Search Results (12)

A non-proportional reduction in strength parameters is widely used in slope stability assessment, but the current asynchronous reduction in strength parameters only considers the cohesion c and internal friction angle φ, which is suitable for slope stability assessment under static loads. Under seismic loads, however, tension at the rear edge of the slope often accompanies the appearance of ground cracks. In order to consider the relationship between tensile strength, cohesion, and the internal friction angle reduction coefficient, starting with the linear softening attenuation law of soil material strength parameters, a functional relationship between cohesion and internal friction angle is obtained. Then, considering that the failure of microelements in the tensile and shear zones conforms to the tension and shear of joint failure, the relationship between tensile strength, cohesion, and the internal friction angle reduction coefficient is derived. By establishing a homogeneous slope model and comparing and analyzing the progressive instability failure modes of slopes under static and seismic conditions, the stability and potential slip surface differences of slopes under two different working conditions are explored. The research results indicate that slope instability is a gradual, cumulative failure process under both static and dynamic conditions. The instability mode of the slope under static conditions is shear failure. In contrast, under dynamic loads, the instability failure of the slope is manifested as shear failure upward at the foot of the slope and tensile failure downward at the top of the slope. The stability coefficient of slopes under earthquake conditions is reduced by 17.3% compared to that under static conditions. Under earthquake conditions, the potential sliding surface under an asynchronous reduction in strength parameters is shallower than that under static conditions and deeper than that without an asynchronous reduction in strength parameters. Overall, the research results provide a reference for slope stability analysis and support design optimization under earthquake loads. Full article

The seepage effect of rock and soil in the process of encountering water follows a nonlinear coupling law between water and rock. According to the permeability of rock and soil during softening with water, changes in particles in rock and soil are related to permeability mechanisms. Based on the assumption of connection between particles in rock and soil, changes in particles before and after water infiltration, the mechanism of water–rock interaction, and the damage to rock and soil are analyzed herein. Combined with fractal theory and percolation theory, the random failure characteristics and nonlinear behavior of water in rock and soil are studied. At the same time, with the help of Fluent 17.0 software, the seepage process of rock samples in water is numerically simulated and analyzed. Taking the permeability coefficient of rock samples, the mass flow rate of water, and the internal pore water pressure of rock samples as tracking objects, it is found that there are obvious nonlinear characteristics in the process of water–rock interaction. The seepage–stress coupling between water and rock forms negative resistance to water seepage. The water infiltration is a slow and then accelerated process and tends to be stable. Research has shown that the coupling effect of seepage between water and rock increases the damage inside the rock and soil, and its permeability fluctuates randomly at different time steps. This feature is a common manifestation of fractal properties and percolation within rock and soil particles. At the same time, there is a non-equilibrium variation law of pore water pressure inside the rock and soil. This leads to a continuous strengthening of the seepage effect, reaching a stable state. The results of this study are crucial. It not only reveals the mechanism of interaction between water and rock but also correlates the degree of internal damage in rock and soil based on the seepage characteristics between water and rock. The conclusions can provide some reference value for relevant construction methods in the analysis of the formation of water flow characteristics, the prevention of rock slope seepage disasters, and the control of water inrush in tunnel excavation. Full article

In recent decades, loess landslide events have attracted increasing attention in the South Jingyang tableland. To elucidate the mechanical mechanism of landslide initiation in the region, this work collected undisturbed loess and paleosol samples taking from the Q₂ strata in the South Jingyang tableland. A range of direct shear tests were carried out to explore the strength evolution law of shear zone soil subjected to a varying initial moisture content. In addition, soil water characteristic curves (SWCCs) were also charted and used for predicting the unsaturated shear strength. The findings show that the basic physical properties of the paleosol are different from those of loess due to their different pedogenic environments. The normal stress level and initial moisture content jointly determine whether the shear behavior is strain hardening or strain softening. The shear strength and strength parameters evidently diminish with an increasing initial moisture content, and cohesion contributes to the vast majority of strength attenuation. Paleosol samples possess higher values in shear strength and strength parameters than loess samples due to their stronger inter-particle cementation. The predictive formulas of unsaturated shear strength for undisturbed loess and paleosol are proposed, respectively, based on the Vanapalli model, and the calculated values of the strength prediction model are in perfect agreement with the experimental values. Full article

Although cemented soil as a subgrade fill material can meet certain performance requirements, it is susceptible to capillary erosion caused by groundwater. In order to eliminate the hazards caused by capillary water rise and to summarize the relevant laws of water transport properties, graphene oxide (GO) was used to improve cemented soil. This paper conducted capillary water absorption tests, unconfined compressive strength (UCS) tests, softening coefficient tests, and scanning electron microscope (SEM) tests on cemented soil using various contents of GO. The results showed that the capillary water absorption capacity and capillary water absorption rate exhibited a decreasing and then increasing trend with increasing GO content, while the UCS demonstrated an increasing and then decreasing trend. The improvement effect is most obvious when the content is 0.09%. At this content, the capillary absorption and capillary water absorption rate were reduced by 25.8% and 33.9%, respectively, and the UCS at 7d, 14d, and 28d was increased by 70.32%, 57.94%, and 61.97%, respectively. SEM testing results demonstrated that GO reduces the apparent void ratio of cemented soil by stimulating cement hydration and promoting ion exchange, thereby optimizing the microstructure and improving water resistance and mechanical properties. This research serves as a foundation for further investigating water migration and the appropriate treatment of GO-modified cemented soil subgrade. Full article

