Full-scale physical modelling of fissure grouting in deep underground rocks

摘要

Parameters predetermination and grouting quality evaluation are of vitally importance issues for rock grouting. Because of emerged new features (e.g. high groundwater pressure) in deep underground rocks with depth of more than 1000 m, estimations on grouting parameters should be reexamined. Due to various aspects of the grout flow especially small sizes of major factors, full-scale physical modelling is considerably suitable for bridging the gaps between theoretical investigations and field works. In this paper, a full-scale physical modelling system is developed to investigate fissure grouting with high pressure in deep underground rocks such as deep coal mining. Developed modelling equipment can run smoothly under high grouting pressure (up to 45 MPa) and high groundwater pressure (up to 15 MPa). The aperture of fissure ranges from 0.2 mm to 8 mm. Surface roughness of the fissure, flow rate of grouts, initial viscosity of grouts to be injected, grouting pressure and time, groundwater, penetration length and permeability of grouted fissures can be qualitatively estimated or quantitatively evaluated.For evaluating whether a lower final grouting pressure could be acceptable in treatment of deep rocks with depth of around 1000 m via pre-grouting from the surface, both experimental trials based on developed physical modelling system and field study are carried out. Because of greatly increased gravity of grouts column in vertical holes, observed results offer a strong support to predetermination of a lowered final pre-grouting pressure (i.e. at 2 times of that of groundwater) within favorable reduced permeability in deep rocks. Measured effective penetrations are just 65-80% of maximum penetrations might due to adverse impacts of the groundwater with high pressure. It also reveals that grouted fissures can successfully stop predefined groundwater (i.e. 10 MPa), provided the length of well-grouted fissure is no less than 0.5 m in model tests. The results might call our special attentions to not only the adverse impacts of groundwater, but also the favorable effects on final grouting pressure caused by increased depth in pre-grouting in deep underground rocks.