Research On Backfill Grouting Material Of Metro Shield Of Nanning Expansive Rock Area

With the extensive application of shield construction techniques, increasing attention has been paid to study of backfill grouting material properties. If the grout performance can not adapt to the formation conditions and construction environment, it will lead to occurrence of disease such as ground settlement oversized, tunneling leakage and instability of the tunnel which brings adverse impact on to the subway tunnel construction and future operation, even a security risk. Currently research on backfill grouting material mainly carried out for certain engineering geological conditions and working conditions which lead to the limitation of applying to other projects. With the nature of swelling, dehydration shrinkage and repeated deformation in Nanning expansive rock area, researches against backfill grouting material of expansive rock area are rarely reported. Therefore carrying out researches against backfill grouting material of expansive rock area has practical significance. Acrossed the swelling rock region of Nanning Rail Transit Line1as the background, this paper mainly research on backfill grouting material of Nanning expansive rock area by indoor mechanical testing, model test and numerical simulation, the main results and conclusions are as follows:(1) Combining with swelling rock geological conditions of Nanning Rail Transit Line1,a evaluation system of backfill grouting material of expansive rock area is proposed by analyzing the characteristics of swelling rock and problem of backfill grouting material of metro shield;(2) Three different polypropylene fiber mixed ratio commonly used in engineering of0.9kg/m3,1.5kg/m3,2.0kg/m3are carried out for grouting material mechanical properties research such as compressive strength, splitting tensile strength, flexural test, and experimental results comparing with the common test block show that:grouting material mixed polypropylene fiber has little effect on its strength while the effect of toughness enhancement is obvious; when the mixed ratio is1.5kg/m3, it can come to the most obvious toughening effect; the deflection increases are more than30%compared to ordinary test block, when the mixed ratio is1.5kg/m3and above;(3) Carry out model test and numerical analysis of the swelling rock and grouting materials by own designed test apparatus (model is made of welded steel plate, body length300mm, width100mm, height600mm, and fixtures), the results show that:compared to ordinary slurry,32%of the expansion force can be reduced by fiber slurry under the same conditions; moment of the segment can be reduced by about30%When the expansion force come to160kPa, fiber slurry better meet the swelling rock formations compared with ordinary slurry.