With the rapid development of high-speed railways in China, it is inevitable that some of the lines will have to traverse through the mine goaf ground, and there is little research on whether the “activation” of the foundation of the mine goaf ground occurs under the influence of train loads. In order to provide a safe and reliable basis for the construction of high-speed railway in mine goaf ground, a new classification method of mine goaf ground activation is proposed considering the stability and railway influence. First, the stability evaluation system of the mine goaf site is established with 3 primary indexes and 12 secondary indexes. The 47 groups’ data of the mine goaf ground site are collected as learning samples. Five machine learning methods including decision tree, discriminant analysis, support vector machine, and classifier ensemble are used to learn and test the data. The optimal algorithm is selected and the stability evaluation model is established to classify the stability of the mine goaf site. Second, influencing factors of railway are graded to establish an extension comprehensive evaluation model. Finally, based on the above two models, a new classification method of high-speed railway goaf ground activation considering the two factors and five sub-factors is proposed. Through the verification of two engineering examples, the prediction result of this method is “easily activation” and the need to treat the goaf area, and the actual construction is also taken to grouting treatment, proving that the method has certain guiding significance for the project.
To evaluate mechanical performances of the transverse rib bar and reveal anchoring mechanism between the grout and steel bar, a series of pull-out tests were carried out, the numerical simulations and theoretical analysis of grout failure modes were also analyzed. Results show that the grout in front of the transverse rib display wedge-shape damage and the simulation results verify this damage forms. The formula of the effective transverse rib angle, the grout strength and anchorage force were derived based on elastic thick-wall cylinder theory. During the pull-out tests, the radial stress of the grout lagged the tangential stress reaching the ultimate tensile strength with the inner pressure increasing. The anchoring force of the transverse rib bar increases with the increase of the grout strength, and with the increase of the effective transverse rib angle. These conclusions provide the theoretical basis and technical support for the engineering practice.
To investigate the mechanical properties and energy evolution characteristics of sandstone depending on the water contents and confining pressure, the uniaxial and triaxial tests were conducted. e test results show that the strain energy was stored in the sandstone samples at the prepeak stage, and that is suddenly released when the failure occurred, and energy dissipation is sharply increased at the postpeak stage. e damage and energy dissipation characteristics of the samples are observed clearly under the stepwise loading and unloading process. e critical strain energy and energy dissipation show a clear exponential relationship. e critical elastic energy decreases linearly as the water content increases. As the confining pressure increases, the critical elastic energy of the samples transforms from linear to exponential. e concept of energy enhancement factor is proposed to characterize the strengthening effect induced by the confining pressure on the energy storage capacity of the rock samples. e energy evolution of the sandstone samples is more sensitive to the confining pressure than that of the water content.
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