Research On Construction Technology And Numerical Simulation Of Underwater Shallow Large Span Tunnel

The accelerated development of science and technology in our country promotes theunceasing progress of human civilization, and simultaneously accelerates the developmentprocess of urbanization. Urban development first demands the progress of transportationindustry, the traffic in the current situation cannot satisfy people’s requirements of productionand livelihood. In the past, the rivers and lakes in the city provide people with a variety ofconvenience, but at the same time become the bottleneck in urban traffic development. Inorder to avoid the impact of water transport, the underwater highway tunnels through the riverbottom are built underwater in major cities at present, but the complexity of the underwatergeological conditions brings many technical problems in construction of the underwatertunnel. By Xiangjiang River tunnel large span section at Camp Road in Changsha as theproject background, this paper probes into construction technology and numerical simulationmethod of underwater shallow large span tunnel in modern city, theoretical achievement ofthis study provides reference for future similar tunnel construction, and has certain theoreticalsignificance and practical value.This paper firstly analyzes the factors influencing the adjoining rock stability ofunderwater shallow large span tunnel, indicating that the factors include two categories,namely geological environmental factor and anthropic factor. Secondly, based onelastic-plastic mechanics, rock mechanics and such relevant theories, stress distribution ofthree section types including circular section, elliptic section and oval section are respectivelyoverviewed briefly, the stress redistribution regularities of surrounding rock in differentsections are generalized. Next, the construction method and auxiliary measuresfrequently-used in the large-span tunnel excavation are summarized, currently six sectionsCRD method and double-side-drift method are used more. Finally, based onthree-dimensional numerical simulation analysis for Ying Pan Lu Xiang River tunnel adoptingsix sections CRD method and double-side-drift method with the finite difference softwareFLAC3D, the deformations, stress distributions and primary lining atress of the excavatedsurrounding rock are calculated respectively in both of these construction methods, and bycomparing and analyzing the calculation, the adoption of double-side-drift method in thislarge-span construction is finalized. After determining the construction method, due to thesignificant influence of different excavating procedures on stress redistribution anddeformations of the surrounding rock, in this paper two excavating procedures are worked out and numerical simulation analysis is made of them. The analytic result shows that the secondexcavating procedure is better than the first one in terms of both displacement and stressdistribution of the surrounding rock, and consequently the final excavating procedure isdetermined. Based on techniques of information-oriented construction, some in-situmeasurements mainly on the selected construction methods and procedures are taken,monitoring items including vault settlement, horizontal convergence, surrounding rock stressand deformation of primary support. By comparing and analyzing the monitoring data inactual construction and the numerical simulation, it is found that the two methods inconstruction are roughly the same in stress-strain changing regularities of surrounding rockand primary support, which plays a guiding role on tunneling under similar conditions infuture.Construction in-situ measurements can keep track of the changing regularities ofsurrounding rock, through the data comparative analysis, the displacement and stressconditions of surrounding rock in construction can be understood in detail, fed back toconstruction to guide constructing and modify design parameters. In the meanwhile,combining with the numerical simulation results, the change of the tunnel structure can beunderstood better, which can ensure safety and quality of the completed tunnel construction aswell.