BUILDING FOUNDATIONS-3

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SOLVING FOUNDATION FAILURES

A building foundation’s primary purpose is to transfer the loads from the superstructure to the underlying soil at a bearable pressure. It serves as an interface between superstructure and substructure. As we discuss foundations, remember that a footing and a foundation are two different elements, one is a subset of the other. A foundation is a complete section of a structure comprising of various elements while a footing supports and transfers column loads thou these exist in different types (Refer to Building Foundations 1)

In relation to Foundation engineering, which is the branch of engineering that deals evaluating a soil’s ability to support a load thereby designing substructures to transfer these loads to the ground, we understand that the foundation of a structure is more than concrete and reinforcement. It closely relates to the substructure of a building or structure.

With the understanding of foundation engineering, facts are drawn that failure of a structure greatly depends on the underlying soil and the load exerted on the ground. (Refer to Building Foundations 1)

EFFECTIVE SOLUTIONS TOWARDS FOUNDATION FAILURES 

Building the foundation on hard or rock surface

This is viable in an area with uneven soil properties. If the position of the structure within the site can be revised, identifying the sections with a stronger soil type can prevent any form of foundation failure. The aim here is to attain the soil  that can carry the building weight by maximum bearing pressure required to carry the load impose on it. This reduces the expected costs if the weak soils were to be stabilized.

Change of foundation details.

Here, the type of foundations would require that it be dictated especially for big projects. In such a scenario, pile foundations will best support the structure since they directly exert the lateral loads into the firmer depth.

Increasing the foundation depth

It is expected that the deeper the soil layers, the firmer and stronger it is. Usually, the stable soil layers are arranged gradually in layers of top soil, clay soil and sand soil. However, this doesn’t guarantee a permanent solution since it greatly depends on the general properties of the soil. It is possible to excavated only to realize one has reached a water table or rather fail to find stable soils.

The footing is set deep enough so that it will be independent of variations in soil moisture. It is also designed to adequately distribute the load without creating unnecessary bulk or mass.

Slab-jacking and hydraulic jacking

Slab jacking solves the problem of a sunken concrete slabs, drive ways and sidewalks, foundation that has reduced in depth due weak underlying soils. This is also known as piering. A mechanical jack is a strategically placed to carefully lift the settled beam to the required level. Here, grout is pumped into a slab or beam to produce a lifting force that restores the member to its original elevation. Steel posts are driven through unstable soil and with the help of hydraulic jacks they are raised high. This stabilizes the different concrete slabs or footings affected by movement of the underlying soil.

Proper soil drainage channels.

This should mainly emphasize in areas that are water logged or with rather a high moisture content so as to minimize the moisture content in the soil. As earlier discussed, expansive soils weaken when wet and stiffen when dry thereby weakening a structural foundation. Drainage in such ground conditions can be provided using weep holes, perforated drain pipes and sumps & surface drainage channels

Foundation details showing a provision of drainage pipe.

PREVENTIVE MEASURES AGAINST FOUNDATION FAILURE

  • Subsurface soil investigation (Geotechnical investigation)
  • Strengthening and stabilizing the foundation of an existing building or other structure
  • Proper structural analysis and design of a design before construction. This prevents construction of a structure with uneven loads
  • Proper supervision of the construction of the proposed structure.
  • Quality control and quality assurance measure instituted by field engineers
  • Providing proper drainage system
  • Proper compaction of proposed area for construction. If the site is identified to have poor /expansive soils, these can be replaced approved soils and compacted at proposed layers and MDD content.

 

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Posted on: December 21st, 2021 by London Building Contractors No Comments

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