The Study For The Start And Run-out Phase Of The Shield Machine Under Soft Soil Condition

The leakage of water and slurry while shield machine is entering into and exiting form thetunnel portal is one of five main risks in shield construction, recent years have witnessed manysevere and large-loss accidents which were result from leakage of water and slurry under weakgeological conditions. Those consequences were alarming and raised high attention ofemployers, designing institutes and superintending offices and construction organizations to theproblem of leakage, therefore, the correspondent entering and exiting plan making was shiftedfrom adventurous to secure, and safety cost correspondently got raised. It has been the hot issuein discussing what kind of measures should be taken to avoid the leakage problem under weakgeological conditions, and how to accomplish both safety and economy.Based on the above background, this paper summarizes domestic and foreign experienceson shield machine entering into and exiting from the tunnel portal, and analyzes the inadequacyin the process of applying the measures like soil reinforcement improvement measure, tunnelportal seal measure and pressure balance measure, and this paper:1. Proposes thickness optimization idea on soil reinforcement, and basing on PietroLunardi and Mohr-Coulomb Criterion, it also proposes the ultimate depth calculation methodswhile the excavated surface remains in the stable condition, which is necessary to rapidly judgewhether the tunnel portal needs to be reinforced or not.2. Tries to build calculation model for improvement measures of soil reinforcement, andproposes correspondent calculation methods, which are applied to calculate the reinforcementthickness of continuous wall and piling.3. Puts forwards selection principles for improvement measures of soil reinforcement, aswell as remedial measures for the possible reinforcement failure.4. Proposes improvement plan to deal with conventional insufficiency of tunnel portal.5. Analyses and studies pressure balance measures, and then proposes construction methodof “tunnel construction first, well second”.The above results are supposed to have some reference value for the development of shieldtunnel construction technology.