高压引水隧洞的有限元计算

THE CALCULATION OF HIGH PRESSURE TUNNEL BY MEANS OF FINITE ELEMENT METHOD

钢筋混凝土高压引水圆型隧洞的设计与计算,其中一个重要的内容是用有限元模型正确模拟地应力,以判断在隧洞开挖后围岩的2次应力场中的应力是否仍大于内水压力在围岩中产生的主拉应力,围岩会不会出现水力劈裂现象?也就是说,要保证运行期间不发生水力劈裂,只有按内水压力作用下的三次应力场中不出现拉应力(或者拉应力远小于围岩的极限抗拉强度)来确定围岩的承载能力方能保证这一点.用变温应力场来模拟地应力能够获得合理的位移与应力计算结果.隧洞混凝土衬体的配筋是由裂缝开展宽度计算确定的.通过模拟钢筋的有限元模型的钢筋工作应力的计算结果来确定混凝土的缝宽,将能够较全面地考虑包括隧洞体型尺寸、围岩弹模与弹性抗力、混凝土标号、衬厚、配筋量以及高压固结灌浆的残余应力等诸因素的影响,合理地确定配筋量.

For the design and numerical calculation of circular high pressure tunnel with reinforced concrete lining, one of the most important numerical treatment is the accurate in-situ stress modelling, so as to make the judgement if the in-situ stresses are still larger than that stresses caused by internal pressure, i. e. it will not lead to the hydraulic fracture in the rockmass. That is to say, for the long-term operation, if there is no tensile stress in the rockmass or the tensile stress is much less than the rock ultimate tensile strength (the tensile stress in the rockmass is equal to the in-situ stress plus the tensile stress caused by the internal pressuse), no hydraulic fracture will take place in the rockmass during the operation. To model the in-situ stresses by thermal stresses can get the satisfactory results for the displacement and stresses. Moreover, the reinforcement of the concrete lining in the tunnel is determinded by the calculation of the development of the crack width. The crack width can be led out by the re-bars' working stresses which are calculated from the FEM model, in which cracked concrete is modelled by anisotropic material elements, and reinforcement is modelled by truss elements. In this way, we can consider the effect by all circumstances concerned the tunnel including dimensions, Young's modulus of rockmass and its elastic resistance, concrete strength and the thickness of the concrete lining, reinforcement, residual stresses from the high pressure grouting, etc. Finally, we can lead to the optimum design of the high pressure tunnel as well.