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Research on the Stratums Movement Law Due to the Ultra-large Box-culvert Jacking

Author: ZhangJian
Tutor: HuangShengGen
School: China University of Geosciences
Course: Disaster Prevention and Reduction Engineering and Protective Engineering
Keywords: box-culvert stratums movement numerical simulation pipe-roof
CLC: U449.5
Type: Master's thesis
Year: 2007
Downloads: 173
Quote: 2
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Abstract


The pipe roof box culvert jacking method has been one of the main construction methods in the underground engineering in our country. The construction technology with box culvert jacking is being widely used in building underground engineering because of its unique characteristics and advantages such as intelligence, safety and quickness, etc. The main issue considered both in the design and construction is controlling of the stratum displacement and keeping the safety of the busy expressway. So, how to summarize the stratum displacement patterns has guiding significance for the design and construction in the future.The stratum displacement induced by the box culvert jacking is researched with theoretical method in the paper. The theory of soil loss caused by the box culvert jacking is researched. The soil loss can be divided into normal loss and abnormal loss, and it is necessary to take effective measures to minish the soil loss. The theories of pore water pressures are studied. The superimposed load and soil disturbance will be induced by propulsion of box culvert jacking. The excess pore water pressure will be caused in the soil around the box culvert. The soil disturbance can be evaluated by analyzing the variety of pore water pressure, and it is a sensitive index. In the pipe roof box culvert jacking process, the pipes are installed in the soil around the box culvert, and it is important during the tunnel construction to some extent. The pipes can be regarded as the initial support in the tunnel construction. To analyze the interaction mechanism exactly has significant meaning. By analyzing the mechanics action of the pipe roof in the construction process. The steel tubes are regard as the elastic foundations above Winkler foundations. Some theories are concluded. The disturbance of soil induced by injection is studied, includes the injection mechanism, the seepage behavior of mud on soil around the box culvert and the injection effect. The grouting has lubricating and supporting function during the construction. The grouting can minish the culvert-soil contact friction and the soil deformation induced by the box culvert jacking. If the lubricative slurry can form more integrated mud layer system around the culvert, the effort of antifriction will be quite perfect. To supply mud for the latter culvert during the advancing is necessary, and the pressure of mud in the gap between the soil and culvert will be in accord with the soil pressure all the time.The paper is based on the subway project crossing under Beijing-Zhuhai expressway located in Zhengzhou. Based on the in-situ data, the numerical simulation of the stratum displacement during the whole construction process is studied systematically by using FLAC3D computer programming. The numerical simulation will mainly consider the stratum movements induced by the box culvert jacking because the stratum movements induced by the pipe roof jacking is very small during the construction. The construction process will be simplified in the numerical simulation, and the effect of factors including the soil pressure on the face of excavation and the grouting pressure will be regarded. The earth pressure on the surface of excavation is based on the original earth pressure on the excavation face, and the force applied on the face of excavation is according to 1.0 times of the original earth pressure during the simulation process. The equivalent layer is substituted for the slurry in the numerical simulation. The simulation will regard the varied mud pressure. The research includes the vertical movement distribution of pavement, the horizontal movement distribution of pipe roof composites, and the horizontal movement distribution of the foundation. By the analysis and comparison of them, the stratum displacement patterns induced by the culvert box jacking is summarized during the process of numerical simulation.The in-situ stratum displacements induced by box culvert jacking construction are monitored. The in-situ testing includes surface deformation, sub-surface movements, pore water pressures, the total jacking forces of box culvert, culvert-soil contact stresses, under ground water levels, deviations in line and level of box culvert. The basis theory and method of in-situ testing are introduced. The results of field-testing are analyzed, and the variety of testing datum include earth pressures, pore water pressures and underground water levels during the course of the construction are studied. Base on the result of monitoring and the problem detected by the monitoring, the process of construction is guided. By combing the analysis and comparison of the site measured results and numerical simulation results, the stratum displacement patterns are summarized. The measures for protecting neighborhood circumstance and relevantly controlling measures for minishing the stratum movements during culvert box jacking are studied.By the calculation and analysis, some results are gained:(1)The grouting has great effect on the stratum movements in the process of box culvert advancing. As the advancing of the culvert box, the effort of grouting descends obviously, and it is necessary to supply mud for the latter box culvert. The grouting pressure should be controlled reasonably. During the numerical simulation, the value of grouting pressure has great effect on the vertical movements of pavement, and the pavement ascends gradually as the increasing of grouting pressure. And the value of grouting pressure has little effect on the horizontal stratum movement.(2)The patterns of the point movement on the pavement can approximately be divided into four steps including little rise, little subsidence, quick subsidence, slow subsidence. The greatest subsidence of the pavement is not on the axis but in the domain, and the distance between the domain and the axis is about half of box culvert span. Reinforcement and treatment is the key in the domain. The stratum movement is controlled by minishing the axis deviation and minishing the gap between the box culvert and pipe roof as far as possible. (3)The deformation area on the pavement induced by the box culvert jacking is very large. The distance between the effected domain and the axis is more than 100 meters. The distance between the mainly effected domain and the axis is less than 25 meters. Because of the support of pipe roof, the pavement does not appear great subsidence in front of the excavation face. The deformation of the pipe roof is continuous. Induced by the deformation of the pipe roof in front of the excavation face, steel tube behind the excavation face will generate little increase and the face of pavement heaves.(4)According with the same elevation of the box culvert axis, the soils in front of excavating face generate the biggest horizontal movements. The soil displacements become small more than 15m below the orifice, and the location is approximately 6m below the bottom of box culvert. The disturbance of the soil at the location is very slight. The box culvert jacking has slight effect on the disturbance of the soil more than 30m below the orifice.(5)The pore water pressure in the front soil will ascend when the advancing velocity of box culvert is larger than the velocity of excavating on the working face, or the pressure will descend. The pore pressure is a sensitive and exact index for monitoring the vibration of soil in the process of box culvert jacking. To evaluate the vibration of soil, monitoring pore water pressure is more effective than monitoring the sub-surface movement. Monitoring the variation of pore water pressure is the first choice regarding different choices of monitoring scheme.(6)The increase velocity of horizontal movements on the pavement descends gradually in the process of the box culvert jacking. During the same step in the construction, the point movements of the pipe roof composites are the biggest. The movements of pavement are the second, and the movements of foundation are the smallest. The horizontal movements of pavement are equal to the composites approximately.(7)The pipe roof box culvert jacking is studied by 3-dimension simulation considering Mohr-Coulmb criterion. The result of the simulation is the same as measurement on the whole. The results can reflect the trend of the stratum movement on the whole.

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CLC: > Transportation > Road transport > Bridges and Culverts > Culvert > Construction
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