STUDY ON LAW AND CONTROL MEASURES OF GROUND DEFORMATION DURING EPB SHIELD TUNNELING PROCESS IN SMALL-SPACING DOUBLE-TRACK TUNNELS
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It is inevitably that the process of EPB shield tunneling disturbs the rock and soil around tunnel, which has intensively caused ground deformation and threatened the safety of surrounding structures/buildings. To study the law and control measures of ground deformation during the EPB shield tunneling process, this paper, based on the Longzhen Exit and Entry lines of Guangzhou Rail Transit Line 18,analyzed the shield construction parameters and ground deformation data caused by the construction of this small-spacing double-track tunnels. The conclusions are as follows:the ground deformation experiences five development stages with four deformation trends during the EPB shield tunneling process in small-spacing double-track tunnels; the ground deformation effect of the pre-built line on the later-built line is generally consistent with the effect of the pre-built line on itself, while the significant influenced area is between the two tunnel axes; the influence factors of ground deformation include shield construction parameters, engineering geological conditions and shield downtime, so optimizing the shield construction parameters, reinforcing the stratums and reducing shield downtime can effectively control the ground deformation. The research results have provided theoretical basis in area of shield construction control of Guangzhou Rail Transit Line 18 and other relevant small-spacing double-track tunneling projects.Keywords:
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Considering the complicated project of four-line overlapped tunnels in Shanghai metro construction, in which Metro Line 11 below-shield and above-shield crosses the existing Metro Line 4 successively, numerical modelling and in-situ monitoring are employed to study the influence of shield tunnelling on the deformation of the existing tunnels. According to the distribution law of earth pressure around the existing tunnels, the shield operation parameters are set to change with the advance of the EPB shield machine. Particular attention is paid to the effect of the chamber earth pressure and grouting pressure on the deformation of the existing tunnels during the below-shield tunnelling as well as the loading scope and its value during the above-shield tunnelling. The results show that the settlement of the existing tunnels stays at the same level as the chamber earth pressure ratio increases, while it increases with the decrease of the grouting pressure ratio. Construction measures, which follow the principle of synchronous loading in the new tunnel mainly and loading in the existing tunnel secondarily, should be taken to control the heave and partial uplift of the existing tunnels during the above-shield tunnelling.
Settlement (finance)
Lateral earth pressure
Line (geometry)
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Research purposes:Based on the shield engineering of some interval tunnel in Beijing subway line eight,it used FLAC simulation to predict the deformation laws of surface and its nearby building caused by shield construction,the goal is to offer a technological support for the determination of reasonable construction parameters and the establishment of the on-site monitoring project when safety through surface buildings in shield tunnel construction.Research conclusions:(1) Numerical simulation was adopted to investigate the laws of surface deformation caused by the tunnel shield construction of Beijing subway,the lateral ground settlement curve is basically symmetrical in horizontal direction,and buildings have greater influence on surface deformation on the surrounding area compared with its region.The maximum differential settlement is 8.09mm.(2) According to the prediction results of numerical simulation,the bi-directional tunnel excavation affected range of surface is 36m that mainly in tunnel center.The excavation face affected area is 24m in the frontage and 20 m in the rear,so it should be mainly monitored during construction.(3) The practice shows that the measured curves are identical with the simulation curves.The numerical simulation is effective means for predicting the laws of surface and adjacent building deformation caused by shield construction.(4) The research results can be used to make adjacent building deformation control scheme caused by shield construction.
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Abstract At present, the mainstream method of urban subway construction is shield construction. What cannot be avoided in shield construction is the settlement and displacement of the ground surface, and the tunneling pressure is closely related to the grouting pressure and the settlement of the soil. For the overlapping tunnel shield construction, this paper takes the shield construction of the overlapped tunnel section of Kunming Rail transit Line 6 as the research object. Using ABAQUS finite element software to simulate overlap shield tunnel construction, the research of shield tunneling parameters and the relationship between the surface displacement of soil. The results show that reasonable selection of excavation parameters can well control ground settlement.
