This is not grouting. This is driving concrete piles. Grouting refers to multiple things when talking about foundations or underground work but here are some

This is not grouting. This is driving concrete piles. Grouting refers to multiple things when talking about foundations or underground work but here are some examples: Jet grouting - high pressure water/grout/air is used to displace and mix the soil and grout to make a soilcrete Compensation grouting - grout is injected under pressure into the soil in order to displace/heave the ground to counteract previous settlement Cutoff grouting - grout is injected into the ground in order to cut off ground water What they're doing at the dam appears to be backfill grouting where they are injecting grout from within the dam underneath it trying to cut off the seepage path of the voids that have formed. This appears to be because they've built the dam on a soluble rock and so voids are constantly created which allow flow paths. They must find the voids and fill them with grout. This is a never ending process until all rock is replaced with grout.