Search

A newly designed triaxial testing system equipped with a high-precision servo motor and local strain sensors is developed to perform the triaxial test. The servo motor (a direct-drive motor) was used to provide the necessary axial displacement, and to measure the induced strain. A set of accessories for preparation of a specimen was used to eliminate bedding errors and tilting errors. Differences of strains measured through the direct-drive motor and the local strain sensor were studied by conducting triaxial tests on both reconstituted samples and tube samples of Taipei silty clay. The results of the tests show that effective confining pressures or shearing rates cause little difference in the strains measured in the two ways: the difference in strain was less than 6% at small strain. The variations in stiffness measured by the two methods at small strain were in the range −3% to +5%. The ratios of strain measured by the two methods near the failure state of the sample were close to 1. The results have shown that measuring axial strain by a direct-drive motor is reliable, and may be used to improve strain measurement for triaxial tests on soft clay under similar testing conditions. [ABSTRACT FROM AUTHOR]

Abstract: The paper describes the computation of the maximum horizontal stress (σ H) magnitude in the vicinity of the Chelungpu Fault, Taiwan, host of the slip zone during the Chi-Chi earthquake (M w 7.6; 1999). The scientific hole B intercepts the Chelungpu Fault at 1136 m. At the depths of logged breakouts (940–1310 m), the vertical stress (σ v) as estimated from density logs increases linearly with depth from 22 to 31 MPa. A series of leak-off tests yielded two reliable shut-in pressures, 23.7 MPa at 1085 m and 29.8 MPa at 1279 m, which are lower than the estimated σ v, albeit by only 2.1 and 0.6 MPa, respectively. In our analysis the shut-in pressures were considered to represent estimates of the least horizontal principal stresses (σ h) at the respective depths, and consequently the test-induced fractures were assumed to have been vertical. Principal stress directions had been previously determined by others (105°–155° for the maximum horizontal stress, σ H, except in the immediate vicinity of the Chelungpu Fault). The contribution of this paper is the estimation of the σ H magnitude by considering that the state of stress at the points of intersection between breakout and borehole wall is in a state of limit equilibrium with the true triaxial strength criterion. The resulting σ H in the range of logged breakouts increases with depth from 55 MPa at 940 m to 59 MPa at 1310 m. Thus, the estimated state of stress prevailing across the Chelungpu Fault is compatible with strike-slip, but marginally also with thrust faulting. However, the likelihood that the shut-in pressures actually represent σ v magnitudes, and that the leak-off test-induced fractures were sub-horizontal, cannot be ignored. In that case the state of stress would clearly favor thrust faulting. [Copyright &y& Elsevier]

AbstractThe effects of ring characteristics on the compressive strength and dynamic modulus of elasticity of seven softwood species in Taiwan were examined. The results revealed good correlation between compressive strength and dynamic modulus of elasticity obtained using an ultrasonic wave technique (correlation coefficient r0.77–0.86). Overall, compressive strength increased with decreasing ring width parameters and increasing ring density parameters. Ring density was related to compressive strength, but was not the sole factor affecting the wood strength. According to our statistical analysis, compressive strength was affected by various ring characteristics. Relationships between ring characteristics and compressive strength are influenced by the anatomic direction. Results revealed that earlywood density and minimum density in a ring are equally important variables for evaluating the compressive strength of wood. [ABSTRACT FROM AUTHOR]