Showing papers on "Lateral earth pressure published in 2022"

Numerical Analysis of Passive Piles under Surcharge Load in Extensively Deep Soft Soil

Abstract: The three-dimensional finite difference method was used in this study to analyze the deformation and stresses of a passive pile under surcharge load in extensively deep soft soil. A three-dimensional numerical model was proposed and verified by a field test. The horizontal displacements of the pile agreed well with the field results. This study investigated the pile-foundation soil interaction, the load transfer mechanism, the excess pore water pressure (EPWP), and the horizontal resistance of the foundation soil. The results show that the soil in the corner of the loading area developed a large uplift deformation, while the center of the loading area developed a large settlement. The lateral displacement of the pile decreased sharply with the increase of the depth and increased with the surcharge load. The lateral displacement of the soil was negligible when the depth exceeded 30 m. The EPWP increased in a nonlinear way with the increase of the surcharge load and accumulated with the placement of the new lift. The distribution of the lateral earth pressure in the shallow soil layer was complex, and the negative value was observed under a high surcharge load due to the suction effect. The proportion coefficient of the horizontal resistance coefficient showed much smaller value in the situation of large lateral deformation and high surcharge load. The design code overestimated the horizontal resistance of the shallow foundation soil, which should be given attention for the design and analysis of the laterally loaded structures in extensively soft soil.

A fiber Bragg grating based earth and water pressures transducer with three-dimensional fused deposition modeling for soil mass

Abstract: A novel fiber Bragg grating (FBG) sensor with three-dimensional (3D) fused deposition modeling (FDM) approach is proposed for effective stress measurement in soil mass. The three-diaphragm structure design is developed to measure earth and water pressures simultaneously. The proposed transducer has advantages of small size, high sensitivity, low cost, immunity to electromagnetic interference and rapid prototyping. The working principle, design parameters, and manufacturing details are discussed. The proposed transducer was calibrated for earth and water pressures measurement by using weights and a specially designed pressure chamber, respectively. The calibration results showed that the wavelength of the transducer was proportional to the applied pressure. The sensitivity coefficients of the earth and water pressures were 12.633 nm/MPa and 6.282 nm/MPa, respectively. Repeated tests and error analysis demonstrated the excellent stability and accuracy of the earth and water pressure measurements. The performance of the proposed transducer was further verified by a model experimental test and numerical analysis, which indicated that the proposed transducer has great potential for practical applications.

Case Study of the Largest Concrete Earth Pressure Balance Pipe-Jacking Project in the World

Abstract: Pipe jacking has been the dominant trenchless technology for constructing small (<2 m) to medium-diameter (<4 m) tunnels. Uncertainties and construction difficulties increase significantly when the diameter of the tunnel exceeds 4 m. This paper presents a case study of the largest concrete pipe-jacking tunnel project in the world, the sewerage tunnel along Jinshan Lake, Zhenjiang, China. In this project, an underwater tunnel with a diameter of 4.67 m was constructed by the earth pressure balance (EPB) pipe-jacking method. The case study reports project background, and geological and hydrogeology conditions. The key techniques such as the selection of pipe-jacking machine, jacking force estimation and control, design of intermediate jacking station, grouting process control, launching, and reception of the tunnel boring machine, trajectory control of pipe jacking, and ventilation and gas monitoring during the construction period were investigated and discussed. Furthermore, to overcome the technical difficulties associated with the oversized jacked tunnel, the corresponding countermeasures were adopted point by point, so that the safety of the whole project could be guaranteed. This study filled the knowledge gap of technical know-how for large-diameter (over 4.5 m) pipe-jacking tunnel and is expected to provide practical guide for future large-diameter pipe-jacking tunnels.

Stress distribution in reinforced railway structures

Abstract: • Geosynthetic Reinforced Soil with Retaining Wall (GRS-RW) vs conventional embankment. • The experiments are carried out in a full-scale testing facility in a laboratory. • Two track forms are considered: a three-sleeper concrete slab and a ballasted track. • The GRS-RW structure showed good performance under both static and cyclic loading. • The pressure levels found in the experiment were compared against literature. This paper evaluates the performance of a geosynthetic reinforced soil retaining wall (GRS-RW) system as an alternative to a conventional railway embankment. The aim is to investigate the behaviour of the GRS-RW system in terms of displacements and stress levels at different locations in the track and substructure. Full-scale laboratory experimental testing is carried out on a GRS-RW structure, supporting sections of ballasted and slab track, under moving loads at 360 km/h. The tracks are supported by a low-level fully confined conventional embankment and a GRS-RW system, which are constructed to high-speed standards. Displacement transducers and earth pressure cells are placed at different locations to record the displacements of the track and the stress levels in the substructure. The test results show that the pressure levels on the GRS-RW wall are negligibly small for the particular test setup, proving the GRS structure under the action of compaction reached its active state. This means that the reinforced soil was self-supporting under its self-weight and train loads, meaning there was minimal pressure on the walls. Therefore, GRS-RW systems are better alternatives to traditional earth embankments due to enhanced soil stabilisation and less land take.

