Based on the response of the surrounding rock (including the relaxed grouted zone and the fault) and the reinforced concrete lining of the pressure tunnel in the full strength model test, this article discusses the stress-changing and cracking characters of the lining and the rock, and investigates the combined action of the reinforced concrete lining and the rock. The conclusion from the test provides the convincing argument for us to choose the reinforced concrete lining for a certain pressure tunnel.
It is very important for designing the pressure tunnel safely and economically to decide the capability of the surrounding rock of bearing the internal water pressure. Thus, it's necessary to study the interaction of the lining and the rock. The complicated surrounding rock had to be simulated, so the geomechanical model test is always used to study the pressure tunnel. But the scale of stress of the geomechanical model is ordinarily smaller than 1, it's very difficult to choose the model material to simulate the prototype on the whole stress-strain path, and the model can not reflect the feature of the prototype directly and truely. The simulants which have the same or near mechanical parameters of the prototype are used in the full strength model test, so the model can tell the feature of the prototype under all conditions, and the results from the full strength model test is direct and reliable. Now, the gypsum model and the geomechanical model have been replaced gradually by the full strength model in the study of the hydraulic structure, but the full strength model is rarely adopted in the study of the underground structure and the rock because of the difficulty of simulating the rock. Herbert E. Lindberg (1982) had used the full strength model to study the effect of the rock joint and the weak plane, and he found that the results from the 1:28 model test were same as the results from the prototype test. In this article, the 1:19 full strength model has been used to study the interaction of the surrounding rock and the lining, and the satisfied results have been gotten from the test.
The tunnel we concern is 9.5 meter in internal diameter and 0.9 meter in thickness of the lining. After poured the 400# reinforced concrete lining, the backfill and consolidation grouting would be taking, and the pressure of the consolidation grouting has been designed as l.0MPa. The geostress is only caused of the dead load and the geostress coefficient of confinement pressure K is 0.37- The normal water head of the pressure is 65 meter and that of the water hammer is 35 meter. The surrounding rock is consisted of the limestone, relaxed grouted zone and fault F26 . The main mechanical parameters of the rock and the lining are listed in Table I.
The full strength model must have these similar conditions as follow.
