Abstract
Elastic modulus is a significant parameter in design and construction for rock engineering. Rock penetration test as a convenient method to evaluate the modulus of rocks has a great potential to be used. Based on the elastic theory, the relationship between rock penetration behavior and elastic modulus was established. In order to evaluate the elastic modulus, the shape coefficient is an important parameter to be determined. However, due to many factors, the value of this parameter is still uncertain. To provide a better insight into the shape coefficient and its factors, a series of penetration tests which used several types of rock samples with different sizes were conducted to study the determination of shape coefficient under different conditions. The test results show that sample size influences the shape coefficient, and with the increase in size, the shape coefficient decreases gradually to a stable value. In contrast, confining pressure has less effect on shape coefficient, and in the moderate and low stresses region, a fixed value can be selected for the test. Different types of rocks correspond to different shape coefficients. The shape coefficient of hard rock is higher than that of soft rock. Shape coefficient should be selected reasonably according to the penetration depth in practical application, and the reason, furthermore, why back-calculated shape coefficient deviates from the theoretical value is also discussed.
Highlights
Elastic modulus is an important parameter for rock deformation
To study the influence of in situ pressure on the shape coefficient, an additional lateral loading apparatus (Figure 2(b)) was used in the test to apply bidirectional confining pressure. e bidirectional loading apparatus was designed as a hollow ring-shaped chamber, which facilitates the application of two independent perpendicular loads. ese two loads were applied to the rock specimen by two servo-controlled hydraulic jacks in the apparatus
Scale effect is an important factor for the application of the test method. e test was 60° α = 2 mm (a) conducted on finite size of the laboratory specimens rather than semi-infinite surface of rock. erefore, the shape coefficients back-calculated from the test results differ from the theoretical value
Summary
Elastic modulus is an important parameter for rock deformation. In rock engineering, it is an important basis for the design and construction. Erefore, to give reliable prediction of the elastic modulus for practical application, it is necessary to provide a better insight into the shape coefficient and its factors. To answer this question, a series of laboratory penetration tests were conducted to study the values and influence factor of shape coefficient. A series of laboratory penetration tests were conducted to study the values and influence factor of shape coefficient For this purpose, various types of rock with different size and confining pressure were analyzed. Suggestions are given to improve the prediction accuracy of elastic modulus based on the penetration test method
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