Martin R. Owen PE, GE

Geotechnical Engineer

 

San Diego County, California

Tel: (619) 813-8462, Fax: (858) 273-1652

Email: martinowen@geotechengineer.com

 

 

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SOIL INVESTIGATIONS AND

FOUNDATION ENGINEERING

Most new buildings require a soil investigation for the design of foundations and other soil-related aspects of construction. A soil investigation is also usually needed to satisfy the requirements of the City or County building department.  A soil investigation is different from a geologic investigation, which may be necessary if the property is located in a landslide or unstable hillside area, has an earthquake fault running through or near it, or has other, known, geologic problems.  If a geologic investigation is required, I will have an engineering geologist assist me with that phase of work and provide me with the necessary geologic information.

A soil investigation typically involves drilling test borings or excavating test pits to evaluate the underlying soil, bedrock and groundwater conditions.   Soil samples are obtained and tested in the soil laboratory for their engineering properties, such as moisture content, dry density, expansiveness, shear strength, and compressibility.

 

These findings are then analyzed and soil design values formulated for the project. They are presented in a written report which is given to the architect and structural engineer to assist them in the building design, and later submitted to the City or County, along with the construction plans, as part of the building permit process.

During construction, I will usually be required to inspect the foundation construction and observe or test any site grading and fill compaction that is done. 

SOIL DESIGN VALUES

The soil design values and geotechnical information most often required for new building construction are as follows:

·       Foundation type and depth

·       Allowable bearing capacity for foundations

·       Allowable passive resistance for foundations

·       Floor slab design values

·       Minimum steel reinforcing for foundations and slabs

·       Estimated building settlement

·       Retaining wall design values

·       Recommendations for site grading and fill compaction

·       Groundwater and seepage recommendations

·       Excavation shoring design values

·       Pavement design values.

FOUNDATION ENGINEERING

Foundation engineering is the process of selecting an appropriate foundation for the type of structure and soil conditions. Foundations can range from shallow, concrete footings to drilled, concrete caissons or driven piles extending several feet below the ground surface.  Residences and low-rise commercial buildings in San Diego County are commonly supported on conventional, shallow footings, 12 to 24 inches deep.  Floors are usually concrete slabs resting directly on the surface soils.  However, when the upper soils are weak or compressible, or the building is located on the side of a steep hillside, it may be necessary to support the building on drilled caissons.  Floors are then structurally supported on concrete or steel grade beams spanning between the caissons.  Another common foundation type, often used in expansive soil areas, consists of post-tensioned floor slabs, which are structurally designed, footing-slab combinations with tightened steel cables running through them.