr-Coulomb failure model and other failure models. Based on the coefficient of determination and root mean square error, the Vipulanandan failure model predicted the results more reliable than the other models. Vipulanandan failure model also predicted the maximum shear strength limit and maximum second deviatoric stress invariant for the soil, whereas none of the other models predicted the maximum shear tolerance for the soil investigated. With the Vipulanandan failure model, the maximum shear strength predicted for the soil was 57 kPa. The maximum second deviatoric stress invariant for the soil in the LL range of 20 and 60% varied from 44 to 30 kPa.

A Plane Stress Failure Criterion for Inorganically-Bound Core Materials.

Inorganically-bound core materials are used in foundries in high quantities. However, there is no validated mechanical failure criterion, which allows performing finite-element calculations on the core geometries, yet. With finite-element simulations, the cores could be optimised for various production processes from robotic core handling to the decoring process after the casting. To identify a failure criterion, we propose testing methods, that enable us to investigate the fracture behaviour of inorganically-bound core materials. These novel testing methods induce multiple bi-axial stress states into the specimens and are developed for cohesive frictional materials in general and for sand cores in particular. This allows validating failure criteria in principal stress space. We found that a Mohr-Coulomb model describes the fracture of inorganic core materials in a plane stress state quite accurately and adapted it to a failure criterion, which combines the Mohr-Coulomb model with the Weakest-Link theory in one consistent mechanical material model. This novel material model has been successfully utilised to predict the fracture force of a Brazilian test. This prediction is based on the stress fields of a finite element method (FEM) calculation.

Behaviour of Square Footing Due to the Effect of Adjacent Excavation in Sand

In today scenario, urbanization and related infrastructure development in the form of an excavation adjacent to the existing structure are inevitable. In this case, the stability of an existing structure closer to the excavation is a serious concern. The main issue here is that, what is the safe distance at which new construction can take place from the existing structure? There are many research articles that states on the failure of an existing structure due to new construction adjacent to it in the form of excavations. Given the above, the paper presents the numerical results based on the finite element analyses that were performed for various parameters to examine the behaviour of existing square footing due to the effect of adjacent excavations in loose sand using PLAXIS3D software. In the finite element analysis, the behaviour of the footing and sheet pile walls were modelled using a linear elastic material and the elastoplastic behaviour of soil was modelled using a Mohr-Coulomb model under drained conditions. The literature available on this topic reveals that the excavation dimensions, shape of the footing, depth of the footing, location of the footing from the excavation, relative stiffness factor and relative density of sand are influencing the response of existing footing. Two different shapes of excavations such as a long length with narrow excavation under plane strain condition and short length of excavation under three-dimensional conditions were considered in this study. Numerical results indicate that the response of the square footing due to the effect of adjacent excavations are very much significant and mainly depends on the size of the excavation. The vertical and horizontal displacement, bending moment of the footing is increasing with an increase in depth of excavation. The footing located very closer to the excavation is significantly influenced as compared to the footing located far away from the excavation. The safe location of the square footing based on the settlement criteria is found to be 1.3 m from the excavation for shorter length excavation under three-dimensional conditions and 10 m for longer length of excavation under three-dimensional conditions.

Three-dimensional finite element analysis of urban rock tunnel under static loading condition: Effect of the rock weathering

Tunnel provide faster, safer and convenient way of transportation for different objects. The region where it is construction and surrounding medium has significant influence on the overall stability and performance of tunnel. The present simulation has been carried out in order to understand the behaviour of rock tunnel under static loading condition. The present numerical model has been validated with the laboratory scaled model and field data of underground tunnels. Both lined and unlined tunnels have been considered in this paper. Finite element technique has been considered for the simulation of static loading effect on tunnel through Abaqus/Standard. The Mohr-Coulomb material model has been considered to simulate elastoplastic nonlinear behaviour of different rock types, i.e., Basalt, Granite and Quartzite. The four different stages of rock weathering are classified as fresh, slightly, moderately, and highly weathered in case of each rock type. Moreover, extremely weathered stage has been considered in case of Quartzite rock. It has been concluded that weathering of rock and overburden depth has great influence on the tunnel stability. However, by considering a particular weathering stage of rock for each rock type shows varying patterns of deformations in tunnel.

