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Deep excavations in over-consolidated clays lead to swelling of the clay, which can exert large swell pressures on the basement slabs. In this paper, four prototype scenarios of basement construction in over-consolidated clay were investigated using both centrifuge modelling and finite element modelling. The main aim was to discern the effects of two aspects of embedment on long-term heave behaviour when relatively flexible and relatively stiff slabs were employed. The extension of diaphragm side walls below the formation level and the presence of a drainage layer between the slab and the clay were investigated. The results confirm that the use of a drainage layer would shorten the time of consolidation as expected. The variations in embedment conditions would also cause some redistribution of heave displacements, though the magnitude of such redistribution is relatively small, both when compared to the overall magnitudes of heave displacement and when compared to the effect of varying base slab stiffness on heave displacement.

This paper describes the techniques used to investigate the conditions, dimensions and stability of underground workings in Silurian limestone in the West Midlands. Drillholes were formed by rotary coring methods through the rock strata overlying the cavities. Rock cores were taken in the drillholes and classified. In situ permeability tests, geophysical logging and a closed-circuit television survey were carried out. The shape and dimensions of the workings in the proximity of the holes were established by ultrasonic surveys. The paper describes the use of a variety of techniques, some of which were primarily developed for use in fields other than civil engineering.

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