What is a Plate Bearing Test & Why Does it Matter for Foundation Design

Making sure your construction project has a solid base is absolutely crucial for a safe and lasting structure. The plate bearing test, also known as a plate load test, plate bearing testing, or just plate bearing tests, is one of the most reliable on-site tests civil engineers use to figure out the bearing capacity and settlement characteristics of soil or subgrade materials at a proposed building site.

By getting a real understanding of the soil’s load-bearing capacity and ultimate load capacity underneath, you can steer clear of excessive settlement, avoid costly failures, and ensure your foundation design meets all the necessary plate-bearing requirements. Whether you’re working with piling rigs, temporary structures, or a permanent build, getting the right foundation design often starts with a plate bearing test to assess the site-specific ground conditions.

This comprehensive guide takes a close look at everything you need to know about plate bearing tests and plate load tests, from setting up the test plate and procedures to interpreting test results, choosing the right plate size and plate diameter, and optimising ground performance for shallow foundations, temporary buildings, crane outrigger pads, and more.

Understanding the Plate Bearing Test

A plate bearing test is an on-site test designed to figure out the safe bearing capacity, maximum bearing capacity, and settlement behavior of soil or subgrade material. The test measures the soil’s response to applied loads delivered through a circular steel plate (or loading plate), which is usually placed directly on the ground, at the desired depth or foundation level.

Engineers at Site Testing Services do the plate loading test on the actual test location to capture real ground behavior rather than relying solely on laboratory samples that may not reflect the actual site conditions or the impact of larger aggregate backfills.

Key parameters drive the design of working platforms and heavy equipment support. The outcome of things like modulus of subgrade reaction, bearing capacity, and expected settlement below the plate all have a say when it comes to deciding how to go about temporary or permanent structures and working platforms, as well as the support needed for heavy construction equipment. For example, things like crane outriggers and piling rigs need to be able to stand firm on whatever ground they’re on, otherwise they can cause a whole host of problems..

How the Plate Bearing Test Works

Equipment & Setup

The main equipment for a plate bearing test includes:

• A circular steel plate or loading plate (the test plate) of a specified plate diameter and thickness, selected based on the particle size and material being tested. We’re talking about quite a specific bit of kit.
• A hydraulic jack to apply the given load to the plate; it’s all about the load here.
• A load cell to accurately measure each load increment, getting the right numbers is crucial.
• Measuring devices for tracking settlement and test results during each load increment, we need to get the data right.

Equipment needs to be set up to ensure the reaction load is supplied by a suitable machine capable of counteracting the force exerted by the hydraulic jack, and the surfaces have to be prepared for even distribution of load, with special care taken to eliminate surface voids or support from rocks underneath that could skew the readings.

Testing Procedure

• The load is applied in set increments, with each one carefully recorded.
• For each load increment, engineers measure the plate’s settlement until it stabilizes, building up to the anticipated load or until the settlement characteristics show a clear trend.
• Observations include how soil strength changes with depth and whether the load-bearing capacity of the soil or tested zone meets requirements for the structure type.
• Tests can be performed directly at the foundation level or within a shallow pit to get the true bearing test response for shallow foundations or working platforms.

The number of load increments will depend on the material and the maximum bearing capacity, anticipated settlement, or a critical performance threshold, such as for traffic surfaces or crane outrigger pads.

Interpreting Plate Bearing Test Results

The outcome of plate bearing testing includes:

• Load-settlement curves to understand the soil or subgrade settlement behavior under applied loads.
• Calculation of modulus of subgrade reaction for pavement, foundation, and platform design.
• Estimation of safe bearing capacity and ultimate bearing capacity for both shallow foundations and temporary structures.
• Determination of California Bearing Ratio (CBR) to compare with CBR tests for road and highway design.
• Analysis of bearing capacity over the test area, including the effect of the tested particle size and larger aggregate backfills forming the base layer of working platforms or piling mats.

Comparing plate load test and CBR test results helps in selecting the right design values for load-bearing capacity and getting a better understanding of the settlement characteristics of the soil underneath.

Common Applications of Plate Bearing Tests

• Verifying working platforms for piling rig or suitable plant use.
• Assessing load-bearing capacity for temporary buildings, construction plant, or crane outrigger pads.
• Evaluating new civil engineering projects, both for permanent structures and temporary structures.
• Quality control of road and traffic surface base layers, especially where larger tested particle sizes are present.
• Confirmation of bearing capacity before using the area as a test location for additional in situ testing or as a foundation.
• Assessing excessive settlement risk for shallow foundations and validating compaction in testing larger aggregate backfills.

Guidelines & Best Practices

Plate Load Test Standards

Main reference standards for Plate Load tests in the UK and internationally, as well as for Plate bearing testing, are BS 1377 Part 9 and ASTM D1194.

Test Preparation

• Where you’re going to be doing a plate bearing test, make sure you choose a spot that reflects where your foundation will be or under where any heavy plant will be parked when construction is underway.
• You should have a flat bit of ground with no holes or big rocks in it, and check that the bit you test is roughly the right size to cover the expected settlement area for your project.
• Before you start testing if you’re getting any sort of readings off a machine, even just something basic like a data logger, make sure you’ve calibrated the thing first.

Interpreting Results for Civil Engineers

For people building stuff, plate bearing and plate load tests give you real results about how well the plate can handle a load, in other words, how strong the soil is and how much it’s going to settle. That helps you design safe foundations that won’t cost too much or get caught out by tricky ground conditions.

By putting those results together with some basic analysis of the soil, you can get a good idea of whether the ground your site is on is going to be able to hold what you want to build on it, permanent structures, platforms, or even just temporary buildings, and make sense of it all in relation to the loads that will be on it. By doing in-situ tests like a plate load or CBR test, you can make the intelligent, safest decisions for your foundation and construction.