邊界元素法控制的標度槽之研發

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，現場試驗是常用的方法。圓錐貫入試驗是一種廣泛使用的現場試 驗方法。然而就像其他的現場試驗一樣，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。標度槽中的試體其橫向邊界可以應力或應變控制。 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用邊界元素法模擬 現地狀況的標度槽系統。橫向邊界以外之土壤用邊界元素法來模擬。新標 度槽採用多個圓環做垂直的重疊來做橫向邊界。試體在每一圓環高度之邊 界橫向位移輸入邊界元素法程式。在每一圓環高度之應力再由邊界元素法 程式計算得知。 標度槽系統之設計是考慮直徑 790mm，高 1600mm 砂土 試體。新系統包括砂土霣落器，油壓系統，及標度槽。本系統之設計和組 件之機械加工已完成。論文敘述邊界元素法控制的標度槽研發的背景及現 況。 Due to the lack of cohesion, it is difficult to obtain undisturbed samples for sand. In-situ testing is often used to determine the engineering properties for sands. The cone penetration test (CPT) is a popular in-situ test method. However, as for many other in-situ test methods, we rely on empirical equations to interpret CPT data. A significant part of these empirircal equations came from laboratory chamber calibration tests. An important drawback of the calibration chamber is its boundary effects. The main objective of this research project is to develop a new calibration chamber system that enables the field conditions be simulated using the boundary element method (BEM). The boundary elements emulate the soil beyond the physical boundary. The lateral boundary of the new chamber is made of multiple rings. The lateral strain at each ring level is measured and fetched into the BEM program. The corresponding stress at that ring level is then determined by the BEM program. The new system includes a sand pluviator, a hydraulic loading system and the chamber. the design of the system and machining of major components have completed. The thesis presents the background and current status of the research.