AN EXPERIMENTAL AND ANALYTICAL STUDY OF DRY-STONE RETAINING WALLS

干石墙是由仔细堆放的石块碎石形成的，不使用砂浆。干石墙遍布世界各地，形成了英国许多地区的独特特征，包括科茨沃尔德、山顶区和湖区。干石挡土墙是一种用于支撑公路、铁路、运河路基和堤防的工程结构。这些墙通常厚约0.6米，由粘合的砖石表面组成，后面堆放着碎石。它们大多建于19世纪和20世纪初。仅在英国的公路网上，就有大约9000公里的这样的城墙，估计替换价值超过10亿。虽然老化的墙体仍然表现良好，但其状况恶化和偶尔突然坍塌是公路维修当局面临的主要问题。这些墙体在荷载下的实际表现以及防止倒塌的安全系数是不确定的。目前对包括三维效应在内的真实倒塌机制缺乏了解，再加上现代设计规范所要求的安全系数，以及设计参数(如土壤性质、墙尺寸、地下水条件和荷载)的不确定性，导致不必要地更换令人满意的墙，并无法识别即将倒塌的墙。尽管干石墙比更现代的挡土方法(如使用当地材料结合自由排水和灵活的结构)具有明显的优势，但工程上的不确定性使得新的和替换的建筑在干石砌块中很少出现。不必要地更换令人满意的墙，通常是用混凝土结构，会导致与建筑相关的高昂成本、交通中断、财产或生命损失风险增加，并可能对环境造成不利影响。目前对干石挡土墙行为的真正机制缺乏了解或许并不令人惊讶，因为自从170多年前进行了一项有限的研究以来，还没有对干石挡土墙进行重大的实验调查。因此，缺乏有关干石挡土墙性能的直接定量数据不仅本身就是一个问题，而且还阻碍了现代基于计算机的数值分析的有效性。只有对这些结构的工作原理有一个适当的、经过验证的、基于理论的理解，并开发适用于现代工程环境的合适的设计方法，才能增加干石挡土墙在维修和新建筑中的使用，并延长现有墙体的使用寿命。目前阻碍对干石挡土墙进行有效和准确评估的两个主要不确定领域是鼓包和墙体厚度。这项研究的目的是通过结合参数三维离散元分析的试验研究，以及进一步发展用于现有干石挡土墙设计和分析的极限平衡分析方法，来加深对这两个关键问题的理解。

Dry-stone walls are formed by carefully stacking blocks of stone rubble, without the use of mortar. Found throughout the world, dry-stone walls form the distinctive character of many areas of the UK, including the Cotswolds, Peak District and Lake District. Dry-stone retaining walls are engineering structures used to support road, railway and canal cuttings and embankments. The walls are commonly about 0.6m thick and are comprised of a bonded masonry face with stacked rubble stone behind. They were mostly built during the 19th and early 20th centuries. There are about 9000 km of these walls along the UK road network alone, having an estimated replacement value in excess of 1 billion. Though the ageing stock of walls is still performing very well, their deteriorating condition and occasional sudden collapse is a major problem for highway maintenance authorities.There is uncertainty about how these walls actually behave under load and what the factors of safety against collapse are. This current lack of understanding of real collapse mechanisms including three-dimensional effects, combined with the factors of safety required by modern design codes and uncertainties over design parameters such as soil properties, wall dimensions, groundwater conditions and loading, leads to the unnecessary replacement of satisfactory walls and the failure to identify walls that are in danger of imminent collapse.Even though dry-stone walls have distinct advantages over more modern earth retention methods (such as the use of local materials combined with a free-draining and flexible structure), the engineering uncertainties are such that new and replacement construction is rarely in dry-stone masonry. The unnecessary replacement of satisfactory walls, often by concrete structures, results in high costs associated with construction, traffic disruption, increased risk of damage to property or life, and potentially adverse environmental impacts. The current lack of understanding of the real mechanisms of dry-stone retaining wall behaviour is perhaps unsurprising given that no significant experimental investigation of dry-stone retaining walls has been carried out since a limited study undertaken over 170 years ago. The resulting lack of direct quantitative data concerning dry-stone retaining wall behaviour is not only a problem in its own right, but has also hampered validation of modern computer-based numerical analyses.Increased use of dry-stone walling for repairs and new construction, and prolonging the service life of the existing stock, can only happen with a proper, validated, theoretically based understanding of how these structures work, and the development of suitable design methods that are applicable in the modern engineering environment. The two main areas of uncertainty currently hindering the efficient and accurate assessment of dry-stone retaining walls are bulging and wall thickness. The objective of the proposed research is to develop a greater understanding of these two key issues by means of an experimental study combined with parametric three-dimensional discrete element analyses, and the further development of limit equilibrium analysis methods for the design and analysis of existing dry-stone retaining walls.