Browsing by Author "HUANG, AB"

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A MICROMECHANICAL STUDY OF PENETRATION TESTS IN GRANULAR MATERIAL
(1993-08-01)
HUANG, AB
;
MA, MY
;
LEE, JS
;
土木工程學系
;
Department of Civil Engineering
Penetration tests. such as the cone (Campanella and Robertson (1988), Proc. of the 1st Int. Symp. on Penetration Testing, Vol. 1, p. 93) or flat dilatometer (Marchetti (1980), J. Geotech. Eng. Div. 106, 299) tests are important field testing methods in characterizing soil properties. For granular materials, field testing is essentially the only alternative because of the difficulty in obtaining undisturbed samples. However, lacking an understanding of the penetration mechanisms, the interpretation of these field tests are empirical. A study was carried out to improve our understanding of penetration mechanisms taking advantage of the recent developments in micromechanical behavior of granular soils. A numerical technique which couples the distinct element method and boundary element method was developed to simulate two-dimensional penetration tests in a granular material. A series of simulated penetration tests of a 60-degrees apex angle penetrometer were performed in a normally consolidated granular deposit. The results showed that as the penetrometer passed the soil element it experiences a stress loading and unloading. The distribution of contact forces concentrates in the vertical direction below the penetrometer. The direction of particle contacts and contact forces rotates towards the penetrometer tip. The average coordination number does not vary significantly around the penetrometer. It appears that the finer particles experience stresses resulted from contact forces up to three times those of larger particles.
A MULTIPLE PURPOSE SOIL TESTING APPARATUS
(1994-06-01)
HUANG, AB
;
HSU, SP
;
KUHN, HR
;
交大名義發表
;
土木工程學系
A relatively compact soil testing system that is capable of performing monotonic/cyclic triaxial and torsional simple sheaf tests has been developed. A high-torque direct-drive, servo/stepper motor is used to provide the driving force. Under the servo mode, the motor could be controlled to provide a constant torque, which is used in stress-controlled tests. Strain-controlled tests are conducted using the stepper control mode. To perform triaxial tests, the rotational motion of the motor is transformed into linear motion using a preloaded ball screw shaft. A preloaded ball spline shaft directly attached to the motor is used to perform torsional simple shear tests. Because there are no gears in the driving system, there is no backlash during reversals of loading directions. The motor is equipped with an encoder and an indexer. The extremely rigid driving system and high resolution of the encoder enable the linear and rotational displacement to be monitored through the encoder/indexer system. Test control and data logging are fully automated using a personal computer. This paper provides details of the apparatus. A set of strain-controlled test data are presented to demonstrate capabilities of the new apparatus.
AN ANALYTICAL STUDY OF CONE PENETRATION TESTS IN GRANULAR MATERIAL
(1994-02-01)
HUANG, AB
;
MA, MY
;
土木工程學系
;
Department of Civil Engineering
A numerical technique that couples the distinct-element and boundary-element methods was developed to simulate a granular soil deposit as a two-dimensional, circular disk assembly. A series of simulated penetration tests of a 60-degrees apex angle cone was performed in normally consolidated and overconsolidated disk assemblies. The simulations allowed the cone penetration mechanisms to be evaluated from microscopic as well as the conventional, continuum mechanics points of view. Results show that the soil loading history can affect the characteristics of the soil failure mechanism and dilatancy. Lateral stress measurement behind the cone base is not sensitive to soil loading history. Finer particles appear to experience higher contact stresses and hence are more likely to be crushed by the cone penetration.
USE OF FUZZY CONTROL IN AUTOMATED SOIL TESTING
(1994-09-01)
HUANG, AB
;
HSU, SP
;
KUHN, HR
;
交大名義發表
;
土木工程學系
A servo-control algorithm that uses fuzzy logic has been developed for automated soil testing. The algorithm emulates the reasoning process of an experienced operator in controlling the pressure. The amount of pressure adjustment and time delay between adjustments is determined by fuzzy inference matrices. The fuzzy control logic provides a framework for the development of intelligent control algorithms which can be adapted in other aspects of automated soil testing. This paper introduces the concept of fuzzy control and its application in soil testing. Results of controlled gradient consolidation tests are presented to demonstrate the efficacy of fuzzy control.