Bearing Capacity of Soil

realy sos but i cant help u there

its structure

Greetings zanzibah,

The factors vary based on composition, density, moisture content, ect. The following is an excerpt from a Geotechnical Engineering Report that may give you some insight. I am only posting two pages of the report as the report contains 33 pages total. If you would like to see the complete report, e-mail me with your e-mail address and I will e-mail it back to you.

Soil Conditions

Conditions encountered at each boring location are indicated on the individual boring logs.

Stratification boundaries on the boring logs represent the approximate location of changes

in soil types; in-situ, the transition between soil types may be gradual. Subsurface

conditions at the borings can be generally described as follows:

Asphalt that ranged from 5 to 7 inches in thickness was encountered at the surface of 6 of

the 10 borings. In the remaining borings, topsoil fill that ranged from 5 to 10 inches in

thickness was encountered. These surface materials were typically underlain by fill and

possible fill materials consisting of crushed concrete, fine to medium sand, silty sand, lean

clay and sandy lean clay. The fill and possible fill typically extended to depths ranging from

about 3 to 8 feet below the ground surface. These materials were underlain by native soil

deposits of stiff to hard lean clay, sandy lean clay, and sandy silt that extended to the

termination of the borings.

The cohesive soils in the upper 30 to 45 feet of the borings exhibit relatively stiff strength

properties. Standard penetration "N" values in the native clays typically ranged from

about 7 to 15 blows-per-foot in this zone, and increased to 20+ blows-per-foot below

that. Pocket penetrometer values for the clay soils in the upper 45 feet of the borings

ranged from about 3000 to 9000 pounds per square foot (psf). Very stiff to hard

cohesive soils commonly referred to as "hardpan" were encountered in the borings at

depths ranging from about 43.5 to 58 feet, but was typically encountered at about 44 to

48 feet.

Please refer to the attached boring logs for the laboratory data and a detailed description of

the subsurface conditions encountered at the individual boring locations.

Groundwater Conditions

The borings were observed while drilling and after completion of drilling for the presence

and level of groundwater. At these times, groundwater was observed in 7 of the 10

borings at depths ranging from about 8.5 to 50 feet below the ground surface. The water

level observations provide an approximate indication of the groundwater conditions

existing on the site at the time the borings were drilled. Some of the relatively shallow

groundwater observations are likely the result of trapped or "perched" water which is often

encountered in more pervious near surface strata such as fill and sand seams. A longer

period of time to monitor the groundwater levels in cased holes or piezometers, sealed

from the influence of surface water, would be required for a better evaluation of the

groundwater conditions on this site.

Fluctuations of the groundwater levels will likely occur due to seasonal variations in the

amount of rainfall, runoff and other factors not evident at the time of this subsurface

exploration. Therefore, groundwater levels during construction or at other times may be

different than the levels indicated on the boring logs. The possibility of groundwater level

fluctuations should be considered when developing the design and construction plans

for the project.

ENGINEERING RECOMMENDATIONS

Geotechnical Considerations

The soil boring data and laboratory test data were evaluated to develop

recommendations for site preparation, as well as, design and construction of

foundations, floor slabs and pavement subgrades. Our draft report contained

recommendations for supporting the proposed building on spread footing foundations

and a structural mat. We understand that these options have been ruled out for support of the proposed structure. Please see our draft report for these recommendations.

Based on conversations with the project structural engineer, we understand that the

proposed building will be supported on drilled shaft (caisson) foundations. For drilled

shafts that bear in the hard clay (hardpan) layer encountered in the borings at depths

ranging from 43.5 to 58 feet, we recommend an allowable bearing capacity of 12,000 psf

(6 tsf). It is our experience that performing the pressuremeter test in the hardpan soils

encountered in the borings would justify a much higher allowable bearing capacity,

which would improve the economy of caisson design.

Some building elements such as entry-ways and structures associated with the power

generation station will be constructed using shallow spread footings. Based on the "N"

values and hand penetrometer data, we would recommend that an allowable bearing

capacity of 4000 psf be used to design shallow spread footings bearing on native soils.

Some miscellaneous fill materials were encountered in the upper 3 to 8 feet of several

borings, we recommend that shallow footing excavations extend through these fill

materials. Shallow foundations could bear at the deeper elevation or the excavations

could be backfilled with 3-inch stone to the original design bearing level.

Our recommendations for design and construction of foundation, the on-grade floor

slabs and pavement subgrades are provided in the following sections.

factors affecting bearing capacity include grain size distribution; structure, orientation and angularity of grains; minerology and stength of mineral particles; organic content and type of organics; particle packing/orientation; particle surface interaction (friction); and hydrogen or chemical bonding. BTW these also affect angle of fiction and cohesions coefficients. Typically load bearing capacities are set by geotechnical engineers based on the designers needs within the calculated limits of the soil, thus if the soil bearing capacity calculates to be 6500 psf, and the designer only needs3500, the geotech will usually report a limit of about 4000 or so.