Study On Key Technology Of Large Section Rectangular Pipe Jacking Construction In Shenzhen Metro Line 9

With the rapid development of urban infrastructures construction in China,the development and utilization of urban underground space has become the necessity of urban development in the new century.Pipe-jacking construction method is often used in the development and construction of urban underground space;it is a kind of laying technology with not open excavation or less open excavation in the ground surface for pipeline construction.It has many advantages,such as little influence on the surrounding environment,no need of a large number of relocation pipelines,no obstruction of traffic,short construction period,high construction safety,low comprehensive cost,and so on.However,under the influence of many factors,such as the complex and diverse natural environment conditions of the city,and the spatial environment conditions of the distribution of the existing ground and underground facilities,it is difficult for the traditional pipe-jacking to meet the needs of modern urban underground engineering construction of large cross-section and long distance and other construction requirements.With the development of equipment manufacturing technology in our country,the emergence of large section rectangular pipe jacking machine with heading machine makes the construction technology of pipe jacking in our country entered a new stage.This new pipe-jacking technology not only has many advantages of traditional pipe-jacking and shield tunneling technology,but also it well facing many new technical problems to be solved.Therefore,it is necessary to carry out the research on key construction technology of large section rectangular pipe jacking for its development in the further.Relying on the construction project of underground pedestrian passages of Shenzhen Metro Line 9,and through the construction practice and engineering technical investigation on site for a year,the study on key construction technology of large section rectangular pipe jacking is carried out in this thesis.Through the analysis and study on some special technical problems encountered in the construction of the project,the key technical measures to solve these problems are explored.And by the analysis on monitoring data in construction process in site,the implementation effect of the key construction technology is discussed.Combining with practice in site and technical research as well as theoretical analysis,the relevant research carried out,and the main research works are as follows.1.Through engineering practice in site and literature investigation,the development process,research status and existed problems of pipe-jacking technology are discussed.On the basis of technical investigations,a comparative analysis for the different characteristics of this new pipe-jacking construction and shield tunneling construction are carried out.On the basis of summing up the previous researches on the construction technology of pipe jacking method,the construction technological process of large section rectangular pipe jacking is analyzed and discussed.2.Through technical investigation in site,the general situation of the project,the engineering geological environment conditions,the main contents of pipe jacking construction and the overall construction scheme are analyzed in detail.The difficult problems in the construction of large section pipe jacking are studied,and the technical schemes to solve these difficult problems in the construction are discussed.3.Based on the analysis of measured thrust data during pipe jacking construction,the influence of pipe jacking resistance on pushing force is investigated,and the resistance reducing mechanism of thixotropic mud is revealed.And a comparative analysis on the effects for the using of this key technology is carried out.4.By analyzing deformation data for ground monitoring points during engineering construction,a series of key technologies for deformation and settlement control,which are applied in this engineering construction,are discussed.Such as ground settlement control,asymmetrical settlement control for underground pipelines,attitude control for pipe jacking machine,pushing speed control,the amount of soil being transported out control,and so on.Furthermore,the effects for the using of these key technologies are analyzed.The influence laws of pipe jacking construction on ground settlements have been investigated,and the influence mechanisms of pipe jacking construction on settlement and deformation of ground have been revealed.5.Some other key technologies in the pipe jacking construction,such as pipe jacking launching,pipe jacking receiving,waterproofing and leaking stoppage for pipe segment,lateral connection between pipe-jacking passageway and subway entrance and exit,and so on,have been all preliminarily explored.Through the above research,the main research conclusions are obtained asfollows.1.Due to the resistance reducing by grouting and other key construction techniques have been used,it makes the actual required pushing force is less than the value by theoretical calculation,in the construction of long distance and large section pipe jacking.So that the pushing force is controlled within the allowable range and the intermediate jacking station