Crack monitoring in underground construction

The appearance of the cracks and the relative movements of the walls along and across them beyond certain limits, in the underground civil engineering structures, may prove to be potentially damaging. For the safety considerations, the measurement of the magnitude and time rate of deformation of the cracks is essential. At Sardar Sarovar Dam Project on Narmada River (India) an underground power house is being constructed. The Central Soil and Materials Research Station has been doing the work of crack monitoring using demec gauge which involves fixing of 6 special pins (3 on each wall) as shown in figure 1. This method is not very accurate. Moreover demec gauge can not measure the deformation beyond 5 mm. To overcome these limitations a simple 3 pin method has been developed using digital vernier calipers of 0.01 mm least count for measurement of the crack deformations to any desired accuracy.