Which is Better: ECP Steel Piers™ or ECP Torque Anchors™? Part 1
D.J. Clayton, PE is part of the Engineering & Training Team at ECP. He will be sharing engineering topics on our blog so check back frequently for updates from Don.
By D.J. Clayton, PE
There are many options from which to choose when selecting foundation underpinning. In addition to steel resistance piers and helical screw piles, other repair methods include drilled caissons that are concrete filled (with or without steel reinforcement), mudjacking, pressing small precast concrete cylinders, high pressure deep grout injection, micro-piles and supplemental concrete spread footings. This is not a comprehensive list of underpinning and other repair methods. It is only presented to acquaint you with some of the more common foundation repair methods.
The way to get the best foundation underpinning repair is to use a product that is manufactured to high quality standards and installed by a trained technicians. Of all of the different underpinning support methods mentioned, the premium products that rise above the others are ECP Steel Pier™ and ECP Torque Anchors™. The important benefit that you receive when selecting and installing an underpinning system manufactured by ECP is that every ECP Steel Pier™ is field load tested after it is installed. ECP Torque Anchors™ have shaft torsion data recorded continuously during installation. These data are used to verify that the required load capacity was actually achieved. These data insure that each underpinning installation provides stable and long term support.
Not only are ECP Steel Piers™ and ECP Torque Anchors™ designed to support the weight of the structure, the design adds a “Factor of Safety”. A Factor of Safety means that these products can support a significantly higher load than is needed for long term everyday foundation support. Immediately after installation, these products have data recorded that verifies the design load capacity. ECP foundation support products are not put into service until each pier has data proving sufficient capacity to support the load requirement plus a Factor of Safety.
“Factor of Safety” is extremely important because it is “insurance” added to each pier design and provides piece of mind. With a Factor of Safety in place, future settlement is essentially non-existent. Most other foundation support methods cannot provide this kind of field data that verifies the design load capacity.
So, which underpinning product is best?
The simple answer is, “It Depends.” It is impossible to say that one method is better than the other. This is why it is a good idea to consult a registered professional engineer before investing a small fortune in foundation repair work. You need to understand the pluses and minuses of the different products and installation methods as they relate to YOUR unique situation. Once you have this knowledge, it is much easier for you to make an informed choice.
Keep in mind that many foundation repair salespersons will attempt to sell whatever repair method they represent. The salesperson does not care whether they offer the best repair method for your situation or not. They are only interested in a quick sale and commission. By comparison, a well established foundation repair company that offers both resistance piers and helical piles is a good place to start searching for the best way to lift and restore your foundation. A company with a long list of successfully completed projects; a company that offers more than one type of foundation support product can suggest to you the best, and most economical, solution for your situation.
Let’s discuss these underpinning products in detail:
ECP Steel Piers™
ECP Steel Piers™ are a premium foundation support product that is installed by carefully pushing high strength steel pier pipe through the failing soil. The installation of pier pipe continues until the bottom end of the pipe encounters solid rock, or load bearing stratum. Once end bearing resistance is encountered, the pier is field tested to verify load capacity and stability. Year after year ECP Steel Piers ™ have proven to successfully provide reliable long term end bearing support under structures.
Some of the benefits of ECP Steel Piers™:
- Small, hand dug access holes are all that are needed to install the ECP Steel Pier™. Once the installation is complete, the excavated soil is replaced and usually it is very difficult to see where the work was done.
- The steel pier installation equipment is portable. No heavy equipment is required. Everything needed for installation; testing and restoration can be carried in a wheelbarrow.
- ECP Steel Piers™ are strong. The strongest ECP Steel Pier™ has an ultimate capacity of more than 57 Tons! How much weight is 57 tons? If you stack eleven 2018 Ford F-150 pick up trucks on top of each other the total weight of all trucks would be just under 55 Tons! ECP Steel Piers™ are robust piers that can be installed from INSIDE the basement in any kind of weather. There is no need to dig 10 to 12 foot deep holes in your yard to reach below the basement footing.
- Hydraulic equipment is used for installation, testing and restoration; which mean that the work is vibration free and relatively quiet. Normally a small gasoline motor or electric motor powers the hydraulic pump.
- Very little overhead clearance is needed to install the ECP Steel Pier™. This is a benefit when installing piers in confined spaces like under elevated decks, under obstructions or balconies and in crawl spaces.
- The very first piece of pier pipe that goes into the ground has a collar at the bottom. The collar is visible in the illustration. The purpose of this collar is to reduce soil friction during installation of subsequent sections of pier pipe. The friction reduction collar allows the additional sections pier pipe to pass through the soil without excessive soil friction limiting the depth achieved. Because of this special collar, the pier pipe can be pushed as deep as necessary to reach the depth of rock or verified suitable load bearing.
