Mohr-Coulomb Strength Theory Research Articles

Experimental Study on the Effect of Fine-Grained Soil Content on the Freezing Strength of Aeolian Sand-Cement Interface

In cold regions, understanding the freezing strength of the interface between soil and structure is crucial for designing frost-resistant foundations. To investigate how the content of cement powder in aeolian sand affects this strength, we conducted direct shear tests under various conditions such as different fine-grained soil content, normal stress, and initial moisture content of the soil. By analyzing parameters like soil properties, and volume of ice content, and using the Mohr-Coulomb strength theory to define interface strength, we aimed to indirectly measure the cementation strength of the interface. Our findings revealed that as the particle content increased, the interface stress-strain curves became noticeably stiffer. We also observed a positive linear relationship between freezing strength and silt content, while the initial moisture content of the soil did not significantly impact the strengthening effect of fine-grained soil on freezing strength. Moreover, we discovered that as the powder content increased, the force binding the ice to the interface decreased, while the friction angle at the interface increased. However, the cohesion force at the interface remained relatively unchanged. Overall, our analysis suggests that the increase in freezing strength due to fine-grained soil content is primarily due to the heightened friction between aeolian sand and the interface.

Effect of corrosion on soil-structure interfacial shearing property and bearing capacity of steel foundation in submarine soil environment

As a common type of foundation in ocean engineering, steel foundation encounters great corrosion risk and serious safety hazards throughout its lifecycle. Besides reducing the thickness of steel members, corrosion also has a significant impact on the soil-structure interfacial shearing property by changing the roughness characteristics of steel surface, and eventually affects the bearing capacity of steel foundation in submarine soil environment. In this study, electrolytic accelerated corrosion experiments are conducted first to prepare corroded steel samples suffered different degrees of corrosion. Then, the effect of corrosion on the soil-steel foundation interfacial shearing property is investigated by interfacial shearing experiment and discrete element numerical simulation. The analysis results show that the interface shearing strength under different corrosion degrees can be regarded as following Mohr-Coulomb strength theory. The shearing strength parameters, i.e. the interfacial cohesion and interfacial friction coefficient, increase with the corrosion degree. Finally, the influences of corrosion on the bearing capacity of a steel pipe pile foundation are studied by finite element simulation, with considering the steel thickness reduction and the variation of soil-steel interfacial shearing strength. The numerical results demonstrate the necessity of considering the variation of the interfacial shearing property induced by corrosion.

Application and Analysis of Bolt Support in Mine Driving Roadway

Mineral resources are one of the main energy sources used in industrial production. While the economy is going up, the mining of coal mines and other mineral resources has also intensified. With the deepening of coal mining, the difficulty of mining has also increased. In order to ensure the safe production of relevant enterprises, it is necessary to vigorously apply the supporting technology of mineral resources excavation to reduce the occurrence of accidents in the mining area. Based on this, this paper, on the basis of collecting the geological conditions of a mine, combined with the stability theory of roadway surrounding rock, the existing bolt (anchor cable) support theory, and the factors affecting the reliability of bolt support, analyzed the bolt (anchor cable) support principle and deduced and calculated the support capacity of a single bolt and a group of bolts in the process of mining excavation through the energy conservation theorem. Through Mohr-Coulomb strength theory and limit line analysis theory, a reasonable mechanical model is established, and it is concluded that the ultimate bearing capacity of the bolt will increase with the increase of the length of the anchorage section no matter what support method is used for roadway surrounding rock support, and the anchorage length and ultimate bearing capacity have a nonlinear positive correlation. However, the ultimate supporting capacity of the suspension bolt cannot meet the actual work demand, while the composite beam and composite arch bolt support meet the conclusion. In addition, according to the conclusion and the suggestion that the design of bolt support mode should start with the study of the mechanism of bolt support on the roadway, the application of bolt support mode in the resource mine heading roadway is comprehensively analyzed.

Stability Evaluation Method of Hole Wall for Bored Pile under Blasting Impact

Blasting impact load may be encountered during the construction of some pile foundation projects. Due to the effect of blasting impact, hole collapse can easily occur in the hole-forming stage of pile foundation construction. In order to prevent hole collapse, it is very necessary to evaluate the stability of a pile hole wall before pile foundation construction. The calculation of hole collapse can usually be attributed to an axisymmetric circular hole stress concentration problem. However, the existing collapse failure theory of pile hole hardly considers the effect of blasting impact load. In view of this, this paper proposes the stability evaluation method of a pile hole wall under blasting impact. Compared with the existing collapse failure theory, the proposed method fully considers the effect of blasting impact stress. Using Mohr–Coulomb strength theory and symmetry analysis, the strength condition of collapse failure is established in this work for accurate evaluation of the stability of a hole wall. The proposed stability evaluation method is demonstrated by a pile foundation construction project of a bridge. Moreover, a shaking table test on the pile hole model was performed to verify the proposed method by experimental data. The results indicate the effectiveness and usability of the proposed method. The proposed method provides a feasible way for the stability analysis of a pile hole wall under blasting impact.

