基于三维裂隙网络模拟和单孔压水试验的裂隙张开度确定方法

Determination method of fracture aperture based on three-dimensional fracture network simulation and water injection tests

岩体裂隙的等效水力张开度(水力学等效隙宽)是岩体的关键力学几何参数之一。目前常采用交叉孔试验等大型试验方法获取野外深部岩体裂隙的张开度,但该方法很少在一个工程中多次使用,且难以分析裂隙张开度在空间上的变化。以三峡大坝右岸地下电站硐室围岩为例,提出了一种联合利用常规单孔压水试验数据和三维裂隙网络模拟,反演确定裂隙等效水力张开度的新方法。利用实测裂隙编录资料取得的统计数据开展裂隙产状随机模拟,构建与压水试验钻孔连通的三维离散裂隙网络渗流模型,拟合单孔压水稳态流量和压力的关系,反演不同深度岩体的裂隙等效水力张开度。结果表明,研究区岩体裂隙的等效水力张开度一般为0.07~0.30 mm,符合对数正态分布的统计特征,多数钻孔反演的裂隙等效水力张开度随埋深呈指数形式衰减,少数钻孔呈现出裂隙等效水力张开度随机性强、随埋深变化不明显的特征。相较传统方法,本方法反演结果显著不同,有待进一步验证。

[Objective]The aperture of fractures(hydraulic equivalent aperture of fractures)of rock fractures is one of the key mechanical parameters of rocks.It has significant indicative significance in water conservancy projects,geological surveys and so on.At present,large-scale test methods such as cross-hole tests are often used to obtain the fracture apertures of deep rock masses in the field,but this method is rarely used many times in projects,and it is difficult to analyse the spatial variation in the aperture of fractures.This spatial variation is precisely what we need to focus on and discuss because it affects the accurate definition and application of the hydraulic equivalent fracture aperture in engineering applications.[Methods]In this paper,taking the surrounding rock of an underground power station cavern on the right bank of the Three Gorges Dam as an example,a new inversion method for determining the hydraulic equivalent aperture of fractures is proposed by using conventional single-hole water injection test data and three-dimensional fracture network simulation.The statistical data obtained from the measured fracture cataloguing data are used to carry out random simulation of fracture characteristics,and a three-dimensional discrete fracture network seepage model connected with water injection test boreholes is constructed to fit the relationship between the single-hole steady-state flow rate and injection.The hydraulic equivalent apertures of fractures at different depths of rocks are inverted.[Results]The results show that the hydraulic equivalent aperture of fractures in the research area is generally 0.07-0.30 mm,which confirms to the statistical characteristics of the lognormal distribution.Most of the inverted hydraulic equivalent apertures of fractures in boreholes decrease exponentially with burial depth,while a few boreholes show strong randomness of the hydraulic equivalent aperture of fractures and no obvious change with burial depth.[Conclusion]Compared to those of traditional methods,the inversion results of this approach are significantly different and require further verification.