Static Earth Pressure Research Articles

Integrated Plug High-Strength Geocell Reinforcement in Foundation Design for Square Footing

This paper develops an analytical model to calculate the ultimate bearing capacity of the integrated plug high-strength geocell (IPGC)-reinforced foundation under a square footing. The high strength and stiffness of the geocell wall and the typical failure of the integrated plug-in joint tearing were considered. The ultimate bearing capacity of the IPGC-reinforced foundation was calculated in two separate parts. The ultimate bearing capacity of an unreinforced foundation was calculated using the modified Terzaghi equation. The increased bearing capacity of the IPGC was calculated as the function of the tearing force of the geocell wall, the height and the diameter of a geocell, the empirical static earth pressure coefficient, and the vertical additional stress coefficient under uniformly distributed rectangular loading. The results showed that the maximum error between the experimental and the theoretical results is less than 18%. The ultimate bearing capacity of IPGC-reinforced foundations decreases with larger geocell diameters. When the diameter of the geocell exceeds 1.8 times the foundation width, the confinement effect of IPGC becomes negligible. The findings of this study offer a robust analytical equation for predicting IPGC-reinforced foundations, along with valuable insights into the efficacy of IPGC reinforcement in enhancing foundation stability.

Calculation Method of Earth Pressure Considering Wall Displacement and Axial Stress Variations

Current earth pressure calculation methods suffer from certain limitations because they do not consider the effect of retaining wall displacement. In this study, the soil behind the wall is assumed to be in a plane strain state, and drawing upon nonlinear elastic constitutive theory, an earth pressure calculation method is proposed, capable of considering both axial stress and wall displacement. To account for changes in soil modulus with confining pressure, the tangent modulus from the Duncan-Chang nonlinear model is introduced. Depending on the direction of the principal stress behind the retaining wall, the static earth pressure point, the major principal stress inflection point, and the minor principal stress second inflection point are determined. The conditions for the existence of the second inflection point are also given. These specific points, together with the limit earth pressure point, divide the earth pressures acting on the wall into six regions. The study provides earth pressure calculation formulas for T (translation) mode, RBT (rotation about a point below the base) mode, and RTT (rotation about a point above the top) mode based on the characteristics of wall displacement distribution in each mode. The proposed method exhibits good agreement with the test results, offering an effective approach for accurately calculating earth pressures related to displacement.

Centrifuge modelling of blast effects in dry sand: Coriolis effect and soil arching

Centrifuge model tests are conducted to investigate the dynamic response of dry sand under blast loading. The characteristics and propagation mode of blast waves in dry sand are studied. The Coriolis effect on blast-induced cratering is carefully scrutinised, and both the theoretical and experimental results are provided and agree with each other. In the explosion-induced cratering process, the sand ejecta is subjected to horizontal and vertical Coriolis forces simultaneously; the former directly determines the horizontal motion offset, while the latter affects the particle motion by altering the flight time, and the Coriolis effect on cratering can only be observed apparently for soil ejecta with a relatively small launch angle. Redistribution of the static earth pressure (blast-induced arching effect) in deep-buried, fully confined explosion events under hypergravity is observed. The friction between sand particles is significantly enhanced by the hypergravity to serve as the supporting arch springing. Conceptual analysis is conducted to further reveal the mechanism of the blast-induced arching effect based on the trapdoor test, from the three aspects of displacement mode, stress development and post-detonation stress distribution.

