During your piling project’s planning and engineering phases, it is crucial to conduct a soil test to determine your bearing capacity, soil conditions, and resistance distribution.
Soil testing is one of the most timely, reliable, and cost-effective solutions for:
- Assessing the scope of your pile driving project
- Choosing which materials and pile types you will need
- Developing a cost estimate for your project
The composition and depth of the bearing layer for shallow foundations can vary from site to site.
The Importance of Testing Soil Conditions as a First Step
This is why it is essential to conduct a thorough soil boring to gain an understanding of the soil conditions you’re working in. This first step is critical for understanding the soil composition, required depths, and bearing capacity. By correlating information from your soil test with corresponding load tests, you can start to develop your piling job’s scope.
A standard penetration test (SPT) determines the cohesion and adhesion, which allows you to establish the angle of friction for each soil stratum. This will help you and your engineering team decide which pile type is best for your project, depending on the unique soil conditions found at your job site.
If the soil conditions on your job site contain softer soils or clay, you will need to conduct a static cone penetration test (CPT) for soft soils; or you will need to conduct a vane shear test for soils containing clay.
Another aspect to consider is the presence of water or other chemicals in the soil, which may corrode your piles and affect which material you ultimately choose to use for your piles. Certain chemicals can corrode timber, concrete, plastic, and steel piles, which could lead to malfunction in the future.
Your soil analysis should include data for the entire depth you intend to drive pile.
Conducting Your Own Soil Testing
You can choose to conduct your own soil testing and send samples to a lab.
Still, typically it’s more cost-effective to consult with a professional soil testing contractor who can perform the testing quickly and has a relationship with a trusted analyst.
Perhaps the most helpful information discovered during a soil boring is the depth of the bedrock. Once you have this measurement, you can begin to determine the depth of your piles, pile driving equipment, and overall bearing capacity.
Prior to conducting your soil investigation, it is helpful to obtain and know:
- Any historical records
- The location of your job site
- Whether or not the job site is on undeveloped land
If your job site is on undeveloped land, it will likely have more static soil conditions than a more urban job site that has been developed or re-developed multiple times. This is especially critical if the site has had backfill dumped for a pre-existing foundation.
Once you have the historical data, you can compare it to your boring results and consult with your engineers to ensure proper piles and bearing capacity, along with the right type of pile drilling rigs or other pile driving equipment that is required for the project.
The Significance of the Overall Bearing Capacity of a Pile
The overall bearing capacity of a pile is based on three factors, and it ultimately represents the maximum load it can hold without excessive settlement into the ground or failure.
The first factor, soil conditions, we discussed earlier.
The next factor is the pile installation method and, finally, the pile dimensions.
Piles transfer the load into the soil in two ways:
- Through tip-in compression, commonly referred to as end-bearing or point-bearing
- Along the surface, known as shear or skin friction.
The ultimate capacity your piles can safely bear is an important consideration and will influence every aspect of your pile job.
Generally speaking, you will only use piles for deep foundation projects where soil conditions cannot support the load.
Conducting a thorough core soil analysis is the best way to determine the number of piles you will need to drive, as well as which material will provide the best bearing capacity while resisting corrosion or failure.
By increasing the depth of your piles, you can also increase the overall bearing capacity of your piles through utilizing denser, more compacted soils at deeper depths.
At the End of the Day…
Ultimately, the soil conditions will allow you and your engineers to get your project planned, and you can begin the process of arranging pile driving rental equipment, consulting contractors, and working with your client to define a cost estimate and develop a schedule.
You can also determine if you will need more load-bearing piles or support of excavation sheet piles.
By understanding what you will need and how to order the correct piles from the early stages of the planning phase, you can save money, time and ensure a system of piles that won’t malfunction.