What Is a Pile Uplift Test (Tension Test)? How Is It Different from a Pull-out Test?

What Is a Pile Uplift Test?

A pile uplift test applies a vertical upward pull to the pile head in increments and measures the pile-head uplift at each increment. The result is a load–uplift curve that shows how much uplift the pile can resist and at what load it starts to move upward.

The reference standard is ASTM D3689/D3689M-25 Standard Test Methods for Deep Foundation Elements Under Static Axial Tensile Load, which specifies the setup, load increments, hold time per increment, measurements and reporting format. It is structured in parallel with ASTM D1143/D1143M-20e1 for compression testing; the difference is the direction of the load.

When a pile is pulled, the only resistance is the skin friction between the pile shaft and the soil plus the pile self-weight, because the pile toe provides no end bearing as it does in compression. The diagram below summarizes this principle in one view: the left panel shows the load path from the jack to the two supports, the right panel shows the curve used to read the results, and the bottom strip compares it with a pull-out test, which is the next topic.

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How Is an Uplift Test Different from a Pull-out Test?

An uplift test tests a whole pile embedded in soil, while a pull-out test tests chemical anchors or threaded studs embedded in concrete. The two terms are often used interchangeably, causing confusion, but they are different tests with different standards and different equipment.

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Table 1 — Pile uplift test vs. chemical anchor pull-out test

Topic	Uplift / Tension Test (pile)	Pull-out Test (chemical anchor/threaded stud)
What is tested	A whole pile embedded in soil	A chemical anchor or threaded stud embedded in concrete
What resists the load	Skin friction between the pile shaft and soil, plus the pile self-weight	Bond between the adhesive and the concrete and steel rod
Standard	ASTM D3689/D3689M-25	ASTM E488
Load range	Tens to several hundred tonnes	Kilograms to a few tonnes
Loading system	Hydraulic jack on a reaction beam resting on two supports	Portable pull tester placed directly on the concrete surface
Question it answers	Can the foundation resist uplift from wind, buoyancy or overturning moment?	Can the installed anchor carry the design tensile load?

In short, if you are looking for a test of whether a pile can be pulled out, this is the article to read. If you are looking for a test of chemical anchors or threaded studs embedded in concrete, read Pull-Out Test: A Guide to Tensile Pull-out Testing of Chemical Anchors and Threaded Studs per ASTM E488 instead.

Which Projects Need a Pile Uplift Test?

Uplift testing is needed for structures whose piles are pulled upward under some service conditions instead of only being pushed down. The main causes are wind uplift, buoyancy from groundwater, and moments that put the piles on one side of a foundation in tension.

• Solar farm projects — wind under the panels lifts the structure while its self-weight is very low, so uplift often governs the design. See the full set of tests for a project in What Pile Tests Does a Solar Farm Project Need
• High-voltage transmission towers and telecom towers — wind moment pushes one leg of the foundation down and pulls the other leg up
• Large billboards — the same mechanism as towers: a large wind area but little self-weight
• Basements and swimming pools resisting buoyancy — when the groundwater level is high, water pressure pushes the structure up and the piles anchor the structure to the ground
• Tall buildings resisting wind or seismic moment — the outer piles of a group may become tension piles when the moment acts fully
• Anchor piles for dams and waterfront structures

How Is an Uplift Test Set Up?

An uplift test setup has 3 parts: the loading system (hydraulic jack and tension bars), the reaction system (a reaction beam on two supports) and the measuring system (gauges on an independent reference beam). The components are similar to a compression test but reversed in direction. A compression test uses kentledge or adjacent piles as the reaction, whereas an uplift test needs a reaction beam spanning over the test pile that transfers the load to two supports.

1. Reaction beam and supports

A steel beam spans over the test pile head, with both ends resting on supports, which may be adjacent piles, concrete blocks or prepared bearing pads. The distance from the supports to the test pile must be sufficient. If it is too close, the support pressure compresses the soil around the test pile and artificially increases the skin friction, so the measured value will be higher than the true value. The spacing used must follow the standard's requirements and the project test plan.

2. Pile-head connection

This is the weakest point of an uplift test, because the tensile force from the jack must be transferred directly into the pile. For concrete piles, reinforcement projecting from the pile head or a purpose-designed anchorage system is required. If the connection cannot carry the load, failure occurs at the pile head before the soil shows its true capacity, and the result will be lower than the true value and cannot be used for evaluation. See more on pile-head preparation in Pile head preparation before testing

3. Uplift measuring system

Displacement gauges are installed at the pile head and mounted on a reference beam that is independent of both the reaction beam and the supports. If the reference beam rests on anything that moves with the loading system, the readings will immediately be wrong.

When all three parts are assembled, the actual site looks like the 3D model below. The trench in front is cut in the view only to show the pile and its skin friction. The right panel lists the testing sequence for one pile, from preparing the pile-head connection to reading the curve, together with a summary of projects that commonly require uplift testing.

