Drystone walling is an ancient form of wall construction, used worldwide wherever there is an abundance of raw building materials. However, very little research has been conducted on these structures, making their analysis difficult. As part of an ongoing investigation, four full-scale drystone retaining walls were built and tested to failure in a bespoke outdoor test laboratory. Through the course of the testing, the distinctive bulge patterns that are found in many in situ walls were successfully recreated. This paper describes the set-up of the test laboratory and instrumentation used, in addition to the proceedings of each wall test. Initial findings of the project tests and a discussion regarding the underlying reasons behind bulging in drystone walls are presented.
A limit-equilibrium analysis program has been developed as part of an investigation into the stability of drystone retaining structures. Initial verification of the program's function was in relation to field trials conducted in 1834 by Lieutenant-General Burgoyne, which have been the main reference to date for checking numerical modelling of drystone retaining walls. Parametric studies and investigations of bulging mechanisms are reported and analysed. Program predictions have been compared with the initial results from new small-scale and full-scale drystone retaining wall tests.
Drystone retaining walls are sustainable engineering structures constructed with locally obtained natural stone. They were commonly built with very slender profiles compared with modern massmasonry structures, leading to a common belief among engineers that they have very low margins of safety. These structures remain critical to the transport infrastructure in many parts of the world, and have proven to be very durable, yet very few new drystone retaining walls are built, and walls which do fail are usually replaced with concrete constructions. We show that these walls are ductile even though their components are brittle, and in having tensile strength through the interlocking of their stones, even though they are assembled without any cohesive material such as mortar. These properties are critical to a proper understanding of their behaviour and durability. Full-scale testing of five drystone retaining walls has shown that bulging, most commonly regarded as a sign of incipient failure, begins as a ductile adaptation of the geometry to the loads imposed on it. Localised bulging can be a consequence of small defects in construction or foundation conditions, or concentrated loading, and may be sustained indefinitely in a wall which is in general wellconstructed. These insights into the behaviour of walls allow the design of new walls which use materials efficiently, and enable existing walls to be kept in service, and may inspire new ways of achieving ductility in engineering materials.
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