饱和-风干循环过程中砂岩次生孔隙率变化规律研究

Research on secondary porosity changing law of sandstone under saturation-air dry cycles

三峡工程竣工后,库水每年将在145 m和175 m水位之间或缓慢或快速的升降,在库水位大幅度涨落的情况下,库岸边坡部分岩体处于"饱和-风干"的循环动态,水-岩循环作用将造成岩体性质劣化。据此,以三峡库区库岸边坡变幅带的砂岩为研究对象,设计了"饱和-风干"循环作用试验。试验结果表明,与常规浸泡试验相比,水压力的升、降变化和"饱和-风干"循环作用对岩体的损伤有累积放大作用,浸泡时水压力变化越大,对离子浓度和次生孔隙的影响越大,而且,"饱和-风干"循环次数越多,岩体的损伤越严重。提出了基于离子浓度变化计算岩石中次生孔隙率变化规律的方法,与实测次生孔隙率变化规律基本一致。因此,可以把这种方法应用到现场监测中去,通过长期监测离子浓度的变化来推测岩体中水化学反应发生的程度,以及次生孔隙率的发育情况。分析成果为研究库岸边坡岩体在"饱和-风干"循环过程中的岩体性质劣化规律奠定了一定的基础。

After Three Gorges Project completion,the reservoir water level will be raised to 175 m and lowered to 145 m every year.During the fluctuation of the reservoir water level,the quality of rock mass of the bank slopes will be deteriorated gradually in water-rock interaction of saturation-air dry cycles.Thereafter,taking sand rock at the fluctuation of reservoir water level as a representative,an experiment model the process of saturation-air dry cycles is designed.Test results show that comparing with the conventional immersion experiment,the rise or decline of water pressure and the cycle of saturation-air dry have cumulative and magnified effect on the damage of rock mass.Tests also show that the greater change of water pressure in immersion,the greater impact on the ion concentration and secondary porosity;at the same time,the more cycles of saturation-air dry,the more serious damage to the rock mass.Based on the change of ion concentration,the computational method of secondary porosity change law in the rock which is consistent with measured changes of secondary porosity is proposed.It can be applied to on-site monitoring,which can speculate the water chemical reaction in rock,and how the secondary porosity rate has developed through long-term monitoring of ion concentration.Research results lay the foundation for the study of rock mass quality of the bank slopes deteriorating in the saturation-air dry cycles.