Construction of the dam foundation is a critical and careful activity to ensure the safe life of the dam. It is seen that a dam does not fail due to overflowing due to a sudden flash flood but the main reason of failure of a dam is due to a failure of the foundation. Dam site geology is a complex phenomenon and it is extremely difficult to envisage its complexity.

This chapter educates readers regarding assessment of actual depth of the foundation on available strata by a geologist. Selection criteria depends on site geology and available geological and geotechnical data collected during investigation. The resident geologist is to decide the safe depth of foundation after necessary exploration during construction. This chapter educates readers about geological logging of the foundation area done by a geologist duly indicating dips, strikes, folds, clay seams, faults if any, along with location, depth and inclination of drill holes in a grid pattern for consolidation grouting to make the foundation water tight.

This chapter teaches about dental treatment of the foundation when a fault zone is detected within the foundation area.

This chapter provides necessary information to readers regarding the critical activity of the washing method of grout holes by application of air and water through packers. This chapter provides ideas about different equipment to be used in drilling, washing and grouting activity.