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

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

Research on the Relationship between Soil Shear Stress Level and Safety Factor

At present, in the design of geotechnical structures, the allowable bearing capacity is mostly designed according to the safety factor specified in the design specification. However, there are two problems that have not yet been clearly explained in theory: (1) why is the safety factor listed in the standard is suitable for the design of geotechnical structures and (2) can the safety factor selected according to the specification guarantee the long-term stability of soil mass. In view of the above problems, according to the statistical law in the rheological properties of soil, the relationship between the shear stress level of the soil and the stability of the soil is studied, and the stable shear stress level of the soil is obtained. The research results show that the stable shear stress level of soil is the corresponding shear stress level under static earth pressure. This conclusion not only verifies the correctness of the theoretical finding that “the earth pressure on the structure develops toward the static earth pressure, and whether the ultimate safety of the geotechnical structure is related to its design bearing capacity is greater than the static earth pressure” in the design code of the retaining structure but also clarifies the source of the safety factor. By calculating the design bearing capacity of the geotechnical structure according to the static earth pressure, the geotechnical structure that maintains long-term stability can be designed, which provides a reliable method for the design of the permanent geotechnical structure.

A temperature gradient test system for investigating thermo-mechanical responses of containment materials of underground storage facilities

Underground energy storage is a promising option for the global ambition of moving towards carbon neutrality. To achieve safe and reliable energy storage in underground caverns, it is essential to understand the contributions of thermal and mechanical loads to the deformation of containment materials (e.g., concrete and geomaterials) and to forecast potential risks related to unexpected failure of these materials. A temperature gradient test system is developed to investigate the thermo-mechanical responses of containment materials under simulated temperature gradient and earth pressure conditions. The test system has advantages of establishing a temperature gradient of over 400 ​°C/m across a large-scale specimen and examining the resulting strain based on the digital image correlation analysis. This study sheds light on 3 typical applications of the test system to examine the thermal and mechanical responses of intact limestone, flawed limestone, and fractured concrete. The results demonstrate that the mechanical load mainly controls the strain evolution of the intact limestone, while the thermal load strongly affects the strain evolution around the circular hole. The failure pattern of concrete primarily influences the mechanically induced strain, and the thermally induced strain is insensitive to the concrete failure. This test system can be modified and upgraded to study various research topics related to underground energy storage.

Numerical Simulation Analysis of the Jacking Force and Its Influencing Factors during the Vertical Tunneling Process

The development of underground space is fast because of the lack of space. To build shafts in underwater tunnels, the vertical tunneling method (VTM) was invented in 1974 in China, which can act as a freshwater intake or sewage outlet. During the operation of the VTM, the jacking force is one of the essential factors that draw attention. This paper conducts a numerical study of the jacking force and its influencing factors during the vertical tunneling process. First, based on the finite element software ABAQUS, a numerical model of the vertical tunneling process is established according to the VTM project in Beihai, China. Second, in accordance with the Latin hypercube sampling method and the multivariate significance analysis, the mechanical parameters are determined or back‐analyzed. Then, the calculated jacking force of the numerical model is compared with the measured jacking force. It turns out that the changing trend of the jacking force in the numerical model and the measured jacking force is relatively consistent. Finally, the influencing factors of the jacking force, such as elastic modulus and the angle of internal friction, are analyzed based on the numerical model. The results show that the elastic modulus and the angle of internal friction of soil are the main influencing factors of the jacking force. The secondary factors are Poisson’s ratio, static earth pressure coefficient, unit weight, and cohesion.

Fe isotope fractionation caused by phase transition of FeS and implications for Fe isotope signatures of the mantle and core

