Soil Types

The easiest way to group soils is into two categories: cohesive and non-cohesive. Fine- grained soils such as clay are considered cohesive. Sand and other coarse-grained soils are non-cohesive.

The classification of cohesive and non-cohesive soils may be further sub-divided based on origin, method of deposition and structure. Soil structure may be classified as deposited or residual. Deposited soils have been transported from their place of formation to an anchor location. Residual soils are formed by physical and/or chemical forces breaking down parent rocks or soils to a more finely divided structure. Residual soils are often referred to as weathered.

Soil structure properties can be divided into loose, dense, honeycombed, flocculated, dispersed or composite. Often these soils are in layers of different thickness of unlike soils, These soils do not necessarily retain consistency of materials at various depths.

Trouble free anchoring demands the careful evaluation of local soil conditions and anchor types. Without proper soil/anchor planning, maximum anchor performance an never be assured.

Almost all of the soil types classified below can be found in the Denver area.

Soil Groupings

Chart

Throughout the Denver area there are a wide variety of soil conditions present. Some areas consist of very sandy conditions that will not support even load designs of 1000 pounds per square foot. While no more than 2 miles away the soils are so expansive that additional design requirements are needed.

Water, Frost and Soil

The typical minimum foundation depth required by code is three feet. This measurement is taken from the top of the soil to the bottom of the footing. The depth is important so that freezing of the ground will not lift the footing and foundation.

If an anchor helix is in a zone of deep frost penetration (cold winter seasons), frozen soil will behave as a stiffer soil and will basically yield greater holding capacity, by hard soil with brittle cracking instead of softer depressible soil. However, when spring begins to thaw out the soil, the overlying zone will be water-saturated while the layer housing the helix remains frozen. The condition is comparable to a hard layer under a soft layer, and may result in sudden anchor failure. Occasionally anchor jacking or movement out of the ground occurs during these conditions. When dealing with permafrost, the helix should be at least three to five feet below the permafrost line; provisions made to prevent solar energy from being conducted down the anchor.

Anchor holding capacity decreases as moisture content increases. If a helix is installed at the water table level, anchor capacity can reduce helix capacity by as much as 50 percent in granular soil.

Water, draining from fine grain soil under load, will permit creep, slow movement of the ground under a steady load. This is similar to the consolidation marvel under a foundation. Rapidly applied loads due to wind or ground tremors have little effect on creep so long as they do not exceed soils shear water slowly drain off. Under such circumstances, creep could become troublesome even though the anchor/ soil system has not structurally failed.