To investigate the expansion deformation of predisintegrated shale as subgrade soil and develop a calculation model to describe its expansion characteristic, the nonloaded and loaded expansion tests as well as expansion force tests were conducted on the typical predisintegrated shale under varying conditions. The results show that the expansion rate of compacted predisintegrated shale is greatly affected by initial water content, dry density, and overburden load, and that its expansion characteristics can be divided into three stages. After compaction, the expansion force of predisintegrated shale has a strong correlation with the initial dry density and initial water content, and 1.45 gcm(-3) can be used as threshold density for the rate of expansion force growth. Moreover, a comprehensive calculation model for the expansion rate and expansion force considering the coupling effects of various factors was proposed. This study proposes an alternative subgrade material using shale, which can efficiently save land resources and reduce engineering costs.

The deformation energy (Wd) of soil-like tectonic coal is crucial for investigating the mechanism of coal and gas outbursts. Tectonic coal has a significant nonlinear constitutive relationship, which makes traditional elastic-based models for computing Wd unsuitable. Inspired by critical state soil mechanics, this study theoretically established a new calculation model of Wd suitable for the coal with nonlinear deformation characteristics. In the new model, the relationship between energy and stress no longer follows the square law (observed in traditional linear elastic models) but exhibits a power function, with the theoretical value of the power exponent ranging between 1 and 2. Hydrostatic cyclic loading and unloading experiments were conducted on four groups of tectonic coal samples and one group of intact coal samples. The results indicated that the relationship between Wd and stress for both intact and tectonic coal follows a power law. The exponents for intact and tectonic coal are close to 2 and 1, respectively. The stress-strain curve of intact coal exhibits small deformation and linear characteristics, whereas the stress-strain curves of tectonic coal show large deformation and nonlinear characteristics. The study specifically investigates the role of coal viscosity in the cyclic loading/unloading process. The downward bending in the unloading curves can be attributed to the time-dependent characteristics of coal, particularly its viscoelastic behavior. Based on experimental statistics, the calculation model of Wd was further simplified. The simplified model involves only one unknown parameter, which is the power exponent between Wd and stress. The measured Wd of the coal samples increases with the number of load cycles. This phenomenon is attributed to coal's viscoelastic deformation. Within the same stress, the Wd of tectonic coal is an order of magnitude greater than that of intact coal. The calculation model of Wd proposed in this paper provides a new tool for studying the energy principle of coal and gas outbursts. (c) 2024 Published by Elsevier B.V. on behalf of China University of Mining & Technology. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

This paper investigates how accounting for contact conditions and a step abutment in the foundation affects the seismic damage behaviour of concrete gravity dams. For this purpose, a pushover analysis was conducted utilising two distinct calculation models based on continuum damage mechanics. The first model uses a continuous mesh between the dam and the soil foundation without modelling any discrete interfaces, while the second considers the dam and soil meshes separately with contact relations. To improve accuracy, the numerical simulations were conducted for each case with three different damage models. The results indicate how considering contact conditions has a significant impact not only on the overall seismic response but also on the distribution and progression of the damage field in the dam. More precisely, the areas where damage occurs in the vicinity of the foundation zones differ between these two models. The first model results indicate damage first appearing near the heel, while with the second model the damage begins near the abutment. This is demonstrated using the Beni-Haroun gravity dam as a structural case study.

This manuscript investigated the thermal stability, crystal reconstruction and microstructure evolution of graphite tailing cement mortar subjected to high temperature. Simultaneously, a computational model for heat transfer and degradation considering chemical transformations had been developed by combining multiscale mechanics with the laws of thermodynamics. The results show that 20% graphite tailings can increase the tobermorite crystal content under high temperature and inhibit its transformation into disordered form. Furthermore, the dormant active SiOx in graphite tailing is gradually activated under the action of high temperature, which catalyzes and induces the formation of more belite crystal in graphite tailing cement mortar. Additionally, 40% graphite tailing can promote the generation of anorthite by the induction of high temperature. Finally, a new multi-scale model considering the chemical transformation is established to calculate the hightemperature degradation process of graphite tailing cement mortar.

As a special type of clay, expansive clay is widely distributed in China. Its characteristics of swelling and softening when meeting water and shrinking and cracking when losing water bring many hidden dangers to engineering construction. Expansive clay is known as engineering cancer, and in-depth research on the unloading mechanical response characteristics and the unloading constitutive relationships of expansive clay is a prerequisite for conducting geotechnical engineering design and safety analysis in expansive-soil areas. In order to obtain the unloading mechanical response characteristics and the expression of the unloading tangent modulus of expansive clay, typical expansive clay in the Hefei area was taken as the research object, and triaxial unloading stress path tests were conducted. The stress-strain properties, microstructures, macro failure modes, and strength indexes of the expansive clay were analyzed under unloading stress paths. Through an applicability analysis of several classical soil strength criteria, an unloading constitutive model and the unloading tangent modulus expression of the expansive clay were constructed based on the Mohr-Coulomb (hereinafter referred to as M-C) criterion, the Drucker-Prager (hereinafter referred to as D-P) criterion, and the extended Spatial Mobilized Plane (hereinafter referred to as SMP) criterion theoretical frameworks. The following research results were obtained: (1) The stress-strain curves of the three stress paths of the expansive clay were hyperbolic. The expansive clay showed typical strain-hardening characteristics and belonged to work-hardening soil. (2) Under the unloading stress paths, the soil particles were involved in the unloading process of stress release, and the failure samples showed obvious stretching, curling, and slipping phenomena in their soil sheet elements. (3) Under both unloading stress paths, the strength of the expansive clay was significantly weakened and reduced. Under the lateral unloading paths, the cohesive force (c) of the expansive clay was reduced by 32.7% and the internal friction angle (phi) was increased by 19% compared with those under conventional loading, while under the axial unloading path, c was reduced by 63.5% and phi was reduced by 28.7%. (4) For typical expansive clay in Hefei, the conventional triaxial compression (hereinafter referred to as CTC) test, the reduced triaxial compression (hereinafter referred to as RTC) test, and the reduced triaxial extension (hereinafter referred to as RTE) test stress paths were suitable for characterization and deformation prediction using the M-C strength criterion, D-P strength criterion, and extended SMP strength criterion, respectively. (5) The derived unloading constitutive model and the unified tangent modulus formula of the expansive clay could accurately predict the deformation characteristics of the unloading stress path of the expansive clay. These research results will provide an important reference for future engineering construction in expansive-clay areas.