An Artificial Poorly Cemented Sandstone and its Mechanical Properties
|關鍵字:||人造軟弱砂岩;頭嵙山層;模型相似律;模數比;強度比;weak sandstones;artificial rock;similitude laws;Toukoshan Formation;modulus ratio;uniaxial strength ratio|
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.
|Appears in Collections:||Thesis|