| There's a wide range of applications of the conventional double-layer lining water tunnel nowadays.However,with the increasing design requirements for the internal hydraulic pressure of the water tunnel project,the double-lining structure will inevitably suffer from different diseases,such as internal water extravasation,external water infiltration caused by the extreme opening of the joints of the segments and severe cracking of lining under high internal hydraulic pressure,etc.To study the mechanical properties of multi-layer lining under internal hydraulic pressure,this paper relied on the experiment of composite lining water conveyance tunnel joints to verify the reliability of the numerical simulation method.At the same time,relative parameters were applied to the new type of three-layer lining structure in the Pearl River Delta Water Resources Allocation Project to study load–carrying properties and failure modes under internal hydraulic pressure of two structural forms,combined loaded structural form and separated loaded structural form,and compare it with the traditional double layer.Based on this,the different surrounding rock conditions and the thickness of the steel sleeve were discussed.The main work and research results of this paper are summarized as follows:(1)The method of numerical calculation was used to reproduce the joint test and the structural test of the composite lining segment joints of the main canal of the Middle Route of the South-to-North Water Diversion Project passing through the tunnel of the Yellow River.The internal lining should be separately applied to sustain the external hydraulic and soil pressure and the composite liner to sustain the internal hydraulic pressure.The reliability of the numerical analysis method was verified by comparing the concrete strain,the amount of joint opening and the change in bolt stress with the test data.(2)Relying on the Pearl River Delta Water Resources Allocation Project,a new type of three-layer lining(combined loaded and separated loaded)structural model named “one ring + two half rings” was established to investigate the mechanical properties and deformation mechanism under the internal hydraulic pressure.According to the development of concrete cracks in the water conveyance tunnel and the analysis of the proportion of hydraulic pressure within each structure under internal hydraulic pressure,it could be concluded that when the cracking area penetrates through the self-compacting concrete lining,the hydraulic pressure suddenly falls sustained by the self-compacting concrete.The stage when internal forces of selfcompacting concrete,segment and steel sleeves redistribute showed that the structure of the water diversion tunnel reaches the ultimate bearing capacity.(3)Selecting the conventional two-layer lining structure type and the new three-layer lining type structure forms,the comparison of the proportion of the concrete lining cracking area,the comparison of carrying capacity under internal hydraulic pressure and the comparison of internal hydraulic pressure sharing ratio of two structure forms were discussed to verify the superiority of new type the three-story lining structure in terms of load–carrying property of internal hydraulic pressure and control of concrete cracking.This paper also summarized the applicability of water pressure in the water conveyance tunnel with different structural forms.(4)Considering complex geological conditions along the Pearl River Delta Water Resources Allocation Project and the actual situation in which the steel sleeve still have a large margin of tensile strength under internal hydraulic pressure,the effects of different stratum resistance coefficients and different thicknesses of steel sleeves on the hydraulic load–carrying capacity of the new three-layer lining(combined loaded)structure form were discussed.The research results can provide reference for the optimization design of the three-layer lining structure. |
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