Research On Soil Replacement Reinforcement Technique By Unstable Excavation Face Of Shield

During the shield construction,sometimes,the worker had to do conduct of removing the mud cake,checking and replacing cutter in cutter chamber,whereas they could not directly open the cutter chamber while the formation was unstable,normally only choose the method of ground reinforcement or compressed air to do the further process.However,the method of ground reinforcement costed higher and took long duration,and the ground of reinforcement could not be determined in advance even unsuited to reinforce.Hence the method of compressed air could take advantage of compressed air to stop water and support excavation face,which method had the advantages of lower cost and shorter construction period.Nonetheless due to the air could not to be held in loose and poor stability formation,(such as sand layer,granite residual soil layer,etc.),the method could not to be applied smoothly.In weak loose formation,the cutter chamber excavating dirt would result in the state of stress concentration in surrounding rock soil caused by excavation surface unloading.The rock and soil,which couldn't bear the role of stress concentration,would move in the cutter chamber and a caved area was formed.After the caved area generating,the stress state of rock and soil would change again,which cause the second collapse,and this collapse would orderly and gradually develop from excavation face to the ground.During the developing of caved,if compressed air could be used to temporarily strengthen rock and soil while the worker injecting solidified slurry into the collapse,then the unstable part of rock and soil had been replaced by solidified slurry,the cutter chamber operation therefore was safe.Base on above opinion,the paper carried out the study on soil replacement reinforcement research on unstable excavation face of shield,the main contents are as follows:(1)To carry out the analysis and research of the shield tunnel excavation face stability,through adding the air pressure to provide the limit pressure actively lead the rock and soil collapse to form caved area,and the caved area is controlled in the range of safety(2)Pursuant to replacement and reinforcement technique,select replacement reinforcement materials.(3)To carry out the mixture ratio test of non-coagulated slurry and coagulated slurry,select the optimal slurry.(4)To carry out the test research on device of non-coagulated slurry to replace coagulated slurry.(5)Above research applied on construction cases.The above research leads to the following conclusions,putting the extreme support air pressure on excavation face during the tunneling could formed a temporarily safe and stable collapse area to satisfy the requirement of replacement and reinforcement.It is practicable that using three-dimensional wedge shape calculation model calculate the extreme support air pressure forming in collapse area.For taking non-coagulated bentonite slurry to replace coagulated bentonite slurry,the density difference of the two slurry were more than 0.16g/cm3 and the rate of replacement was above 90%,would be better.