Research On Preferential Flow Dissolution And Surface Deformation Of Tunnels In Residual Soil Layer Of Water-rich Granite

The Water-rich weathered granite strata have the characteristics of uneven weathering,softening with water,disintegration and loss with water.Among them,the composition of fully weathered granite is uneven,and pore water occurs;strong weathered granite is a fractured rock body,and fracture water occurs.When the tunnel passes through the fully weathered and strongly weathered water-rich granite formation,it is easy to form large pore preferential flow and fissure flow in the overlying stratum of the tunnel,and the formation of preferential flow will cause the dissolution leakage and complete Long-term anchor bolts have a loss of bond strength dissolution,which affects the durability of the tunnel 's supporting structure.At the same time,as the seepage continues,the amount of water in the tunnel increases,and fine particles in the overlying soil layer will also be lost with the water,which will cause the surface Subsidence and deformation induce geological disasters.In view of this,this paper mainly studies the formation mechanism of preferential flow in the water-rich uneven weathered granite stratum overlying the tunnel,the durability of the grouting material in the tunnel caused by the continuous seepage of the preferential flow,and the prediction of the ground settlement deformation caused by the seepage and water inflow in the seepage tunnel.The main research content and results are as follows:(1)Mechanism of preferential flow in water-rich and unevenly weathered granite formations.Combined with the Jun Chang tunnel engineering background,the overlying stratum of the tunnel was surveyed by high-density electrical method and inter-hole CT method.According to the results,there is a clear preferential flow phenomenon in the unevenly weathered granite stratum.By comparing the detailed survey data of the stratum and inversely analyzing the mechanism of preferential flow formation,it is concluded that when the permeability difference of the soil layer exceeds 2 to 3 orders of magnitude,the preferential flow phenomenon will occur,and the preferential flow seepage will take away the soil layer.The fine particles,which are lost with water erosion,affect the surface of the tunnel and produce uneven settlement.(2)Comparison of anti-erosion performance of tunnel grouting materials.Due to the existence of preferential flow,the continuous leakage causes the corrosion damage of the grouting material in the tunnel.The chemical erosion method was used to evaluate the anti-erosion performance of the tunnel grouting material.The comparison found that when the fly ash content was between 15% and 30%,the anti-erosion performance of the tunnel grouting material was significantly improved.At the same time,the erosion loss of curtain grouting plus solid and anchor bond materials is evaluated.Based on the erosion equation and erosion flux j,the erosion durability calculation of grouting material is derived.Combined with the specific engineering background,the quantitative calculation and prediction of the change of the dissolution depth with time,as well as the corrosion durability of the grouting curtain and anchor rod.(3)Prediction method of surface deformation caused by tunnel preferential flow leakage.Due to the phenomenon of preferential flow,the fine particles in the stratum will be lost with water,and the seepage will take away the soil particles and water in the overlying soil layer,resulting in an increase in the effective stress of the overlying layer of the tunnel,causing settlement deformation on the surface.Combined with the specific engineering background,through the establishment of a single well pressure pumping model,the Theis function is derived and calculated,and the quantitative calculation formula of the surface settlement curve and the influence range caused by the tunnel seepage is obtained.With reference to the influx of water within a reasonable influence range,Guide the design of the water-proof and drainage facilities inside the tunnel to ensure the safety of the tunnel structure and the surface of the overlying soil layer.