is have not started.The research shows,that the technology which is used in this engineering of resistance reducing by grouting is successful.2.By injecting proper amount of pressure lubricating mud into the outer wall of pipe segment,not only the friction resistance can be reduced greatly but it also created the favorable conditions for pipe jacking rapidly pushed on and for its axis control,when pipe jacking is being pushed forward.3.In order to ensure the soil transportation is smoothly and the construction safety,it is necessary to improve the soil in front of the excavation face by grouting,so that the fluidity and the plasticity of soils in soil warehouse are improved successfully,in the course of excavation.Furthermore,the watertight properties of the improved residual soils have been improved obviously.Because of the properties of soils are improved,it makes the transportation of soil dregs are smoother,it also plays a certain role for reducing the total pushing force in the process of pipe jacking being pushed forward.4.Through the comparative analysis on monitored settlement data before and after reinforcement by grouting,it is shown that the settlement values of ground and pipeline all have been effectively controlled,after the measures of grouting reinforcement are adopted.In the whole process of pipe-jacking construction,for ground passage and underground pipe network,there is no any impact happened.5.In order to ensure the axis of the pipe-jacking does not produce larger deviation,by measuring and controlling the attitude of pipe jacking,and by rectifying its deviation,are the prerequisites for success,in the pushing process.According to the designed line,pipe-jacking is pushed forward smoothly,and it passed through several important underground pipelines successfully,but there is not any contact happened with them.So that,there is not any pipeline is destroyed.6.By adopting the technology which is to adjust and to control the balance of earth pressure in the soil bunker,it is ensured that the amount of mud out and mud taken in the process of excavation are basically the same.Because of this technology is adopted,the ground settlements,building tilts and cumulative settlements are effectively controlled.From the point of view of the effect of engineering implementation,there is not any ground uplift or horizontal displacement of soil mass is happened,due to there is not excessive pressure in the soil bunker.Similarly,there is not any ground settlement or groundwater spew is happened,due to there is not too lesser pressure in the soil bunker.7.Due to the limitation of underground pipeline and field conditions,the horizontal grouting reinforcement with sleeve valve pipe is adopted at the end of the working well.It is proved by engineering practice that this reinforcement effect is good.8.The engineering effects of waterproofing and water sealing are good,on account of the relevant technologies are adopted in this project.Due to a whole has been formed between pipe section and another,no any leakage has been found during engineering construction.9.In the part A(east-west passage)of this engineering,the pipe jacking machine cannot get out from the receiving well normally,because of the blocking in nearby drainage box culvert and subway tunnel.After the study,the pipe jacking machine has been moved 17m in the tunnel and then is disassembled.Finally,it is lifted out from the reserved subway air shaft which with a net width of only 3 m.The difficulty problem that pipe jacking machine getting out from the well has been solved for the construction of large section pipe jacking project.10.In the part A(east-west passage)of this engineering,the thrust axis of pipe-jacking is orthogonal to the axis of subway shield tunnel that has been constructed;the distance between them is only about 1.9 m.By using the method of subsurface excavation,a passageway has been formed,which can connect pipe jacking tunnel with subway tunnel.Finally,the difficulty problem that pipe jacking tunnel connecting with subway entrance and exit is solved.In summary,the study on key technology for the construction of large section rectangular pipe jacking which is used as an underground pedestrian passage in Shenzhen Metro Line 9 from ShangSha to XiaSha,is carried out in this thesis.Based on the analysis of the difficult problems encountered in the construction of large-section pipe-jacking engineering under the conditions of urban complex geological environment,the key technical measures to solve these difficult problems have been explored.By using these key technologies,the difficult problems in the engineering construction are have been solved,which are included pipe jacking launching and receiving,resistance reduction by grouting,waterproof and water sealing,jacking speed control and rectifying deviation control and so on.The research results as above are of great significance to promote the development in construction technology and theory of large section rectangular pipe jacking.It also provides the technical reserve that can be used as reference for the application of similar large section jacking pipes in urban underground space.At the same time,it will also greatly promote the normalization and standardization for the construction of large-section rectangular pipe jacking.