This study investigated the distribution and evolution characteristics of the temperature field during the freezing and excavation of inclined shafts, with the freezing open-excavation section of Shengfu Mine’s main inclined shaft (located in Shaanxi Province) as the project background. Utilizing field-measured data and the finite element software COMSOL Multiphysics, a 3D freezing temperature-field numerical calculation model was constructed to examine the temporal and spatial evolutions of the temperature field during the construction of the inclined shaft. The findings showed that after 88 days of freezing, the average temperature of the frozen wall in the open-excavation section was below −12 °C. The frozen wall thickness in the sidewalls of different layers exceeded 4 m, and the thickness at the bottom plate exceeded 5 m, meeting the excavation design requirements. For the same freezing time, the average temperature of the frozen wall in the fine sand layer was 0.28 to 2.39 °C lower than that of the frozen wall in the medium sand layer, and its effective thickness was 0.36 to 0.59 m greater than that in the medium sand layer. When the soil was excavated, and the well side was exposed, a phenomenon known as “heat flow erosion” occurred in the soil at the well-side position, causing the well-side temperature to rise. Nevertheless, this increase was generally limited, and when continuous cooling was applied, the well side could maintain a very low negative temperature level. Consequently, there was no spalling phenomenon. The effective thickness of the frozen wall during excavation did not decrease, with the average temperature remaining below −10 °C. Consequently, there was no large-scale “softening” of the frozen wall during excavation, thus ensuring construction safety. The numerical calculation model in this paper can be used to predict the development law of the freezing temperature field of the water–rich sandy layers in Shengfu Mine and adjust the on–site cooling plan in real time according to the construction progress. This research provides valuable theoretical insights for the optimal design and safe construction of freezing inclined-shaft sinking projects. Full article

The interaction between soil and structure is a research hotspot in ocean engineering, and the shear performance of interfaces is an essential factor affecting the bearing capacity of offshore structures. Taking the Yellow River Underwater Delta as the research area, the Softening/Hardening damage model of the silt–steel interface and the determination method of model parameters are proposed based on the statistical damage theory. Through the interface monotonic shear test under the conditions of different normal stress, roughness and water content, the shear mechanical properties and volumetric deformation laws on the silt–steel interface are analyzed, and the damage model parameters are obtained. Finally, a FRIC subroutine for the damage model was developed based on ABAQUS. The research results indicate the following: (1) The interface between silt and steel exhibits two characteristics, softening/hardening and shear shrinkage/expansion, under different conditions. Roughness significantly impacts interfacial cohesion, while water content mainly affects the internal friction angle. (2) The softening model based on the classic rock damage model can better simulate the stress–strain relationship of the silt–steel interface under high normal stress and low water content. In contrast, the hardening model based on the classic hyperbola model can better simulate the stress–strain relationship under low normal stress and high water content. The calculated results of the softening/hardening model agree with the experimental results, and the model has 7 parameters. (3) The developed FRIC subroutine can effectively simulate the nonlinear mechanical behavior of the interface between silt and steel. The research results provide a reference for exploring the stability analysis of offshore structures considering interface weakening effects. Full article

Solidifying shield muck with calcium carbide slag and fly ash as curing agents was proposed as a highly efficient method for reusing waste shield muck. The compaction test, unconfined compression test, and dry–wet cycle test were used to evaluate the compressive strength, water immersion stability, and durability of the cured soil. The stress–strain curve and microscopic test were employed to analyze the compression damage law, mineral composition, and microscopic morphology of the cured soil, and to analyze the mechanism of calcium carbide slag–fly ash-cured shield muck. It was found that calcium carbide slag–fly ash can significantly improve the compressive strength of shield muck, and the strength of cured soil increases and then decreases with an increase in calcium carbide slag and fly ash and increases with curing age. The strength was highest when the content of calcium carbide slag and fly ash was 10% and 15%, respectively. Dry–wet cycle tests showed that the specimens had good water immersion stability and durability, and the stress–strain curve of the specimen changed from strain hardening to strain softening after dry–wet cycles. The internal particles of the cured soil were mainly cemented and filled with C-(A)-S-H colloid and calcium alumina (AFt), which both support the pores between the soil and form a skeleton structure to enhance the strength of the soil and lend it good mechanical properties. Full article

