The relationship between physical and mineralogical properties of weathered igneous rocks were studied to define a quantitative measure of the degree of weathering. Variation of longitudinal wave velocity with respect to water content was measured for various rock types by ultrasonic pulse method, and the relation between rock texture and longitudinal wave velocity was investigated.

Rock Specimens

The rock specimens chosen for this study are given in Table 1, and Fig. 1 shows the Places where rock samples were collected. Based on the research of structure of weathered zones at four places, some criteria on the degree of weathering were proposed in Table 2. About seventy rock sam- Ples, of which sizes are nearly 15×15×15 cm, were picked out from the first zone to the fouth zone, and then they were burried inthe concrete block of 20×20×20 cm. After measuring the rebound value by Schmidt test hammer, cylinders of 3cm,×6.5cm or cubes of 5×5×5 cm prepared to measure various physical properties.

(Figure in full paper)

Experimental procedure

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where Wd and Wh are the weight at dry and saturated states. Ws is the weight of specimen measured in water. The rock specimen was dried by the use of oven at 105 °C until its weight becomes constant. To make a saturated state, sample was immersed in water after de-airated in vacuum.

Longitudinal wave velocity was measured by the ultrasonic pulse method. 200KHz barium titanite discs of 30mm in diameter were used for both transmitter and receiver. On the other hand, 3.3MHz barium titanite plates of 20×10×1 mm were used for transversal wave velocity measurements. Longitudinal wave velocity was measured in both evaporation and suction processes under room temperature and atomospheric pressure.

The degree of saturation (Sr) is calculated by the following equation:

Sr =(Wi - Wd)/(Wh - Wd)× 100(%) where Wi is the weight of specimen when the longitudinal wave velocity is measured.

Uniaxial compressive strength was measured in specimens of dry state under a loading speed of 5Kg/cm2 /sec. Rebound value by Schmidt test hammer was obtained to hit the smoothly prepared surface downward by N-type hammer. The process of mineral destruction and alteration were mainly measured by microscopic observation, X-ray powder diffraction method and differential thermal analysis.

Experimental Results

The degree of mineral weathering and physical. properties are summarized in Table 3. From the investigation Of alteration of main minerals, it is observed that cracks grow with progress of alteration of main minerals such as feldspar and biotite. Hence the altered area in feldspar was measured as a "measure of altered area" by means of Integraining Stage. As shown in Fig. 2, it is possible for quartz diorite to classify the degree of destruction of quartz and the degree of alteration of feldspar and biotite.

On the other hand, the experimental results in the case of other three kinds of volcanic rocks indicate that the alteration of groundmass is well marked, and that the alteration of main minerals follows the sequence: primary mineral-montmorillonite mineral-halloysite mineral.

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