Study On The Key Technique Of Composite Grouting For Water Blockage In Weathered Slot Of Subsea Tunnel

According to the geological exploration data, Xiamen Xiang'an subsea tunnel will pass through the four deep weathered slots of troughs, F1,F2,F3,F4, where the strata are complete or strong weathered weak rocks. These strata have high permeability coefficients, huge water amount, high water pressure, and high risk of water and silt pouring in tunnel with infinite seawater supply. Passing through unfavorable geologic bodies and strata interface is one of the most difficult problems during subsea tunnel construction. So tunnel geological forecast ahead, grouting reinforcement schemes and construction method optimization are important issues to guarantee the safety of subsea tunnel construction. Due to the complicated geological and water conditions, composite grouting technique is introduced, which can take advantage of different grouting technologies and materials.In this paper, based on domestic and foreign documents, integrated Xiamen Xiang'an subsea tunnel passing through the weathered slot F1 project, meso-mechanical simulation of groundwater inrush pathway formation between the weathered slot and the tunnel are discussed by using PFC software, appropriate parameters of grouting circle for tunnels with limiting discharge lining is proposed, which can provide reference for the design and construction of composite grouting in weathered slot Fl. Meanwhile, theoretical study and meso-mechanical simulation on composite grouting in the strong-weathered granite stratum are analyzed, grouting materials is introduced by the seawater corrosion test of strength concrete. Combined with above study and engineering case, the key technique of composite grouting for water blockage in weathered slot of subsea tunnel is presented.The work in the present paper can be summarized in the following:(1) Based on the weathered slot configuration and the spatial relation between the weathered slot and the tunnel, the weathered slot water burst is divided into different geological modes. Combined with above study, numerical tests with PFC under coupling environment are conducted to investigate the initiation of fractures, activation of weathered slot and formation of groundwater inrush pathway during the tunnel passing closely through the weathered slot structures with high water pressure. Keeping the completeness and stability of the rock pillars is of key importance to avoid water burst and to minimize there relevant loss when the tunnel passing closely by the weathered slot structures. To find the appropriate parameters of grouting circle is the key issue to perfectly blocking ground water and limiting discharge. The effects of grouting circle will not share the external water pressure on lining with tunnel lining, but to block ground water and reduce the external water pressure on lining remarkably with low discharge. The study can provide instructional advice for the design and construction of composite grouting in Xiamen Xiang'an subsea tunnel passing through the weathered slot F1 project.(2) Based on the theory of particle flow, the domain of flow is defined by using Fish language implemented in PFC and the formulas for flow and pressure are put forward respectively. Furthermore, the Contact-Bond Model is introduced due to the complicated properties of low permeability soil to build PFC model, which can reflect Fluid-solid coupling between particles flow and flow domain. Combined with above study, the process of fracture grouting in soil is simulated from micro-viewpoint under coupling environment. In addition, the emergence and development of crack and grouting pressure in soil is analyzed under different grouting pressure and soil properties.(3) It shows that grouting diffusion radius of bingham fluid is related to grouting pressure difference, gap width, flow velocity and time-dependent behavior of rheological parameters. So it is unreasonable to miss the time-dependent behavior of grouts in computing diffusion radius.The interval of 2.5m can form complete curtain grouting in strong-weathered granite and the mechanism of grouting is fracture grouting no more than penetrate grouting.(4) Grouting materials test indicates that the use of seawater causes an earlier strength compared to the same with tap water. However, after a long period the use of seawater may results in the formation of deeper corrosion compared to tap water, especially the influence is found to be significant for higher W/C. It is understood that at the early age, the microstructure of concrete improved due to the use of seawater. Then it reduces gradually, because seawater may cause deterioration of concrete strength after a long time. Based on the grouting test, it recommended that High Strength Concrete(HSC) and Portland Cement have an satisfactory effects in the strong-weathered granite stratum. Especially, malisan grouting play a improtant role in water-enriched weathered slot.(5) Characteristics and design principles of composite grouting are achieved. Composite grouting is a economic and effective measure to strengthen the weathered slot to the fullest extent, which means grouting in the ground by using different grouting technologies and materials according to a special time and space sequence. In order to assure that the subsea tunnel can pass the weathered slot F1 successfully, the technique of composite grouting is adopted to reinforce the soil to block up the water and a good result is gained. The geological condition, grouting mechanism, scheme and parameters, and the verification and appraisal of the construction technology and grouting effect are introduced in this paper, and therefore composite grouting key technology is formed.