101 How To Plan A Construction Site Soil Investigations Program

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The article presents the latest methodologies in the planning, execution, and interpretation of the various exploratory investigation methods, and the development of appropriate soil and rock parameters for engineering applications.

The proper discharge of the geotechnical engineerís duties requires that he or she be involved from the very beginning of the planning stage of a project. A geotechnical engineer may provide, based on prior knowledge
and research for example, guidance in the location of a proposed tunnel or road which may result in reduced cost, improved constructibility and other advantages. When the services of the geotechnical engineer are introduced into the project after the final project location is determined, a very important value engineering benefit may be missed.

Concepts and Formulas

Site Characterization - Strategy

A step by step strategy for site characterization is summarized below:

  1. Obtain an understanding of the potential geologic and geotechnical conditions of the proposed site by reviewing regional studies. Also, consult with other professionals who have worked in the area to obtain their opinion regarding potential conditions and issues at the site.
  2. Obtain aerial photography (historical and recent), geologic and soil maps and other sources of subsurface information.
  3. Obtain drawing of the facilities planned for construction including the footprint of the building,  foundation locations, areas of cut and fill, utilities, property lines, etc.
  4. From this information, develop a first phase of the investigation to improve your understanding of key issues and obtain the data necessary to complete preliminary engineering analyses.
  5. Perform the assessment and calculations of the phase 1 data to understand the sensitivity of the analyses to key soil and groundwater input. The potential range of outcomes should be estimated by varying the key inputs within the possible ranges suggested by the characterization data.
  6. From the phase 1 assessment, decide if the conditions at the site and the performance of the geosystem fall with the following  categories:
    1. Safe or adequate performance expected 
    2. unsafe or with inadequate performance likely
    3. unknown condition or performance
  7. In case, 6.1., decided if additional data or analyses are needed, if any, to complete the design. For case 6.2., decide what design modification and/ or ground improvement is necessary to obtain acceptable performance.  In some cases, other foundation types and construction methods will need to be used. In a few instances, the planned site will have to be abandoned and another location selected.  For case 6.3., decide what key conditions must be better defined to complete the design and plan a phase II investigation.


Existing Data Sources

The first step in the investigation process is the review of existing data. There are a number of very helpful sources of data that can and should be used in planning subsurface investigations. Review of this information can often minimize surprises in the field, assist in determining boring locations and depths, and provide very valuable geologic and historical information which may have to be included in the geotechnical report.

Following is a partial list of useful sources of geological, historical, and topographic information:

The majority of the above information can be obtained from commercial sources (i.e. duplicating services) or U.S. and state government local or regional offices. Specific sources (toll free phone numbers, addresses etc.) for flood and geologic maps, aerial photographs, USDA soil surveys, can be very quickly identified through the Internet.


Review of Proposal

The initial step of a field exploration is the review of the project proposal or work plan and a discussion of the project’s scope and objectives of the Project Manager. This initial meeting provides the basis for completion of the fieldwork and is the time to raise any questions regarding scope, procedures, schedule,  and any other issues that are not clearly understood.  Particular attention should be given to:

The figure below presents a field instructions form to assist the Field Representative  (and the Project Manager) in the field exploration.


Site Exploration Planning

Planning for the site exploration must first address a general understanding of the topographic and geologic conditions at the site. Information  sources include:

This review will help guide selection of the type of field exploration methods and the expected extent of the exploration.  In some instances, borings may not be the appropriate exploration tool. Site reconnaissance and mapping, shallow hand probes, test pits, or geophysical tools may provide the necessary information without the disruption and cost incurred by borings. If borings are needed, the planning must address the type and diameter of the borings and the type and number of samples. 


Site Visit / Plan-in-Hand

It is almost always necessary (and desirable)  to visit the project site prior to initiating field activities. The following is a list of the items that should be checked during the site visit.

During site reconnaissance,  the planned location(s) of the exploration  point(s) should be visited and suitable  locations should be determined  for: 

Where possible, these locations should be approved by the client representative and should be selected to minimize interference with client activities and damage, while providing appropriate safety and security. 
After the site visit, a field report documenting the observations,  conversations, and other pertinent information gathered during the reconnaissance should be prepared by the field personnel and given to the Project Manager. If possible, the client’s field representative should receive and sign a copy of the field report. 


Underground Structures and Utilities

Location of underground  utilities and structures can be located by the following: 

It is extremely important that the boring locations be cleared for utilities prior to beginning the first boring. Underground alert services generally must be contacted at least two working days prior to the commencement of fieldwork.  The underground alert service will notify affiliate companies that have underground utilities in the project area. The individual companies will send representatives to the site to check utility locations. The locations of borings, pits, etc., must be marked (often with white paint) prior to the utility clearance or arrangements must be made to meet the alert service personnel.  The following  information  is generally required:

The alert service will provide a ticket number and list of companies that the alert service will notify. This information should be recorded for future reference. It should be noted that there are companies  and agencies which are 
not members of alert services and the alert service may not provide information regarding all underground lines and structures (for example, city sewer lines). Any utility companies  not contacted by the alert service should 
also, be contacted. In addition, the alert services do not have maps of underground utilities on most private properties;  they typically mark the underground utility location to the point where it enters private property.



The time and cost involved in obtaining permits for regulatory and public agencies can place substantial constraints on the performance of a project if not adequately addressed in the planning stages. It is important to acquire all necessary permits for access, drilling, sampling, and well construction in a systematic, timely manner. 

As a first step in obtaining required permits, it is necessary to identify private and public agencies that might have permitting requirements.  ]Private clients commonly provide us with the permit and access to the property for sampling and other required field activities. Public clients commonly require geotechnical firms obtain permits and to coordinate site access. When obtaining permits, make certain that geotechnical is not assuming any liability that should be the client's. 


Equipment and Supplies

The geotechnical  Field Representative must take all forms, scales, testing equipment, and marking pens needed to prepare the boring logs and to mark the sample containers. This equipment must be with the Field Representative or arrangements must be made to have the driller provide the equipment.
Each project will require a specific type and amount of specialized equipment, supplies, and materials.  In-house equipment should be requested at least one day prior to the commencement of field activities. All equipment must be inspected, the batteries charged, calibrated,  and properly signed for prior to mobilization for the project.


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