Study On The Influence Of Pipe Jacking Through The Main Canal Of The Middle Route Of South-to-North Water Transfer Project And The Control Deformation Parameters

The main canal of Middle Route of South-to-North Water Transfer Project passes through Henan,Hebei,Beijing and Tianjin provinces（municipalities directly under the Central Government）with a total area of 155,000 square kilometers and a total length of 1432kilometers.With the continuous improvement of supporting facilities,there will inevitably be pipelines along the project and the South-to-North Water Diversion Middle Route Project crossing.Pipe jacking underpass is a common construction method for pipeline crossing,but the construction technology of some crossing projects is complex and there are many safety control factors,which inevitably affects the main canal.In order to select the appropriate deformation control parameters,minimize the influence of construction on the disturbance deformation of the main canal of the middle line,and provide security for the water diversion project,this paper carried out the research on the disturbance influence and control deformation parameters of the pipe jacking under the main canal of the middle line.The main research contents and results are as follows:Combined with the investigation,the disturbance effect of crossing the main canal under different construction conditions is analyzed.The influence of geological conditions,overburden thickness,grouting pressure,jacking pressure and rectification on deformation disturbance of main canal is analyzed.Based on the undercrossing project of’ Yinyue to An’diversion pipeline in Anyang section of the main channel of the central line,the deformation law and value of the soil under the main channel are calculated by using the Mindlin formula of elastic mechanics.The modified Sagaseta analytical formula was used to calculate the deformation law and deformation value of soil under the main canal caused by soil loss.The front additional thrust mainly causes the settlement behind the uplift of the soil in front of the excavation,and the influence of friction is similar.The deformation caused by both is small.The settlement deformation of the main canal is mainly caused by the formation loss.When the front additional thrust is 20 k Pa,the formation loss rate is 1%,the friction of the pipe jacking machine is 20.35k Pa,and the average friction of the pipe and soil is 5 k Pa,the final settlement displacement of the soil under the floor of the main canal is about 3.7 mm.The model of pipe jacking crossing main canal is established by FLAC3D finite difference program.Through comparative analysis of numerical simulation and theoretical calculation,the rationality of model establishment and simulation construction is verified.The influence of main canal disturbance deformation caused by pipe jacking construction with different front chamber pressure,grouting pressure,friction resistance,pipe jacking machine and pipe diameter difference,pipe jacking diameter and pipe jacking buried depth was studied.The deformation control measures are proposed as follows:when the normal operation is satisfied,the small diameter pipe jacking is selected as far as possible,and the friction effect is reduced by full grouting during construction.The diameter difference between pipe jacking machine and pipe section is controlled within 10 mm,so as to reduce the settlement of the main canal caused by stratum loss.The control deformation parameters are:the pressure value of the front chamber P=（0.72～1.29）P₀（P₀-the static earth pressure at the center of the face）,the grouting pressure value 1.0～1.1 times the overburden weight,and the buried depth of the top pipe is not less than 5 D（D-the diameter of the top pipe）.