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This study investigates the seismic response and failure mode of a pile–structure system in a liquefiable site by employing a numerical simulation model combined with the shaking-table results of a soil–pile–structure dynamic system. The pile and soil responses obtained from the numerical simulations agreed well with the experimental results. The slopes of the dynamic shear-stress-shear-strain hysteretic curves at different positions also exhibited a decreasing trend, indicating that the shear strength of the soil in all parts of the foundation decreased. The peak acceleration of the soil and pile was not clearly amplified in the saturated sand layer but appeared to be amplified in the top part. The maximum bending moments appeared in the middle and lower parts of the pile shaft; however, the shear forces at the corresponding positions were not large. It can be observed from the deformation mode of the pile-group foundation that a typical bending failure is caused by an excessive bending moment in the middle of the pile shaft if the link between the pile top and cap is articulated, and sufficient attention should be paid to the bending failure in the middle of the pile shaft.

In this study, a series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency fon the pre-liquefaction (shearing contractive (SC) period and initial shearing dilative (ISD) period) and post-liquefaction (late shearing dilative (LSD) period) deformation properties of saturated Fujian sand. The secant shear modulus Gand damping ratio λin the entire cyclic loading process, and the unloading tangent shear modulus GL1and flow deformation tangent shear modulus GL2in the ISD and LSD periods were adopted to quantitatively characterize the evolution of hysteresis loop with an increase in shear strain amplitude γa. The test results show that the effect of fon Gof saturated Fujian sand in the SC period is not apparent. However, all the G-γa, GL1-γa, and GL2-γacurves in the ISD and LSD periods showed a downward trend with an increase in f. This study also proposes a modified method for calculating λto compensate for the analytical error caused by the non-closure of hysteresis loop. Compared with the classical curves that mainly applied in geotechnical engineering, the λfirst increases and then decreases with the increase of γa. Furthermore, the λevaluated by the modified method is approximately 10%–15% more than the λevaluated by the traditional method when the λreaches its peak value.

Particle shape governs the macro-mechanical behavior of high explosives. This study develops 3D computational geometry techniques to determine commonly used sphericity and roundness definitions of typical high explosive particles, including HMX (octahydro-1,3,5,7-tetranitro- 1,3,5,7-tetrazocine), RDX (1,3,5-Trinitroperhydro-1,3,5-triazine), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane). This technique can automatically determine principal dimensions, volume, surface area, minimum circumscribed sphere, maximum inscribed sphere, and the 3D convex hull of 3D particle geometries and determine commonly used 3D sphericity descriptors of high explosive particles. This technique can also automatically identify corners on the 3D particle surface, fit appropriate spheres to these corners, and compute Wadell’s roundness of high explosive particles. This study demonstrates that the qualities of 3D particle geometries affect the computational results of particle sphericity and roundness descriptors of high explosives. These descriptors display a hierarchy of resistance to the effects of low image quality. Therefore, the minimum requirements for ensuring reliable shape characterization of these parameters are established for high explosives. This study systematically compares 2D and 3D particle shape characterizations of around 15,000 particles from three high explosives (HMX, RDX, and CL-20). Results show that 2D sphericity and rounded definitions either underestimate the corresponding 3D definitions or vary within large ranges leading to uncertainties for inferring 3D particle characteristics from 2D images of high explosives.

To achieve the goal of carbon emission reduction, the hydrate is widely concerned for its outstanding advantages such as high calorific value and low pollution. As the output of natural gas still cannot meet the requirements of commercial exploitation, multi-well exploitation will become a technological trend in the future. Therefore, the depressurization mining of hydrate reservoirs under multi-well systems was simulated. The influences of the well branch number, well spacing, and wellhead radius on the soil depressurization characteristics were analyzed. Moreover, two new parameters, depressurization and decomposition areas, are defined to analyze the reservoir depressurized effect and production efficiency. The results show that the more the number of wells, the better the depressurization effect and the longer the duration. The decomposition efficiency of multi-well production in the late mining stage is much higher than that of single-well production. The gas production by multi-well cooperative production is much higher than that by single well production with the same number.

In small-scale geotechnical experiments, using a tactile pressure sensor (TPS) to measure soil pressure distribution on a curved surface can effectively reduce errors of mismatch caused by size, stiffness, and incomplete fitting with the measured object. TPS has more benefits than soil pressure cells in measuring curve surface pressure, but some issues remain unclear, such as the effect of negative-piezoresistivity and particle size on the measurement. In this article, the author first puts forward a method to effectively reduce the errors of TPS in the low-pressure measurement zone. Then, through a load test in six types of narrow-graded sand, the ratio of the maximum particle size to the size of the sensor unit is obtained, and the effect of negative piezoresistivity on the measurement is evaluated. Finally, a small laboratory test proves that TPS can comprehensively and meticulously reflect the pressure on the pile. After careful calibration and considering the effect of deflection and particle size, it is shown that the measurement errors can be kept within an acceptable range.

