Research On The Construction Control Technology Of Power Shield Tunnel Crossing The Bahe River

When the tunnel is constructed under the river,the shield machine is excavated in the water-rich sand layer with rich water content and strong permeability.During the construction,it is difficult to control the disturbance and deformation of the stratum.The high water head pressure makes the construction safety seriously challenged.Relying on the Xi’an 330kV Power Shield Crossing Bahe Project,this paper uses theoretical analysis,laboratory tests,numerical simulation,on-site monitoring and other methods to study the major risks and technical difficulties of power shields crossing the Bahe River,and propose safety control measures.The research results provide safety guidance for the construction of electric shield tunnels under the Bahe River,accumulate relevant engineering experience,and provide reference and reference significance for the shield tunnel construction of shield tunnels under the river.The main research contents and conclusions are as follows:(1)Apply the analytic hierarchy process and fuzzy comprehensive evaluation method to evaluate the risk level of the construction of the power shield under the Bahe River,and get the main risk factors with a higher level in the construction process,and get the conclusion:the power shield The construction under the Bahe River has "medium risk" and is easy to rise to "high risk".The major risks of shield tunneling are mainly derived from construction method factors and geological and hydrological factors.Therefore,reasonable and effective control measures need to be taken to reduce construction safety risks.(2)Taking silty clay and sandy soil as test objects,foaming agent and bentonite as modifiers,and slump test,adhesion test,direct shear test,and penetration test as evaluation indicators,the slag soil improvement test was carried out.The test results show that the optimal injection ratios of silty clay foams with different moisture contents are quite different;when the moisture contents are 18%,21%,24%,27%,and 30%,the optimal foam injection ratios are 70%,70%,and 30%,respectively.55%,45%,30%,22%,for the improvement of silty clay,water can be added first to increase the moisture content of the soil,and then foaming agent can be used to improve it.Sodium bentonite mud with a soil-water ratio of 1:8 can effectively reduce its permeability for sand,and the optimal volume addition ratios of fine sand,medium sand and coarse sand are 8%,10%,and 16%.The on-site slag discharge situation shows that the test results are good for shield construction improvement,the silty clay basically has no mud cake phenomenon,and the sandy soil has no face or screw conveyor spouting.(3)Comprehensively using the orthogonal test and numerical simulation methods,a three-dimensional model of the power shield tunnel passing through the Ba River was established,and the sensitivity of the soil bunker pressure,grouting pressure,and grouting layer thickness to the formation deformation was studied,and the power shield tunnel passing through the Ba River was determined.Main excavation parameters.The results show that when the maximum subsidence of the surface,the maximum vertical displacement of the stratum,and the maximum horizontal displacement of the stratum are used as the evaluation indicators,the primary and secondary order of the sensitivity are grouting pressure,grouting layer thickness,and soil bin pressure.Therefore,in the construction of shield tunneling through the river,the changes of synchronous grouting pressure and grouting amount should be controlled preferentially according to the monitoring data and parameter feedback,and the optimization and adjustment should be carried out in time.(4)Through theoretical calculation,the theoretical values of the total thrust of the shield,the torque of the cutter head,and the pressure of the soil bin are determined,which are compared and verified with the field-measured excavation parameters,and effective control measures are proposed for the main risks of construction.The recommended values for the tunneling parameters of the small-diameter electric shield tunnel through the Bahe River are:the total thrust is controlled at 9000kN,the cutter head torque is 11 00kN m,the soil bin pressure is 0.15MPa,the grouting pressure is 0.18MPa,and the synchronous grouting amount is 4.05～5.06m3,and the construction speed is kept between 20～40mm/min.