Changes In Earth Pressure Research Articles

Evolution of Long-Term Load Reduction Using Borrowed Soil

AbstractThe effectiveness of load-reduction techniques often diminishes due to creep behavior observed in geomaterials, as loess backfill is used, the load reduction rate of high-filled cut-and-cover tunnels (HFCCTs) after creep will decrease by 10.83%, posing a threat to the long-term stability of deeply buried structures such as HFCCTs. Therefore, a geotechnical solution is crucial to ensuring sustained effectiveness in load-reduction strategies over time. This study utilizes a finite-difference method to examine three promising measures for mitigating creep effects. Our analysis focuses on the time-dependent changes in earth pressure atop the cut-and-cover tunnel (CCT) and the internal distribution of cross-sectional forces, including bending moment, shear force, axial force, and displacement. Results indicate that the creep behavior of load-reduction materials significantly influences the internal force distribution. Furthermore, sustained load reduction is achieved when utilizing low-creep materials like dry sandy gravel as backfill soil, which needs to be borrowed from other sites. Additionally, integrating concrete wedges with load-reduction techniques facilitates a more uniform stress distribution atop CCTs.

Mechanical characterization of subway tunnel construction in urban shallow distributed karst stratums

To address the challenges posed by rapid urban and population growth, China has undertaken extensive urban subway construction. In order to explore the mechanical characteristics of subway tunnel construction in urban shallow karst environment, based on the first phase project of Guiyang rail transit line 3, the concept of “distributed Karst” is proposed according to the occurrence characteristics of karst in urban environment. The dry ice and model soil were used to characterize the karst strata, and the similar model test study on the influence of different volume karst rates on subway tunnel construction was carried out. The influence of tunnel excavation on surrounding rock disturbance, internal force of arch structure and ground settlement under distributed karst stratum condition is studied comprehensively. The following key findings emerged:(1) Karst presence causes an abrupt change in the release curve of surrounding rock earth pressure. Higher degrees of karst development result in smaller changes in earth pressure on the arch top and shoulder after tunnel excavation, with final earth pressure changes of 91.1 kPa, 83.5 kPa, and 74.8 kPa for volumetric karst rates of 5%, 10%, and 20%, respectively. (2) Distributed karst in the tunnel arch has a limited impact on the lateral excavation displacement of the arch girdle but significantly affects the vertical settlement of the tunnel vault. Increasing volumetric karst rates by twofold (from 5% to 10% and 20%) reduces arch settlement by 48.9% and 55.6%, respectively. (3) At volumetric karst rates of 5%, 10%, and 20%, the axial force values at the tunnel top are 58.2 kN, 52.8 kN, and 50.3 kN, while the corresponding bending moment values are 49.6 kN-m, 37.1 kN-m, and 26.0 kN-m, respectively, indicating a more significant difference in bending moment values than axial force values. (4) Karst presence leads to increased surface settlement, with a 48.8% increase in peak ground settlement observed as the volumetric karst rate rises from 5% to 20%.

Theoretical and Numerical Analysis of Cohesive-Frictional Backfill against Battered Retaining Wall under Active Translation Mode

The appropriate prediction of horizontal earth pressure against retaining walls can lead to a safer and more efficient design of such structures. Retaining walls are among the structures in which the arching phenomenon plays an essential role in distributing horizontal earth pressure. In this research, based on the limit equilibrium condition and considering the arching effect, a new theoretical method is proposed to estimate the earth pressure against a battered wall under translation movement with a cohesive-frictional backfill soil. A parametric study is conducted for assessing the effect of the surcharge pressure, cohesion, internal friction angle, wall–soil friction angle, and wall inclination on lateral earth pressure. In addition, a series of numerical models is employed to implement the finite difference method. The development of shear bands inside the backfill and the changes in earth pressure behind the wall are studied. The outcomes of the suggested analytical solution are compared with the numerical data as well as with some other theories. It is concluded that the proposed method is applicable to a wide range of cohesive-frictional soils retained with walls, covering a variety of batter angles and face frictional conditions.

