How do you build pile foundations in deep and soft soils?

1 Types of piles

There are two main types of piles: end-bearing and friction piles. End-bearing piles rely on the bearing capacity of the soil or rock layer at the tip of the pile, while friction piles generate resistance along the shaft of the pile due to the interaction with the surrounding soil. Depending on the material and method of installation, piles can also be classified as driven, bored, or cast-in-situ piles. Driven piles are pre-fabricated and hammered into the ground using a pile driver, while bored piles are formed by drilling a hole in the ground and filling it with concrete. Cast-in-situ piles are similar to bored piles, but they use a temporary casing or a hollow auger to form the hole and inject the concrete.

2 Design of piles

The design of pile foundations involves several steps, such as determining the number, size, length, and spacing of piles, as well as the pile cap and connection details. The design criteria depend on the type and magnitude of the load, the soil properties, the pile material and installation method, and the safety and serviceability requirements. The design methods can be based on empirical formulas, analytical models, numerical simulations, or field tests. The most common field test for pile design is the static load test, which measures the pile settlement under a known load.

3 Installation of piles

The installation of pile foundations requires careful planning and execution, as it can affect the performance and integrity of the piles and the surrounding soil. The installation method depends on the type and material of the pile, the soil conditions, the site access, and the environmental impact. Some of the factors that need to be considered during installation are the pile alignment, penetration depth, driving resistance, soil displacement, noise and vibration, and quality control. The installation of piles should be supervised by qualified engineers and technicians, and documented by records and reports.

4 Testing of piles

The testing of pile foundations is essential to verify the design assumptions, assess the quality and condition of the piles, and evaluate the load-bearing capacity and settlement of the pile group. The testing methods can be divided into two categories: static and dynamic tests. Static tests apply a gradual load to the pile and measure the resulting displacement, while dynamic tests use a drop hammer or a device that generates an impact load and measure the resulting force and velocity. The test results can be interpreted using various methods, such as load-settlement curves, bearing graphs, or wave equation analysis.

5 Advantages and disadvantages of piles

Pile foundations have several advantages and disadvantages compared to shallow foundations. These include the ability to support higher loads and reduce differential settlements, reach deeper and more stable soil or rock layers, accommodate various soil and site conditions, and resist uplift, lateral, or seismic loads. However, pile foundations are more expensive and complex to design and install than shallow foundations, may cause damage or disturbance to the surrounding soil or structures during driving or drilling, require special equipment and skilled labor, as well as permits and regulations, and may be affected by corrosion, deterioration, or damage due to environmental or construction factors.

6 Maintenance and repair of piles

Pile foundations require regular inspection and maintenance to ensure their durability and safety, depending on the type and material of the pile, the soil and environmental conditions, and the signs of distress or damage. Common inspection and maintenance techniques include visual inspection, sounding, probing, coring, ultrasonic testing, or load testing. Additionally, cracks or spalling of concrete piles due to overloading, corrosion, or freeze-thaw cycles can be repaired with grouting, epoxy injection, or jacketing. Settlement or heave of pile foundations due to soil consolidation, swelling, or liquefaction can be fixed with underpinning, grouting, or compaction. Lastly, lateral displacement or buckling of pile foundations due to lateral or seismic loads, or soil movement can be repaired with bracing, anchoring, or strengthening.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?