Wenhao Shi

To address the low interpretation accuracy of ground penetrating radar (GPR) images for existing strip foundations of buildings, a recognition method for GPR image based on adaptive threshold segmentation is proposed. This method determines the individual optimal threshold by analyzing the threshold response curve and then calculates a globally unified threshold to achieve adaptive binarization of the image. Forward simulations were performed using a three-dimensional similar numerical model to compare the proposed method with the conventional OTSU method in identifying the response characteristics of strip foundations. Physical model tests were also conducted for verification. The results show that the adaptive threshold segmentation method clearly reveals three typical waveform structures: the top surface of the foundation, the internal reinforcement grid, and the bottom surface. It exhibits better adaptability to signal attenuation and multi-scale targets than the OTSU method. Application of the method in a foundation detection project for a residential community in Jiangsu Province demonstrates its effectiveness in identifying the reflection characteristics of the foundation top. The inverted depth and width parameters of the foundation top agree well with the design drawings. This study provides a methodological reference for nondestructive detection and quantitative interpretation of strip foundations and offers a preprocessing foundation for artificial intelligence-based interpretation of GPR images.

Aiming at the damage evolution and energy release characteristics of sandstone in failure process, uniaxial and cyclic loading experiments were conducted with the average temperature, infrared temperature field, acoustic emission (AE), and displacement field being monitored simultaneously. The results show that in the low stress stage, the initial pores and fissures are compressed and the thermoelastic effect is insignificant. At the same time, the AE events are active, but most of the events are released with low energy. Then, the surface of the specimen shows stratified displacement phenomenon in the vertical direction. In the following stage, the thermoelastic effect is significant, and the average temperature of specimens shows a linear correlation with stress, whereas the AE is relatively inactive, and vertical surface deformation shows further homogenization and saliency. Because of the top and bottom constraints, the horizontal displacement field shows axis symmetrical distribution of double half-ellipse like a drum. During the yielding phase and the rupture moment, the average temperature rises obviously because of the heat from the friction of the rupture surface, and the temperature field also appears the phenomenon of differentiation; in the meantime, a large amount of AE events occur and the proportion of high energy events increases; further, the deformation field is significantly gathered near the ruptured position. Finally, the time sequence of the multiple physical parameters (AE parameters, average temperature, temperature fields, horizontal and vertical displacement fields) is summarized, which can be a reference for the stress state and failure analysis.

A large number of statistics indicate that broken rock mass always transforms into a flowing channel and leads to water inrush disasters in mining engineering, such as fault, karst, and strongly weathered rock mass. During the process of water inrush, the structure of the broken rock mass is constantly changing due to seepage erosion under high-velocity flow. Therefore, it is of vital importance to quantitatively evaluate the flow behavior of the water inrush related to the seepage erosion in order to prevent or reduce the risks. This study described a coupled nonlinear flow model, which couples the high-velocity seepage, the small particle migration, and the evolution of the broken rock mass structure. The model was verified firstly for simulation of nonlinear flow behavior by comparing with the traditional one. Then, the proposed model was used to simulate the evolution of particle migration and seepage properties of the water inrush through broken rock mass by a numerical case. The simulation results generally agree well with the existing experimental results. The simulations indicate that small particle migration causes the unstable characteristics of the seepage and the heterogeneity properties of the broken rock mass, which lead to the nonlinear flow behavior of the water inrush in both time and space. From a different perspective, it also indicates that the proposed model is capable of simulating the interaction of high-velocity seepage, small particle migration, and evolution of broken rock mass structure in the process of water inrush.

Statistics indicate that granular rock mass frequently acts as the flow channel and cause water inrush disasters under high water pressure in underground mining and tunnel engineering. The flow velocity of water inrush is so high that the flow behavior shows nonlinearity and cannot be described by Darcy’s law. During the water inrush, the non-Darcy flow behavior associated with the porosity of granular rock mass is constantly changing due to seepage erosion. Therefore, this paper aims at the non-Darcy flow behavior of the granular limestone with a wide range of porosity (from 0.242 to 0.449). The non-Darcy flow properties were experimental investigated under steady-state condition by a self-designed apparatus. Based on the experimental data, an empirical hydraulic conductivity-porosity relation together with the expression of inertial coefficient was proposed. Then the non-Darcy flow regime was quantitative studied by the hydraulic conductivity-based Reynolds number. And the Forchheimer number associated with porosity was used to determine the critical flow velocity of the non-Darcy flow. From the point of view of seepage, two reasons for water inrush frequently occurred through granular rock mass with high porosity were finally discussed.

Stratified rock mass is a common rock mass structure and distributed widely on the earth’s crust. High-density distribution of stratified structural planes in the stratified rock mass has a great influence on the mechanics properties of the rock mass, such as anisotropy of stress and seepage. Therefore, anisotropy is the inherent characteristic that must be considered in the stratified rock mass as well as the stratified rock slope stability. According to the anisotropic characteristics of stratified rock mass, an anisotropic seepage-stress coupled model for the mechanical behavior of stratified rock slope is proposed based on the anisotropy elasticity theory. The model is validated by simulating seepage and stress fields of an idealized slope using the finite element method. The deformation and stress-dependent permeability of the slope are predicted and compared well with the previous study, thus confirming its capability in characterizing the response of rock slope that is dominantly affected by rock anisotropy. Finally, the model is used to simulate the anisotropic properties of a stratified rock slope of Fushun west open-pit mine, China. The simulation is in good agreement with the actual measurement, which means the proposed model is capable of simulating anisotropic properties of the stratified rock slope.

In a groundwater outburst through a fault, the velocity is generally so high that the relationship between the velocity and the hydraulic gradient deviates from the linear Darcy regime. This study uses the Forchheimer equation to model the flow in both the aquifer and the fault zone. The model is used to investigate the effects of non-Darcy flow on a specific inrush episode at the Zhongguan iron mine by varying the fault permeability. It shows that the flow behavior in the aquifer was not always Darcy flow or non-Darcy flow, but changed depending on the fault permeability. The region in the aquifer near the fault is most likely affected by non-Darcy flow, and the non-Darcy-effect region expands away from the fault with the increase of the fault permeability. Considering a 10% non-Darcy effect for engineering, the Forchheimer equation can be approximately used to describe the flow mechanism from Darcy to non-Darcy. Furthermore, the Forchheimer equation is also acceptable for predicting the groundwater inflow during groundwater outburst through fault.

A non-linear flow model that couples three flow types is built based on flow transition to investigate the flow behavior of water inrush induced by KCC.