•Three centrifuge shaking table tests are carried out for the seismic response of subway station structures under three kinds of soft soil sites, and the test procedures are described in detail.•The seismic response patterns of the sites and structures under soft soil sites are obtained, and the effects of site specificity on the seismic response of the structures are analyzed.•The performance evaluation of subway station structures under different seismic magnitudes in soft soil sites is carried out.

Volume averaging is a standard method for the development of macroscopic balance equations for modelling the thermodynamic behaviors of multiphase porous media. However, work conjugate principle which is a common practice in continuum mechanics is not emphasized by the volume averaging technique resulting in the macroscopic balance equations are not capable of comprehensively describing the kinematic behaviors of multiphase porous media due to the loss of essential macroscopic variables. This study derives the macroscopic mass and momentum balance equations for the pore fluid of a fluid-solid porous medium by use of the volume averaging technique. We show (1) if the procedure of the volume averaging is implemented in its traditional manner, only the average flux of the pore fluid described by its mass average velocity is captured; (2) if the work conjugate principle is employed to define a work-conjugate velocity for the pore fluid at the macroscale, both the average flux (described by the mass average velocity) and the dispersive flux (described by the deviation of the mass average velocity from the work-conjugate one) are reproduced. This theoretical analysis demonstrates that the work conjugate principle is an essential thermodynamic constraint to improve the volume averaging technique, in the sense that the macroscopic balance equations are required to be capable of comprehensively describing the macroscopic kinematic behaviors of multiphase porous media.

In order to ensure the effectiveness of the Tapered Head Grouted Sleeve (THS) joints and reduce its impact on prefabricated components, three-dimensional numerical analysis models were established based on the large-scale general finite element analysis software ABAQUS. On the basis of verifying the validity of the model, numerical uniaxial tensile tests were carried out on THS joints of different sizes, this research mainly considered the influences of the diameter and embedded length of the bar and the diameter, angle and length of the sleeve on the connection performance and strain characteristics of the THS joints, and a theoretical model for the tensile strength of THS joints was proposed. In addition, based on the numerical tensile test results of THS joints with different parameters, the concept of diameter-angle ratio (ζ) suitable for THS was established, and a simple calculation method was proposed to predict whether the connection of THS joint is effective. The results illustrated that: THS joint embedded length should be at least 6 times the diameter of the bar; Increasing the embedded length or reducing the sleeve diameter are beneficial to reduce the tensile strain of the sleeve; The calculated results of the theoretical model were in good agreement with the numerical results; When the minimum embedding length is satisfied, the range of diameter-angle ratio that the THS joint need to meet is 0.52≤ζd≤0.63.

According to the theories of wave propagation in visco-elastic continuum and Rayleigh-Love rod, a simplified model in axisymmetric conditions for the longitudinal vibration of large-diameter pipe pile (LDPP) in radially heterogeneous surrounding soil with viscous damping is presented. The relevant analytical solution for dynamic impedance at pile head is derived by using complex stiffness transfer method, which is also validated via independent comparisons with previous solutions. Besides, parametric analyses are carried out to reveal both the radial heterogeneity of surrounding soil and the lateral inertia effect of pile shaft on the dynamic impedance of LDPP. The obtained analytical solutions are suitable for the longitudinal vibration issues of floating LDPP in visco-elastic surrounding soil with radial heterogeneity, which can be conveniently degenerated to describe the longitudinal vibration of a floating solid pile in soil with radial heterogeneity as well as a floating LDPP or solid pile in radially homogenous soil.

Ensuring formation stability is vital to realizing the commercial development of hydrate reservoirs. Therefore, studying the formation subsidence in the hydrate mining process is essential. This study proposes a method for predicting the maximum surface subsidence using the hydrate dissociation front. Firstly, to more realistically evaluate the hydrate dissociation characteristics and reservoir deformation during the hydrate mining process in permafrost, soil permeability experiments under different hydrate saturations were conducted, and the dynamic permeability model was established. On this basis, combined with the multifield coupling model, the depressurization process of the hydrate reservoir is simulated. The hydrate dissociation property and stratum subsidence response under different parameters are analyzed. In addition, the parameter sensitivity is evaluated, and the corresponding relationship between the hydrate dissociation front and the maximum surface subsidence is established. According to the research results, assuming that the safety limit of surface subsidence is set to 0.3 m, the safe hydrate dissociation range within soil permeability K= [20 mD, 120 mD] is about [0 m, 77.7 m]. For every 20% decrease in wellhead pressure, the hydrate dissociation range increases by 30%. It is worth noting that the three points A, B, and C (located at the upper, middle, and lower positions next to the well perforation end) show completely different deformation trends during the mining process.