Numerical simulations of arbitrary evolving cracks in geotechnical structures using the nonlinear augmented finite element method (N-AFEM)

This paper presents an integrated numerical algorithm based on the nonlinear augmented finite element method (N-AFEM) to accurately simulate the arbitrary evolving strong discontinuities (cracks/slip lines) and failure behaviors in geotechnical structures. A novel nonlinear elemental augmentation and condensation scheme was first proposed within the N-AFEM framework, which allows the consideration of nonlinear coupled intra-element cracks without the need of additional nodes or nodal DoFs. Then a modified exponential cohesive zone model (CZM) that considers the coupling effects between tension/compression and shear at the fracture surface was proposed to describe the fracture process of geomaterials. Besides, a nonlinear yielding function based on the Mohr-Coulomb strength theory was introduced into the framework and serves as the fracture initiation criteria for geomaterials. Finally, several benchmark examples were simulated and the predicted results were compared with existing numerical or experimental data to demonstrate the validity of the proposed method.

Interfacial mechanical properties of recycled aggregate concrete reinforced by nano-materials

This paper evaluates the effect of Nano-SiO2 and multi-walled carbon nanotubes addition on the interfacial tensile and shear strengths of recycled aggregate concrete. Tension and shear tests were conducted for the interfacial strengths between the new and old mortars. Scanning electron microscopy was also conducted to identify the change of the microstructure of the nanomaterial modified interfacial transition zones. The results indicated that addition of the Nano-SiO2 and the carbon nanotubes can generally improve the interfacial tensile and shear strengths at dosages not exceeding 1.0 and 0.2 wt%, and the maximum tensile and shear strength improvements, 51% and 53%, respectively, were both obtained by use of the carbon nanotubes. Scanning electron microscopy results confirmed that the strength improvement came from the nucleation and filling effect and pozzolanic activity of the Nano-SiO2 and the nucleation, filling and bridging effect of the carbon nanotubes. An interaction diagram between the interfacial tensile and shear strengths were established following the Mohr-Coulomb strength theory. The internal friction angle of the modified recycled aggregate concrete was found to be in close range with the reference specimens (±8%), possibly due to the similar influencing mechanism of the nanomaterials on the shear and tensile strength of the interfaces.

Characteristics of Direct Shear and Particle Breakage of Pebble Gravel Materials

Particle size is an important factor affecting the Thermal-Hydraulic-Mechanical (THM) coupling behavior of graveled rock mass, especially for the shear mechanical properties. In this study, three groups of the particle size range and nine particle grading samples are designed for a large-scale direct shear test. The relationships between shear stress and shear displacement, shear strength, stress ratio, shear strength parameters, and particle breakage of pebble gravel are analyzed. The influence of particle size range and grade on the strength and particle breakage of gravel material is discussed. Results show evident particle breakage in the process of direct shear, and the degree of fragmentation is controlled by the normal load and the particle size distribution of the sample. The shear strength of the sample is no longer applicable to Mohr-Coulomb strength theory because of particle breakage that is more in line with the power function relationship. Shear strength of pebble gravel material has scale effect, and a corresponding relationship model between friction coefficient f of material and characteristic particle size of the sample is proposed.

Experimental Investigation on the Mechanical Properties of Self-Compacting Concrete under Uniaxial and Triaxial Stress.

To explore the influence of fly ash (FA) and silica fume (SF) on the mechanical properties of self-compacting concrete (SCC) under uniaxial and triaxial, the compressive strength test, splitting strength test, ultrasonic testing test, and triaxial test were performed in this paper. The results show that the 3 days compressive strength and splitting strength of SCC decreased with the increase of FA substitution rate. The 28 days, 56 days, and 91 days compressive strength and splitting strength of SCC increased first and then decreased with the increase of FA substitution rate. The peak stress and peak strain of SCC gradually increased with the increase of confining pressure. The peak stress and strain of SCC increased first and then decreased with the increase of FA substitution rate. Moreover, the relationship models between compressive strength and splitting strength, between compressive strength and amplitude, between peak stress, peak strain and confining pressure under different FA substitution rates were proposed. As a conclusion, the addition of SF can increase the strength of SCC obviously. Under uniaxial stress, SCC failure mode is splitting failure, under triaxial stress, SCC failure mode is shear failure. Based on the Mohr-Coulomb strength theory, the failure criterion of SCC with FA and SF was discussed.