Iron is the most important component of the cores of terrestrial planets, and iron sulfide (FeS) is one of the preferred candidates present in these cores. FeS is also ubiquitous in Earth’s crust, peridotites, and extraterrestrial samples. Knowledge of the phase stability of FeS and Fe isotope fractionation between FeS phases and mantle silicates is of great importance for understanding the interior of the Earth and terrestrial planets. In this study, first-principles methods were used to study the pressure-dependent phase stability of FeS and equilibrium Fe isotope fractionation in FeS, hexagonal close-packed (hcp) Fe, and mantle silicates at the pressure of Earth’s interior. FeS underwent four phase transitions at 0 K. The first is the transition from FeS I to FeS II at 2.8 GPa, the second from FeS II to FeS III at 7.5 GPa, the third from FeS III to FeS VI at 74.2 GPa, and the fourth from FeS VI to FeS VII at 122.2 GPa. Apart from the fact that the transition from FeS I to FeS II causes negligible Fe isotope fractionation, other phase transitions can cause measurable Fe isotope fractionation at corresponding pressures along the geotherm. Fe isotopes exhibit measurable fractionation between FeS and mantle silicates under mantle pressure–temperature conditions. Each phase was more enriched in heavy Fe with increasing depth in the pressure range of 7.5–90 GPa. If the silicate mantle is enriched in heavy Fe relative to the core or Fe has negligible isotope fractionation between them under the core-mantle boundary (CMB) conditions of the Earth, the Fe2+/(Fe2++Mg) in (Fe2+, Mg)SiO3 post-perovskite is less than 50%. At the temperature–pressure conditions of Earth’s core, equilibrium Fe isotope fractionation between hcp Fe and FeS VII can be neglected. FeS III is more likely to exist in the Martian core relative to FeS VI.

Effect of Duxseal on Horizontal Stress and Soil Stiffness in Small-Amplitude Dynamic Centrifuge Models

Abstract The constitutive behavior of soil is stress dependent. Therefore, geotechnical centrifuges are widely used to replicate full-scale stress fields, thereby ensuring the correct soil response within reduced-scale centrifuge models. A vibration-absorbing material (such as Duxseal) is commonly employed to reduce the effect of reflected waves generated at the boundaries of rigid containers in dynamic centrifuge tests. However, such a material has the potential to deform laterally under the high horizontal stresses applied within centrifuge tests and consequently the initial at-rest lateral earth pressure condition will not be maintained. A procedure to back-calculate the lateral earth pressure coefficient (K) is presented in this paper. In addition, two experimental methods that are implemented to evaluate K by measuring the shear wave velocity from centrifuge-based air hammer testing and triaxial-based bender element testing are described. Results demonstrate that significant lateral earth pressure and soil stiffness reductions are observed within the upper soil region (top third of the model depth). In addition, the appropriate manipulation of the cross-correlation method used to process shear wave signals is discussed and an empirical equation to predict the small-strain shear modulus of the dry silica sand (HST95 Congleton sand) used in this study is provided. Outcomes of this study are directly applicable to small-amplitude dynamic centrifuge tests such as ground-borne vibrations; some factors relating to large-amplitude seismic studies, such as soil inertial effects and higher shear strains, are not considered.

The Strength Behavior and Desiccation Crack Development of Silty Clay Subjected to Wetting–Drying Cycles

It is commonly accepted that wetting–drying cycles have an effect on the soil strength behavior. Crack development in soil is observed by many engineers during wetting–drying cycles, which may give a good explanation for the change in soil strength. A series of laboratory tests were conducted in this study to investigate the desiccation crack development and the strength change law for silty clay subjected to different numbers of wetting–drying cycles. The results show that the desiccation cracks at the end of drying process developed in two stages: the stage of rapid growth and the stage of steady state. The change law of soil strength is similar to the cracking that decreases quickly in the former stage and slowly in the latter stage, which indicates that the cracking in the soil is the main reason for strength reduction. Based on the assumption of an isotropic and linear elastic soil mass at rest earth pressure conditions, an equation for the depth of desiccation cracking after different numbers of wetting–drying cycles was obtained with soil mechanics for unsaturated soils. Finally, the applicability of the equation was verified compared with the experiment results.

