Soil Type/Bearing Capacity

Soil Type/Bearing Capacity Under the Federal Standards, manufacturers are only required to provide one acceptable method for installing the home. However, manufacturers usually provide installation instructions that can be applied to a number of sites. These "generic" instructions commonly specify a minimum acceptable bearing capacity of the soil. Additionally, the manufacturer may offer options for acceptable footing sizes based on the bearing capacity of the soil. Installer/transporters and inspection personnel should first determine the bearing capacity of the soil in order to determine the proper size footing or foundation. Different soil types will have different bearing and holding capacities. The bearing capacity of the soil is the load per unit area that can be supported safely by the ground. The performance of the ground anchor is also related to the soil's holding capacity. In the absence of borings, test pits, and other soil investigations that provide information on the proposed site, the following description of soil types in Table II may be used for homes installed in Mississippi. TABLE II – BEARING CAPACITY/SOIL TYPE* Bearing Capacity, psf Bearing Capacity kg/m2 Soil Type Loose sand clay soils or medium soft clay 14647 Firm or stiff clay 19530 Loose fine sand or compact inorganic silt soils 29295 Compact sand clay soils 39059 Loose coarse to medium compact fine sand *Note: The above table may be used if the soil characteristics are known. If the soil type is unknown, the following resources may be consulted to determine the soil type/bearing capacity: (a) LAHJ. (b) Soil conservation district. (c) United Sates Geological Survey. (d) The Resource Conservation Agency of the U. S. Department of Agriculture. (e) Highway Department. (f) Qualified Professional Engineer; and/or (g) Other methods approved by the Commissioner. A pocket penetrometer (see Figure 8) is a simple instrument used to estimate allowable soil bearing capacity in areas where the support pier footings are to be placed. The following provides instructions on the use of the pocket penetrometer. a. Select a location that will be used for placement of a footing and clear a one square foot area (12 inches x 12 inches) to the depth of the bottom of the thickness of the footing to be used. b. Using the instructions provided with the pocket penetrometer, slowly insert the tip of the probe in the soil until the engraved mark on the tip is level with the surface of the soil. c. Take a minimum of five (5) readings in the area cleared for the footing. d. Discard the high and low reading and average the remaining readings. e. Compare the resulting average value with the values shown in Table II. f. Round the resulting average down to the match the nearest soil bearing value in Table II. Figure 8. Pocket penetrometer In lieu of determining the soil bearing capacity by the methods described above, an allowable bearing capacity of 2000 psf may be assumed unless the site-specific information requires the use of lower values based on soil classification and soil type.