水工有压隧洞衬砌双K断裂理论分析及裂缝宽度计算

Double-K fracture theoretical analysis and crack width calculation of hydraulic pressure tunnel linng

2005年制定的我国电力行业标准《水工混凝土断裂韧度试验规程》以双K断裂理论为理论依据,该理论所发展的闭合解析解形式简单且物理意义明确,试验技术方法简易可行,能够很好地描述裂缝的起裂、稳定扩展和失稳扩展。本文以该理论为出发点,对进行的大比尺水工有压隧洞模型试验中存在的三种衬砌结构断面即素混凝土断面、单筋断面和双筋断面进行了断裂力学分析,推导计算了它们在不同内水压下的应力强度因子,确定了三种不同衬砌结构的双K断裂参数,为研究水工有压隧洞衬砌结构的裂缝扩展过程和破坏机理提供了一种有效的方法。此外,给出了基于断裂力学的裂缝宽度计算式,计算了单双筋衬砌结构在不同内水压力下的裂缝宽度,并根据SLT191—96规范和DL/T5195—2004规范计算了裂缝宽度,发现断裂力学计算值、SLT191—96规范计算值与试验结果三者吻合很好,DL/T5195—2004规范计算值小于试验结果。

China power industry standard ＂Norm for Fracture Test of Hydraulic Concrete＂ established in 2005 is based on double-K fracture theory, which well describes the initiation of crack, stable development and unstable development in crack extension process. The closed-form formula proposed in double-K fracture model is simple in theory and clear in physical meaning, and the experimental method required for determination of fracture parameters is feasible and simple. This paper mainly presents the application of double-K fracture theory for hydraulic-pressure tunnel lining structures. For three typical sections of tunnel lining structures, i.e. , plain concrete, single-layer reinforced concrete and double-layer reinforced concrete, the stress intensity factors under different water pressures are calculated and double-K fracture controlling parameters determined. It is found that the fracture mechanics approach provides an effective technique for better understanding of the mechanical behavior and potential failure mechanism of such structures. In addition, an expression for determining crack width is developed based on the fracture mechanics approach. The crack widths of the single- and double-layer reinforced concrete lining structures under hydraulic pressure are calculated using the proposed formula and then compared with experimental results and the existing two design codes, the SLT 191--96 code and the DL/T5195--2004 code. It is found that the values calculated by the fracture mechanics approach are close to both experimental results and values calculated using SLT 191--96 code, while the DL/T 5195--2004 code underestimates crack width when compared with the experimental measurements.