ASSESSMENT OF MATERIAL PROPERTIES OF CONCRETE GRAVITY DAMS – AN INDIAN CASE STUDY
5. Study on the Mechanical Properties of Rock Samples
About ten rock samples of 150mm and 100mm diameter were extracted from the rock near the left and right bank on the downstream side. The test results from the rock samples are given in Table 4. The equivalent cube compressive strength of the samples of 150mm in diameter varied from 54.75N/mm2 to 68.80N/mm2, with an average compressive strength of 64.60N/mm2. Poisson’s Ratio of rock samples varied from 0.171 to 0.209, with an average of 0.186. The modulus of elasticity of the rock samples varied from 14,135N/mm2 to 15,794N/mm2, with an average of 14,944N/mm2. The dry and wet density of the rock cores varied from 2589.3kg/m3 to 2643.68kg/m3 and 2614.66kg/m3 to 2669.51kg/m3, respectively.
Table 4. Test results of rock samples
A petrography study of the rock samples indicated that the rock was a fine- to medium- grained textured, poorly foliated, partially weathered random sample. The ultrasonic pulse velocity values from the rock cores varied from 2.93km/sec to 3.41km/sec. One of the reasons for a lower pulse velocity and modulus of elasticity, as indicated from petrographic studies, is that the rock samples under investigation are fine- to medium-grained textured, poorly foliated and partially weathered. The coefficient of permeability for these samples was determined using a relationship developed between the permeability and porosity of the sedimentary rocks by Na Zhang et al (pore structure characteristics and permeability of deep sedimentary rocks determined by mercury intrusion porosimetry).
The porosity of rocks extracted from the left and right bank on the downstream side portion of the dam were obtained using mercury intrusion porosimetry. The permeability coefficient of the rock mass was determined using mercury intrusion porosimeter apparatus (PASCAL 140 and PASCAL 440), having the capability to determine pore size and volume in the range of 1.8nm and 7500nm of radius through mercury intrusion at high pressure. The porosity values (%) obtained for the left and right bank rock samples were 6.397 and 6.543, respectively. The following relationship developed by Na Zhang et al was used for calculating permeability:
Vol XXXII Issue 1
DAM ENGINEERING
17
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