Lateral earth pressure
Settlement (finance)
Section (typography)
Adina
Tunnel Construction
Ground movement
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With the rapid development of the subway network,the phenomena of shield tunnels going across the adjacent tunnels are becoming more and more common.The interaction between shield tunneling and nearby tunnels is more complicated than the ordinary shield tunneling in intact soil strata.Based on the project of Shanghai Bund Passage crossing Metro Line 2,the method of centrifuge modeling together with the field measurement is employed to study the effects shield tunneling on nearby strata and existing tunnels.In centrifugal model tests,the effects simulation techniques considering the unloading of excavation,ground loss and grouting are developed to analyze the longitudinal settlement of the shield tunnel and the existing tunnel induced by the shield tunneling.Besides,the deformation distribution and settlement curves of the existing tunnels during shield construction are studied by using the monitoring data.
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Diaphragm (acoustics)
Lateral earth pressure
Stress field
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The main issue considered both in design and construction in urban environments is constrolling ground movement to keep the safety of existing buildings.Based on a shield tunnel construction in Shanghai,the ground displacement distribution around tunnel is studied by field measurement and numerical analysis.It is shown that the influence of shield excavation on soils around tunnel can be divided into three stages,including shield approaching,crossing and leaving the measuring holes.While the shield approaches and crosses the measuring holes,the ground movements of lateral soil behave heaving,moving along the shield tunneling direction and outward the tunnel.Settlement,moving along the shield tunneling direction and inside the tunnel are main deformation characteristics when the shield leaves the measuring holes.Settlement and forward movement the soils above tunnel because of the large buried depth.According to the calculated layered settlement above tunnel,modified Peck formula used to predict the settlement of deep soils is established;and the results are compared with those of simulation.
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Ground movement
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EPB shield is widely used in the construction of Metro tunnels. Ground surface settlement induced by shield tunneling directly affects the safety of the tunnel construction. The authors use different theoretical methods to calculate the range of the pressure on the tunnel face in a shield-bored tunnel on Line 3 of Chengdu Metro. The shield boring process with different ground loss ratios and different pressures on the tunnel face is simulated by ABAQUS software embedded by constitutive model of soil stress path. The law of ground surface settlement induced by shield boring in gravel strata is obtained. The comparison and contrast between the ground surface settlement measured in the field and that obtained by means of theoretical calculations proves that the constitutive model adopted is rational. Proper range of the pressure on the tunnel face is determined. In addition,the relationship between the pressure on the tunnel face and the ground loss ratio is investigated and summarized so as to provide reference for similar projects in the future.
Settlement (finance)
Lateral earth pressure
Line (geometry)
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Based on a project of subway constructed near elevated high speed railway, FEM method is adopted to analyze the effect of shield tunneling on the horizontal and vertical displacement of pile foundation of the viaduct as well as the pile caps on the condition that the nearest clear distance is 5m. The results show that with appropriate parameter control of shield tunneling, the effect of EPB shield tunneling on the displacement of piles in the three directions, i.e. horizontal displacement along and perpendicular to the longitudinal direction of the rail line and vertical displacement, is little. The same goes for the differential settlement between pile caps.
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Vertical displacement
Foundation (evidence)
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Taking the shield tunnel project at the No.2 Line of Suzhou Subway as the research background,the paper has the deep research on the ground deformation caused by the neighboring parallel tunnel construction,and analyzes the influence of the tunnel buried depth,the spacing,support pressure of the excavated face and the ground loss rate on ground settlement,so as to provide some helpful conclusion for the parallel shield method construction.
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Tunnel Construction
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By the consolidation of grouting and high-pressure spiral grouting, the differential rigidity between tunnel structure and surrounding soil can be reduced, the stress of soil can be distributed evenly, the resisting force can be increased, the settlement of soil caused by shield tunneling can be controlled effectively. Based on the case of engineering, the design plan for shield tunnels undergoing the railway is fully introduced, coherent measures are extracted, the safety of railway and train can be ensured during the process of construction of shield tunnel.
Consolidation
Rigidity (electromagnetism)
Railway tunnel
Settlement (finance)
Lateral earth pressure
Tunnel Construction
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