Model Test Study of the Synergistic Interaction between New and Existing Components of Sheet Pile Walls

New and existing components of retaining structures are often combined in the width section. When combining the design and use requirements of the existing and new structures, the synergistic interactions between the existing and new structures and the design and working conditions require clarification. In conjunction with an actual project, a sheet pile wall consisting of existing and new components is proposed to retain an embankment. Indoor model tests were carried out to simulate the excavation and compaction and investigate changes in earth pressure, pile bending moment, shear force, and load-sharing ratio of the new and existing sheet pile walls at different stages. The results show that the earth pressure of the cantilever section of the existing and new piles increases with an increase in the fill volume or the upper uniform load. An inflection point is observed in the earth pressure curve halfway between the pile top and the ground due to sudden changes in the pile and soil stiffness. The bending moment of the new and existing piles increases and decreases with the distance from the top of the pile under different working conditions, and the maximum bending moment occurred at 0.485 and 0.9 m from the bottom of the existing pile and the bottom of the new pile, respectively. The lateral displacement of the new and existing piles decreases with the distance from the top of the pile. Due to the adjustment of the structural force in the cantilever section and the soil reaction force in front of the pile, the displacement curves of the new and existing piles are similar in the cantilever section. The displacement in the anchored section is initially larger for the existing pile than for the new pile but then becomes similar for both piles. In working condition 5, the top displacement of the existing pile was 6.531 mm, exceeding the control value (5.6 mm). The earth-pressure-sharing ratio of the existing pile decreases with an increase in the width of the filling material or the load. When the load was applied, the earth-pressure-sharing ratio of the existing pile was 0.451, indicating that the structural design of the combined sheet pile wall is reasonable.

From “De la pression des terres et des revêtements” to the seismic analysis of retaining structures

In his Essai, Charles-Augustin Coulomb showed that the earth pressure on a retaining wall can be calculated maximising the force obtained by considering equilibrium and strength compatibility. This same approach is still of practical relevance in some design situations and, more importantly, its basic assumptions have paved the road for the numerous successive developments that lead, among other factors, to consideration of the changes in earth pressure induced by seismic forces. A modern approach to the seismic design of structures entails the evaluation of their performance under different shaking intensities, including seismic actions strong enough to activate the system resistance. This paper intends to show that the basic ingredients of the Coulomb’s analysis, that is, equilibrium and strength compatibility, can be used in a rational way not only to predict limit values of the earth pressure, but also to evaluate the performance of retaining structures subjected to moderate and severe seismic actions.

Experimental Study on the Deformation and Mechanical Properties of Bamboo Forest Slopes

In this paper, model tests on a plain soil slope and a bamboo-rooted slope under slope top loading were carried out to analyze the slope surface displacement, the change in earth pressure, and the failure mode of the slope. Furthermore, the influence of rainfall on the deformation and mechanical properties of bamboo-rooted slope sliding was studied. The results show that: (1) the failure mode of the plain soil slope was block sliding failure, while the failure mode of the bamboo-rooted slope was progressive backward failure. (2) Under the slope top load, the slope displacement shows the rule that the top of the slope was large and the foot of the slope was small. The presence of bamboo rhizomes had a negligible effect on the slope displacement, but it significantly contributed to the sliding area’s increase. (3) Compared with the plain soil slope, the earth pressure in the area of the foot of the slope under the same level of the load was elevated more obviously by the bamboo-rooted slope, which indicates that bamboo rhizomes could play a specific role in reinforcing the slope. Still, the scope of its influence was limited and mainly concentrated in the shallow soil. (4) There was a significant increase in the displacement of the bamboo-rooted slope under rainfall conditions, and the magnitude of the upward slope earth pressure was small in the process of step-by-step loading. The test results may have important guiding significance for the in-depth study of the instability law and disaster prevention in bamboo forest areas.

