模擬現地狀況下砂土中之圓錐貫入試驗

Abstract

由於砂土缺乏凝聚力，所以砂土的不擾動土樣幾乎不可能取得。 為量測砂土的工程性質，現地試驗是常用的方法。 圓錐貫入試驗是一種廣泛使用的現場試驗方法。 由於圓錐貫入土壤中是一種大應變的行為， 要以理論分析的方法來合理的解釋試驗結果， 有其限制性與困難度。 所以對於所擷取資料的分析與解釋， 則大多由經驗公式而來。而經驗公式大多來自於試驗室中的標度試驗。 標度試驗的重要缺陷是它的邊界效應。 對於解釋圓錐貫入試驗結果的某些爭論或許即是邊界效應所導致。 現今尚難以在可控制的環境與沒有邊界效應的狀況下， 操作圓錐貫入試驗，以證實經驗公式的正確性。 一套能夠模擬現地情況的軸對稱模擬系統已研發完成。 此系統用20個鋼環內覆可膨脹的矽膠膜圓環來替代傳統標度槽單一的橡皮膜。 圓錐貫入時，每一圓環皆可各自量測與控制其變形及側向應力。 試體的側向應力與應變關係可直接由側向壓縮試驗求得。 自試體邊界至無窮遠處土體的應力狀態以擴孔理論來模擬。 在現地模擬系統中已完成一系列的圓錐貫入試驗， 用以了解錐尖阻抗和應力狀態間的關連性。試驗結果顯示， 錐尖阻抗和圓錐貫入前的初始平均有效應力間有較佳的關連性。 錐尖通過後所造成的試體側向邊界上之應力與錐尖阻抗間有明確的正相關性存在。 以前學者所提出的錐尖阻抗和圓錐貫入前的初始側向應力間所具有的正相關性則並不明顯。 本論文介紹解釋砂土中圓錐貫入試驗的理論、圓錐貫入標度試驗的觀念、 新研發之現地模擬系統的架構、模擬現地狀況的圓錐貫入試驗結果， 以及根據試驗結果探討錐尖阻抗與砂土狀態間的相關性。

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.