I agree with PEinc, sounds like this should have been a soldier pile and lagging wall. You indicate there is no groundwater and adequate soil profiles. Why did you select sheet piles?
I'll agree that 10% sounds reasonible, but the bottom line is it should be in the specifications. If they are going to tell you that this testing has to be done, then they should also be telling you how often.
Typically, the piling contractor performs an index pile program, by selecting pile...
I agree with oldestguy, roots should not cause an issue provided they are relatively small and the soil is firm and relatively dense. My rule of thumb for good practice... I advise the contractor to remove any organics larger than the diameter of his thumb.
I'm going to agree with TopKnot's idea, I like this system for SOE because the support types can be adjusted as needed with depth or as conditions change. Soil and rock conditions can be imporved if needed with special grouting and variuos types of anchors. I also agree with oldestguy, you...
I agree with concretemasonry, good on-site oversight will ensure quality. However, many engineers want to see a number, we typically collect non-shrink grout samples in 2x2x2 cubes and test according to C109.
