Pipeline And Environmental Deformation Control Of Large Diameter Cross-river Concrete Pipe Jacking

In the development of urban underground space,large diameter concrete pipe jacking is widely used in drainage engineering and power tunnel engineering because of its low cost,short construction period and small environmental impact.When concrete pipe jacking requires long-distance construction across rivers,the interaction between pipelines and soils is complex,prone to large deformation and even accident risk due to unknown stratum conditions,complex environment and high water head pressure.Therefore,it is urgent to study the deformation mechanism and control method of pipeline and environment under the river bottom environment to ensure the safety of large diameter pipe jacking construction.Based on a large diameter concrete pipe jacking project in Shanghai,aiming at the characteristics of varying thickness of overburden soil and high water pressure at the bottom of the river,this paper discusses the influence of pipe jacking under the river on soil and dam deformation,and evaluates the deformation control effect of different alignment adjustment measures after pipe settlement,aiming at the problem that pipe jacking alignment is very easy to migrate in the soft soil layer at the bottom of the river.The main research results of this paper are as follows:1.Considering the change of the thickness of the overlying soil layer on pipe jacking and the influence of the high water head pressure on the bottom of the river,the whole process numerical simulation of large diameter concrete pipe jacking piercing embankment construction was carried out.The effects of support pressure,modulus of drag-reducing slurry and drag-reducing effect of slurry on the deformation of stratum soil and embankment were studied.The results show,reducing the support pressure of excavation surface can reduce the settlement of surface soil and dam,and reduce the uplift of surface soil above machine head.The specific support pressure of the excavation face in the concrete construction should be less than 10% of the self-weight stress of the soil at the center of the pipe jacking.2.The internal forces of the adjacent segments of large diameter concrete pipe jacking are simulated by numerical method at different deflection angles.Steel sleeve ring,weak cushion layer and rubber ring are set at the junction of the segments to obtain the internal forces distribution of the segments and joints.The results show,when pipe jacking subsides and there is a deflection angle between the segments,the internal force of segment is mainly concentrated at the junction of concrete and steel plate,and the most obvious is above and below.3.The alignment of pipe jacking with continuous settlement is numerically simulated,the distribution of internal force in pipe is analyzed,and the possibility of alignment adjustment is verified.The alignment adjustment of grouting lifting in situ is simulated at different grouting angles and different grouting positions at the bottom of pipe section in settlement section,and the lifting effect of each alignment adjustment condition is compared and analyzed.On this basis,a construction method of in-situ alignment adjustment for large deformation control of pipeline axis is proposed,which provides support for engineering implementation.