Pile‐Spacing Calculation of Anti‐Slide Pile Based on Soil Arching Effect

Anti‐slide pile is one of the most frequently used measures in landslide control globally. Pile‐spacing has always been determined by the load capacity of single piles or according to engineering empirical experience. Many engineering practices and laboratory experiments show that the soil arching effect exists in landslide control with anti‐slide piles. In this study, we aim to calculate pile‐spacing in terms of the soil arching effect. We investigated the pile‐soil interaction mechanism and propose that, at the limit, the pile‐back soil arch resists landslide thrust only. According to Mohr–Coulomb strength theory and limit equilibrium theories, we derived a new pile‐spacing calculation equation. We verified the derived pile‐spacing calculation equation with real projects. The calculated results are similar to those of practical engineering designs, in which the difference is within 10%. The equation can be used in anti‐slide pile preliminary design. This study can be a reference for pile‐spacing calculation based on the soil arching effect.

Experimental Studies on Interfacial Shear Characteristics between Polypropylene Woven Fabrics

Geotextile tubes are used in dam construction because fine tailings are difficult to use. The shear characteristics of geotextile tubes during dam operation are closely related to those of the materials used to construct the tubes. Pull-out tests can accurately reflect the interfacial shear characteristics between geosynthetics in practice, so pull-out tests were carried out for different interfacial types of polypropylene woven fabrics under dry and wet states. The effects of the type of interface and dry-wet states on the interfacial shear characteristics were investigated, and the impact mechanisms were also discussed. The results indicated that P-type interfaces (the warp yarn on the interface is parallel to the pulling direction) tended to harden. However, PTP-type (the warp yarn on the interface is perpendicular to each other) and T-type (the weft yarn on the interface is parallel to the pulling direction) interfaces softened first and then tended to plateau after reaching peak shear stress, and softening became more obvious at higher normal stresses. The displacement corresponding to peak shear stress (referred to as “peak displacement” in this paper) of interfaces was positively correlated with the normal stress, and the wet state reduced the interfacial peak displacement. For different types of interfaces, the peak displacement of the T-type interface was the largest, followed by PTP-type and P-type. Interfacial shear characteristics conformed to Mohr–Coulomb strength theory and, compared with quasi-cohesion values ranging from 1.334 to 3.606 kPa, the quasi-friction angle significantly contributed to the interfacial shear strength. The quasi-friction angle of the interface was composed of a sliding friction angle and an occlusal friction angle. The shear strength of the interface was more sensitive to the interface types than whether they were in the dry or wet state. For different types of interfaces and dry-wet states, the change in the interfacial shear strength is respectively affected by the occlusal friction angle and the sliding friction angle on the interface.

Physico-chemical nature of clayey soils strength

The principles of soil mechanics based on Mohr–Coulomb strength theory and Terzaghi effective stresses theory give us the idea about the nature of clay strength. However, these theories consider the clay as a solid body and do not take into account their internal structure. In the present paper, the problems in determining the strength of clayey soils are considered from the standpoint of the physicochemical theory of effective stresses. This theory is based on the ideas of the internal structure of clays. The main idea implies that the structure of clays depends on the contacts formed between mineral particles, where the external stresses transmitted to the soil are concentrating. Water in clayey soils not only fills the pore space but also interacts with the mineral particles forming hydrate films around them. The prevailing type of structural contacts in clays determines the properties of latter. Strength is an intrinsic property of soil determined by its composition and internal structure, independent of the conditions of load application to it and characterized by the actual effective strength value. The value of actual effective strength in clays is determined by the total strength of individual contacts. This is the maximal stress transferred to the soil contacts, the structure being ruined upon exceeding this value. The actual effective strength in soils with the same predominant type of contacts depends on the number of contacts. The numerical strength characteristics of contact types are determined for different clay soil varieties to characterize the actual effective strength. The parameters of relationship between the actual effective strength in clays and their strength characteristics are obtained from the soil testing by standard methods.