Development and Application of Similar Materials for Foundation Pit Excavation Model Test of Metro Station

Geomechanical model tests provide an intuitive and convenient method for observing physical phenomenon due to their easy implementation compared to in situ tests and prototype tests. The success of model tests depends heavily on the appropriate selection of model materials and proportions. Therefore, a new similar material is developed by utilizing the orthogonal experimental design method to conduct a series of proportioning tests. The new material is mixed with barite powder, iron ore powder, quartz sand, liquid paraffin, rosin, gypsum powder, and water. The physical and mechanical properties are studied through uniaxial compressive tests, Brazilian splitting tests, and direct shear tests. The influences of various raw material factors on the parameters of the similar material are systematically studied through range analysis. The results demonstrate that the mechanical parameters of similar materials have wide variation ranges; the adjustment range is 42.0–279.0 MPa for the elastic modulus, 0.37–5.37 MPa for the uniaxial compressive strength and 2.23–2.65 g/cm3 for the density. The new similar material has illustrated advantages in terms of performance stability, low price, and convenient production, which can simulate the similar relationship with different geomechanical model tests. The similar material is applied to a 3D geomechanical model test of the foundation pit excavation of Shenzhen metro station, which proves that the similar material can realistically reflect the change of earth pressure in the excavation process. With the deepening of excavation, the earth pressure curve shows significant fluctuations, and as the retaining structure is displaced, the parts with large earth pressure changes should be strengthened. The research methods and results can provide reference for further geological engineering research.

Integral bridge abutments in response to seasonal temperature changes: State of knowledge and recent advances

Expansion and contraction of integral abutment bridges due to temperature changes force integral bridge abutments (IBAs) to move toward and away from the backfill, thus increasing horizontal earth pressures behind the abutments and inducing bending moments on pile foundations. This paper presents the state of knowledge and recent advances in understanding the behavior of IBAs in response to temperature changes including abutment movement, pile response, and horizontal earth pressure behind the abutment, examines the effect of bridge skew on the behavior, and discusses possible measures to mitigate temperature change-induced problems for IBAs. Field data show that both bending moments of piles near the bottom of abutments and axial loads of piles fluctuated with temperature. Redistribution of dead loads among bridge components due to planar temperature gradients and earth pressure changes behind the abutment contributed to axial load fluctuations in piles. Magnitude and distribution of horizontal earth pressures behind the abutment depend on factors such as abutment movement and abutment movement mode. Most of the current design methods overestimated the horizontal earth pressures at the bottom of the abutment during bridge expansion. Compressible inclusions placed behind the abutment, geosynthetic-reinforced backfill, and lightweight backfill in place of typical aggregate backfill are helpful to reduce horizontal earth pressures behind the abutment at high temperatures and temperature change-induced backfill settlements.

Supporting mechanism of rigid-flexible composition retaining structure in sand ground using discrete element method

The supporting mechanism of a rigid-flexible composite retaining structure (RFCRS) is investigated by the discrete element method (DEM) using the rolling resistance linear (RRlinear) contact model. A DEM model with a natural initial stress state is first generated by the brick filling method (BFM) and the effectiveness and accuracy of the modelling process are further checked. Then, a relation between the macroscopic and microscopic parameters is constructed and calibrated. The mechanical characteristics of the RFCRS in terms of the stress field, displacement field, force chain and energy field are explored by comparison with rigid retaining structure (RRS). Numerical results have revealed that compared with the RRS, the earth pressure of the RFCRS is reduced by approximately 13.96%, and the peak earth pressure of the RFCRS is reduced by approximately 47.86%. The supporting mechanism of the RFCRS is divided into two aspects. On the one hand, flexible materials deform under earth pressure, and thus the lateral earth pressure changes from the at-rest to the active state. On the other hand, flexible materials absorb part of the energy through deformation. Additionally, as the thickness of flexible materials increases, the lateral earth pressure decreases and the tendency of decreasing earth pressure tends to weaken.

Field Study on Earth Pressure of Finite Soil Considering Soil Displacement

The classical earth pressure theory assumes a semi-infinite soil behind the wall, which is no longer applicable to the problem of earth pressure in the case of finite soil. A field study was conducted to investigate the earth pressure of finite soil at different excavation depths. The earth pressure cells were used to measure the change in earth pressure along the depth, and the measured earth pressures were compared with the calculation results for finite soil. Moreover, the influence of the width-to-depth ratio, cohesion, and internal friction angle on the earth pressure of finite soil was also analyzed based on the theoretical calculation method. The research results show that compared with the Rankine active earth pressure, the active earth pressure of finite soil was more suitable for the calculation of earth pressure for a finite soil situation. The difference in the earth pressure of finite soil under different width-to-depth ratios would increase with depth, while the cohesion and internal friction angle had little effect on the earth pressure of finite soil.