- Every ECP Steel Pier™ that is installed is field load tested before being approved. Once rock or suitable end bearing is encountered, each ECP Steel Pier™ is subjected to a field test load that is much greater that the force required to recover lost elevation and to provide long term support. Taking the time to load test every pier that is installed verifies load capacity and documents that the pier has a suitable factor of safety against future downward movement. It is a very solid repair!
ECP Torque Anchors™
ECP Torque Anchors™ obtain support directly from dense and stable soil located deep below the ground surface. The helical screw pile is advanced into the soil by rotating the pile shaft. As the shaft rotates the pile advances downward at a rate of three inches per shaft rotation. One or more helical plates are welded to the bottom end of the shaft. The shape of the helical plates is much like a single thread on a wood screw.
The question is, “How does one know when the helical plates are embedded into a stratum of soil having suitable density for support?” This is a very good question. If an on-site soil test boring and analysis is available, the target soil and depth would be clearly defined in a geotechnical boring log and report. The problem is that residential projects are usually not candidates for soil testing. Soil boring and geotechnical analysis is usually cost prohibitive and quite intrusive on a small residential lot. Soil boring equipment is mounted on a truck and the truck must drive on to the job site to perform a test boring and soil penetration tests.
OK, if there is no geotechnical data; how does an installer know when the helical screw pile has encountered a layer of soil that has suitable strength to properly support the structure? The answer: The installer must monitor the torsion (twisting) of the pile shaft during installation to determine if the soil stratum is suitably dense.
Helical screw piles have been in use since the late 1800’s. Over the years scientific testing has allowed engineers to develop an empirical formula for converting the amount of torsion applied to the shaft (The amount of twisting of the helical pile shaft.) to arrive at a highly accurate estimated of the installed ultimate pile capacity.
Well qualified and experienced installers usually have a good idea of how deep they need to go to reach a suitable stratum of soil in a given neighborhood. This layer of soil has sufficient bearing capacity for structural support. These companies use a regional map to plot the depth-to-load-bearing for each project that they complete. Over years, depth-to-load-bearing patterns can be seen on these maps. It is from this data the installer or engineer can estimate quite accurately the target depth at a given location.
Very heavy structures with full basements and fill soil against the wall may not be the best choice for helical screw piles for inside the basement installations. This is due to the limited overhead clearance available in most basements. However, if the soil outside of the basement wall is removed, then screw piles are excellent products for foundation support and restoration.
Some of the benefits of ECP Torque Anchors™:
- Small, hand dug access holes are all that are needed to install ECP Torque Anchors™. Once the installation is complete, the excavated soil is replaced. All is left clean and neat.
- ECP Torque Anchors™ are the best choice when rock is situated very deep. In such cases, the helical plates encounter load bearing at dense soil at a more shallow depth than the depth required for an end bearing steel pier to encounter rock. In this case ECP Torque Anchors™ are a lower cost option.
- The ECP Torque Anchors™ installation equipment is hydraulic and portable. In slab applications, new construction and repairs with walk-out basements; the product works very well.
- The use of hydraulic installation equipment means that pier installation is vibration free and relatively quiet.
- Every ECP Torque Anchors™ has the shaft torsion (shaft twist) monitored and recorded continuously during installation. Based upon the estimated structural weight that the pile must support, the technicians know the minimum shaft torsion that is required to achieve the foundation support requirement for the project. Of course, an additional “Factor of safety” to insure long term trouble free support is always included when determining the minimum shaft torsion requirement.
- Should an ECP Torque Anchors™ not develop the anticipated capacity when fully installed on site, it is not a problem. Occasionally this can sometimes occur, even when there is geotechnical soil data. The solution is simple. The installer will “unscrew” the helical pile, much like removing a wood screw, then the installer can add an additional helical plate to the existing configuration or a change to a different ECP Torque Anchor™ that has a larger helical plate area to increase the load capacity. There is no money lost or any product wasted.
To Be Continued….
Earth Contact Products, LLC:
ECP is a manufacturer of ECP Steel Piers™ and ECP Torque Anchor™ brand of helical piles. These products are manufactured in the USA from certified quality steel under continuous quality control. ECP has independent certified installers that are trained in underpinning repair, anchor installation, waterproofing and external drainage systems.
It is very important to choose a qualified and certified installer. Better yet, consider investing in the knowledge and opinions of a licensed engineer. If you have a foundation settlement problem, cheap and fast is definitely NOT the way to go. Eventually you will have to do it right, so why not do it right the first time? Look into underpinning options from professionals near you.