RELATIONSHIP BETWEEN THE MICROCRACK DENSITY AND MECHANICAL PROPERTIES OF MARBLE

Marble is widely distributed in Yuanlang area of Hong Kong. The mechanical properties of the marble influence directly the safety of construction in the area. We have used ultrasonic detection technique, uniaxial compression test, and observation of thin section of the rock under microscope for understanding the internal structural change and mechanical properties of the marble. The obtained result shows that the mechanical properties of the marble in the area change significantly. In general, the dense black marble shows higher ultrasonic velocity, higher compression strength, and brittleness.Its P wave velocity ranges in 6. 2～6. 5 km. s-1, S wave velocity in 3. 0～0. 60 km.s-1, and its compressionstrength ranges in 88～66 MPa. But the coarse rained white or greymarble has its largely varied ultrasonic velocity, lower compression strength, and ductility. Its P wave velocity ranges in 4. 2～6. 9 km. s-1, Swave velocity in 2. 4-3. 20km. s-1, and compression strength in 52～63 MPa. The P wave is inversely proportional to crack density. The compressions trength is linearly inversely proportional to crack density. But the slope of curve for the brittle marble is higher than that for theductile marble by many times. The internal microscopic structures of themarble, such as cracks and grain size, are the main factors affectingits mechanical properties.