模擬現地狀況下CPT之標度試驗

Abstract

由於砂土缺乏凝聚力，所以砂土的不擾動試樣很難取得。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。然而圓錐貫入試驗 的結果多靠經驗公式來分析，經驗公式大多經由試驗室中的標度試驗而來。標度試驗的重 要缺陷是它的邊界效應。常用的方法是將標度試體，如三軸試驗一樣的裝在單一的橡皮膜 中。標度槽試體的橫向邊界可以施加固定應力或零應變，這兩種邊界都無法模擬介於兩者 之間的真正現地情況。有人提出以修正係數的方法來抵消邊界效應，但是修正係數方法的 正確性與邊界影響之機制至今都尚未得到證實。本研究的主要目的是研發一套能夠模擬現 地情況的標度槽。標度槽直徑 790 mm、高度 1600 mm，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。每一圓環皆以環形應變計量測其橫向變形。砂土在 不同高度因圓錐貫入而產生之邊界橫向位移用環形應變計量測。在不同高度每一圓環之側 向應力以試體橫向應力與應變的關係計算得知。為測試此一新標度槽系統已完成了一系列 應力、應變和模擬現地控制的 CPT 標度槽試驗。 本論文敘述此一新標度槽系統之架構與 試驗結果分析。 Due to the lack of cohesion, it is difficult to obtain undisturbed samples of 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. However, as for many other in-situ testing methods, we rely on empirical rules to interpret CPT data. A significant part of these empirical rules came from laboratory chamber calibration tests.An important draw back of the calibration chamber is its boundary effects, The sand specimen is typically encased in a rubber membrane as in the case of a triaxial test. The lateral boundary of the specimen in a calibration chamber is either stress controlled or rigid.Neither of these two boundary conditions can truly duplicate the field conditions which lies somewhere in between. Correction factors have been proposed to account for these boundary effects. However, the validity of the use of correction factors and the mechanisms of boundary effects have not been independently verified. The main objective of this research project is develop a chamber system that is capable of simulating field conditions. Instead of using a single membrane to encase the specimen, twenty inflatable rings are placed around the specimen and the size of the new chamber system is diameter 790mm and 1600mm high. The boundary movement induced by the cone penetration is measured at each ring level by an extensometer. The lateral stress at each ring level is determined by stress-strain correlation of the specimen. For testing the new chamber system, we completed a series of CPT chamber tests by stress or strain and field-simulator controlled. This report describes details of the new chamber system, and presents available test results.