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Compression Piles vs. Tension Piles: What Is the Difference?

A compression pile uses both shaft friction and end bearing, while a tension pile relies only on shaft friction plus the pile self-weight. The results of the two tests therefore cannot substitute for each other.

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Table 2 — Compression piles vs. tension (uplift) piles

Topic	Compression	Tension / Uplift
Resisting mechanism	Shaft friction + end bearing at the pile toe	Shaft friction + pile self-weight (no end bearing)
Effect on soil stress	Pushing compresses the soil around the pile	Pulling reduces the stress in the soil around the pile, so friction drops accordingly
Failure modes to watch	Pile toe plunges into the soil, or the pile crushes under compression	Whole pile pulls out, pile splice fails, or the pile-head concrete cracks at the connection
Typical comparative value	Higher	Clearly lower, especially for piles that rely mainly on end bearing
Standard	ASTM D1143/D1143M-20e1	ASTM D3689/D3689M-25

For details of compression testing and how to read the curve, see Static Pile Load Test: Testing Pile Load Capacity by the Static Method. For an overview of all pile testing methods, see How many types of pile testing are there?

Why Is Uplift Capacity Lower than Compression Capacity?

Uplift capacity is lower than compression capacity for two main reasons: end bearing is lost, and skin friction in tension is lower than in compression.

First, end bearing is lost entirely. When a pile is pushed, the soil below the toe carries load together with the shaft friction. When the pile is pulled up, the toe lifts away from the soil and that contribution disappears, leaving only shaft friction plus the pile self-weight. Piles designed to rely mainly on end bearing, such as piles with their toe in dense sand or rock, show this difference most clearly.

Second, skin friction in tension is lower than in compression. Shaft friction depends on the normal stress the soil exerts against the pile surface. When the pile is pulled up, its cross-section tends to contract slightly (the Poisson effect) and the surrounding soil loosens, so the normal stress decreases and the friction actually mobilized is lower than in compression.

What Should You Watch Out for in Uplift Testing?

Five issues commonly cause errors in uplift test results: accounting for pile self-weight, pile splices, the pile-head connection, the support spacing, and the time allowed for soil recovery.

Agree in advance whether to include the pile self-weight. The pile self-weight already helps resist the pull. Some specifications count it as part of the uplift resistance; others deduct it to look only at the soil capacity. The two approaches give different numbers, so this must be stated clearly in the test plan before starting, not interpreted afterward.

Pile splices are a risk point. Piles joined in segments with welded splices are designed mainly for compression. When pulled, the entire load must pass through the welds. If a weld is defective, the pile may break at the splice before the soil shows its true capacity. In this case, check the weld quality before deciding to test.

Pile-head concrete cracking at the connection. Concrete has very little tensile strength. Transferring tens of tonnes of tension into a concrete pile head requires a connection designed to transfer the load properly through the reinforcement. If the concrete cracks first, the test must stop and the result cannot be used to evaluate the soil capacity.

Reaction beam supports must be far enough away. As noted in the setup section, supports placed too close compress the soil around the test pile, so the measured skin friction is higher than actual, which is an error in the unsafe direction.

Time allowed for soil recovery after installation. As with compression testing, a pile that has just been driven or bored has not yet reached full capacity, because the surrounding soil is disturbed and excess pore water pressure has not yet dissipated. Testing too early gives values lower than the true capacity. The appropriate waiting time depends on soil type and installation method and should be set together with the designer.

How Do You Read Uplift Test Results?

Uplift test results are read from the load–uplift curve, in a similar way to a compression test curve, by checking 3 points

1. Total uplift at the maximum test load must not exceed the specified limit
2. Residual uplift after unloading must be within the limit
3. Curve shape must not break sharply upward before reaching the maximum test load, because that shows the whole pile has started to move up

All limit values are set in the project specification. Example curve shapes for all three points are shown in the right panel of the principle diagram near the start of this article.

Failure in uplift is usually clearer than in compression, because once skin friction is fully mobilized the pile keeps moving up with almost no increase in load, giving a distinct break in the curve. In compression, the pile toe still carries part of the load even after skin friction is exhausted.

How Much Does an Uplift Test Cost, and What Needs to Be Prepared?

There is no fixed flat price for uplift testing, because it depends on the maximum pull required, pile type and size, the reaction beam and support arrangement, the number of test points and the site location, so it is priced per project based on the actual scope. Test prices exclude travel and equipment mobilization, which are charged extra based on the distance to site.

Information to prepare for a quick estimate: the design uplift load and maximum test load per specification; pile type, size and length; the pile-head connection detail; the space around the pile for placing supports; and the project location. Send the information to get a free quotation within 24 hours. SPN provides pile testing nationwide in all 77 provinces. See all services on the Pile Testing page.