Structures and Geotechnics Laboratory

Structures and Geotechnics Laboratory

In these laboratory classes attention is drawn to the importance of the interaction of soil and structures in determining the strength en masse of soils. Two common geotechnical structures are being considered; first retaining wall structures supporting soil at different levels in front and behind the wall are examined and second the damaging effects of ground water flow on foundations of bridges and dams are highlighted through a number of case studies which the students are prompted to find and report upon by searching documented cases readily available on the internet.

A simplified explanation of typical retaining walls, an introduction to the lateral pressure of soil, and the measurement of the angle of repose of a sand are followed by a reduced-scale experiment carried out in the laboratory by the students. A device developed in-house is used to simulate a retaining wall moving towards and/or away from a mass of sand while the force exerted by the sand mass on the wall is being measured by load cells mounted on the wall. Apart from simple calculations of stresses along the wall, the main thrust of these experiments is to improve the understanding on the prevailing mechanisms resisting soil deformation, to measure the limiting horizontal stresses developed in the sand at large deformations and observe the failure mechanisms.

Ground water flow is examined in a Darcy apparatus developed in-house. The effects of changing the inlet and outlet pressures in a cylindrical sand pack can be observed on the surface through model footings as well as through the transparent cylinder.  Phenomena such as seepage, piping and sand boiling due to upward flow of water, as well as liquefaction due to seismic loading, are explored in the laboratory on a sand sample to improve understanding on the key factors affecting the performance of soil-structure systems e.g. catastrophic damage due to internal erosion and/or erosion underneath a dam, a bridge abutment etc. The students have to report on hazards to infrastructure using case studies.