ALLOWABLE LOAD-BEARING VALUES OF SOILS(IBC 09)

There are maximum allowances that you must adhere to for foundation pressure, lateral pressure, or lateral sliding-resistance values. These must not exceed the values allowed by code unless you have data to verify the use of a higher value. Any higher values must be submitted and approved for use.

Do not assume that mud, organic silt, organic clays, peat, or unprepared fill have an acceptable load-bearing capacity unless you have the data to back that up. I believe we all know what happens when we assume something to be true. And it would be a great deal of time, money, and energy wasted if you assume that the use of a material is acceptable without the data to back it up. That being said, there is however, an exception to this. An acceptable load-bearing capacity is permitted to be used if the building official considers the load-bearing capacity of mud, organic silt, or unprepared fill to be adequate for the support of lightweight and temporary structures.

Presumptive load-bearing values of foundation materials :

Class of materials	Load-bearing pressure (Pounds per square foot)
Crystalline bedrock	12,000
Sedimentary and foliated rock	4,000
Sandy gravel and/or gravel (GW and GP)	3,000
Sand, silty sand, clayey sand, silty gravel and clayey gravel (SW, SP, SM, SC, GM and GC)	2,000
Clay, sandy clay, silty clay, clayey silt, silt and sandy silt (CI, ML, MH and CH)	1,500

***Where the building official determines that in-place soils with an allowable bearing capacity of less than 1,500psf are likely to be present at the site, the allowable bearing capacity shall be determined by a soils investigation.

To determine the resistance of structural walls to lateral sliding, calculate by combining the values from the lateral bearing and sliding resistance. Remember you have to submit the reasons or data for this and obtain approval. In the case of clays, such as sandy, silty, or clayey silt, under no circumstance can the lateral sliding resistance be more than one-half of the dead load. It is possible for increases to be allowed for lateral sliding resistance. For each additional foot of depth to a maximum of 15 times the tabular value.