Going Vertical: How CSP Supports Deep Foundation Construction | Part 1

Deep foundations play an important role in projects where the ground can't adequately support the structure above. From buildings and bridges to wind turbines and electric transmission lines, these applications often require foundations that extend well below the ground surface.

But before those foundations can do their job, contractors need a reliable way to manage the excavation and complete the construction process. That's where vertical casings, including corrugated steel pipe (CSP), can come into play.

Let's look at how CSP is used in vertical construction, where it makes sense, and what engineers need to consider before selecting a solution.

What Exactly Is a CSP Caisson?

In the applications discussed here, CSP serves as a casing or form that helps maintain the opening while the contractor constructs a cast-in-place concrete foundation.

It's important to understand the difference between the casing and the completed foundation. A casing may serve primarily as a temporary construction aid rather than as a component intended to provide long-term structural support.

In other words, just because the casing remains in place doesn't automatically mean it's designed to carry the structure's loads. That depends on the project specifications and engineering design.

This distinction matters because the casing must be evaluated for the conditions it will encounter during construction, while the completed foundation must meet the structural requirements of the building or infrastructure it supports.

Where Are Vertical Caissons Used?

Vertical caissons are used across a wide range of infrastructure and construction projects, including:

• Buildings: Supporting structures where shallow foundations may not provide adequate bearing capacity or acceptable settlement performance.
• Bridge piers: Transferring loads to suitable bearing materials below the surface.
• Electric transmission lines: Providing deep foundation support for transmission structures.
• Wind turbines: Supporting substantial structural loads that must be transferred into the ground.
• Light poles: Providing a foundation support as an alternate to spread footings.

The right casing configuration depends on the foundation's dimensions, subsurface conditions, and construction method.

Contech offers HEL-COR CSP for vertical applications, along with structural plate options for larger-diameter configurations. These products can help contractors establish the opening needed for foundation construction, but the appropriate solution still depends on project-specific engineering.

It's also worth noting that not all vertical pipe applications serve the same purpose. A foundation casing, a utility access shaft, a crane enclosure, and a seismic isolation casing may look similar at first glance, but their functions and design requirements can be very different.

Understanding the intended application is the first step toward choosing the right solution.

How Do Soil Conditions Affect Installation?

One of the biggest factors influencing vertical casing installation is the ground itself.

Some excavations can remain open temporarily while a preassembled casing is lowered into place. Others require continuous support as excavation progresses to prevent the surrounding soil from collapsing into the shaft.

Depending on site conditions and the construction approach, contractors may use:

• Preassembled CSP or structural plate casings: Lowered into an excavation where the opening can remain stable long enough for installation.
• Segmented tunnel liner plate: Assembled in stages as excavation advances, providing support as the shaft is constructed.

Neither method is automatically right for every soil type. The installation approach needs to account for actual ground conditions, excavation depth, groundwater, and the sequence of construction.

For example, the Robert Crown Community Center project, discussed in Part 2, used HEL-COR CSP temporary casings in non-cohesive ground. The project demonstrates how CSP can support foundation construction under challenging conditions, but it doesn't establish a universal installation method for similar soils.

Worker access is another important consideration. When personnel must enter a vertical shaft, maintaining excavation stability becomes especially critical. The construction plan must address appropriate ground support, access procedures, and worker safety requirements.

Why Construction Planning Matters

A successful vertical casing installation starts well before the casing arrives on-site.

Engineers and contractors need to understand what the casing is expected to accomplish, how the excavation will be supported, and what conditions the casing will encounter during installation.

That includes considering soil stability, groundwater, nearby equipment, and construction sequence.

Getting these details right helps establish the requirements for casing stiffness, connection strength, and overall structural performance.

And that leads to another important question: How do you determine whether a casing can withstand the loads it will experience during construction?

That's where engineering gets more involved.

In Part 2, we'll look at the key design considerations for vertical CSP applications, including lateral earth pressure, groundwater, construction surcharge, buckling, material selection, and a real-world deep foundation project.