Soil Mechanics and Foundation Engineering最新文献

Evaluating the liquefaction capacity of saturated loose sandy and clayey soils is an important task to be completed in the course of implementing new construction projects in seismic areas. This article addresses the main characteristics and input parameters of three soil models, including HS small, UBC3D-PLM, and PM4Silt. The behavior of the “soil base–pile foundation–structure” system is examined by using these models to simulate the soil behavior during an earthquake. The results demonstrate the main differences between these models and draw attention to the importance of the choice of a soil model for seismic analysis, particularly when soil liquefaction is considered.

It is a high-risk project in most cases for urban subway tunnels to pass through structures at close distances. In order to effectively control the stratum deformation and reduce the construction disturbance, it is extremely critical to select a practical tunnel construction method. Based on the Jing-Zhang high-speed rail shield tunnel under an extremely small interval of the subway section of Beijing Line 12 in China, a numerical simulation was conducted regarding the bench-cut method, the temporary inverted arch (TIA) method, the center diaphragm method, and the center cross diaphragm method. The key issues are discussed in detail, such as the laws of the stratum deformation, the surface subsidence pattern, the deformation of the shield segment, and the force characteristics of the supporting structure. The research results show that the maximum deformation of the shield segment caused by subway construction is within the range of ±15 m from the central section of the double interval. The TIA method not only reduces the stress caused by the bending moment of the initial support, but also takes full advantage of the locking effect of the anchor pipe, and the stratum deformation is well controlled.

Variants of solving the problem of collapse arch pressure on the support of an underground work by variational methods are presented. Ritter’s scheme is used as a basis. The interaction between the collapse arch and surrounding soil mass is described based on the “passport” of strength characteristics for rock soil. Most of the solutions are given in closed form. The numerical calculation results obtained by the limit analysis method for the maximum pressure on support in rock soil are close to the theoretical values.

The existing jacking force estimation formula considers the jacking pipe as a rigid body, which is inconsistent with the actual working state of a thin-walled slender jacking pipe. This study established a finite element displacement control model to estimate the jacking force of a slender thin-walled pipe, and obtained a jacking force fitting formula considering the deformation of the jacking pipe, the contact range, the friction coefficient of the contact surface, and the normal stress of the contact surface. The relationship between the jacking force and the jacking distance was established under certain conditions. One-quarter contact can better reflect the actual force state of a slender and thin-walled jacking pipe. From the viewpoint of accurately predicting the jacking force, the displacement control finite element method outperforms the theoretical formula, and the calculation time is controllable.

Laboratory experiments on clayey soils under dynamic triaxial compression were conducted to establish a nonlinear relationship between the dynamic modulus of soil deformation and the frequency of impact. The most significant increase in the dynamic modulus of soil deformation is observed under an increase in frequency from 5 to 10 Hz. In comparison with fluvioglacial soils, the dynamic deformation modulus in glacial loams grows slower under an increase in frequency. This confirms the dependence of the obtained relations on the genesis of soils. The research results were used to develop vibration protection systems for high-precision equipment in high-tech industries.

We investigate a deep foundation pit for urban substation construction in Chengdu, China. The pit was excavated in a sandy gravel layer and has a depth of 24.6 m. Detailed field surveys and monitoring were carried out to investigate the deformation characteristics of the foundation pit and its supporting structure related to excavation. Flac3D software was used to analyze the influence of pile anchor design parameters, including pile diameters, pile spacing, anchor cable prestress, anchor angle, and the number of rows of anchor cables, on deformation of the deep foundation pit. The results showed the pile diameter was the most critical influencing factor for pile deformation. The influences of anchor cable prestress and anchor angle on the horizontal displacement of the pile were inferior to the influence of the pile diameter and the number of anchor cable rows. The results reported in this paper provide guidance for the optimal design of foundation pits in settings with similar geological conditions.

To assess the sensitivity of impulse response testing to potential poor support zones or voids beneath the foundation slabs, numerical simulations were performed using the finite element method. These simulations covered a range of scenarios, including soil-loosening zones, sub-slab cavities, and slab cracks. The analysis of the simulation results employed two distinct techniques: the normalized acoustic response method and the ASTM C1740 mobility spectrum approach. These methods allowed the parameters and attributes derived from changes in input signals to be described in relation to the specifications within the synthetic models.

The Muzhailing Tunnel, Gansu Province, China, runs for most (84.5%) of its length through layered slate. To study the mechanical properties of rock masses containing interbedded soft and hard layers, mechanical tests were conducted in the laboratory on hard limestone and soft carbonaceous slate. To simplify the application of mechanical analysis, an equivalent alternative strength model for soft and hard media was derived based on the strain energy equivalence criterion and the Mohr–Coulomb strength theory, and expressions for calculating the ultimate equilibrium stress point and failure azimuth were obtained. Based on the strength differences between soft- and hard-rock layers, an equivalent substitution calculation model was established for different thickness ratios and stress conditions with a strength ratio of 4:1. The influence of the thickness ratio and stress state on the ultimate stress curve was analyzed.

The compatible deformation behavior of a clay core dam is an important safety-related factor; however, it has not attracted sufficient attention, especially when the zone layouts are different along the direction of the dam axis. In this study, three centrifuge modeling tests were performed to investigate this problem. Model MY1 includes only a homogeneous clay zone, MY2 includes inclined clay core and rockfill zones, and MY3 is a composite dam. MY3-D1 and MY3-D2 denote two dam blocks in MY3, and their dam types are identical to those of MY1 and MY2, respectively. The results show that the maximum settlements along the elevation occur at the half-way point of the height of the dam body during construction and are approximately 1% of the dam height. Nearly 90% or more of settlements occur primarily during the construction period. The postconstruction additional settlement difference between MY3-D1 and MY3-D2 is less than 2 cm; and the settlements induced by reservoir filling are very similar at 14.7 and 15.8% of the entire postconstruction settlement, respectively. This result indicates that the working characteristics of the composite dam are stable, and the compatible deformation of different zone layout sections of the dam is acceptable.

An approximate solution that can predict phreatic line through similarity transformation by directly using second-order nonlinear partial differential equations, which is used for one-dimensional unsteady seepage flow analysis is proposed. The proposed approximate solution, derived using similarity transformation, confirms the change of the phreatic line over time in the earthen dam. To evaluate the applicability of the approximate solution, the prediction of the phreatic line using similarity transformation is then compared with that of conventional methods by Kozney, Casagrande, and Schaffernak-Iterson, as well as with numerical and experimental test results. It is noted that the approximate solution can predict the phreatic line reasonably well in homogeneous earthen dams.