人造軟砂岩之研製與性質

Abstract

軟弱砂岩其膠結不良、遇水軟化之特性，致使鑽探取樣的岩心試體受高度擾動，加上本身的微裂隙與異向性，皆使室內試驗結果具有高度變異性存在。為了克服這些缺點導致試驗上的限制，以模擬材料製作人造軟弱砂岩是值得嘗試的方向。人造軟砂岩具有均質均向，容易製作之優點，但必須能夠控制與天然軟砂岩之性質相似。 台灣中北部麓山帶軟弱砂岩(卓蘭層及頭嵙山層等)是本研究之人造軟砂岩欲模擬的對象，針對該地質材料特性，本研究構想以目標地層之岩屑作為模擬材料，使用過200號篩溼篩的方式將研磨過的岩屑分為粗粒料與細粒料水溶液。依配比拌和、灌入模具後，以高壓壓密的方式製作人造軟砂岩試體。經過本研究測試與改良，制訂出製作人造軟砂岩試體的標準製作流程，並以此進行各項物理與力學試驗。 製作完成之人造試體單壓強度介於2.5~6.5MPa符合ISRM定義之軟岩強度範圍。再根據模型相似律，本研究之人造試體五個無因次項分別為：模數比介於70~115間，強度比約5~10、卜松比介於0.17~0.24、破壞應變介於1~2%、內摩擦角約38.7度。本研究之人造試體屬低模數比，破壞應變稍大，其他應力應變行為與天然試體極為相似，若再作進一步改良，應可提供模型試驗之用。

Based on its lithification, sandstone is a highly nonhomogeneous geo-material. Additionally, due to the poor cementation of weak sandstones, the drilling cores are easily disturbed. Hence, the laboratory experimental results of the cores are hight variable. In order to decrease the variables in the experiments for developing the material model, it needs to prepare an artificial rock satisfied with similitude laws. It means that the artificial rocks should be homogeneous and isotropic, and have similar properties with nature weak sandstones. In addition, it could be easily reproduced. This thesis presents a technique to produce an artificial rock to simulate the poorly cemented sandstones in the mid-northern Taiwan (including the Cholan Formation and Toukoshan Formation). The material used to form the artificial rock is natural rock itself. The detritus are ground down to the particles and these particles are separated into two parts by washing through the sieve #200. According to designated percentage, the two parts including sand and solution of fines are blended and cast into a mould. Then, the mix is loaded using a rock creep test device. Based on different loads and loading period, the artificial rocks with different physicial and mechanical are formed. The standard process for preparing the artificial specimens has been tried and improved. These specimens are adopted for conducting a serious of laboratory experiments for determining the physical and mechanical properties. Experimental results indicate that the uniaxial compressive strength of the artificial specimens is about 2.5-6.5 MPa, which is satisfied the definition of weak rocks according to the ISRM suggestion. Based on the experimental results, five dimentionless parameters of similitude laws are as follows, modulus ratio lies within 70-115, uniaxial strength ratio lies within 5-10, Poisson’s ratio lies within 0.17-0.24, failure strain lies within 1-2%, friction angle is 38.7o. Compared with the nature rock, the modulus of the artificial specimens is lower and failure strain is a little large, but the stress-train behavior is similar to natural specimens. Based on the similitude and the experimental results, the presented artificial rock is well enough for modelling the natural poorly cemented sandstone.