Why Texas Clay Soil Is Tough on Fence Posts Texas clay soil is known for its heavy, dense texture. It holds water tightly and expands when wet, then shrinks as it dries. This constant swelling and shrinking can cause serious problems for fence posts. Soil Movement : When clay soil absorbs water, it swells and pushes against fence posts. As it dries, it shrinks and pulls away. This back-and-forth movement loosens posts over time . Poor Drainage : Clay soil doesn’t drain well.