1-G experimental study of the collapse effects on buried steel gas pipelines

Collapse disasters are commonly occurring geological disasters around buried gas pipelines and severely threaten the safety of pipeline operations. In this study, to investigate the soil deformation characteristics and mechanical response law of the pipeline under collapse, an experimental box (6 m × 1 m × 1.2 m) was built, and 1-G collapse experiments with different pipe diameters and burial depths were performed. The soil deformation laws, change in earth pressure around the pipeline, and mechanical response of the pipeline during the expansion of the collapse range were obtained by comparing and analysing the experimental results. Pipeline collapse disasters can be divided into two stages: before and after large-scale collapse disasters. The burial depth has an influence on pipeline collapse disasters mainly in a small-scale collapse range. As the collapse range increases, the influence of the burial depth on the strain distribution of the pipeline gradually decreases. However, an increase in pipe diameter can lead to a significant increase in the large-scale collapse range. Large-diameter pipelines bear greater strain than small-diameter pipelines after a large-scale collapse. This study provides data support for further research and serves as a valuable reference for pipeline safety evaluation in collapse disasters.

Quantification of the Active Lateral Earth Pressure Changes on Retaining Walls at the Leading Edge of Steep Slopes

Retaining walls may become unstable when the steep slope angle of the top of the wall (β) is greater than the internal friction angle of the earth behind the wall (φ). To examine this behaviour, an active earth pressure model test setup was designed with inclined backfill behind the wall, and corresponding finite element simulations were performed at the same dimensions. The active earth pressure variation patterns of the retaining wall under two displacement modes were studied: translation (T mode) and rotation around the bottom of the wall (RB mode). The experimental results corresponded well to the finite element simulation results. The study found that the experimental results coincided well with the results of the finite element simulation. The active earth pressure and the location of the resultant force points are both connected to the wall displacement pattern and slope angle.

Influence of Foundation Pit Excavation on Tunnels at Different Locations

To evaluate the tunnel deformation law and soil stress distribution between foundation pit excavation and tunnel in different locations, numerical analyses using the hypoplastic model are conducted based on reported centrifuge model tests. Two cases are designed to investigate the effects of the foundation pit excavation on the deformation of existing tunnels. In case C, an existing tunnel is directly located underneath the foundation pit; in case S, the tunnel is located at one side of the foundation pit. Three-dimensional tunnel deformation mechanisms along the tunnel axis are observed through the variation of stresses change in the soil circumambient tunnel. It is found that compared with case C, there are minor Earth pressure changes in case S. The different Earth pressure changes around the tunnel lead to different modes of tunnel deformation. The maximum additional tunnel bending strain appears at the crown and invert, while the minimum value appears at the spring lines in case C. In case S, the maximum values appear in the right shoulder and left knee, while the minimum values appear on the left shoulder and right knee. The additional tunnel bending strain and stress reduction at different tunnel cross sections in case S is much smaller than those in case C. In case C, after the excavation, lateral Earth pressure coefficient changes ΔKxz and ΔKyz rise to 70% and 150%, respectively, of their initial value at shoulders, while little changes can be found at spring lines. However, in case S, the maximum absolute value of both ΔKxz/(Kxz)0 and (ΔKyz/(Kyz)0) is no more than 10%.

