Investigation Of The Effect Of Shield Tunnel Constructed Under Viaduct In Sand And Weathered Granite

The work is based on the engineering example of tunnel crossing the viaduct Taiping spike Dongguan Shenzhen intercity railway project, using the methods of theoretical analysis, field measurement data analysis and numerical simulation, is devoted to the study of the following issues:(i) the influence law of the single line tunnel and double line tunnel construction on Soil, pile foundation and surrounding environment;(ii) the rule of stratum loss changes of soil deformation, the influence of internal force of tunnel lining;(iii) the buried depth of the tunnel and the grouting effect rule of the existing bridge structures. The main results are as follows:(1) Complicated stratum shield also pass through the combination of sand and weathered granite, high physical and mechanical properties of difference between the two, cutter soil cutting disturbance is easy to cause sand liquefaction; at the same time, hard and soft soil have different cutting difficult easy degree, sand easy cutting and quickly into the soil compartment, and difficult to broken rock, this directly affects the establishment of excavation face earth pressure balance. Construction control areas by jacking force for the next area of jacking force 2.1 times around the region, control of jacking force balance to ensure the accuracy of the axis, to realize the stable control of excavation.(2) The research and analysis of shield crossing construction parameters change, the viaduct before and after research showed that: Shield Crossing the viaduct, maintain the cutterhead torque constant, respectively, to the top of the thrust and soil tank pressure increased by 3.6%, 6.7%, can put the control in the 5mm within the limits of settlement pier, ensure the safety of bridge structure.(3) The effect of the rule of double line shield construction environment was studied by the analysis of engineering test data. Experimental results show that:①The ground subsidence history associated with the shield machine head position, the shield machine head through the rapid growth of settlement point, growth rate is less than 0.85mm/ days; each measuring point of the final settlement and incision through the measurement point driving velocity, settlement point relatively small test driving fast, slow driving test point settlement the amount is relatively large, even if the driving speed to 0(tool change during settlement), will continue to develop.②The deep soil settlement in shield machine head through measuring points before and after the development of about 15 days in soil obviously, located near the settlement of tunnel buried depth of 9~15m maximum, with the increase of depth, the settlement is gradually reduced.③The earth pressure by measuring points before and after 5~10 days to fluctuate in shield machine, with maximum depth of 9.5m~12.5m depth soil pressure change. soil pressure at different depths or up or down, or 28.5% of the largest, the largest decline in 17.9%.(4) This study analyzes the impact of the loss ratio of the stratum of soil deformation and internal force of lining through numerical simulation, the influence of further research on the buried depth of the tunnel and the grouting on the pile foundation, study shows:①Influence of stratum loss of soil deformation and internal force of tunnel is nonlinear; stratum loss rate is greater than 2%, the rapid development of soil deformation; in the construction of double track tunnel, should be reduced as much as possible double difference of stratum loss; at the same time control each of the tunnel ground loss ratio should not be greater than 1.4%.②The pile top settlement decreases with the increase of the depth of tunnel, the grouting length decreases with increasing; in special geological conditions of Guangdong area and the combination of whole weathered granite sand under the optimal depth of 12~16m and tunnel grouting length should not be more than 8m.