The type of soil determines the strength and stability of trench walls. In most Canadian Provinces, soil types fall into four categories.
Canadian Soil Classifications
|Type 1||This type of soil is so hard that it is close to rock.|
|Type 2||Easily excavated with backhoe, remains intact for short time only – i.e. silty clay|
|Type 3||Previously excavated, flows through fingers – i.e. sand|
|Type 4||High moisture content, sensitive to vibration – i.e. quicksand, clay|
In the U.S. there are also four types of soil, but the naming convention is different.
U.S. Soil Classifications
|Stable Rock||Natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed.|
|Type A||Cohesive soils. i.e. clay, silty clay, sandy clay, clay loam|
|Type B||Cohesive soils but less than Type A – i.e. angular gravel; silt/silt loam; previously excavated|
|Type C||Cohesive soils but less than Type A/B – i.e. gravel, sand and loamy sand, submerged soil, soil w/ freely seeping water, unstable submerged rock|