Are you a driller looking at adding a soil testing service to your business? If you’ve been in the drilling business for any length of time, or if you’ve been involved in drilling around sites that are being prepped for construction or development – you may have crossed paths with a Cone Penetration Test (CPT) operation.
If you have been curious about this service, you probably noticed that the operating conditions of CPT are pretty comfortable. You may have also heard that the daily rates or rates charged per foot of depth for CPT are usually quite a bit better than what you can get for drilling. Adding soil testing services to your business can be a good way to diversify your workload and ensure a steady income for your business and your family.
What you may not know, is that the skills you’ve acquired to drill are a good basis for entering the CPT business. What do you need to get started? A good place to start is to start comprehending the reasons why customers need a soil testing service and the basics of how this type of soil testing works. This will help you to start thinking about the needs in your area and the types of things you’ll need to learn in order to be successful in the business.
Why a Soil Testing Service?
When engineers are in the early stages of designing infrastructure, such as roads, bridges, or foundations for buildings, they need to know the characteristics of the ground that is going to be built on. Depending upon the type of construction, they may need to understand how soil, clay and rock are layered below the surface. This can help them to decide what the construction process will look like. For instance, will blasting or soil improvements be required? It also helps to ensure that their designs take into account the strength of the ground beneath their structures since heavy structures can have load bearing impacts to surprising depths.
Testing to get a picture of how the soils are stratified underground is called geo-technical testing. There are many other uses for CPT but geo-technical testing is where most people enter the business. So what exactly is CPT and how can you use it to figure out what the soil looks like hundreds of feet underground?
The Basics of How CPT Works
In the Cone Penetration Test (CPT), a specially shaped and hardened cone is mounted onto a rod and pushed into the ground. Much like you would add drill pipe sections to let you drill deeper, in CPT you add lengths of rod to allow the direct push to go deeper. By advancing the cone deeper at a consistent rate (usually around 2 centimeters per second). The CPT equipment tip load cells measure how much pressure it takes to push the cone through overburden materials at the depth you are pushing. Because the push rate is held steady between practical limits, the instrumentation is also gathering information on the friction that is against the sleeve behind the tip load cell..
After completing a variety of soundings in various ground conditions, you will have a comprehensive understanding for how the CPT process functions. The higher the pressure it takes to push the cone through, the harder the soil. The friction on the sleeve gives an idea of what type of sediment is at that depth. As you can imagine, there’s more friction when pushing through sand then through clay. Based upon decades of soundings, ASTMI standards and graphs have been developed that take the data from the CPT report and convert it into a description of the soil strata.
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