How can I calculate the soil resistance by soil mechanics（when a ship was towed on the soft soil）?

I can imagine the soil should be clear before the ship dragged. But I think sometimes the ship may be blocked by small amount of soil though the soil resistance is very small. Then I think the shape of embedment of ship/boat into soil can be simpled as vertical surface because we skid it on soil. To say the least, If the ship is a square box which is blocked by small amount of soil， How can we calculate the soil resistance？