CALCULATION OF VERTICAL DEFORMATIONS OF THE FOUNDATIONS ON THE SOFT SOIL IMPROVED BY GEOTEXTILE ENCASED STONE COLUMNS

The article provides information on research in the field of improving weak clay bases by installing vertical soil piles in a shell of geosynthetic materials (geotextile encased stone columns). This method has proven to be effective for strengthening the foundations of large areal objects in certain soil conditions, but has not become widespread as a method for improving the foundations of building foundations, which, among other things, is due to the lack of simple engineering methods for calculating the improvement parameters. The article presents an engineering technique for determining the settlement of shallow foundations on a weak clay base which is improved by the geotextile encased stone columns. The technique is based on considering the elementary cell of the improved foundation for which the pressure distribution in the weak soil and the improvement element is determined by the iterative enumeration process. This distribution should ensure equality of the vertical deformations of the improvement element and the soft soil, which should be the same due to the stiffness of the foundation of the building or structure. The calculation of the deformations of a geotextile encased stone columns is carried out by solving the Lamé problem and the deformations of soft soil by standard methods presented in the regulatory literature. Comparison of the calculation results by the proposed method with the data of numerical modeling in an axisymmetric setting is presented. In the numerical modeling of the soil, the Mohr-Coulomb elastic-plastic model was used. Geosynthetic reinforcement was modeled using a special element that only accepts tensile stresses. The rigidity of the foundation of the base is taken to be infinitely large. The analysis of the presented simulation results showed good convergence of the calculations with the data of experimental studies and the data of numerical simulation using the finite element method.

Numerical Simulation of the Interaction between Fibre Concrete Slab and Subsoil—The Impact of Selected Determining Factors

Shape and material optimization of building structures, including reducing the amount of concrete used, are very important aspects in sustainable construction. Numerical modelling is currently used very effectively to design optimized and sustainable structures, including their interaction with the surrounding rock environment. This paper is focused on the three selected factors of numerical modelling of fibre concrete slab and subsoil interaction: (1) the constitutive model of fibre concrete slab, (2) deformational and strength characteristics of subsoil, (3) effect of interface elements. The specialized geotechnical software Midas GTS NX, based on the finite element method, was used for the modelling of this task. Numerical results were compared with the experimental measurement of vertical displacements on the upper surface of slab. In the presented study, three constitutive models of slab recommended in MIDAS GTS NX code for modelling concrete behaviour (elastic, Mohr-Coulomb and Drucker-Prager) were applied. In addition, the sensitivity analysis with respect to the deformational and strength characteristics of subsoil was performed. The numerical study also presents the effect of the interface elements application on the slab behaviour. The numerical results of maximum vertical displacements based on the Drucker-Prager and elastic model underestimated both the experimental results and numerical results based on the Mohr-Coulomb model. From the qualitative point of view (shape of deflection curve), the numerical simulation showed the better agreement of the Mohr-Coulomb constitutive model with the experimental measurements in comparison with the other two investigated constitutive models. The performed parametric study documented that reduction of the strength and deformational characteristics of subsoil leads to the increase of maximum vertical displacements in the centre of slab, but the experimentally measured deflection curve, including uplift of slab and gapping occurrence between the slab and subsoil, was not achieved without the interface application.

The Effect of Geocell Reinforced Embankment Construction on the Behaviour of Beneath Soil Layers Using Numerical Analysis

Geocell soil reinforcement method is became one of the common improvement method used in different aspects of geotechnical engineering. The experimental investigation using physical modelling is somehow complicated and needs more financial support especially when using saturated or partially saturated soil. That’s why nowadays, researchers are trying to use updated numerical methods to simulate the soil behaviour considering above conditions. In this paper, Geocell reinforcement method in embankment construction has been studied using Mohr-Coulomb model. The embankment is overlaid on two layers of soil with different moisture content conditions. The first layer beneath the embankment is a five-meter layer of dry soil and the second layer considered fully saturated soil. The results indicate that embankment reinforcement by Geocell has no significant effect on the excess pore water pressure while the settlement and stress distribution beneath the embankment is highly affected.

