過去傳統分析土壤研究中,常忽略土壤伸張強度,但在實際情況下,土壤本身會發生伸張現象。若忽略土壤伸張行為,不僅無法清楚瞭解土壤伸張性質,在許多的情況下土壤會受到伸張,例如:邊坡滑動上部土壤受到伸張作用、深開挖造成土壤解壓發生伸張作用、基礎發生滑動部分土壤受到伸張作用,因此藉由非飽和土壤伸張試驗之研究,可以讓我們初步瞭解非飽和土壤能承受伸張強度,藉由土壤的伸張強度和伸張應變,瞭解非飽和土壤受到伸張時之變化情況。 本研究在探討非飽和紅土伸張強度,及基質吸力變化對非飽和土壤伸張強度的影響。針對林口紅土台地之現地擾動土樣,製成重模試體,利用改良非飽和三軸儀器,進一步求得非飽和土壤之伸張強度,由三軸伸張不排水試驗(EU)和三軸伸張排水試驗(ED),根據不同基質吸力及淨正向應力條件下,在固定圍壓的情況,減少位移量,使試體受到伸張作用,以求得各條件下非飽和土壤伸張強度,由一系列的試驗資料可求得非飽和伸張破壞包絡面,進而建立非飽和土壤伸張資料,以便未來現地穩定性分析與破壞機制之數值模擬時,可將伸張強度列入分析考量。
In some practical applications, such as the investigation of the soil strength in the base of deep excavation and the tensile crack propagation at the crest of slope, the use of triaxial extension test in soil behaviour simulation is more appropriate than the triaxial compression test. This study aimed at finding the triaxial extension strength of unsaturated lateritic soil, which can be found in many places in tropical countries. To be able to understand the mechanism of tensile crack development at the crest of slope and the subsequent slip failure associated to it, a series of triaxial extension tests have been conducted on unsaturated lateritic soil specimens. Detailed description of equipment and testing procedures used in the tests has first been outlined. The extension shear strength of the study soil has been obtained and compared to its compressive shear strength. An extended extension strength envelope for the study soil has been proposed; and finally, reasons for the unexpectedly low extension shear strength of the tested material were also discussed.