| Based on the long-distance tunneling practice of a10.22-m diameter earth pressure balance (EPB) shield on Beijing subway Line14, and making good use of the existing shield tunneling technologies and experiences, the ground surface movement law and corresponding control technologies of rapid tunneling of the big diameter shield was studied by means of theoretical analysis, numerical calculations, in-situ measurements and indoor tests. The highest level attained of the big diameter EPB shield tunneling is641m per month and on average the driving length is492m per month. The finding presented are of great significance and helpful to the innovation of line layout and construction method of Beijing subway from the traditional "double-tube-double-line" to the "single-tube-double-line". The six main technologies involved are as follows.1) The big diameter shield tunneling induced ground surface movement(1) The ground surface settlement trough conforms to the Peck curve (Gauss curve). The maximum settlement of ground surface is about12.0-36.4mm, which is12.0-25.9mm in case of clayey roof soil, and20.4-36.4mm in case of sandy roof soil.(2) The ground surface settlement trough width coefficient is proportional to the tunnel depth, and the coefficient of proportionality k is about4.7and the ground loss ratio0.40%on average in case of the clayey roof soil; and the coefficient k is about3.5and the ground loss ratio0.45%on average in case of the sandy roof soil. Overall the ground loss ratio is around0.31-1.04%.(3) There approximately exists the expositional relation between the ground loss Vs and the grout injection ratio; the ground surface maximum settlement and the settlement trough width decrease with the increase of the grout injection amount and the earth chamber pressure field observations show the grout injection ratio of145-175%attains a good control of the ground surface settlement.2) The ground surface movement prediction method(1) Based on the least square support vector machine (LS-SVM), the model was set up to predict the ground surface maximum settlement and the ground surface settlement trough width. Different from the traditional prediction methods the LS-SVM model, convenient for engineering applications, can take into account the effects of the crucial technical parameters of shield tunneling, the tunnel depth and mechanical properties of the roof soil on ground surface settlement.(2) Calculation results show the RBF kernel possesses the higher statistical learning and generalization ability in comparison with the linear and the polynomial kernels, and it is especially suitable to the modeling analysis of the ground surface maximum settlement and the settlement trough width.(3) Using the LS-SVM model, the explicit expressions of the ground surface maximum settlement (the settlement trough width) and relevant influence factors can be gotten. Therefore, the action mechanism between the important characteristic parameters of the ground surface settlement and corresponding influence factors can be more clearly displayed.3) The key start technologies of the big diameter shield(1) The successful launch of the big diameter shield shows that using jet grouting to reinforce ground is feasible mainly according to the engineering experiences and the safety factor of2.7for the thrust load of the reaction frame is on the safe side. It is sensible that adopting measures before assembling the partial segments to guarantee the erection quality of the segments, and that laying out steel plates on tracks to allow trolleys turning along the small radius curve. The above ways of doing provide good references for similar engineering projects.(2) The setting installment precisions of the starting reaction frame and the base are reasonable for the difficult launch conditions of the350-m radius curve and the27%o longitudinal slope, which meet the demand of the big diameter shield starting.(3) Theoretical modeling and calculations show the reverse torque from the friction between the shield and the base can't meet the demand of rotary cutting of the cutter head during the big diameter shield starting, and measures against turning around of the shield body must be taken.4) Technologies of soil conditioning and mix ratio of simultaneous backfilling grouting(1) The schemes and methodologies for soil conditioning and backfilling grouting meet the demand of convenient for engineering applications and are successful, including the soil conditioning plan with foam of5%concentration and slurry of8%concentration, and the equipment of slurry and foam device for mixing the conditioned soil, the separate layout of the pipelines, and the amount and locations of the additive injection ports.(2)The practice shows it is successful that the simultaneous backfilling grouting plan using the two-liquid type grout with mix ratio of water:cement:slurry:retarder=1:1:0.3:0.013, together with the injection amount per ring of14.1-15.3m3.5) In-tunnel movable trolley station system(1) Breaking through the limitations of the traditional fixed stations, a new type of in-tunnel movable double-turnout-four-track station, fitting for different slopes and easy for quick erection and crucial to the higher efficient in-tunnel horizontal transport, was put forward and help realize the advantages of safety, high-speed and environment protection of the big diameter shield tunneling.(2) The models for station locations and transport distance provide the results of station locations of1km and1.7km away from the starting shaft, which give good references for building long and big tunnels of other types.6) Control technologies of adjacent construction(1) The core of small disturbance of the10.22-m diameter shield tunneling centers on the active control system consisting of reasonable selection of shield driving parameters, well prepared plan of soil conditioning, comprehensive grouting and etc., together with performing status detections of nearby surroundings and adjacent structures, numerical simulation of the construction process, and taking necessary measures to reinforce the ground and structures in close proximity, according to complexities of the surrounding conditions.(2) The equipped function of the active articulation and reasonable manipulation of the shield machine is of paramount importance when tunneling along a small radius curve, which is one of the key technologies of the big diameter shield attitude control and of reducing tunneling induced ground disturbance. While perfect information construction and timely feedback of measured data are the guarantee of strict control of ground settlement by means of the simultaneous backfilling grouting and the secondary grout injection through segment holes. |
PDF Full Text Request