3种条件下砂岩超声波波速的试验研究

Experimental study of the longitudinal wave velocity in sandstone under three different constraints

利用自行研制的岩石高温加热装置,对砂岩试件单向约束、双向约束、无约束3种试验条件下高温前后的纵波波速进行试验研究.结果表明:单向约束试验中,随着温度的升高,砂岩Y,Z方向波速与温度的关系曲线基本成二次函数变化,X方向近似直线下降,700℃时砂岩波速降到了2.096km/s;双向约束试验中,砂岩3个方向的纵波波速随温度升高均呈直线下降;700℃时双向约束试验中砂岩纵波波速最多下降了51.793%,无约束试验中1 200℃时砂岩纵波波速最多下降了80%.高温作用后,岩石内部微结构发生变化,温度越高变化越大,主要表现为岩石内部水分不断蒸发,含水矿物的脱水、相变和岩石部分熔融,孔隙率增加,颗粒边界裂纹出现、发展、贯通,微裂隙产生、演化,矿物成分分解,胶结物强度降低,内部结构热应力扩散,矿物颗粒相互摩擦挤压等.

The longitudinal wave velocity of sandstone under unidirectional, bidirectional, or non-restrained conditions was investigated using the high temperature experimental system de-signed in house. The experimental results show that for unidirectional restraint the longitudinal wave velocity of the sandstone and the temperature are related by a quadratic function alongthe Y or Z axes The longitudinal wave velocity decreased linearly with increasing temperature along the X axis. The longitudinal wave velocity of the sandstone fell to 2. 096 km/s at a tern-perature of 700 ℃. With bidirectional constraints the longitudinal wave velocity of the sand- stone in either the X, Y, or Z directions decreased linearly as the temperature increased. The maximum decrease in longitudinal wae velocity was 51. 793% at a temperature of 700 ℃ in thebidirectional restraint experiments. The wave velocity showed the largest temperature of 1 200 ℃ in the non-restrained experiments. After being peratures the internal micro-structure of the rock changes. The higher decrease of 80% at a exposed to the temperature, temthegreater the change will be. The water in the rock evaporates constantly. The hydrous minerals dehydrate and change phase and rock partially melt due to them. This causes the porosity to in-crease and for cracks to appear that cut through to the side of the particles. There are microfissures present that develop from the exposure to heat. The mineral decomposes, the cementstrength decreases, the internal heat stress diffuses, and the mineral particles rub and distort.