受船行降水作用的内河航道岸坡护面设计：一种概率化无限边坡分析

摘要

为使德国内河航道沿岸堤岸免受船行降水所致的局部滑坡破坏，工程上主要采用岸坡护面加以防护。大段堤岸的设计往往只依据数量有限的现场与室内试验，因而在土体力学与水力特性方面存在不确定性。现行设计标准以偏于保守的设计假定和经验知识来处理这些不确定性。本文借助一维随机场与经改进以计入船行降水的无限边坡模型，考察沿垂向非均质的地基特性对所需护面层厚度的影响。在无限边坡假定的适用范围内，研究了内摩擦角与水力传导系数空间变异的影响，并与确定性基准算例相比较。结果表明，确定性设计所获得的安全水准强烈依赖于特征值的选取，其中水力传导系数尤其决定设计的可靠度。某些情形下，水力传导系数取 5% 分位值并不能给出偏安全的所需护面层厚度估计。就有效内摩擦角而言，对透水性较好的土体，取 5% 分位值可能高估所需护面层厚度；对透水性较差的土体，5% 分位值则与随机场分析结果相当。对于有效内摩擦角与水力传导系数同时随机的组合，所考察的各基准算例似乎均能保证工程安全，但对应的可靠度水平并不相同。据此，本文就场地勘察以及水力传导系数与有效内摩擦角特征值的选取提出了建议。

Abstract

To protect embankments along German inland waterways against local slope sliding failure caused by ship-induced water level drawdown, they are mainly secured by bank revetments. Often, large embankment sections are designed on the basis of a limited number of field and laboratory tests. Thus, uncertainties arise with regard to the mechanical and hydraulic ground properties. Current design standards account for these uncertainties by conservative design assumptions and empirical knowledge. This paper investigates the effects of vertically non-homogeneous ground properties on the required armour layer thickness using 1D random fields and an infinite slope model, which was modified to account for ship-induced drawdowns. Within the limitations of the infinite slope assumptions, the effects of a spatially variable friction angle and hydraulic conductivity are investigated and compared to deterministic benchmark cases. The investigations show that the level of safety obtained with the deterministic design depends strongly on the choice of the characteristic values. Particularly, the hydraulic conductivity determines the reliability of the design. In some cases, the 5 % quantile of the hydraulic conductivity does not yield a conservative estimate of the required armour layer thickness. In the case of the effective friction angle, the 5 % quantile may overestimate the required armour layer thickness for permeable soils. For less permeable soils, the 5 % quantile meets the solution of the random field analyses. For the combination of random effective friction angle and random hydraulic conductivity, all investigated benchmark studies seem to ensure engineering safety, but on different reliability levels. Based on these findings, recommendations regarding site exploration and choice of characteristic values of hydraulic conductivity and effective friction angle are provided.