Successful construction planning depends on contributions from civil, mechanical and systems designers. As a project manager or developer, you are wise to add the expertise of a qualified geotechnical specialist that you trust on your team. Geotechnical engineering, literally, ensures the project starts with a firm foundation upon which subsequent building phases and the life of the structure depend.

THE ROLE OF THE GEOTECHNICAL EXPERT

Geotechnical consultants are called upon in the construction industry in two areas:

• Detailed, professional analysis of soil conditions at building sites to determine the most reliable, efficient and cost-effective foundation designs
• Ground improvement or remediation where the earth is deteriorating due to erosion, instability or damaging man-made events or natural disasters

STEPS TO A LIFETIME FOUNDATION DESIGN

1)   Developing an Effective Investigative Plan

In collaboration with members of the project team, your geotechnical contractor examines existing site studies, blueprints, materials specifications and the job site itself. The resulting soil investigation plan provides an accurate estimate of structure loads and their locations. It also considers the area’s known geohazards.

The next step is the examination of the soil surface and subsurface conditions through qualitative and quantitative testing.

2)   Soil Testing

According to the plan, soil samples from the surface and subsurface strata are obtained. In-situ testing may be performed at several points within your job site also. As the subsurface may be stratified, each stratum must be tested to determine its bearing capacity.

In-situ tests frequently include the creation of test pits, trenching or soil boring. Tests include visual soil examination, standard penetration testing or cone penetration tests as required. Laboratory tests include soil consolidation testing, shear tests, sieve tests, specific gravity tests and so on. A competent geotechnical professional only specifies tests that are appropriate for your projects.

Once tests are complete and documented, your consultant presents the precise physical, mechanical and chemical characteristics of the earth at all levels.

• Which soil and rock types are present and their relative depth
• Soil particle sizes
• The water and air content of strata
• Soil permeability
• Swell and consolidation characteristics
• Groundwater pH and sulfate/chloride content
• The soil’s liquid, plasticity, and shrinkage Atterberg limits

Based on these and other relevant characteristics, your geotechnical engineer is prepared to develop specifications for safe, cost-effective structure support solutions.

3)   Designing Safe and Effective Support

The proposals provided to you include detailed bearing capacities of the surface and subsurface layers along with recommended site preparation approaches.

In some cases, shallow support structures, such as spread footings or slabs, may be appropriate. Otherwise, deep foundation types, such as piles, piers or earth stabilized columns, etc., may be recommended.

GROUND IMPROVEMENT AND SOIL REMEDIATION

A geotechnical specialist also assists project developers by assessing ground conditions in the remediation industry. Causes for deterioration include extreme weather events, adjacent construction activities, failing support structures and so on. In Florida, their expertise is often called upon due to failing seawalls along coastal properties.

Common signs you may observe that remediation or improvement is required include sinking soil levels, soil loss, water pooling, sinkholes or cracks in slabs or retaining structures.

GROUND IMPROVEMENT TECHNIQUES

A thorough geotechnical assessment of earth bearing capacity and erosion resistance may lead your consultant to recommend one or more remediation methods:

•  Compaction by use of vibration methods
• Reinforcement by adding helical piles
• Replacing existing earth with a heavier material
• Strengthening by mixing in cementitious admixtures known as compaction grouting
• Injecting a fluid polyurethane grouting material

SLOPE STABILIZATION

Ground slopes in Florida frequently require a retaining structure such as a gravity or cantilever wall to stabilize them. Your geotechnical professionals will devise long-term solutions based on soil characteristics, drainage options and the magnitude of hydraulic forces. Otherwise, you are likely to waste money on either over-built structures or repairs due to short-term wall failure.

TIPS ON CHOOSING A QUALIFIED PROFESSIONAL

When evaluating geotechnical consultants, perhaps the most important criterion is their experience. Not only should you ask how long they have been in the business but also ask about the variety of projects they have worked on.

Your due diligence should include several other questions such as:

• Do you have up-to-date licensing and adequate insurance?
• What are your methods for developing an accurate cost estimate?
• How do you mitigate unexpected problems or delays?
• How do you ensure the qualifications of any subcontractors?
• What safety measures or procedures do you employ?
• Can you provide at least three client references for jobs that are like ours?

A WORD OF CAUTION ABOUT LOW-BID GEOTECHNICAL CONTRACTORS

As a homeowner, building owner or project developer, you may be tempted by low bids when employing a geotechnical firm. Doing so, however, may result in greater costs over the long run.

Some geotechnical engineers cut corners by performing a subset of the tests necessary to get the full picture. Instead of developing a comprehensive and accurate assessment of a job site’s soil conditions, they simply apply overly conservative recommendations based on worst-case scenarios.

This style of appraisal often leads to needless project expenses including over-excavation and unnecessarily large support structures. This is unfortunate since these additional costs frequently dwarf the additional expense of more thorough testing and bearing capacity analysis.

ENSURE YOU GET A CORRECT, LONG-TERM SOLUTION

Professional recommendations balance long-term safety of projects against their costs. Good planning, even before groundbreaking, thorough testing and proper analysis regularly lead to multiple cost-effective solutions from which you can choose.

Whether your project involves new construction, ground improvement or remediation of soil-related problems, it is crucial that you seek consultation from a qualified firm that you trust.

The best firms have many years of experience and a full suite of services including remediation. They can complete the job from start to finish. They are flexible and listen to your needs. They are also adept at dealing with any unexpected difficulties should they arise.

Following our advice will lead you to the most worthwhile, practical and economical solution for your earth support or stabilization undertakings. Contact Helicon today to discuss your next geotechnical project at 844-HELICON.