Study On Construction Technology Of Railway Tunnel With Extremely Weak Surrounding Rock And Large Cross-section Based On BIM

The geological conditions in the central and western areas are very complicated and undetermined.In some local regions,unfavorable geological phenomena such as faults,folds,karst and underground dark rivers are universal.In the process of tunnel excavation,the characteristics of weak and extremely weak surrounding rock mightily prevail,such as complex and variable stratum,low strength,poor self-supporting ability and strong water richness.Additionally,due to the large cross-section of the tunnel,disasters such as large deformation,landslides,roof fall,mud rushing and water blasting are extremely prone to occur in the early excavation stage.For this kind of high-risk large-section tunnels with extremely complex engineering geological conditions,research on the new railway tunnel construction method and construction management concept based on BIM(Building Information Model)technology has promoting and practical significance in improving construction efficiency,ensuring construction quality and realizing the construction goal of "fast,safe and efficient".Based on the Shigu mountain tunnel of Baoji-Lanzhou High-speed Railway,this paper applied the BIM technology to solve the specific problems faced in the construction.The main research work includes the following four parts:(1)A 3D geological modeling method for the long and large mountain tunnels based on CATIA considering the geological characteristics of band-shape and closely related to geology is developed.A 3D geological models of the Shigu mountain tunnel were built by the proposed method.The results show that the it can satisfy the constraint demands of 2D geological materials and the precision demanods in construction drawing.This verified the feasibility and reliability of the proposed 3D geological modeling method.Furthermore,the lightweight processing method of BIM model using Skyline software is studied.A file conversion interface from CATIA to Skyline was developed to realize the lightweight display of the above 3D geological model of Shigushan tunnel.(2)A new "three platforms with nine steps" excavation method is proposed.The primary mode of this excavation method is to reserve core soil in arc pilot excavation.In this method,the large cross-section is divided into nine small units and reserved core soil with temporary inverted arches are adopted on the same step to exert the bearing capacity of the initial support structure effectively.To treat the phenomenon of water rushing and sand blasting in gravel silty clay stratum with high water-content,an advanced grouting reinforcement technology by deep hole with double pipes in the form of backward was proposed.A standardized BIM model for the detailed construction process of the above tunnel excavation and support technology is established by using CATIA software,which lays a foundation for the realization of 3D visualization technology.(3)The monitoring of surrounding rock and the advanced geological prediction based on BIM technology is developed.A tunnel and ground surface monitoring information system(TGMIS)is built.This system realizes automatic data processing and sends out hierarchical early warning by transmitting the monitoring results to the BIM management platform in real-time.Also,the 3D geological prediction model in front of the tunnel face is easily obtained by combining the existing advanced geological prediction technology with BIM techsnology,and the scientific prediction of the stability of the tunnel face is realized by further combining with the cloud model,which provides a technical guarantee for construction safety.(4)Based on the BIM collaborative management platform and BIM model,this paper carries out 4D virtual construction simulation and forms a 4D+real scene schedule management mode with oblique photography technology.The effective combination of construction simulation and progress managing effectively avoided the waste of building materials and reduced the construction cost.As a result,the precise and meticulous tunnel construction management technology based on the 4D concept is built,which significantly improves the construction efficiency and management level.The application of the above mentioned technologies of tunnel excavation,supporting,monitoring and construction management based on BIM in Shigu mountain tunnel shows that:(i)the new excavation method not only speeds up the construction progress and enhances the construction safety,but also improves the construction space of the working surface.It provides a suitable environment for mechanized operation.(ii)During the tunnel excavation process,the combination of the TGMIS monitoring system and the BIM platform has successfully warned more than 20 times of abnormal vault settlement deformations and automatically sent early warning information to the corresponding responsible person to avoid the occurrence of serious vault collapse accidents.(iii)The BIM technology application saved about 10% of the budgeted building materials and completed the project more than 20 days ahead of the expected construction period.The construction cost is effectively reduced on the premise that the construction quality is in line with the relevant standards.