| Abstrakt: |
The research of mechanical properties of karstified rock mass is helpful to the study of slope stability, foundation bearing capacity and mechanism of karst-induced disasters in karst area. However, it is difficult to obtain suitable rock samples for mechanical tests of karstified rock mass, or there exist experimental results with large differences. Nowadays, many scholars have studied mechanical properties by numerical simulation and have achieved greatly. In this kind of research, the stochastic method to simulate the karstification process is mainly adopted, whose algorithm is relatively simple but with less accurate response to the kasitified characteristics of rock mass, thus leading to the limitations of the results. Relevant literature shows that the epikarst zone presents characteristics of negative exponential relationship between the dissolution rate and depth, uneven distribution of dissolved pores caused by the difference of dissolution morphology, and more vertical karstification than horizontal karstification. In this study, two parameters of the karstification characteristics--the dissolution rate (the quantitative index of dissolution degree of rock mass) and dissolution uniformity coefficient (representing the uneven distribution of dissolution fractures)--have been set to analyze its characteristics in the epikarst zone. According to the characteristics of limestone joint in a typical karst area in Guizhou, the equivalent model of jointed rock mass has been established by using the Flat Joint Model (FJM), Smooth Joint Model (SJM) and Discrete Fracture Network (DFN). Based on the cellular automata algorithm and the dissolution of the equivalent model of jointed rock mass, the kastified rock mass model with different dissolution rates and different dissolution uniformity coefficients has been obtained. According to the numerical uniaxial compression test and the acoustic emission events in the process of loading rock mass. A total of 48 groups of test samples were collected in terms of 8 grades of dissolution rate and 6 groups of dissolution uniformity coefficient. The results show that the loading process of karstified rock mass can be divided into six stages: (1) stage of compaction; (2) stage of elastic deformation; (3) stage of stable fracture development; (4) stage of unstable fracture development; (5) stage of post-peak strain softening; (6) stage of post-peak rapid strain softening. The karstification reduces the cementation between rock masses and destroys the skeleton of rock mass, which leads to the following effects. With an increase of dissolution rate, the uniaxial compressive strength decreases. The curve shortens at the stage of elastic deformation. The number of acoustic emission events decreases significantly when the rock mass is damaged. The failure mode of rock mass gradually changes from brittle failure to ductile failure. The strength after failure mainly comes from the locking effect of rock bridge and the friction between fracture surfaces. At the same time, with the continuous increase of dissolution rate, the compressive strength of rock mass declines from rapid to slow rate. The higher the dissolution uniformity coefficient is, the smaller size the dissolution pore and the more uniform distribution of dissolution fractures may become. Under these conditions, the formation and penetration of macro cracks need to go through a longer process, and the curve of unstable fracture development increases. The internal stress of rock mass is more divergent, and the rock mass changes from local failure to overall failure. The fitting of uniaxial compressive strength and karstification characteristic parameters (k, U) indicate their negative exponential relationship, and the exponential constant C is related to the uniformity coefficient u. The relationship can be used as the basis for determining the strength of karstified rock mass. In practical engineering, the deformation state of karstified rock mass can be judged according to this acoustic emission characteristics, and thus corresponding treatment measures can be taken. In the evaluation of rock mass quality, the dissolution uniformity coefficient can be used as an auxiliary evaluation basis, in addition to the dissolution rate as the main feature of dissolution development. [ABSTRACT FROM AUTHOR] |
