Full-Scale Model Experimental Investigation On The Bearing Mechanism Of Superimposed Linings Structure Subjected To High Inner Hydraulic Pressure

The shield water conveyance tunnels have played an important role in solving the problem of water shortage and unequal distribution of water resources between cities in China.With the single-layer and double-layer lining of shield water conveyance tunnel unable to meet the increasing inner hydraulic pressure requirements,the three-layer lining structure has attracted more and more attention in the engineering field.Based on the Pearl River Delta Water Resources Allocation Project,in this paper,to investigate the bearing capacity and the failure mechanism of the water conveyance tunnel of concrete segment-self compacted concrete(SCC)-steel tube superimposed linings under the combination loading of the inner hydraulic pressure and the external pressure,a full-scale experimental test was conducted.Without being subjected to inner hydraulic pressure and being subjected to inner hydraulic pressure are two parts of the test,which simulate the two operating conditions of the shield water conveyance tunnel structure when the internal water is not filled and when the water is full of pressure.In this paper,11 measurement indexes of the three-layer superimposed linings structure are analyzed in detail,and the load sharing proportion of the three-layer superimposed linings is discussed.Some structural response laws and understandings are obtained,which can provide some suggestions and references for the design optimization and engineering application of the water conveyance tunnel structure.The main work and achievements of this paper are summarized as follows:(1)In the test,12 sets of jack loading schemes are used to simulate the external load of the superimposed lining structure,and a method of applying high internal pressure by special flexible bladder and internal reaction steel frame is proposed.(2)The advantages and disadvantages of traditional point sensors and distributed optical fiber sensors are compared.The advanced nature of optical fiber sensing technology and applicability in the full-scale test are demonstrated.The measurement scheme of "optical fiber based and traditional matching" is adopted.(3)Without being subjected to inner hydraulic pressure,the test results show that the superimposed linings structure is still in elastic working state under the action of constant external load,which shows that the external pressure bearing capacity of the structure system still has a great space to play.In the superimposed linings,the SCC layer bears the largest proportion of external load,the segment takes the second place,and the inner steel tube bears the smallest proportion of external load.(4)Being subjected to the variable inner hydraulic pressure,the test results show that the superimposed linings structure undergoes three stages of elastic,elastic-plastic and failure,which is characterized by continuous failure——Firstly,when the inner hydraulic pressure was less than 0.6Mpa,the SCC layer is the main bearing structure and remains elastic,the loading was carried by all linings.Secondly,when the inner hydraulic pressure reached 0.6Mpa,the SCC layer cracked and the inner hydraulic pressure transferred to the outer lining rapidly,which indicated that the mechanical behavior of the structure entered the elastic-plastic phase.Finally,as the inner hydraulic pressure increased,the segment joint bolt yielded when the inner pressure reached 0.965 Mpa.Meanwhile,the outer lining gradually lost its bearing capacity and the inner pressure was mainly carried by the inner steel tube,which demonstrated that the structure entered the failure phase.