Effects of Barrier Stiffness on Debris Flow Dynamic Impact—II: Numerical Simulation

The destructive and impactful forces of debris flow commonly causes local damage to engineering structures. The effect of a deformable barrier on the impact dynamics is important in engineering design. In this study, a flow–structure coupled with Smoothed Particle Hydrodynamics model was presented to investigate the effects of barrier stiffness on the debris impact. A comparison of the results of physical tests and simulation results revealed that the proposed smoothed particle hydrodynamics model effectively reproduces the flow kinematics and time history of the impact force. Even slight deflections of the deformable barrier lead to obvious attenuation of the peak impact pressure. Additionally, deformable barriers with lower stiffness tend to deform more downstream upon loading, shifting the deposited sand toward the active failure mode and generating less static earth pressure. When the debris flow has a higher frontal velocity, the impact force on the barrier is dominated by the dynamic component and there is an appreciable effect of the stiffness of the deformable barrier on load attenuation.

Extending Mononobe-Okabe theory to account for arbitrary backfill topography and variable density of surcharge

Coulomb proposed a formula for the static earth pressure acting on a rigid gravity retaining wall supporting a soil. Many researchers have generalized this theory and several analytical studies were achieved regarding the evaluation of seismic action. Following the work of Mononobe and Okabe, investigations have considered cohesive backfill, and with some restrictions the topography of the backfill and the pattern of surcharge acting on its surface. In this work an extension of the Mononobe-Okabe theory was proposed to deal with the most general case of backfill having an arbitrary shape and also vertical surcharge acting with variable density at the ground level. Equilibrium of Coulomb wedge was applied to express the active earth pressure coefficient related to a given orientation of the failure plane. Then, numerical optimization was performed to fix the critical angle providing its maximum value. Parametric studies were conducted after that. It was found that both the upward and downward vertical seismic acceleration should be considered. The obtained results indicate that the backfill surface shape and surcharge density have a significant effect on seismic action. The maximum relative variation of the pressure coefficient with regards to the reference case is however limited to 20%.

Analysis of Situ Test Results of Earth Pressure and Pile Internal Force under Pile-Anchor Support in a Deep Foundation Pit in Xi’an

At present, in deep foundation pit engineering, on the one hand, practice is ahead of theory, and on the other hand, theory can not correctly reflect the actual construction process and environmental effects. In order to further study the distribution and change law of earth pressure and internal force of pile body in deep foundation pit pile-anchor supporting system, field monitoring test of earth pressure and pile body reinforcement stress was carried out. The monitoring results show that before excavation, the distribution of earth pressure has a great relationship with the layering of the soil, and it is distributed in sections along the depth. Compared with the theoretical static earth pressure, the measured data of the upper depth is relatively small; after excavation, the overall earth pressure is distributed along the depth in a “z” shape under the non-limiting state. As the excavation progresses, the magnitude of the reduction of the earth pressure varies from place to place, and the magnitude of the decrease of the soil with better properties is not large; after the excavation, the stress and earth pressure of the pile reinforcement correspond to each other, and the distribution is also nonlinear. The existence of anchor tension has an obvious effect on improving the internal force of the pile. The selected earth pressure calculation methods have some discrepancies in the calculation of the earth pressure value of the project, and they need to be further improved. The research in this paper can provide reference and reference for the calculation of earth pressure and support design of pile-anchor supported foundation pit.

Study on the Modification of Confining Rock for Protecting Coal Roadways against Impact Loads from a Roof Stratum

Promoting the ability of anti-bursting of the confining rock of a coal roadway is of significant importance to the safe production of a coal mine. In particular, in deep-buried coal mines, highly frequent rock burst occurs due to large earth pressure and complex geological conditions, which needs serious improvement. This paper investigated a type of confining rock modified method, which can modify the physical properties of the surrounding rock and form a crack region and a reinforced region by blasting and grouting reinforcement. Based on a set of physical model experiments and numerical modeling, the results of a comparative analysis between a normal roadway and the modified roadway in the static stress redistribution, dynamic stress, damage evolution, and energy dissipation suggest that the modified confining rock is capable of protecting the coal roadway against rock burst from roof stratum, obviously reducing and transferring the concentered static–dynamic stress out of the cracked region, dissipating the dynamic energy by plastic damage in the cracked region, and keeping the integrity of the reinforced region. In addition, the velocity of the dynamic stress vibration wave at the surface of the modified coal roadway is obviously reduced, which is beneficial for decreasing the movement of cracked rock blocks and protecting the lives and goods in the coal roadway.

