| The anhydrous sand pebble stratum is a typical mechanically unstable stratum.Due to the few cohesive forces between the pebble particles,it is very easy to break the original balance of the pebble soil particles during the rotary cutting of the cutter during the shield construction.The state causes the excavation face and the cavity wall to lose stability,and the "chain reaction" type causes the surface deformation.Urumqi City Rail Transit Line 1 Civil Engineering 16 Xuan Rentun Station ~ Dadiwopu Station shield section is a shallow tunnel buried under the loose pebble backfill area,the porosity of the pebble in the backfill area is >40%,and the grain size is larger than 60 mm.The material accounts for 70%,while the pellets less than 2mm only account for 0.7%.The grading is single,without any cementation,and the self-stabilizing ability is extremely poor.Therefore,how to effectively carry out the reinforcement of the stratum and select the suitable synchronous grouting ratio becomes the key to the success of shield tunnel construction.In this paper,the key technical parameters of the earth pressure balance shield construction are studied in the pebble backfill area widely distributed in Urumqi,combined with the theoretical calculation of Peck formula,actual monitoring and numerical simulation.The specific work is as follows:(1)Select the classic Peck formula,based on the pebble stratum characteristics and shield parameters,use the actual monitoring of land subsidence data inversion and linear regression to correct the single-line Peck settlement prediction formula of the left-line tunnel.On this basis,consider the construction superposition effect.The modified twoline Peck settlement prediction formula applicable to the stratum condition of the backfilling area is analyzed and the parameters such as the tunnel spacing,the buried depth of the tunnel axis and the soil loss rate in the two-line Peck settlement prediction formula are analyzed.(2)For the engineering characteristics of the loose pebble backfilling area,the single-liquid inert slurry is selected as the synchronous grouting slurry,and the basic performance indexes of the grouting grout are evaluated according to the requirements of stratum excavation.The orthogonal test design is carried out,and the simultaneous grouting slurry test is completed.The sensitivity analysis of the main performance indexes of the slurry raw materials was carried out,and the optimal mixing ratio of the simultaneous grouting of the earth pressure balance shield in the pebble backfill area was finally determined.(3)In order to solve the stability of the shield tunneling surface and reduce the surface settlement to some extent,the pre-reinforcement paste grouting reinforcement before the shield tunneling is proposed,and the stratum valve to be cracked and infiltrated by the sleeve valve The compaction and other functions are combined with the soil to form a certain strength of the consolidated soil consolidation body and the dendritic network vein,which greatly improves the stability of the formation.The experimental study has obtained a ratio of grouting slurry to solid water suitable for the pebble backfilling area.And through a small test to verify its rationality and applicability.(4)Establish a three-dimensional calculation model of parallel two-line shield with MIDAS/GTS NX,and study the surface deformation control of the loose pebble backfill area in shield construction.The deduced Peck settlement prediction formula is compared with the measured data and numerical simulation data to verify the applicability of the formula in the backfill zone and the accuracy of numerical simulation.The numerical simulation is used to investigate the influence of various factors on surface settlement in grouting reinforcement.According to the simulation results,the suggestions for controlling surface settlement during actual construction are given. |
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