Analysis of Shaking Table Tests of Underground Structures considering the Influence of the Structure-Soil Interface

To investigate the seismic performance of underground structures under the action of the structure-soil interface, in this study, experiments were performed using plexiglass structures (two pieces) and a concrete structure (one piece) as the research objects. The surface of one plexiglass structure was prepainted with a layer of cement mortar as the contact surface between the structure and soil, and the other plexiglass structure was not treated and used for comparison. A rigid model box measuring 2.25 m × 2.25 m × 1.5 m was placed on a 3 m × 3 m shaking table, and the box was filled with the configured model soil and the underground structure prepared in advance. Input transverse uniform excitation was imparted to the whole system. A shaking table model test was performed on the underground structures to analyse the acceleration response, stress strain, and earth pressure changes in the underground structure, and the influence of the contact surface on the seismic dynamics of the underground structure was evaluated. The test results showed that under uniform excitation, the dynamic characteristics of the underground structures were greatly affected by the intensity and depth of the seismic waves. (1) When the soil-structure contact was considered, the stress and strain of the structures increased significantly, and the stress-strain value was significantly greater than the stress-strain value of the soil-structure interface in a fully bonded state. (2) There were inconsistencies between the acceleration peak curve of the plexiglass structure considering the contact effect and the acceleration peak curve of the plexiglass structure without considering the contact effect. The difference between the two lies mainly in the corresponding maximum peak acceleration and the Fourier spectrum amplitude. With respect to the value and frequency composition, regardless of whether the input acceleration intensity was 0.2 g or 0.5 g, the peak acceleration of the organic structure was greater when the contact surface effect was considered than without the contact surface effect. Therefore, the structure-soil interface needs to be considered in actual engineering. The presence of the contact surface improves the safety of the structure and is helpful for seismic design. The results of this study provide a basis for further research on the influence of soil-pipe contact on the seismic response of underground structures.

Optimization Effects of Load Reduction for Earth Pressure on High-Filled Cut-and-Cover Tunnels Using the Discrete Element Method

In the Northwestern part of Loess Plateau of China, the ravine and valley are numerous; therefore, high-filled cut-and-cover tunnels (HFCCTs) play a major role in meeting traffic needs and creating a great deal of usable land. However, due to higher backfill soil, a high earth pressure is generated, which affects the safety of HFCCTs. To this end, using the discrete element method (DEM), three load reduction measures were introduced to evaluate HFCCT: the cross section types of HFCCT; the combination of optimized cross section type with load reduction using expanded polystyrene (EPS); and the combination of optimized cross section type with load reduction using the EPS and concrete wedge (CW). We evaluated changes in earth pressure of HFCCTs with reference to the density and laying position of EPS and the height as well as width of CW. Parametric DEM studies were performed to characterize these influential factors. It was found that different cross section types of HFCCT have a certain influence on earth pressure distribution, and load reduction effects of EPS were extremely obvious, resulting in a sharp drop in vertical earth pressure on top of HFCCT and a slight growth in lateral earth pressure on the sides of HFCCT. Moreover, installation of CWs reduced the VEP and LEP of HFCCT. These factors were also shown to exert important effects on load reduction mechanisms of HFCCT. Based on their influence on earth pressure of HFCCT from a macroscopic and microscopic view, optimal values for influential factors were derived.

Centrifuge modeling of effectiveness of protective measures on existing tunnel subjected to nearby excavation

Various countermeasures are adopted to mitigate nearby excavation-induced deformations and internal forces of an existing tunnel. The effectiveness and function mechanism behind the measures are not yet fully understood. In this study, three three-dimensional centrifuge tests are carried out to investigate the responses of the tunnel and ground due to a nearby excavation in dry sand. Soil improvement below the excavation base (cement-sand mixing column) and grouting around the tunnel (grouted body) are considered in these tests. It is found that, due to the excavation, earth pressures on the tunnel right springline and right heel decrease, while these on the left shoulder and left springline increase. Mindlin Green’s function underestimates the reduction magnitude of earth pressure on the right springline, but overestimates the tunnel heave and soil heave at the excavation base. Soil improvement, due to its restriction effects on the diaphragm wall and ground, achieves a desirable effectiveness on mitigating the ground settlements, earth pressure changes around the tunnel, soil heave at excavation base, tunnel heave and bending moments. In comparison, grouting around the tunnel also exhibits a certain degree of effectiveness, which might resulting from its effects on strengthing the tunnel-soil interactions.

