科研之友
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摘要
One of the significant aspects of permeation grouting is the prevention of soil fracturing during construction. In this study, a newly designed laboratory apparatus including an overburden pressure modelling system, grouting chamber, grout injection control system, back-pressure monitoring system, and high-efficiency grout mixer is developed. A wet-raining method is adopted to prepare two 45-cm-diameter, 50-cm-high, poorly graded sandy soil specimens. A bleeding test is first conducted to select a cement-bentonite mixture with minimal bleeding. A series of both water injection tests and grout injection tests are carried out to investigate the threshold seepage velocity, the fracture initiation pressure, and the factors affecting the fracture initiation pressure, using a plot of injection pressure (p) against injection rate (q). In the water injection test series, tests are repeated at two effective overburden pressures, 49 kN/m(2) and 98 kN/m(2), and in the grout injection test series, tests are carried out at an effective overburden pressure of 98 kN/m(2). The initial orientation of the fractures and their subsequent development are mapped and discussed. In the future, the fracture initiation pressure and the threshold seepage velocity can be evaluated by reference to the p-q curve suggested in this paper using a series of modelled p-q curves for different overburden pressures. Prior to field permeation grouting work, trial grouting is deemed necessary to verify the correctness of the obtained laboratory results, in order to prevent hydrofracturing of the soil.
