Study On The Improvement Of Sandy Gravel Property In Foam

The shield tunneling method has been widely used in the urban subway tunnel,and the engineering geological conditions of the tunnel crossing the stratum have become the key factors affecting the safe construction of the shield tunnel.Our country has a vast territory and the geological conditions is very complicated,which can lead to many technical problems,when crossing the special and complicated geological conditions,need to be solved.The sand gravel stratum in sandy pebble soil has the characteristics of internal friction angle,poor fluidity,permeability coefficient,the shield construction sand and cobble stratum will cause difficulties,unearthed cutter wear,spewing groundwater and other issues,has a great impact on driving efficiency and economic benefit of the shield,Therefore,it is of great practical significance to carry out the experimental study on foam modified sandy pebble soil.The main contents and results are as follows:First of all,the foaming agent solution with the concentration of 1%,2%,3%,4%,6%,and so on.It was found that the concentration of foaming agent had a significant effect on the half life and foaming rate of foam.The half life and the foaming rate of the foam are nonlinear with the increase of the concentration of the foaming liquid,and the foam is obtained.The foaming liquid concentration is 2%~3% when the rate and half-life are ideal;Through the mud optimization test on soil and water quality ratio of 1:9,1:10,1:11,1:12,1:15 bentonite mud,found the same soil water mass ratio of the Na-bentonite slurry viscosity is better than that of Ca-bentonite,the optimal soil water quality of Na-bentonite slurry ratio was 1:10,the optimal puffing time is 18 h.Second,a sand gravel stratum based on Chengdu Metro Line 7 mixed gravel content was 20%,40%,60%,the 80%,through the incorporation of foam,the indoor large shear test,slump test and permeability test,with foam injection rate increases,increases the bubble and soil sand pebble soil with bubbles in soil the composition of gravel wrapped in foam and foamed soil,shear strength and internal friction angle decreases nonlinearly,the slump increases gradually,the impermeability is improved obviously,and the different content of stone sand pebble soil in shield construction to meet the ideal condition of the "soil" requirements of the foam injection rate.Finally,according to the content of stone used alone foam modified 80% sand pebble soil effect,using foam mud mixed indoor improvement on the test,found that foam injection rate of 30% with the slurry injection rate increases,increasing the viscosity of sand pebble soil,sand separation phenomenon gradually disappeared,the shear strength and internal friction angle a nonlinear decrease,the slump increases gradually,and the improved soil permeability has not been significantly improved,at the same time,improved formulation parameters of sandy pebble soil stone content 80% ideal for foam injection rate of 30%,slurry injection rate was 15.3%.The above research results has certain practical value and guidance to determine the improving scheme of sand pebble soil,on this basis,the mechanism of modified of the sand pebble soil has been studied deeply.