Research On Grouting Influence And Mechanism Of Shield Tunneling In The Sand-Gravel Stratum

Deformation of the soil body may be difficult to be controlled when tunneling by earth pressure balanced shield in the sand-gravel soil stratum with high permeability and easily collapsed. Grouting methods are ordinary methods to deal with the sand-gravel stratum in the shield construction process. Although grouting technique in the tunnel has been widely applied, the current grouting theory study of penetration is not perfect. Grouting construction still largely relies on experience at present; construction of blindness is very easy to waste materials or to result in potential safety hazard. To make clear penetration mechanism of sand-gravel soil stratum is an important task of grouting process control.The key to the success of earth pressure balanced shield construction is to adjust the soil dug down from excavation surface to a "state of plastic flow" in the pressure cabin. Gravel and sand into the pressure cabin are hard to this kind of "plastic flow state”, which not only affects dump characteristics and the propulsion torque of the shield machine but also causes component wear and tear. All of the above will bring difficulties to the shield construction. To solve the above problem, the usual approach is to inject some additives into the pressure cabin to improve soil properties. The slurry additives is added to improve features of plastic and flow,water sealing should be simultaneously ensured because of the high permeability in the sand-gravel soil stratum.Soil displacement, scheme optimization of backfill grouting, the relationship of every construction parameters and the calculation of the penetration distance are studied systematically and thoroughly in this thesis through the interior model experiments for large-size sand-gravel stratum on subway shield construction. The detailed contents in this thesis are as follows:1. The grouting theoretical study will lead to great difficulties because of the complexity and variability of internal structure in sand-gravel soil stratum. The existing theory of permeation grouting in the sand-gravel stratum are set up in their assumption of the ideal conditions which varies from practical engineering considerably. In this thesis, the fractal dimension theory was used to study the proliferation law of the permeation grouting in the sand-gravel stratum based on the rheological properties of slurry and the fractal characteristics of the sand-gravel soil. Infiltration situation of the Bingham grout in sand-gravel soil was researched with the fractal dimension non-linear theory, and then the constitutive model about infiltration of the Bingham grout in sand-gravel soil was constructed. Calculation expressions of the permeability and the starting pressure gradient of Bingham grout in sand-gravel stratum were acquired according to the fractal infiltration constitutive model.2. The mechanical behavior, the effect of different proportions, applicability and mechanism of shield cutter additives slurry were researched in terms of construction in the sand-gravel stratum. Several shield cutter slurry additives of shield tunneling in the sand-gravel stratum were researched in this thesis. The shield cutter slurry additives were tested on their viscosity, variation of dehydration, permeability coefficient and slump of their mixture with cutting sand-gravel soil. Finally, according to test results, recommendations about the choice and proportion of the shield cutter slurry additives were obtained. And the addition amount of the additives in sand-gravel stratum was put forward for engineering reference.3. The characteristics of the grout on simultaneous grouting were studied in this thesis. Three important characteristics including viscosity, setting time and initial setting strength of C-S grout (mixed grout of cement-silicate) in backfill grouting of shield tunneling were researched by the laboratory study. It was discussed in this thesis that the characteristics of cement-silicate mixed grout were deeply affected by different cement, different modulus and different ratios of sodium silicate. Experimental curves about viscosity, setting time and initial setting strength of the C-S grout were got, which provides a basis for grouting designers and constructors to choose the optimized formula in tunneling construction.4. The backfill grouting effects of shield tunneling in the sand-gravel stratum were studied in this thesis. The scope of the grouting rate was proposed in such sand-gravel stratum. The impact of grouting parameters on soil body displacement and soil surface settlement, the effect of grouting material, the relationship of every grouting parameters and the calculation of the penetration distance are studied systematically and thoroughly in this thesis through the interior model experiments of shield construction in the sand-gravel stratum.