Analysis of deformation and failure characteristics of undisturbed loess under three axis test

The water content has a very obvious influence on the deformation and strength characteristics of loess, which is related to the safety of geological environment. In this paper, the triaxial test of loess is carried out, and the deformation characteristics of the loess are studied. The strength characteristics of different loci are studied. The study shows that as the water content increases, the effective cohesion of loess decreases and the effective internal friction angle changes. The amplitude is not large, indicating that the water content only affects the effective cohesion of the loess and does not affect the effective internal friction angle. When the water content reaches a certain value, the effective cohesion is no longer reduced and remains stable. The corresponding moisture content corresponds to the plastic limit. The Mohr-Coulomb strength theory is suitable for fitting shear failure and bulging deformation. While Griffith The strength theory is more suitable for fitting the splitting failure, indicating that the strength theory suitable for different failure modes is different.

Mechanisms of wetting-induced loess slope failures

Frequent occurrence of landslides induced by rainfall or irrigation has seriously threatened the urban and rural development in the Loess Plateau, China. The increase in pore water pressure has been identified as a key factor for understanding wetting-induced loess slopes failures. However, experimental studies are limited regarding the increase in pore water pressure of the collapse loess from an initial negative value until failure occurs under constant total stress condition. An old landslide with progressive retreat development at an early stage of the construction of the Lvliang Airport was selected as a case study. Field surveys including exploration wells and boreholes revealed very fresh sliding shear planes and clearly visible cracks, suggesting the creeping movement of the old landslide. In case of heavy rain or long-term rainfall, this old landslide may be resurrected, threatening the stability of the airport site. To examine the mechanism of the failure induced by wetting for this unsaturated loess landslide, loess specimens were taken from the field, followed by performing a series of laboratory tests, including triaxial shear tests at constant matric suctions and wetting tests at constant deviator stresses. The test results revealed that the wetting-induced deformations of the loess included volume and shear deformations, reflecting compression and shearing behaviour induced by wetting. The failure behaviour of the loess along a wetting path was dependent on the stress level and the loss degree of matric suction as well as the hydro-mechanical path, and could be well described by the linear form of the Mohr-Coulomb strength theory. On this basis, the threshold value of the stress level was identified, which could be used to judge whether the wetting-induced failure of the loess occurs. The threshold value of matric suction at failure was also identified to analyse the loss degree of matric suction from stable conditions to failure. The mechanism of the failure of the soil due to wetting revealed from the present study could interpret the rainfall-induced landslide in unsaturated loess.

Active Earth Pressure Against Rigid Retaining Wall Considering Effects of Wall-soil Friction and Inclinations

This paper reports a new method for calculating the active earth pressure acting on inclined rigid retaining wall with inclined backfill, considering wall-soil interface friction angle. Based on Mohr-Coulomb strength theory and Mohr stress circle, new formulae of the active earth pressure and the active rupture angle are derived. The effects of internal friction angle, backfill-surface inclination, wall-back inclination on the active earth pressure and the active rupture angle are investigated. In order to facilitate calculation, special solutions of presented formulae are discussed under various particular conditions. Finally, the calculated results from the presented formula and existing formulae are compared with existing small-scale test results. The comparison shows that the presented method satisfactorily predicts active earth pressure.

Effect of sediment particle size on the mechanical properties of CH4 hydrate-bearing sediments

Previous study proved that the methane hydrate reservoirs in clay permafrost regions have great potential for exploitation. However, the widespread gradation of sediment matrices in hydrate-bearing sediments (HBS) would seriously affect the stability of the hydrate reservoirs, causing uneven distribution of pressure at the wall of the exploitation wellbore, and leading to a severe engineering hazard. Therefore, the effects of the sediment particle size on the mechanical stability of hydrate reservoir need to be investigated before the large-scale commercial production of methane hydrate. In this paper, sediments matrices containing different proportions of clay, silt and sand were prepared and mechanical properties of HBS were investigated and compared with each other. The results show that a bigger proportion of large-particles in the sediment matrix could significantly enhance the failure strength of HBS under different confining pressures, temperatures and strain rates. A better graded size distribution would also boost the failures strength of HBS, it's also found that the failure strength of HBS firstly increases and then declines with the rise of confining pressure, and that material exhibits greater failure strength at lower temperatures and higher strain rates. Finally, an analysis using Mohr-Coulomb strength theory indicates that the internal friction angle plays a dominant role in the failure strength increase of HBS with a greater proportion of large-particles in the sediment matrix.

Experimental Study on Artificial Cemented Sand Prepared with Ordinary Portland Cement with Different Contents.

