Cone Penetration Tests in Sand under Simulated Field Conditions
|關鍵字:||砂土;圓錐貫入試驗;標度槽試驗;邊界效應;軸對稱現地狀況模擬系統;擴孔理論;sand;cone penetration test;calibration chamber tests;boundary effects;axisymmetric field simulator;cavity expansion theory|
Due to the lack of cohesion, it is essentially impossible to obtain undisturbed samples in sand. In-situ testing is often used to determine the engineering properties for sands. The cone penetration test (CPT) is a popular in-situ testing method. Because of the large strain induced by cone penetration, the theoretical analysis of CPT has been difficult and hence limited. The interpretation of CPT has been mostly empirical. Some of the empirical equations are based on CPT in a calibration chamber. An important drawback of performing CPT in a calibration chamber is its boundary effects. It is possible that some of the controversies that exist amongst existing CPT interpretation methods are stemmed from boundary effects. There has been little knowledge of performing CPT in a controlled environment and under no boundary effects to validate any of the existing empirical equations. An experimental system that is capable of simulating axisymmetric field conditions has been developed. The new simulator consists of a stack of twenty rings to house the sand specimen. These rings are lined with an inflatable silicone rubber membrane on the inside. The boundary expansion and stress are measured and individually controlled, respectively at each ring level during CPT. The soil from physical boundary to infinity is simulated using a non-linear cavity expansion curve derived from a lateral compression test on the specimen. A series of CPT calibration tests have been performed in the new simulator system to correlate cone tip resistance ( ) with stress state. Results show that the correlation of and the initial mean effective normal stress (prior to cone penetration) is stronger than the other components of initial stress state. The horizontal stress on the physical specimen boundary after the cone tip passage has a clear and positive relationship with . The relationship between and the initial horizontal stress in sand prior to cone penetration is not nearly as obvious as reported previously. This thesis reviews available theories that analyze CPT in sand, introduces the concept of chamber CPT calibration tests, the new field simulator system developed in this research, presents CPT data obtained in the new simulator, and discusses implication in the interpretation of as it relates to the state of sand in light of the new findings.