This paper discusses research on the dynamic response characteristics of a heavy-haul railway tunnel and the surrounding soil under the conditions of substrate health and a base void. The detection results of the base condition of 20 double-track tunnels for a heavy-haul railway show the main distribution law of base voids. Based on this, a 1:20 scale test model of a heavy-haul railway tunnel is established. The vibration load of the train is established by a vibration exciter arranged at the tunnel invert. The dynamic response and attenuation law of a heavy-haul railway tunnel lining structure and the surrounding soil are tested using acceleration sensors, strain gauges, and soil pressure boxes. The research results show that most of the diseases are concentrated below the heavy-haul line. The base void causes the peak acceleration of the nearby tunnel invert to increase by 55.6%. Tunnel annular construction joints reduce the conductivity of the vibration waves in the axial direction of the tunnel. The acceleration attenuation rate of the soil above the tunnel invert is significantly less than that under the invert. The base void reduces the acceleration of the nearby soil layer by 19.4% and increases the stress on the surface of the nearby tunnel invert by 21.3%, and the stress change amplitude increases by 0.55%. The tunnel structure in the area of the base void experiences fatigue damage. The base void causes the compaction and bearing capacity of the nearby soil to decrease and the softening speed of the tunnel basement soil layer to increase. Therefore, for the basement damage to heavy-haul railway tunnels, “early detection, early treatment” should be performed. Full article

In order to study the variation law of shear frictional characteristics of the steel pipe jacking and sand interface under different working conditions, the shear stress–strain curve between five different particle sizes of sand and steel pipe jacking under different normal stress and slurry lubrication conditions was measured by using a direct shear device, and the internal friction angle, friction coefficient and cohesion of the pipe–soil interface were calculated by regression analysis. The test results show that the shear stress between sand and steel pipe jacking decreases with the increase of the average particle size of the sand, and the strain-softening phenomenon occurs. The normal stress does not change the trend of the shear stress–strain curve at the pipe–soil interface, and the peak and residual values of the shear stress increase with the increase of the normal stress. The peak and residual values of the shear stress at the pipe–soil interface under the slurry lubrication condition are smaller than those under the no slurry lubrication condition. The peak shear stress between the pipe and soil under the lubricated slurry condition decreases by about 20%. The internal friction angle and friction coefficient of the pipe–soil interface decrease with the increase of the particle size, and there is no obvious pattern between the cohesion quantity relationship and the average particle size. Full article

Adding biochar to soil can improve the soil’s physical–chemical properties, microscopic pore structure, and bacterial habitat. This affects the soil’s strength characteristics and the oxidization of methane. Using a Humboldt pneumatic direct shear instrument, this study investigated the effect of the amount of biochar in the soil, the soil’s methane-oxidizing bacteria, aeration time, and carbon content on the strength characteristics of a biochar-amended clay. The results show that when the biochar content is low, the soil’s stress–strain curve shows a strain hardening state as the strain increases. When the biochar content is greater than 10%, the methane-oxidizing bacteria increase as the shear strain increases. The stress–strain curves of the biochar–clay mixture all showed a softened state. Under the same biochar content, the soil’s stress–strain curves show strain softening as the methane filling time increases. However, with an increase in the amount of biochar, cohesion gradually increased and the internal friction angle did not change significantly. A scanning electron microscope (SEM) image of the biochar–clay mixture with methane oxidizing bacteria revealed the influence of the evolution law of the samples’ micropore structure on the soil’s stress–strain curve and strength properties. Full article

Climate change is accelerating its adverse impact on ecosystems and infrastructure systems in cold regions. For extensive carbonate saline soil areas, their response to the freeze-thaw cycle remains uncertain. By considering the continuous intensification of freeze-thaw cycle frequency, the mechanical characteristics of carbonate saline soils are analyzed for different salt content (0.6% to 2.1%) based on the mechanical test in this paper. The purpose is to reveal the change law of shear strength and its parameters of carbonate saline soils under the scenario of continuous freezing and thawing cycles. The micro-characteristics of the carbonate saline soil before and after freeze-thaw cycling were analyzed by scanning electron microscopy, indicating changes in the structural soil properties caused by the combination of freeze-thawing and salinity. The scanning electron microscope images reveal the cumulative effect of frost heaving and salt expansion, i.e., increasing the number of pores between particles, reducing the effective contact between particles, and weakening the interaction force, resulting in cracks development. A series of mechanical tests demonstrate the stress-strain behavior of carbonate saline soils for different numbers of freeze-thaw cycles under different confining pressures. A transformation from strain-softening to strain-hardening is observed with an increase in the salt content from 0.6% to 2.1%. Furthermore, the shear strength of the carbonate saline soil decreases as the salt content and number of freeze-thaw cycles increase. The shear strength degradation mechanism is attributed to the cohesion and the internal friction angle. These shear strength parameters are critical in geotechnical analyses, such as evaluating of load capacity of foundations and slope stability in similar saline soils. Full article

This paper establishes a non-equilibrium thermodynamic constitutive model that can predict the undrained shear behavior of saturated sand. Starting from the basic laws of thermodynamics, the model does not require the classical concepts in elasto-plastic models, such as the yield function, the flow rule, and the hardening rule. It is also different from the existing thermodynamic constitutive models in soil mechanics literatures. The model does not use a complex nonlinear elastic potential as usually and introduces a coupling energy dissipative mechanism between the viscosity and elasticity relaxation, which is essential in granular materials. Then this model was used to simulate the undrained shear test of Toyoura sand. The model can predict the critical state, dilatancy-contraction and hardening-softening characteristics of sand during undrained triaxial shearing. Full article