Research On The Calculation Method Of Steel Pipe Jacking Force And Pipe Mechanical Characteristics In Rock Formation

With the deep development of urbanization construction,traffic congestion,construction noise and a series of"urban diseases"have caused serious impact on people’s lives,and the development and utilization of urban underground and space engineering can effectively avoid such problems.As a kind of non-excavation construction technology,pipe jacking method occupies an important position in the municipal underground pipeline construction project.The pipe jacking method usually focuses on the construction in the soil,the corresponding jacking force calculation theory and the research of the mechanical properties of pipelines have been relatively mature,and have been well verified in many practical projects.With the increasing development of pipe jacking machine,pipe jacking machine for rock strata is gradually applied to actual projects,but the research on the force condition of pipe jacking in rock strata and the calculation of pipe side friction resistance and face resistance is still in the initial stage.Based on a curved rock pipe jacking project of"one gate and three lines"water allocation project in Min-jiang estuary of Ping-tan,Fujian,this paper has carried out a detailed study on the law of stress change and contact pressure of pipe,and calculation of jacking force during the construction process through theoretical analysis and field monitoring methods,and the main research contents and results are as follows.(1)Based on the assumption of pipe and soil contact,the calculation model of pipe side friction resistance of pipe and rock under different contact conditions and construction state is established,the elastic resistance and cohesion between pipe and rock under full contact mode are considered,and the contact angle and contact pressure when pipe and rock are partially contacted are derived by combining Hertz and Persson elastic contact theory,and on this basis,a pipe slag contact is proposed according to the actual field situation model,which is probabilistically distributed along the sinker zone.Finally,the calculation model is validated and analyzed according to engineering examples,and the results show that:in soft rock strata,the jacking force calculation results in full contact condition overestimate the actual measurement,while the calculation results based on the Terzaghi theory method in hard rock strata can better evaluate the actual.Under the slurry injection condition,the pipe and rock are in point or line contact model under ideal conditions when considering tunnel stability.When considering the pipe and slag contact compound reality,the measured curve is basically enveloped between the upper and lower limits of pipe slag contact when the slag zone is occupied along the line.(2)In the curve jacking state,with reference to the"Construction Procedures for Water Supply and Drainage Pipelines",considering the additional coefficient of curvature,combined with the pipe slag contact model in the straight-line jacking state,a curve jacking force calculation model was established,and it was shown through engineering example verification that when the curve steel pipe jacking in the rock formation,the curvature additional coefficientK_c was real,and when the radius of curvature R=3000D pipe diameter,theK_c value after fitting was 1.12,and the error allowable range could be directly considered for calculation of the straight-line jacking model.(3)Considering the penetration resistance of steel pipe in hard rock stratum when the tool interacts with the rock,and based on the dynamic balance principle of mud and water balance between the tool plate and the soil and water pressure on the palm surface,the head-on resistance calculation method of pipe in hard rock stratum is proposed,which consists of two parts:the combined force of the frontal thrust of the hob and the static water pressure in front of the tool plate.Combined with the field engineering example shows that:in hard rock formation,the penetration resistance of the tool is an important part of the topping force,the frontal thrust of the hob obtained by CSM model is greater than the static water pressure,the combination of the two is in good agreement with the measured head-on resistance value.(4)Through the field monitoring test,the pipe stress distribution law and pipe rock contact pressure change law of pipe jacking under different construction conditions were obtained.The monitoring results show that:under the effect of continuous jacking,the circumferential stress changes are relatively stable,the change law is not obvious,the same monitoring section shows completely opposite trend at different jacking positions,the overall performance of the value is top≈bottom>left≈right,which is mainly influenced by the grouting pressure,stopping time and stratigraphic changes,and the grouting pressure plays a controlling role;the pipe axial stress is locally shown to be under tension,and the same monitoring This is due to the fact that the pipeline is easily in the spatial curve under the joint action of grouting and deflection,which makes the inner side of the bend bear extra grouting pressure while the outer side of the bend generates extra rock resistance;the measured points of pipe and rock contact pressure show the values is bottom>top>left≈right,which is basically consistent with the performance of circumferential stress.Under the continuous loading condition,the axial stress is significantly affected by the top force loading,and each measurement point shows a sudden increase after the resumption of jacking;the circumferential stress has a certain increase in each measurement point under the influence of coupling deformation,but the change trend is not obvious;after stopping jacking,the pipe rock contact pressure shows an obvious fall back,which is mainly related to the withdrawal of grouting pressure,linear direction and other factors.