Simulation analysis of a shallow-covered large cross-section rectangular pipe-jacking crossing highway

In this paper, based on a large cross-section shallow overburden rectangular pipe jacking project, using numerical simulation method to analyze the impact of pipe jacking construction on the highway, taking into account the positive jacking force of pipe jacking machine head on the soil, grouting pressure of slurry sleeve, setting of isolation steel pipe concrete curtain, friction-reducing slurry sleeve and other factors. The main conclusions are as follows: (1) the front jacking force is between the theoretical Rankine active earth pressure and the Rankine passive earth pressure. With the increase of jacking force, the road surface appears different degrees of uplift. When the jacking force is set between the active earth pressure and the static earth pressure, the uplift rate is the largest. In order to facilitate the construction control, it is suggested to control according to the theoretical static earth pressure; (2) the theoretical grouting control pressure The top of the pipe jacking is taken as the overlying water and soil pressure at the top of the mud jacket, and the bottom of the pipe jacking is taken as the sum of the overlying water and soil pressure and the hydro-static pressure of the mud sleeve. Based on the analysis of 0.8 times, 1.0 times and 1.2 times control grouting pressure, with the increase of grouting control pressure, the pavement heave gradually increases. It is recommended to adopt 0.8 times theoretical grouting pressure to ensure the thickness of the slurry sleeve meets the requirements and reduce the impact on the pavement; (3) setting concrete-filled steel tube curtain or anti friction slurry sleeve can reduce the impact of pipe jacking construction When the steel pipe curtain has been set up, there is no obvious back soil effect without the anti friction mud sleeve.

Failure modes of highway tunnel with voids behind the lining roof

Small-scale (1:30) model tests were performed to investigate the failure modes of highway tunnels that have single voids with different scales immediately above the lining roof. The tunnels employed have horseshoe-shaped cross-sections which match those typically used to carry two lanes of traffic. In the absence of a void, the mechanical behavior of the tunnel lining is directly related to the ratio of the horizontal to vertical stress, λ. Failure occurs when the compressive stress experienced is high, and the eccentricity is small. Furthermore, it is the shoulders and knees of the tunnel lining that are most susceptible to compressive failure. In the presence of a void, the sign of the bending moment can become reversed, and failure occurs due to bending-induced tension. The intrados of the roof lining is prone to moment-induced tensile stress. It experiences less thrust as well as higher eccentricity which is completely different from the behavior without a void. In other words, the void converts the tendency of the tunnel lining to undergo thrust-induced compressive failure into a tendency to undergo moment-induced tensile failure. When the void angle (angle subtended by the void at the center of the tunnel) is larger than 50°, the failure mode of the tunnel lining is entirely dependent on the void, rather than the earth pressure conditions. That is, the locations and sequence of formation of the cracks formed are almost identical, regardless of the value of λ. Understanding the differences in these failure modes (i.e. with and without voids), should assist in making tunnel maintenance much more efficient. The tunnel lining’s most vulnerable positions can be made less vulnerable by careful choice of the tunnel’s structural parameters, and other supporting measures can be implemented to ensure the safety of the tunnel.

Transient temperature field model for a cutterhead during slurry shield tunneling

Due to the friction between the cutterhead and the soil, the temperature will rise continuously during shield tunneling, which expedites thermal damage and wear of the cutterhead. In this study, a transient model for predicting the cutterhead temperature is proposed. Both the driving parameters and geological factors are considered in this model. The shield driving parameters include the cutterhead rotation speed and penetration depth, while the geological factors consist of the friction coefficient, elastic modulus, Poisson's ratio, coefficient of static earth pressure, and the unit weight of soil. A comparison is made between the proposed model and field tests, indicating the validity of the model. A parametric study is conducted and the results indicate that the temperature of the cutterhead presents cyclic heating-cooling during shield tunneling. Reducing the rotation speed is a more effective option for temperature control if necessary. Comparatively, the cutterhead heats up faster in sandy soils than in clayey soils.