Influence of the Spatial Variability of Soil Shear Strength on Deep Excavation: A Case Study of a Bangkok Underground MRT Station

This paper investigates the effects that the spatial variability of a soil's undrained shear strength has on lateral wall movements and ground surface settlements when performing a deep excavation stability analysis. A random finite-element method is employed to statistically assess a deep excavation. A case study based on an actual deep excavation project in Bangkok's subsoils was used to validate the methodology. The two-dimensional spatial variability of the undrained shear strength in the clay layers of Bangkok's subsoil is simulated using the random field theory and Monte Carlo simulation. The Mohr–Coulomb model is used to predict lateral wall movements and ground surface settlements, while the stability analysis of the deep excavation is evaluated by the factor of safety using the strength reduction approach. The results show that spatial variability highly affects the distribution of lateral wall movements and ground surface settlements, as well as the scatter of the factor of safety corresponding to progressing stages of excavation.

Three-dimensional finite element modeling of corrugated metal pipes

The mechanism of the soil-structure interaction in buried corrugated metal pipes (CMPs) depends primarily on the relative stiffness of the flexible buried pipe and the surrounding compacted backfill material. Several geometric, mechanical, and material characteristics control this complex composite interaction, including the shape and dimensions of the pipe, its burial depth, the effect of the backfill compaction, and existing in-situ conditions. Numerical techniques such as the finite element method (FEM) have proved useful in capturing the soil-structure interaction. This paper presents three rigorous three-dimensional finite element models of circular, horizontal ellipse, and arch pipes with spans of 600 mm, 1800 mm, and 6000 mm, respectively. The models developed account for the effect of compaction on the soil behaviour. These models were validated by using three full-scale tests of underground CMPs. The FEM results are compared with recorded measurements of deformation and internal forces in each pipe structure. The effectiveness and suitability of three commonly used constitutive soil models, the Mohr-Coulomb (MC) model, the hardening soil (HS) model, and the hardening soil with small strains (HSs) model, are also examined. The HSs model exhibited the best fit in simulating the interaction of the backfill soil and buried pipes with different types of loading.

Settlement Response of a Multi-Story Building

The settlement calculation of a multi-story building is a challenging task due to the variation of soil properties and the use of an appropriate constitutive model for the reliable representation of soils’ stress-strain behaviors. In this study, the settlement response of a multi-story building was calculated with the simple Mohr-Coulomb Model (MCM) and the Hardening Soil Model (HSM). The effect of soil modulus of elasticity using both models was investigated on the overall settlement response of the building. Results indicated that MCM overestimated immediate settlement in a range of 50 to 65% compared to HSM. The settlement response of the building calculated with both models was within the allowable range. The results of this study can be helpful for geotechnical engineers working on reliable predictions of the settlement of multi-story buildings.

Numerical Analysis of Pipeline Uplift Resistance in Frozen Clay Soil Considering Hybrid Tensile-Shear Yield Behaviors

Pipeline uplift resistance plays an essential role in the design of buried pipelines in permafrost regions or artificially frozen ground. The uplift resistance of a frozen soil is dependent on the soil’s mechanical properties, which are needed to characterize plastic zones in the frozen soil that surrounds pipes. Owing to the presence of unfrozen water, frozen soils (especially frozen clay) display complex mechanical properties that vary with temperature. There are limited amount of research studies with a focus on frozen soil–pipe interactions that consider temperature change within the literature. In this study, numerical modeling is conducted to investigate frozen soil–pipe interactions at different temperatures. A pipe is simulated with vertical displacement-controlled or vertical load-controlled conditions. The temperature-dependent mechanical parameters of frozen clay soil are examined in the simulation. Both tensile yield and shear yield behaviors are included in the modeling with the consideration of temperature-dependent failure criterions. Simulated stress paths in monitoring points are collected and displayed. The results from the Mohr–Coulomb model with the Rankine tensile cut off, and the hyperbolic Drucker–Prager model are compared and analyzed. The results indicate that hyperbolic Drucker–Prager model is effective for analyzing soil plastic zones surrounding a pipe. The applied hyperbolic Drucker–Prager model with reduced strength parameters can produce a more conservative uplift resistance–displacement relation when compared with that from the Mohr–Coulomb model. Thermally induced plastic strain may have a significant impact on the uplift resistance analysis, since a significant thermally induced uplift displacement is expected if there is a heat transfer process from a buried pipe to the surrounding frozen soil.

