Earthworks, complete offer or better by hours worked?

We are currently desperately looking for an earthworks contractor. We have enclosed the soil survey, floor plans, sections, and area calculations as documents. 4 out of 10 earthworks contractors say they can only hardly make a complete offer because they charge 90% based on time and materials.

Can I even properly supervise this alone if it is based on time and materials? We are building with a general contractor on a slab foundation. If I can’t supervise it with time and materials, would the general contractor do that?

Is it even reasonable to charge based on time and materials, or should I insist on a complete offer?

We are currently a bit desperate.....

Ask for the hourly rate and a rough estimate of the hours he is allocating. A complete offer, every civil engineer will play it safe and estimate too much. We only received an estimate for earthworks as well, and it was billed by the hour, but the estimate and total were close together. I did not supervise it. I trusted that he was not cheating. Karsten

What is included in your earthworks? We had a fixed price offer for the cistern, excavation, creation of rainwater drainage to the cistern. Nothing was billed to us based on hourly work.

Have an architect create a bill of quantities [LV] for you as a basis for a unit price offer. What it costs you, compared to an hourly billing, you will earn back three times over.

What is included in your earthworks? We had a fixed price offer for the cistern, excavation, creation of the rainwater drainage to the cistern. Nothing was charged to us on an hourly basis

Of course, we need excavation, a soil replacement (approx. 1.05m) due to load-bearing capacity, a clean layer, construction of drainage and its connections to the transfer chamber, house water connection.

If it helps you, I can write to you on Wednesday about the offer our architect presented to us regarding [Tiefbau] and [Rohbau] and the associated payment terms. Maybe you can draw some conclusions from it.