Study On The Optimal Selection Of Multi-way Branch Vertical Shaft Structure In Mining Cable Tunnel

The situation of urban development is becoming more and more serious,and the power load is more and more heavy.Cable tunnel emerges as the times require.The shaft is vertical tunnel that excavate at the top of the tunnel and connect with tunnel,as the intersection of the field of excavation engineering and tunnel engineering,the selection of the design concept depends on the type of supporting,the choice of the supporting type mainly depends on the geology,hydrology,surroundings and purpose.The depth of mining cable tunnel is greater than 10 m in general,the vertical shaft’s depth from 10 m to 30 m in Shijiazhuang area had been studied by means of MIDAS GTS NX finite software,the main works are as follows in this paper:(1)The clearance dimension of three or four-way branch typical shaft were recommended,which cross section shape is square and circular,combined with the characteristic and the sphere of application of the relevant supporting structure,the suitable supporting type and the detailed supporting scheme were selected for Shijiazhuang.(2)Soldier pile wall supporting calculation model of 10 m,15m,20 m,25m and30 m were established,the finite element analysis was carried out from two aspects:pile diameter changed,net spacing between pile unchanged and pile diameter unchanged,net spacing between pile unchanged,the change regularity of displacement field and internal force field were obtained,and taking the simple economy and applicability into consideration,the suitable supporting type of retaining piles for different depth of shaft were recommended.(3)Shotcrete and rockbolts supporting calculation model of 10 m,15m,20 m,25m and 30 m were created,which shape is square and circular,the change regularity of displacement field and internal force field were analyzed.In this paper,the radial load of circular shaft was discussed,and the design method of circular shaft structure in the load structure method was summarized.combined with the simple economy andapplicability,the suitable supporting type were obtained.(4)Taking the four-way branch vertical shaft called F7 in the 220 kV power tunnel project of Kunlun main street in high-tech zone as the engineering background,Establishing the calculation model of real working condition,the correctness of numerical simulation was verified by comparing FEM results with in-situ monitoring,besides,the influence of advanced small pile grouting on the shaft was analyzed,and numerical simulation of tunnel excavation sequence at the bottom of the shaft was carried out,Some suggestions of ingate construction were provided.