Experimental Investigation Of Propagation Mecha Nism Of Chemical Grout Injection Into Porous Media Under A High Pressure And Closed Environment

Quicksand is a common type of geological hazards in underground coalmines. Chemical grouting is one of the effective methods to prevent coalmines from quicksand hazard by grouting into the low permeable loose soil layers. The investigation of the propagation mechanism of chemical grout injection into porous media under a high pressure and closed environment will provide a theoretical basis for the grouting practice. Supported by National Natural Science Foundation of China, an experimental investigation of chemical grouting into sand under a high pressure and closed environment was carried out in this dissertation.The author has conducted nine scaled tests of chemical grouting under a high pressure and closed environment and one test under a low pressure. The spread model and propagation mechanism of chemical grout in porous media was investigated through a series approaches, which include: (1) analysis of the changes in permeability of the grouts during its curing process; (2) analysis of the changes of the pumping pressure and pore water pressure during grouting; (3) analysis of the characteristics of stabilized shapes; (4) anatomical observation on stabilized sand mass; (5) analysis of images by MATLAB and Photoshop software; and (6) comparison of the results with those from test under a low pressure, with in-situe measurements and the literature. The main achievements are as follows.(1) An engineering geological model for chemical grouting into saturated sand layer in the deep Quaternary System was established.(2) The design of high pressure grouting model was explained in detail, and a patented high-pressure grouting equipment was developed.(3) The concept of the"Flocculation time"was proposed according to the characteristics of the variations of grout infiltration capacity into porous media. The flocculation time was defined as the time interval from the moment the main agent and curing agent mixed until the moment the maximum diameter of the flocs was up to 2.0mm. This definition is useful for analyzing the infiltration capacity changes of time-dependent viscosity grout in practice. Based on the influence of dispersed particles on infiltration capacity of chemical grout in porous media, the grout curing process was divided into four stages: condensation; flocculation; gelling and curing.(4) The similarity for the scaled test of chemical grouting under a high pressure and closed enviromnet was analyzed. The experimental results show that the spread of chemical grout injection in saturated porous media under a high pressure and closed environment was categorized into three patterns. They are a) spherical spread, b) fingering spread and c) planar spread.(5) According to the analysis of experimental results, the propagation mechanism of chemical grouting under high pressure and closed environment into saturated porous medium was summarized into three types, and they are a) mechanism of"replacement to move forward", b) mechanism of"preferred path", and c) mechanism of"layering enrichment".(6) The macro-process and micro-process conceptual model of grout spread under high pressure and closed environment were established, the movement characteristics of grout in space from grout-outlet to exterior margin and during the time from the beginning to the end of grouting were discussed in detail.