Caisson load tests

Data from a few full scale load tests under different loading and ground conditions have been made available to the author and are discussed below. 

Based on the limited data available, there seems to be an empirical relationship between shaft friction and UCS of rock samples collected from the bearing rock. For completely weathered granite, the commonly used relationship = 2iV seems to be reasonable. The tests proved that the caisson ring could transfer load onto the soil provided construction is carried out carefully. 

Limited plate load tests have been carried out within the base of an excavated caisson (Amp 1996 to 2001). The end bearing mobilized was relatively high (fi = 501V). The modulus E was found to be 70,000 kPa. 

Shaft friction was evaluated by placing a series of jacks within a gap between constmcted caisson rings and applying load to push them apart. This simple test showed that the caisson ring could transfer load onto the soil. The commonly used relationship= 21V seem to be acceptable. 

Very few lateral load tests results are available to the author. One lateral load test was carried out at a hill-site on a 1.2 m diameter caisson embedded on sloping ground. The applied lateral load of 80 ton caused a maximum 30 mm deflection. Back-analysis of the data indicate a relationship of = 15001V and A , =0.5. 

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The procedure described above is straightforward in principle. However, in practice, great care must be taken in the test fixture design to assnre that applied loads cause a uniform state of stress in the test specimen. Two types of tests that have been developed for this purpose include (1) the simple tensile test for uniaxial states of stress, (2) the thin-walled tube subjected to combined torsion and internal pressure, for biaxial states of stress. Some theoretical aspects of the simple tensile test are developed in the sample problem which follows. For a more detailed discussion on experimental procedures for characterizing the material properties of composite materials, see Caisson and Pipes and Whitney et al. ... 

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