Deformation and Mechanical Characteristics of Existing Foundation Pit and Tunnel Itself Caused by Shield Tunnel Undercrossing

Abstract: This paper establishes a three-dimensional symmetrical shield model to investigate the influence of a double-line shield tunnel undercrossing an existing foundation pit and of changed grouting pressure on the deformation and mechanical characteristics of both the foundation pit and the tunnel itself, and it proposes a method of symmetrical segmented pressure, in which different grouting pressure is applied in different sections of the tunnel. The monitoring data are used to verify the reliability of the model, and the maximum relative error is 5.44%. The numerical results show that the maximum subsidence of the retaining pile and anchor are 3.76 mm and 10.33 mm, respectively, and the maximum tensile stress of the anchor is increased by 32.4%. The subsidence shape of the foundation pit raft is an arch with four corners warping upward and the maximum subsidence difference is 3.17 mm. Uneven subsidence of the tunnel occurs along the longitudinal direction, and large and small subsidences are located at the outside and underpart of the foundation pit, respectively, and the maximum and minimum values are 11.15 mm and 2.13 mm, respectively, and the maximum subsidence difference is 9.02 mm. The deformation and mechanical characteristics of both the foundation pit and the tunnel are significantly decreased by appropriately increasing the grouting pressure, and it is recommended that the grouting pressure should not exceed 300 kPa. The proposed method of segmented pressure can reduce the differential subsidence by 47.2% and the maximum tensile stress by 27.2%, so it can significantly reduce the uneven subsidence of the tunnel and improve the tunnel stress condition. The research results can provide a theoretical basis for the safe construction of shield tunnels under the existing foundation pit.

Earth Pressure Estimation of Undrained Soil–Wall Systems with Head Rotation

Abstract: Semianalytical or analytical models for calculating active and passive earth pressure coefficients for undrained soil–wall systems subjected to head rotation are rare. To fill this gap, this study proposes a semianalytical theoretical model that describes the real failure features of wall–soil systems with head rotation and under undrained conditions. A continuous velocity field (CVF) that is decomposed into circular and radial velocity components is generated to characterize the movement of undrained soils in the plastic zone. The closed-form solutions of active and passive earth pressure coefficients are formulated based on the upper-bound limit analysis (UBLA) theorem. A comparison with numerical simulations and Rankine’s theory are performed to illustrate the importance of wall movement and the contributions of undrained cohesion. The analysis outcomes demonstrate that (1) the conventional stress-based method that ignores the head rotation of walls leads to an error of earth pressure coefficients up to 15.7%; and (2) the active and passive earth pressure coefficients have linear relationships with undrained cohesion. Finally, an application to shallow excavation is conducted, showing the good performance of the proposed model.

Temperature-dependent lateral earth pressures in partially saturated backfills

Abstract: Abstract Stability analysis of retaining structures supporting variably saturated backfills is a topic of great significance in civil engineering. However, the backfill soil may be exposed to elevated temperature; this may result in changes of the saturation state, thus posing temperature-dependent effective stress, variable suction stress and different hydro-mechanical characteristics to partially saturated soils. In the present work, the significant impact of elevated temperature is incorporated into the soil-water retention curve and suction stress-based effective stress formulations. Accordingly, the lower bound theorems of limit analysis in conjunction with finite element and second-order cone programming are adopted so as to thoroughly examine the impact of elevated temperature on the coefficients of lateral earth pressure acting on a model retaining wall backfilled by two hypothetical partially saturated soils; a granular material (sand) and a cohesive material (clay). The effective stress-based formula for the strength of variably saturated soils is implemented to modify the conventional Mohr–Coulomb yield criterion. In general, it was shown that for unsaturated clay backfills, the active lateral earth pressure decreases while the passive lateral earth pressure increases with increasing the induced temperature; however these influences were observed to be small for the sand backfill.

A generalised analytical framework for active earth pressure on retaining walls with narrow soil

Abstract: Active earth pressure on retaining structures supporting a narrow column of soil cannot be properly analysed using Coulomb's theory. Finite element limit analysis (FELA) shows that the soil form multiple failure surfaces if the soil column is sufficiently narrow. This paper proposes a framework for active earth pressure estimation for narrow soils by combining an arched differential element method and a sliding wedge method. The analytical framework considers both soil friction and cohesion, soil arching effects and shear stress between adjacent differential elements. The solution obtained is validated against experimental data and FELA results. Through parametric studies, the effect on the active earth pressure of the aspect ratio, the soil friction, the soil cohesion and the wall-soil interface roughness are examined. To facilitate the use of the proposed framework in design, a modified active earth pressure coefficient and an application height of active thrust are provided.

