Study On Construction Technology Of TBM Pear Gravel Backfill Grouting In Water Source Project Of Lanzhou

The full-section tunnel boring machine was used for construction the Liujiaxia Reservoir Water Source Project in Lanzhou City.The TBM(Tunnel Boring Machine)had many advantages such as rapid excavation,stable lining of prefabricated segments,and has been popularized in the construction of water conveyance tunnels.In the TBM construction process,TBM excavation,prefabricated segment lining,pea gravel backfilling and grouting were the three major control links of TBM construction.Among them,pea gravel backfilling and high-efficiency grouting technology were the quality guarantee after the formation of TBM tunnel.These restricted the quality of the forming tunnel and determined the success or failure of the TBM construction project.At present,TBM pea gravel backfilling and high-efficiency grouting technology are still in the state of exploration at home and abroad.In practical engineering applications,the lack of mature construction techniques and specifications can be used for reference.In this paper,the compaction degree and high-efficiency grouting technology of TBM pea gravel backfilling were studied.It is of great significance to solve the technical difficulties of TBM pea gravel backfill grouting and make it reach the domestic leading level.Based on the TBM construction project of water source in Lanzhou,and through the theoretical study on TBM bean gravel grouting support,laboratory material performance test,outdoor grouting technology test,and the grouting system reformation,pea gravel backfill grouting compressive strength test for core samples,the TBM pea gravel backfill grouting construction technology were studied.The following conclusions were drawn:(1)The longitudinal force of the prefabricated segment was analyzed.The results show that the first and second ring segments are subject to the frictional force of the TBM shield and the thrust decreases linearly.From the third ring to the fifth ring,since the cement mortar is in the initial setting period,the friction force provided to the prefabricated tube piece is limited,so the thrust maintains a relatively stable state.From the fifth ring to the eighth ring,the thrust of the segment is rapidly reduced until the cement mortar behind the prefabricated segment is gradually condensed until it reaches zero.Therefore,when installing prefabricated segments,it is necessary to pay attention to the installation of prefabricated segments of the first 8 rings to avoid the problem of misalignment due to thrust.(2)The combined support characteristics of the pea gravel grouting backfill layer and the prefabricated tube sheet were studied.According to the three indexes of stress sharing ratioU_p,deformation ratioU_u and stiffness reduction coefficient K,the backfill grouting layer of pea gravel was determined between prefabricated tube and surrounding rock.It mainly plays the role of transmitting stress and deformation,and does not improve the support stiffness of the combined support.(3)The backfilling grouting material of pea gravel was studied.In pea gravel,cement,water glass and additives can meet the regulatory requirements under the premise,the gradation test has been used to determine the gradation of pea gravel.(4)The grouting material was designed,and the strength of slurry was calculated according to the specifications.Through the test of slurry characteristics of different grouting slurry water to cement ratio,the mixture ratios of normal pressure section and water rich tunnel section were 0.60:1 and 0.55:1,respectively.(5)Through the process test and the field bottom arch grouting test,the TBM pea gravel backfill technology was improved,and the technology of quick setting cement slurry was improved through the simulation of bottom arch and double-slurry grouting test outside the tunnel.The bottom arch grouting slurry can achieve the purpose of rapid setting,drainage and full filling under the condition that the cement paste mixture ratio was 0.6:1 and the water glass content was 4%of the cement weight.(6)The grouting system was reformed,and the change of the pea gravel tank feeding port to the hydraulic opening and closing system reduced the safety hazard.The capacity of the original equipment of TBM was added to solve the problem that the original equipment could not continuously grouting.The trailer tail was equipped with a three-cylinder pump and a slurry tank for the trailer tail to independently complete the lumbar top arch cement mortar.The trailer's tail grouting not affected by the driving change step and the quality of grouting could be ensured.In this paper,the improvement of the construction technology of TBM pea gravel backfill grouting was studied.It has a high engineering application value for guiding the pea gravel backfill grouting construction similar to the TBM project.