Abstract

Four NX-diameter holes were diamond-drilled in competent granite. Samples of the recovered core were used in laboratory tests. A borehole, plate-bearing device known as a Goodman jack was used to perform load-deformation tests on the rock in the core hole. The samples used in the laboratory tests were taken from depths in the hole at or within 5 ft of those at which the jacking tests were made. Borehole camera records, compressional and shear-wave velocities, and densities were measured. Dynamic elastic constants were computed for the in-situ material, while comparative data [except camera records] were obtained in the laboratory. These data were examined to evaluate the significance of the in-situ modulus of deformation [Ed], the value computed from Goodman-jack tests. Average test results show an excellent correlation between in-situ and laboratory data. The ratio of laboratory to field deformation modulus ranges from 9.82 to 7.21 for 3,000- and 9,000-psi stress levels, respectively. The dynamic modulus ratio, ED field/ED lab, is 1.02; the compressional wave velocity ratio, Vp field/ Vp lab, is 0.94; the shear-wave velocity ratio, Vs field/Vs lab, is 1.12; and the density ratio, gamma field/gamma lab, is 0.95.

Introduction

This paper presents and discusses some of the test results obtained from a large rock mechanics program. That portion of the program discussed in this paper was conducted program discussed in this paper was conducted for purposes of developing data for use in a computer code used in connection with the design of a medium-size structure. As an outgrowth of the analysis of these data, several questions arose. One concerned the accuracy of the in-situ deformation modulus [Ed]; i.e., was the Ed calculated from pressure-displacement data, the value computed pressure-displacement data, the value computed from NX plate-bearing tests, realistic? The plate-bearing device used in this program was plate-bearing device used in this program was the Goodman jack.

Several approaches could have been used in getting a reasonable answer to the above question. One approach would be to evaluate other similar devices in the same rock mass in which the Goodman jack was used; however, the expense would be prohibitive. Other deformation moduli tests, such as flat-jack and radial jacking tests and large plate-bearing tests, are described in Ref. 2. Another approach would be to rely on published data that would give an approximate figure. Coons states that in-situ tests indicate that the Ed is generally from one-half to one-tenth of the laboratory modulus of elasticity. This range is given for a large number of other types of plate-jacking tests; however, one could assume plate-jacking tests; however, one could assume it applies to borehole deformation tests also. An examination of comparative values suggests that the in-situ Ed obtained for the rock mass in question was reasonable.

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