The soils of this class include mud, silt, quicksand, etc., and it is necessary to remove them entirely or to reach a more solid stratum under the softer soil; or sometimes the soil can be consolidated by adding sand, stone, etc. The manner of improving such a soil will be discussed later. In the same way that water will bear up a boat, a semi-liquid soil will support, by the upward pressure, a heavy structure. For a soil of this kind, it is very difficult to give a safe bearing value; perhaps 500 to 1,500 pounds per square foot is as much as can be supported without too great a settlement.