Mechanical properties of a new string capsule drainage anchor and its supporting effect in deep foundation pit

With the increase of the scale and depth of urban underground space construction in coastal soft soil area, the traditional anchoring technology has been difficult to meet the requirements of deep foundation pit excavation and support. This paper puts forward a new type of string capsule drainage anchor supporting structure, introduces its structure composition, analyzes its working mechanism and mechanical characteristics, the calculation formula of ultimate bearing capacity of small cylindrical shear failure between anchor and surrounding soil is given, finally, the supporting effect of the new structure in deep foundation pit engineering is simulated and analyzed by finite element software. It is concluded that the stress of the new type of anchor can be divided into three stages: static earth pressure, plastic zone development and plastic zone breaks through; the new anchor can quickly dissipate the pore water pressure in the surrounding soil, which is more conducive to the stability of foundation pit; the axial force distribution presents a “sawtooth” shape, and the axial force increases sharply in the expanding section; the supporting effect of the new anchor is more obvious than that of the traditional anchor, which can more effectively inhibit the horizontal displacement of the slope.

Limit analysis of seismic collapse for shallow tunnel in inhomogeneous ground

Shallow tunnels are vulnerable to earthquakes, and shallow ground is usually inhomogeneous. Based on the limit equilibrium method and variational principle, a solution for the seismic collapse mechanism of shallow tunnel in inhomogeneous ground is presented. And the finite difference method is employed to compare with the analytical solution. It shows that the analytical results are conservative when the horizontal and vertical stresses equal the static earth pressure and zero at vault section, respectively. The safety factor of shallow tunnel changes greatly during an earthquake. Hence, the cyclic loading characteristics should be considered to evaluate tunnel stability. And the curve sliding surface agrees with the numerical simulation and previous studies. To save time and ensure accuracy, the curve sliding surface with 2 undetermined constants is a good choice to analyze shallow tunnel stability. Parameter analysis demonstrates that the horizontal semiaxis, acceleration, ground cohesion and homogeneity affect tunnel stability greatly, and the horizontal semiaxis, vertical semiaxis, tunnel depth and ground homogeneity have obvious influence on tunnel sliding surface. It concludes that the most applicable approaches to enhance tunnel stability are reducing the horizontal semiaxis, strengthening cohesion and setting the tunnel into good ground.

Model test on the behavior of tunnel linings under earth pressure conditions and external water pressure

154-km long tunnels of major highways in Shanxi Province of China are observed, and 5120 crack distributions are obtained that are largely dependent on both earth pressure conditions and external water pressure. By conducting 1:30 scaled model tests, the cracking patterns of the mold lining induced by earth pressure are notably different from those induced by external water pressure. Under high external water pressure, moment-induced tensile failure occurs at the knee of the tunnel lining, and then flexural failure appears at the invert. Increasing the earth pressure can rapidly decrease the bending moment, moderately increase the axial thrust, and considerably enhance the structural safety of the tunnel lining provided that the earth pressure is less than 0.3 MPa. The ultimate water pressure, influenced by earth pressure, increases by approximately 17%, regardless of the ratio of horizontal to vertical stresses K. For a tunnel under high earth pressure, the upper parts of the tunnel lining are the locations most susceptible to failure, whereas the invert is safe with a large safety margin. Imposing external water pressure could substantially increase both the axial thrust along with the bending moment and suddenly worsen the structural soundness of the tunnel lining. Furthermore, the failure positions and cracking sequences are highly correlated with the values of K. These findings are supported by three-dimensional nonlinear finite element numerical modeling. Finally, the interaction of water pressure and earth pressure conditions is investigated under various ratios of horizontal to vertical stresses K in the ultimate limit state.