Analysis Of Key Technology Of Treatment To Multilayer Large Goaf Underlying Railway Subgrade

In recent years, with the rapid development of railway engneeering construction, the problem of coal mine and its goaf could not be avoided in many newly-built projects, and the goaf has a more and more important influence on railway construction. Stability evaluation of the goaf beneath the roadbed under the railway additional loads, the remediation method, scope and depth under different loads, the stress and strain in the process of the remediation of the goaf, the residual settlement changes, the quality of the remediation of large and complex goafs and the safety evaluation of railway, all of which are technical issues needed to be urgently solved in the process of the remediation of the goaf beneath the railway.The newly-built railway named Dongdu-Pingyi line goes through the mine of Shen village in the section of DK1+360-DK3+700, acrossing a large complex multi-layer goaf. The mining goaf is about2.16km with a long history, presenting a characteristics of large-scale, multi-layered, mining without rules, complex conditions of hydrogeology and engineering geology, incomplete mining data and repeated exploitation. The goaf deformation causes the ground and the houses to deform, subside, even to sink. It has a characteristic of both large subsidence basin and small coal mines with ancient empty area collapse, which is the largest goaf once acrossed in the railway construction of our country. The existence of the goaf will affect the construction and the normal operation of the Dong-ping railway. The total cost of remediation measures in the preliminary design is up to180million RMB, accounting about15%of the static investment.Taking the such goaf as the research object, based on the geological data and physical and mechanical parameters of the overburden rock, this thesis focuses on the following three key technology:1) The roof rock stability of quantitative analysis and evaluation based on the three-dimensional geological model. According to the deformation characteristics of overlying strata of the goaf, the collapse on the surface and residual deformation of surface mobile basin are respectively analyzed, the critical burial depth for security of each mined coal and residual deformation of moving basin of each section under the newly-built railway line are also calculated and the roof stability beneath the railway is then evaluated. In order to reduce the processing layers and the depth, the four representative three-dimensional geological models are established in the test section, according to the different sections with different distribution of engineering geology characteristics along the railway. And then the stress and strain of the surrounding rock and stability on the roof of each mining layers before and after grouting are analyzed and simulated. So the grouting reinforcement depth and layers of the multilayer goaf along different sections are proposed, that is, taking DK2+200as an example, the grouting for reinforce in that point is only up to the13th layer to the small mileage, while to only up to the15th layer to the big mileage.2) The determination of the key parameters of the ratio of grouting material. To save the engneering cost, indoor and outdoor tests of grouting material mixed with fly ash cement grout ratio are performed, such as test of different water-cement respectively under different ratio of cement and fly ash and different ratio of solid particles, test of different ages and test of compressive strength after the mixed slurry condensation. On the basis of the analysis of the test results, the optimum mixture ratio of the ash cement-fly ash is proposed.3) The comprehensive detection method of grouting treatment in the test section. To ensure the grouting quality, the contrast of DC sounding and shallow seismic, cross-hole electromagnetic wave CT and elastic wave CT test and the grouting amount of checking holes and grouting holes before and after grouting are studied, based on the analysis on the earth geophysical characteristics before and after grouting in the goaf. On the basis of the test results, the comprehensive detection method of grouting treatment to large-scale multi-storey goaf is put forward, that is, it should combine point (check hole) with surface (electrical sounding), combine area (DC sounding) with local (electromagnetic CT、elastic wave CT), and study the contrast of grouting amount of checking holes and grouting holes, to ensure the detection accuracy and reliability of the grouting quality.