Previous life but we used to used put the soil is large metal trays/pans to dry overnight in a large soil drying cabinet or use fans if there were too many samples to fit in the oven. Then break up the soil by placing the pan on the ground and using a soil tamper or sledge hammer (like a soil tamper). Once the sample pieces are relatively small you can rely on the water from the proctor to help break it up more. Just mix the sample after you have added water and let it sit then remix.