At present, much attention is being focussed on problems of deformation and strength of rock comprising the foundation of structures. A variety of in situ and laboratory tests are available for investigation of foundation rock. Due to such factors as weathering, geological discontinuity and anisotropy resulting from stratum structure, mechanical behaviour due to deformation and strength characteristics is difficult to analyse. As another complication factor, it is conceivable that the rock shows varying responses in accordance with different testing method, loading patterns andtest conditions.
The authors have had the opportunity to perform both in situ testing and laboratory testing under a variety of conditions on soft, tertiary, homogeneous rock. This testing has provided good data on the influence ontest results of various testing methods applied to the same type of rock under various conditions.
In this paper we will explain the results ofthese tests and the implications of results obtained. Finally, we will consider theextent of influence on the characteristics of rock obtained by different testing methods.
The rocks in which the authors conducted testing was classified as pliocene, massive, non-bedding sedimentary rock. The rock was formed in a sedimentery enviroment, with no folding or fault action effects visible.
Slightly closed cracks were found at several meter intervals. General physical and mechanical values of this rock are shown in Table 1. Most of rock samples were taken from test adits and borings. As a result of many boring surveys, seismic velocity measurement by geophysical fan shooting and logging in test adits, it became clear that the rock is highly homogeneous.
(Table in full paper)
Table 2 shows the various types of tests that were performed on these rocks. The tests may be basically classified as in situ or laboratory tests. Deformation testing is either static or dynamic.
Because the plate loading test shows a general tendency for strain to decrease with depth, average strain was calculated.
In direct rock shear testing, average strain was calculated using the same method, and assuming that the base of the block (60 × 60 cm) was circular with a 60 cm diameter. Next, the strain of a columnar specimen was determind. In this test, because the deformation coefficient for only the specimen was determind, only this strain was used in a deformation modulus. In addition, in the borehole load test, average strain was postualted using the thick cylinder theory, and average strain from borehole wall to a point twice the diameter of the borehole was calculated.
(Table in full paper)
Next, different results obtained according to varying conditions and deformation and strength tests will be discussed.
With the exception of berehole load testing, for each of the in situ testing method, deformation coefficients which were taken at various depths showed relatively little scattering, with deviation from average in the range of 3.1% to 25%.
