Which foundation to choose if the groundwater level is high and water stagnates in the excavation pit?

Clay and loam expand when they freeze. If groundwater is close to the surface on the site, a pile or floating slab foundation is required.

Pile Foundation

A pile foundation is suitable for any type of soil except rock. In addition to the versatility of pile structures, their installation costs are also low. If the groundwater level on the construction site is high, a pile foundation will require the least amount of time and effort.

This type of structure consists of reinforced concrete pillars or metal supports installed along the perimeter of load-bearing walls at a specific spacing. They are sunk into the soil to the bearing layer, below the frost line. The upper portion of the supports is further reinforced with sheathing material. Steel profiles or large-section timber, used for lightweight buildings, are used for sheathing. Types of Pile Foundations

There are three types of pile foundations: driven, bored, and screw. Each has its own advantages and disadvantages:

• Reinforced concrete piles demonstrate reliability, durability, and the ability to withstand heavy loads. Installation of such structures requires specialized equipment.

• Screw piles differ from other types in their ability to compact, rather than loosen, the soil around them during installation. Screw piles are stable and ideal for lightweight structures such as timber frame buildings, SIP panel houses, and other structures. Installation can be done mechanically or manually.

• Bored piles are considered the most cost-effective option and are also easy to install yourself. This requires manually drilling holes, reinforcing them, and filling them with concrete.

The piles must rest on a solid soil layer that does not freeze, does not become saturated with water, and does not move. This will prevent the foundation from being affected by frost heaving. Sometimes, the soil layer suitable for supporting the foundation is located at a depth of more than three meters. Pouring a concrete foundation at such a depth is extremely expensive, so piles are the only option in this situation.

Floating Slab

To select the type of foundation to be installed on problematic soil, it is necessary to carefully study the type of rock in the construction area. While pouring a concrete strip foundation with the base buried to a frost-free depth is sufficient for sandy soil, with loam or clay, their susceptibility to frost heave must be considered.

This type of soil retains water, which turns to ice during freezing, crystallizing and expanding. Frost heave is one of the most common causes of concrete foundation deformation, cracks in the walls, and, consequently, building failures. If it's impossible to drive the piles into a solid, bearing soil layer due to its significant depth, then a slab foundation will be required for brick, block, frame, or wooden houses.

Pouring the foundation is more challenging if the groundwater table is too close to the surface, and lowering the level to the required depth is impossible. In this case, installing a ring drainage system around the construction site would be advisable.

If a floating slab is chosen, the first step is to calculate its thickness. This characteristic is influenced by the soil type and the expected load. It's best to entrust these calculations to a specialist.

A significant advantage of a floating slab is its resistance to deformation and damage. The slab moves with the soil, protecting the walls from destructive loads. This type of foundation is more expensive than a pile foundation.

Among the disadvantages, it's not suitable for installation on steeply sloping sites, as well as the inability to build a house with a basement.