Long-term behavior of earth pressure around a high-filled cut-and-cover tunnel

The Northwest Loess Plateau in China is mountainous and contains deep valleys which consist mostly of loess. Tunnels constructed in such deep valley and backfilled with soil are called high-filled cut-and-cover tunnels (HFCCT). Several studies have been conducted on HFCCT, but the creep behavior of loess backfill has not been fully explored. Post-construction settlement in loess is large, and it is difficult for stability to be reached in a short time. Therefore, it is necessary to predict long-term behavior of earth pressure around an HFCCT to ensure long-term safety. The primary purpose of this paper is to investigate changes in earth pressure and displacement of soil with time after the completion of the backfill process. This is achieved using FLAC3D software (finite difference method). The results show that discrepancies in soil settlement and surface settlement will gradually increase and eventually reach stability. The distribution and value of earth pressure also becomes redistributed. Meanwhile, influencing factors such as slope angle and valley width gradually weaken with time, and only affect the time needed to reach stability.

Thermal induced horizontal earth pressure changes of pipe energy piles under multiple heating cycles

This paper explores the potential use of a pipe pile as a heat exchanger. The comparison between the thermomechanical characteristics of the solid energy pile and pipe energy pile was analyzed by using the model test method. The potential effects of thermal cycles on the horizontal earth pressure and the pile resistance redistribution were analyzed and discussed. Moreover, this paper also presents a preliminary investigation on the thermally induced contraction of the surrounding sandy soil. The results showed that the repeated expansion and contraction of energy piles would induce decreases in the horizontal earth pressure and impose an increased tip resistance to balance the shaft resistance reduction during the thermal cycles. Settlement would gradually accumulate at a reducing rate for the energy piles, and the accumulation of the pile settlement could be accompanied by the thermal contraction of the sandy soil. After three thermal cycles, the solid pile accumulated a 20% greater percentage of pile settlement than the pipe pile. However, the reduction in the shaft resistance of the pipe pile was larger than that of the solid pile. Hence, for the practical design of pipe energy piles, attention must be paid to the potential impact of thermal cycles on the pile structure.

Model Test of Deformation Evolution and Multi Factor Prediction of Anchorage Slope Stability under Rainfall Condition

The stability of the anchorage slope on the Baiyang Yangtze River Highway Bridge in Yichang, China, was investigated under different rainfall conditions using model test, numerical simulation, and factor analysis. The results of the study are as follows: (1) with the increase of rainfall intensity, the change of earth pressure can be divided into three stages. However, when the rainfall intensity was larger than a certain value, the change of earth pressure of cut slope became two stages; with the increase of rainfall intensity, pore water pressure increased with the increase of rainfall time, while at a certain stage after the rainfall, the pore water pressure in the cut slope did not decrease immediately, but increased for a period of time. (2) When the rainfall stopped, the stability coefficient of the anchorage slope continued to decrease, then slowly increased, and finally tended to be gentle. Meanwhile, when the rainstorm reached a certain intensity, the main factor that restricted the rainfall infiltration rate became the geotechnical permeability coefficient of the cut slope, which was no longer the rainfall intensity. (3) Factor analysis shows that the rainfall intensity and rainfall duration were the most important factors for anchorage slope stability, while earth pressure, pore water pressure and slope displacement were much less significant.

Experimental study on effect of underground excavation distance on the behavior of retaining wall

The changes in earth pressure and ground settlement due to underground excavation near an existing retaining wall were studied experimentally according to the separation distance between the underground excavation and the retaining wall. In addition, this study attempted to experimentally prove that the arching phenomenon occurred during the construction of the underground space. A model tank having 120 cm in length, 160 cm in height, and 40 cm in width was manufactured to simulate underground excavation through the use of five separated base wall bodies. The variation of earth pressure on the retaining wall was measured according to the underground excavation phase through the use of 10 separated right wall bodies. The results showed that the earth pressure on the retaining wall was changed by the lowering of the first base bottom wall; however, the earth pressure was not changed significantly by the lowering of the third base bottom wall, since the third base wall had sufficient separation distance from the retaining wall. Lowering of the first base wall induced a decrease in the earth pressure in the lower part of the retaining wall; in contrast, lowering of the first base wall induced an increase in the earth pressure in the middle part of the retaining wall, proving the arching effect experimentally. It is necessary to consider the changes in earth pressure on the retaining wall in designing earth retaining structures for sections where the arching effect occurs.