Assessment of pore pressure, wellbore failure and reservoir stability in the Gabo field, Niger Delta, Nigeria - Implications for drilling and reservoir management

This work investigates a 3400m thick Tertiary succession from the prolific Gabo hydrocarbon field in the Niger Delta and presents a well-scale geomechanical model to address the pore pressure, borehole stability and fault slip potential attributes. The Tertiray stratigraphy is dominated by cyclic clastic sedimentation and it produces hydrocarbon from the Eocene Agbada Formation. An average vertical stress gradient of 0.85-0.90 PSI/feet is interpreted from the density logs. Extensive direct downhole measurements indicate a sub-hydrostatic pressure gradient of 0.325 PSI/feet in the Upper Agbada reservoir sands, while the lower producers are presently in hydrostatic regime (0.435 PSI/feet). Pore pressure against the shales are estimated by Eaton’s disequilibrium compaction method, which are found to be mildly overpressured (0.49 PSI/feet). The minimum horizontal stress (Shmin) gradient ranges between 0.59 and 0.70 PSI/feet. Wellbore stability is addressed by the Mohr-Coulomb failure model and the assessed failures are corroborated with the caliper log observations. Drilling mud weight used in the studied wells were found to be less than the shale collapse pressure gradient, resulting in selective wellbore over-gauging in the Eocene shales, intercalated with the sandstone reservoir intervals. Safe and effective downhole pressure window is inferred from the interpreted pore pressure, collapse pressure and Shmin to avoid any kick, loss or compressive wellbore failures by optimum mud weight designing. Inferences on drilling optimization are discussed which will be helpful for better planning of the infill injector wells. A fault slip analysis indicates that pore pressure could be increased by 1100-1200 PSI during the repressurization in the Upper and Lower Agbada reservoirs without inducing reservoir instabilities as well as caprock failure.

Calculation Method for Unstable Rock Stability based on Dominant Fissure Model

In accordance with in-situ exploration and years of experience in unstable rock-related design, this paper states that the Mohr-Coulomb model is insufficient for the selection of the shear strength parameters of the dominant fissure of unstable rocks. Therefore, a JRC-JCS model of dominant fissure for three types of unstable rocks was established, which is more applicable to construction practice. Based on this model, calculation methods were obtained for the three types of unstable rocks, and the stability coefficient expressions of the unstable rocks were determined. The stability of five typical unstable rocks in Wanzhou District, Chongqing Municipality, China, namely, W12, W22, W59, W4, and W16, was calculated by these methods. As indicated by the calculation results, the unstable sliding rock W12, unstable toppling rock W22, and unstable falling rock W4 are stable, while the unstable toppling rock W59 and unstable falling rock W16 remain unstable and thus need reinforcing. These calculation results are relatively in line with the actual situation, according to a verification by in-situ monitoring from 2003 to 2013. This further verifies the practicality and applicability of the above calculation methods, which are based on the dominant fissure model. These methods also offer a theoretical basis for the amendment of the local standard, namely, Chongqing’s design specification for prevention and control projects of geological hazards (DB50/5029-2004), in terms of calculation methods for unstable rock stability.

Deformation and Force Analysis of the Pile Foundation System of Deep Foundation Pits in Soil–Rock Combination

This study uses the construction of the Shengli Bridge Station of Qingdao Metro Line 1 as the engineering support for in-depth research of the deformation and mechanical characteristics of the retaining structure of pile-support systems during deep foundation pit excavation under the complex geological conditions of soil–rock combination. This study adopts the finite element software modeling analysis method to simulate the excavation of the foundation pit and the 3D finite element numerical calculation method to calculate the deformation. The modified Mohr–Coulomb model is selected as the constitutive model, and the natural gravity of each layer of soil is considered. The calculated load includes the dead load of structure and soil. The boundary conditions of X, Y, and Z directions at the bottom are fixed constraints, and the top ground is a free boundary. The displacement of soil around the foundation pit and the stress and deformation of retaining piles and crown beams under different working conditions are studied. The deformation law and force mechanism of the supporting structure of the pile-support system are analyzed. The research results reveal the relationship between the synergy of pile-support system and soil deformation, serving as a reference for similar engineering constructions.