Settlement and Horizontal Earth Pressure behind Model Integral Bridge Abutment Induced by Simulated Seasonal Temperature Change

Abstract: Expansion and contraction of an integral abutment bridge cause an abutment to move toward and away from its backfill due to seasonal temperature changes, thus causing high horizontal earth pressures behind the abutment and backfill surface settlements. This paper presents the results of four model tests conducted to simulate both translational and rotational movements of abutments and investigate horizontal earth pressures behind the abutment and the backfill surface settlements. The test results showed that the translational movement of the abutment likely prevented soil ratcheting from occurring in the upper portion of the backfill due to stress adjustments in the backfill after simulated seasonal temperature changes (i.e., causing limited earth pressure increase behind the abutment). Furthermore, the existing methods used to predict the horizontal earth pressures behind the abutment overestimated the pressures at the bottom of the abutment if the translational movement of the abutment was permitted. In addition, the backfill surface settlement near the abutment, induced by the seasonal temperature changes, was a function of footing rigidity and the displacement magnitude of the abutment and continued even after 30 cycles of abutment movement.

Experimental and numerical analyses of buried box culverts in trenches using geofoam

Abstract: In embankment construction, earth pressure on buried culverts is reduced either by placing them in a trench in the ground or by inserting a soft zone in the fill over the culvert to create an ‘induced trench’. Although the performance of both methods has been studied in the literature, there are limited findings for applying the two methods in combination. A study was therefore carried out on the earth pressure exerted on box culverts buried in a trench with a soft zone included above. Laboratory tests and numerical analyses were conducted to study the performance of the proposed combined method. A surcharge load was applied to the backfill, and earth pressure around the buried box culvert was measured. After validation of the test results by a numerical method, parametric studies were performed to investigate the effect of the expanded polystyrene geofoam properties and the culvert dimensions. The results showed that culvert installation using the proposed method significantly decreased the earth pressure applied to the walls of the buried box culvert, especially when compared to the trench-only method. Using a width 1.5 times greater than the culvert width and a low-stiffness geofoam, earth pressure transferred to the buried culvert can be significantly decreased.

Active Earth Pressure of Finite Width Soil Considering Intermediate Principal Stress and Soil Arching Effects

Abstract: Traditional earth pressure theories are based on the assumption of semi-infinite space. The existence of intermediate principal stress and soil arching effects is ignored, which will cause significant errors in the application of finite width soil. This study introduced the intermediate principal stress based on the twin-shear unified strength theory; the stress deflection caused by soil arching and the uniform surcharge on the retained soil surface were also considered. An improved calculation method for cohesive soil’s lateral earth pressure coefficient, an analytical solution for active earth pressure of finite width soil, the resultant force, and its action point were proposed. The lateral earth pressure distribution of finite width cohesive soil was studied by calculation examples. In addition, relevant parameters were also analyzed. The results indicate that due to the influence of the intermediate principal stress and soil arching effects, the resultant active earth pressure is lower than the traditional method. The lateral earth pressure coefficient gradually increases with the depth, but it is always lower than the traditional one. As the soil width increases, the resultant force action point presents a nonlinear trend that first decreases, then rises, and stabilizes. The proposed method was compared with the previous studies and got better results; it can provide a new idea for estimating the active earth pressure of finite width soil.

Analysis and Intelligent Prediction for Displacement of Stratum and Tunnel Lining by Shield Tunnel Excavation in Complex Geological Conditions: A Case Study

Abstract: This paper presents the analysis and intelligent prediction for the displacement of stratum and tunnel lining of Qingdao Metro Line 4 by earth pressure balance (EPB) shield tunnel excavation in complex strata. When the tunnel is excavated in different stratum sections, the tunneling parameters of shield machine are systematically analyzed and compared, and the vertical displacement of the tunnel crown and the horizontal convergence deformation on both sides are investigated. When the tunnel body passes through the soft soil stratum and rock stratum, the curves of the vertical displacement of the stratum surface with time are respectively discussed. A machine learning method for predicting stratum surface deformation induced by shield tunnel excavation in complex strata is developed, where extreme learning machine (ELM), particle swarm optimization (PSO) algorithm and $k$ -fold cross-validation method are comprehensively considered. 65 data samples are collected from the field monitoring data of Qingdao Metro Line 4 and each data sample includes seven input values and one output value. The developed PSO-ELM has good prediction performance for stratum surface vertical displacement due to shield tunnel excavation. The case study in this work can provide a practical reference for similar tunneling projects.

Analytical Solutions for Active Lateral Earth Force

Abstract: Analytical solutions are presented for the active force on a retaining wall from a single wedge of unreinforced soil, as obtained from a general Coulomb-type limit equilibrium analysis. The solutions can accommodate variable wedge geometry, pore pressure, shear-strength parameters, surcharge stress, applied loads, pseudostatic seismic coefficients, and a tension crack zone. Closed-form expressions are derived for the critical angle of the base failure plane and corresponding maximum effective normal force on the wall for a triangular soil wedge. Verification checks show exact agreement with existing analytical solutions for simplified conditions, including Coulomb and Mononobe-Okabe active earth force. A numerical example is provided to demonstrate the method for a gravity retaining wall.