英文篇名
Strain controlled cyclic triaxial tests under small to medium strains
作者
林靜怡、何輔仁、黃安斌
關鍵字
動態三軸試驗、剪力波速、模數遞減、阻尼係數
摘要
土壤模數(剪力或楊氏)與阻尼係數為大地工程動態行為分析中重要之參數,試驗結果通常以割線模數或阻尼係數與應變之關係來展示,這些關係可以統稱為土壤非線性動力性質。為了分析的需求,非線性動力性質試驗所必須涵蓋之應變範圍通常在10-4%至1.0%之間。早期因受限於試驗儀器之功能,應變10-2%以下之動態土壤行為以共振柱試驗來量測,當應變大於10-2%時則使用另一試體進行動態扭剪、單剪或三軸試驗。由於應力路徑或/和試體間之差異,此一程序不但需要許多昂貴之試驗設備而且其模數和阻尼係數與應變之關係曲線常在試驗方法更換之處發生不連續的現像。因此使用單一試體在所需之應變範圍下以同樣之受剪模式來進行土壤非線性動力性質試驗,可以避免前述之問題並可改進試驗之品質。作者採用高精密度、高扭力輸出之步進馬達作為載重單元輸出及控制,配合非接觸式趨近儀作為微小位移之量測以求得局部應變量,並加入bender element剪力波速量測元件另外單獨求得最大剪力模數,進而建立在中小應變範圍下之連續非線性動力性質。本文敘述作者所發展之試驗儀器與使用方法並展示其結果。
英文摘要
Soil modulus (shear or Young’s modulus) and damping ratio are important parameters in geotechnical dynamic analyses. Test results are typically presented as relationships between secant modulus or damping ratio and strain, these relationships are referred to as the non-linear dynamic soil properties. In order to provide the necessary parameters for analyses, the non-linear dynamic soil properties must include the soil behavior under a range of strain from 10-4% to 1.0%. Because of the limitation in the experimental capabilities, when the strain was less than 10-2%, the dynamic soil parameters were usually determined by resonant column tests. When the strain exceeded 10-2%, a separate specimen tested under a torsional, simple shear or triaxial shearing mode would be required to establish the dynamic properties. Due to discrepancies in stress path and/or those between soil specimens, this procedure requires the expenses to set up a multiple-unit experimental system and a discontinuity often occurs in the modulus or damping ratio – strain curves where the test method changes. Thus, using a single specimen to perform the dynamic testing under the required strain strange can avoid some of these experimental problems and improve the quality of test data. Using a high torque stepper motor as the driving system, coupled with a high resolution non-contact proximiters and bender element shear wave velocity measurement devices, the authors developed a triaxial test apparatus capable of performing strain controlled cyclic triaxial tests under small to medium strain range. This paper describes the development of this apparatus and presents a series of results to demonstrate its capabilities.