Case Study on Synchronous Construction Technology for Secondary Lining of Large-diameter Single track Shiel Shield-bored ored Tunnel

The synchronous construction of the secondary lining during the boring of large-diameter shield faces challenges such as the design of the lining jumbo,the high requirements on the performance for the lining jumbo,the organization of the construction activities in the small and confined area,the horizontal transportation for shield boring and high safety management requirements.A super-long invert lining construction jumbo,as well as the matching California switch,is developed,which provides solution for the confliction between the invert lining construction and the horizontal transportation.The procedure and method for the synchronous operation of the shield boring and the secondary lining are developed by referring to the synchronous construction of the secondary lining during the boring of the TBMs in hard rocks.Due to the adoption of the synchronous operation of the shield boring and the secondary lining,the construction period is shortened and the construction cost is reduced.The paper can provide reference for the synchronous construction of the secondary lining in similar projects in the future.

Failure mechanism of large-diameter shield tunnels and its effects on ground surface settlements

A new technique for the analysis of the three-dimensional collapse failure mechanism and the ground surface settlements for the large-diameter shield tunnels were presented.The technique is based on a velocity field model using more different truncated solid conical blocks to clarify the multiblock failure mechanism.Furthermore,the shape of blocks between the failure surface and the tunnel face was considered as an entire circle,and the supporting pressure was assumed as non-uniform distribution on the tunnel face and increased with the tunnel embedded depth.The ground surface settlements and failure mechanism above large-diameter shield tunnels were also investigated under different supporting pressures by the finite difference method.

Influence of secondary lining thickness on mechanical behaviours of double-layer lining in large-diameter shield tunnels

In large-diameter shield tunnels,applying the double-layer lining structure can improve the load-bearing properties and maintain the stability of segmental lining.The secondary lining thickness is a key parameter in the design of a double lining structure,which is worth being explored.Based on an actual large-diameter shield tunnel,loading model tests are carried out to investigate the effect of the secondary lining thickness on the mechanical behaviours of the double lining structure.The test results show that within the range of secondary lining thicknesses discussed,the load-bearing limit of the double-layer lining increases with growing secondary lining thickness.As a passive support,the secondary lining acts as an auxiliary load-bearing structure by contacting the segment.And changes in secondary lining thickness have a significant effect on the contact state between the segment and secondary lining,with both the contact pressure level and the contact area between the two varying.For double-layer lining structures in large-diameter shield tunnels,it is proposed that the stiffness of the secondary lining needs to be matched to the stiffness of the segment,as this allows them to have a coordinated deformation and a good joint load-bearing effect.

Research on the design method for uniform wear of shield cutters in sand-pebble strata

During shield tunneling in highly abrasive formations such as sand–pebble strata,nonuniform wear of shield cutters is inevitable due to the different cutting distances.Frequent downtimes and cutter replacements have become major obstacles to long-distance shield driving in sand–pebble strata.Based on the cutter wear characteristics in sand–pebble strata in Beijing,a design methodology for the cutterhead and cutters was established in this study to achieve uniform wear of all cutters by the principle of frictional wear.The applicability of the design method was verified through three-dimensional simulations using the engineering discrete element method.The results show that uniform wear of all cutters on the cutterhead could be achieved by installing different numbers of cutters on each trajectory radius and designing a curved spoke with a certain arch height according to the shield diameter.Under the uniform wear scheme,the cutter wear coefficient is greatly reduced,and the largest shield driving distance is increased by approximately 47%over the engineering scheme.The research results indicate that the problem of nonuniform cutter wear in shield excavation could be overcome,thereby providing guiding significance for theoretical innovation and construction of long-distance shield excavation in highly abrasive strata.

Numerical study of the mechanical process of long-distance replacement of the definitive lining in severely damaged highway tunnels

Mountain road tunnels are prone to water leakage and lining corrosion under the complex geological conditions and corrosive envi-ronments,which will reduce the strength of the lining structure until it loses its load-bearing capacity;eventually,the definitive lining will need to be replaced.In this paper,a highway tunnel in a mountainous area in Southwest China is taken as an example.Field investi-gation found that the tunnel was seriously corroded by sulfate,the strength of the definitive lining decreased,and large-scale cracks and spalling appeared on the surface,so the operator decided to replace the definitive lining by the method of interval replacement.Based on the data obtained from drilling and coring,a numerical model of long-distance replacement of the definitive lining of the damaged tunnel is established.First,the back analysis of the calculation parameters is carried out,and the modified calculation results are com-pared with the field monitoring results for verification.Then,the deformation trend of the tunnel and the development of the plastic zone during the process of long-distance replacement of the definitive lining are studied.Finally,the construction scheme is optimized.Numer-ical analysis results show that the replacement of the definitive lining of the tunnel mainly leads to the settlement of the arch crown and the uplift of the inverted arch.The deformation of the tunnel shows two rapid growth stages and two stable stages during the replace-ment process;after replacement,the deformation of the arch crown and the inverted arch is divided into two buffer zones and one stable zone.In the progress of the replacement of the definitive lining,the plastic zone does not change.Regarding the reinforcement measures,with the increase in the grouting range,the grouting efficiency decreases,and the effect of the temporary steel arch on controlling the overall deformation is not obvious.The length of the replacement of the single section should be determined according to the geological conditions of the replacement section and the monitoring data during construction.The research results can provide a reference for sim-ilar projects for the replacement of the definitive lining.

Tunnel face stability and ground settlement in pressurized shield tunnelling

An analysis of the stability of large-diameter circular tunnels and ground settlement during tunnelling by a pressurized shield was presented. An innovative three-dimensional translational multi-block failure mechanism was proposed to determine the face support pressure of large-shield tunnelling. Compared with the currently available mechanisms, the proposed mechanism has two unique features:(1) the supporting pressure applied to the tunnel face is assumed to have a non-uniform rather than uniform distribution, and(2) the method takes into account the entire circular excavation face instead of merely an inscribed ellipse. Based on the discrete element method, a numerical simulation of the Shanghai Yangtze River Tunnel was carried out using the Particle Flow Code in two dimensions. The immediate ground movement during excavation, as well as the behaviour of the excavation face, the shield movement, and the excavated area, was considered before modelling the excavation process.

Response of operating metro tunnels to compensation grouting of an underlying large-diameter shield tunnel:A case study in Hangzhou

Due to the shield tunneling underneath,long-term settlements may develop in the existing metro tunnels.The compensation grouting is applied worldwide to stabilize the settlement of ground and existing structures.Few field studies concerning large-diameter shield pass-ing tunnel from below have analyzed the interaction between the compensation grouting and the existing tunnel.This paper presents a case study on the response of the operating metro tunnels to the compensation grouting of an underlying large-diameter tunnel in muddy clay stratum.The tunnel deformations before,during,and after the compensation grouting were monitored and analyzed.The long-term tunnel settlements were mitigated and stabilized by the timely compensation grouting.Smaller settlement rates were observed during the grouting treatment,and the settlement was gradually stabilized three months after the grouting.The grouting holes at the tunnel invert were used initially for better grouting efficiency.The horizontal displacement and convergence developed during the grouting construc-tion and remained stable after the grouting process.Moreover,some limitations of the grouting treatment were discussed.The tunnel settlement in the section close to the center-line of the south-line tunnel cannot be prevented effectively.The differential displacement cannot be reduced by this grouting program.