Unified constitutive model for granular–fluid mixture in quasi-static and dense flow regimes

Most granular materials encountered in nature and industry lie either in the quasi-static regime or the intermediate dense flow regime. Debris materials are a typical granular material with viscous interstitial fluid and show solid-like behaviors before failure and fluid-like behaviors after failure. Based on Bagnold’s pioneering work on granular–fluid flows, we propose a framework for constitutive model development, which has an additive form. Based on this framework, a unified constitutive model for granular–fluid material in the quasi-static and dense flow regimes is developed. The main intergranular interactions and granular–fluid interactions controlling the mechanical behaviors are taken into account using the Mohr–Coulomb model and a Bagnold-type relation. Dry granular flows in three simple configurations, i.e., plain shear, vertical chute flow and flow on an inclined plane, are studied. Analytical solutions based on the presented unified model are obtained. Comparisons between results from the presented model and the $$\mu (I)$$ model indicate that the explicit partition of frictional and collisional stress components provides insights into dense granular flows. In addition, the new model is used to predict the stress–strain relations in two annular shear tests. The applicability and advantages of the unified model are discussed.

Determination of Mohr-Coulomb Parameters for Modelling of Concrete

Cohesion is defined as the shear strength of material when compressive stress is zero. This article presents a new method for the experimental determination of cohesion at pre-set angles of shear deformation. Specially designed moulds are created to force deformation (close to τ-axis) at fixed pre-set values of angle with respect to normal stress σ. Testing is performed on series of concrete blocks of different strengths. From the compressive side, cohesion is determined from the extrapolation of the linear Mohr–Coulomb (MC) model, as the intercept on the shear stress axis. From the tensile stress side (from the left), cohesion is obtained using the Brazilian test results: first, indirect tensile strength of material σtBT is measured, then Mohr circle diagram values are calculated and cohesion is determined as the value of shear stress τBT on the Mohr circle where normal stress (σ)t = 0. A hypothesis is made that cohesion is the common point between two tests. In the numerical part, a theory of ultimate load is applied to model Brazilian test using the angle of shear friction from the MC model. Matching experimental and numerical results confirm that the proposed procedure is applicable in numerical analysis.

FEM Simulations of Granular Matter Behaviour Under Triaxial Tests

This article presents the results of a numerical simulation carried out from a series of standard triaxial tests conducted on limestone sand from a quarry situated in Algiers (center of Algeria). The main objective of the investigation is to obtain from a numerical analysis a simple soil model to represent the behaviour of the studied material. The 2D Plaxis program is used in this study with the introduction of a model based on the work of Brinkgreve et al. (in: Benz T, Nordal S (eds) Numerical methods in geotechnical engineering, CRC Press, Boca Raton, 2010). Corrections were made to the formulas used, which are based on the relative density, in order to improve the quality of the results in terms of soil behaviour, mechanical strength and deformation. The comparison of the experimental and numerical results for the Mohr–Coulomb model gives a considerable appreciation on the deformation and resistance. However, it fails to represent properly the stress–strain curve. The use of Duncan and Chang model (Hardening Soil Model-HSM) leads to an underestimation of the resistance characteristics (values of the friction angles) with an overall error of 7.98%. Our work consists of the application of two corrections to the HSM model. The first correction is based on the work of Brinkgreve et al. (2010), which focused on the common parameters between the HSM and the HSSM. An overestimation of the deformations was observed with an overall error of 155.96%. The second step consists of canceling the correction of the elastic modules ( $$E_{50}^{ref}$$ , $$E_{oed}^{ref}$$ ) which reduces the error to 1.53%.

Numerical Simulation of Predicting the Shaft Capacity of Single Pile in Unsaturated Soil

Pile foundations that placed above the groundwater table zone where the soil is typically in a state of the partially saturated case have been considered in this study. To appreciate the effect of the matric suction on the skin resistance of single pile foundations that placed in unsaturated clayey soil. A series of small scale and full-scale single model pile are simulated using the software Plaxis 3 D. Mohr-Coulomb model (Elastic-perfectly plastic model) that takes into account the effect of the matric suction has adopted in the analysis. Also, in this study comparison among numerical models and laboratory, small scale single and full-scale pile models have done. In general, the value of shaft capacity obtained by the numerical investigations are in good agreement with laboratory model pile test results.