The Importance Of Soil Investigations
Soil is composed of loosely bound mineral grains of various sizes and shapes, organic material, water and gases. The bonds holding solid particles together in
most soils are relatively weak. SOILS SHOULD NOT BE EXPECTED TO FOLLOW SIMPLE PATTERNS OF BEHAVIOR. Soil borings determine the type of soils and their
relative locations. By performing the soils borings it can be determined whether or not the materials present can safely support the proposed building, addition,
roadway or swimming pool. At the present time, Palm Beach County, Broward County and Dade County require Standard Penetration Borings to be performed on all
new construction. This is becoming the standard throughout Florida.
Subsoil Investigation:
Plans for new buildings or additions shall bear a statement as to the nature and character of the soil under the structure. Where the bearing capacity of the
soil is not known or is in question, or the load imposed on the soil is unusual, the Building Official may require examination of subsoil investigation by a registered
Professional Engineer.
The information obtained from a standard penetration test is used to determine the shear strength and the bearing capacity of the soil. From this information a
foundation recommendation outlines the procedures to follow to ensure a proper and safe foundation system. The report includes the proper method of backfilling
and compacting* to finished elevation and the type of foundation system needed along with the permissible soil bearing pressures. This information will determine
the type of structure which may be built upon that particular soil type.
Borings should extend down sufficiently far enough to determine those engineering and geological properties relevant to the project design. Borings should be
sufficient in number to allow analysis of the following:
 Location of proposed construction both vertically and horizontally
Development of detailed subsurface investigation for specific structure
Information on soil stratas
Location of natural water table
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The standards for performing the Standard Penetration Test (SPT) are determined by the American Society for Testing and Materials (ASTM). The test method is
ASTM Designation: D1586 STANDARD METHOD FOR PENETRATION TEST AND SPLITBARREL SAMPLING OF SOILS.
The method describes the procedures generally known as the Standard Penetration Test (SPT) for driving a split-barrel sampler into the soil to obtain a representative soil
sample and a measurement of the resistance of the soil to penetration. A split-barrel sampler is driven into the soil is recorded, the sampler retrieved, and the
sample visually observed for soil type and classification. The sample is then labeled and returned to the lab for further analysis as needed.
 Failure to perform soil borings can lead to differential settlement of the foundation system due to the presence of unsatisfactory soil materials under the proposed
building. Buildings which are built upon unsatisfactory materials will suffer some type of settlement due to the weight of the building. Settlement which
occurs may lead to cracking of walls and floors, doors and windows which do not open, and could lead to the complete structural failure of the building. |
* What is Compaction?
The process of compaction refers to the act of mechanically (Example: by a vibrating roller) increasing soil density or unit weight. In this process the soil particles are moved and rearranged
closer to each other, and the air that has been trapped between, these particles is forced out
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| Loose Soil | Compacted Soil |
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*Densities
A density test determines the degree of compaction of the tested layer of material only.
A density test does not replace a soil
bearing capacity determination. |
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