Artificial cemented sand test samples were prepared by using ordinary Portland cement (OPC) as the cementing agent. Through uniaxial compression tests and consolidated drained triaxial compression tests, the stress-strain curves of the artificial cemented sand with different cementing agent contents (0.01, 0.03, 0.05 and 0.08) under various confining pressures (0.00 MPa, 0.25 MPa, 0.50 MPa and 1.00 MPa) were obtained. Based on the test results, the effect of the cementing agent content (Cv) on the physical and mechanical properties of the artificial cemented sand were analyzed and the Mohr-Coulomb strength theory was modified by using Cv. The research reveals that when Cv is high (e.g., Cv = 0.03, 0.05 or 0.08), the stress-strain curves of the samples indicate a strain softening behavior; under the same confining pressure, as Cv increases, both the peak strength and residual strength of the samples show a significant increase. When Cv is low (e.g., Cv = 0.01), the stress-strain curves of the samples indicate strain hardening behavior. From the test data, a function of Cv (the cementing agent content) with c′ (the cohesion force of the sample) and Δϕ′ (the increment of the angle of shearing resistance) is obtained. Furthermore, through modification of the Mohr-Coulomb strength theory, the effect of cementing agent content on the strength of the cemented sand is demonstrated.

Analysis of Structural Soil’s Shear Strength under Arbitrary Degree of Consolidation

Mohr-Coulomb strength theory is the most widely used in practical engineering, however, it is difficult to predict the cohesion and internal friction angle precisely. In fact, soft clay’s shear strength varies with the change of stress path and consolidation history, so it is vital to predict the shear strength in different construction phases, and the influence of soil structure is necessary to be taken into consideration to predict the shear strength under under arbitrary degree of consolidation. This study proposed a simple shear strength fomula under arbitrary degree of consolidation considering the enfluce of soil structure. The derived formula is much more convenient to plug the changing strength index into program.

Experimental research on the mechanical properties of methane hydrate-bearing sediments during hydrate dissociation

This paper describes studies of the effect of hydrate dissociation on the safety and stability of methane hydrate-bearing sediments. Methane hydrates within the sediments were dissociating under the conditions of a confining pressure of 0.5 MPa, 1 MPa, 2 MPa and a temperature of −5 °C. After 6 h, 24 h, or 48 h, a series of triaxial compression tests on methane hydrate-bearing sediments were performed. The tests of ice-clay and sediments without hydrate dissociation were performed for comparison. Focusing on the mechanical properties of the sediments, the experimental results indicated that the shear strength of the ice-clay mixtures was lower than that of the methane hydrate-bearing sediments. The strength of the sediments was reduced by hydrate dissociation, and the strength tended to decrease further at the lower confining pressures. The secant modulus ES of the sediments dropped by 42.6% in the case of the dissociation time of the hydrate of 48 h at the confining pressure of 1 MPa; however, the decline of the initial yield modulus E0 was only 9.34%. The slower hydrate dissociation rate contributed to reducing the failure strength at a declining pace. Based on the Mohr–Coulomb strength theory, it was concluded that the decrease in strength was mainly affected by the cohesive reduction. Moreover, the mathematical expression of the M–C criterion related to the hydrate dissociation time was proposed. This research could be valuable for the safety and stability of hydrate deposits in a permafrost region.

Study on Shear Strength Experiments Base on the Modified Direct Shear Apparatus for Unsaturated Soils

The unconsolidated-undrained fast shear tests of saturated-unsaturated remolded soil samples under different moisture content which is 1.1%, 10.1%, 14.9%, 19.9%, 24.2%, 29.9%, 37.7% respectively, and normal stress which is 50kPa, 100kPa, 200kPa, 300kPa, 400kPa respectively, were studied by the modified SDJ-1-type strain direct shear apparatus and U.S. Lab VIEW data acquisition system. The shear strength parameters of unsaturated soil samples, i.e. general cohesion and general internal friction angle were obtained based on Mohr-Coulomb strength theory. The test results showed that the general cohesion firstly increased and then reduced with the moisture content increasing, and the general internal friction angle increased with the moisture content decreasing. The function between the general shear strength parameters and the moisture content was studied. The concept of general shear strength parameters was proposed in the paper, and would provide a simple and practical method to obtain the strength parameters for engineering practice.

Research of Brittle Shear Failure Strength of Rock Materials

In order to get brittle shear characteristics of rock material, acoustic emission accompanied with triaxial stress-strain test was applied to monitor the emergence and development of micro cracks. Theoretical analysis and data processing were conducted based on the theories of fracture mechanics and general rock mechanics, relations between the feature strength of three stages and the stress state were obtained, and a method was put forward for analyzing the brittle shear failure of rock material. The relationship of the Mohr-Coulomb strength theory, Griffith strength theory and Hoek-Brown criterion with the brittle-shear strength model were established. Strength analysis of mixed granite in Shuichang slope was carried out by the brittle shear failure model, and the theoretical value and experimental value has a good consistency.