軟弱岩層現地力學及水力性質

Abstract

軟弱之年輕地層，其組成之砂岩普遍具有固結差、膠結不良、遇水極易軟化之特性，於原地層中尚如固化之岩石，然以手用力捏擠或經水浸泡即成一團砂土，利用水為介質之鑽探，甚難取得供試驗室試驗之不擾動岩樣。因此本研究利用現地透水試驗、現地孔內震波試驗及軟岩用高壓傍壓儀試驗之結果並與其他室內之試驗結果比較，以探討軟弱岩層之現地力學及水力性質。 本研究之試驗地點主要在新竹寶山地區，其地層為頭嵙山層香山相岩層，現地透水試驗之結果顯示，其透水性主要與距地表之距離有關，愈接近地表的Lugeon值愈高，原因為地表解壓，岩體滲透性變大，或因為試驗點靠近解壓之河谷處，造成水頭差太大之影響所造成。 又本研究之現地孔內震波試驗以日製之懸垂式P-S波探測儀器進行，此種試驗方式優點為施作時僅需一鑽孔及小區域的操作空間、且可快速量測及可以量測較深之地層；經由本研究試驗結果顯示S波波速從135 m/s至694 m/s間，而P波波速從1249 m/s至2380 m/s間，地表之波速有較低的趨勢。 另於新竹寶山地區完成兩孔高壓傍壓儀試驗共計17組試驗，根據加壓解壓（unload-reload loop）循環之膨脹曲線斜率推算得之剪力模數介於30∼396Mpa之間，與懸垂式P-S波探測儀之波速所換算之剪力模數值有良好之趨勢對應。

The young strata in the western Taiwan, such as the Cholan formation and the Toukoshan formation, often contain very low to low strength rocks. The major rock type of the strata is the poorly cemented sandstone. The poorly cemented sandstone is easily weakened in water because of the poor lithification of the rock. The geo-material may be as hard as a rock in original state, but it is easily crashed by hands and easily disturbed with water. Also, it is not easy to take an undisturbed core specimen for the rocks using the drilling water as the flushing media. Hence, in situ tests may be suitable for determining the mechanical properties of the poorly cemented sandstone. In this thesis, three types of in-situ tests including Lugeon tests, suspension P-S logging tests and pressuremeter tests are conducted for determining the mechanical and hydraulic properties of very low strength to low strength rocks. The in-situ tests are performed in Bao-San, Hsinchu. The results of Lugeon test show that water conductivities of the rocks are related to the depth of the test section. The Lugeon value at a shallow ground is larger than that at a deep ground. The fact reflects that the consolidated loads are released due to the surface erosion and the micro-fissures are formed at the ground near the surface. The OYO (Japan) suspension P-S logging test instruments are adopted for tests due to the advantages of the easy operation, fast data logging, and suitability of deep distance measurements. The results of the P-S logging test show that the values of S wave velocity are between 135 m/s and 694 m/s while P wave velocity are between 1249 m/s and2380 m/s. The 17 sets of pressuremeter tests are conducted in the site. The results of the pressuremeter tests show that shear modulus of the rocks are between 30∼396Mpa.