In the world of construction, the terms “foundation” and “ground” are critical yet often misunderstood components that play vital roles in the stability and durability of any structure. Understanding these elements is crucial for architects, engineers, builders, and even property owners. This article delves into the definitions, classifications, and methods associated with foundations and grounds, providing a comprehensive understanding of these fundamental construction elements.
Definition of Foundation and Ground
Foundation
A foundation is a structural component designed to transmit the various loads of a building to the underlying ground. It serves as the load-bearing member of the building below ground level, carrying all loads from the superstructure and transferring them, along with its own weight, to the ground. The foundation ensures that the building remains stable and secure, preventing excessive settlement and structural damage.
Ground
The ground refers to the soil or rock body that supports the loads transmitted from the foundation. The stresses and strains generated by the foundation decrease with the depth of the soil layer and become negligible after a certain depth is reached. The soil layer that directly bears the building loads is known as the holding layer, while the layer below it is called the subgrade layer.
Difference Between Foundation and Ground
The foundation is the part of the structure that bears the loads from the superstructure below the outdoor ground level. It is generally divided into various types based on use, bearing capacity, and materials, such as rough stone foundations, concrete foundations, reinforced concrete foundations, pile foundations, box foundations, and raft foundations. On the other hand, the ground is simply the natural or artificial layer of soil below the foundation that carries the loads of the foundation and the superstructure.
Classification of Foundations
Foundations can be classified based on the materials used, the depth of burial, the force performance, and the construction form.
By Material
- Grey Soil Foundation: Utilizes grey soil as the primary material.
- Brick Foundation: Constructed using bricks.
- Wool Stone Foundation: Made from uncut or roughly cut stones.
- Concrete Foundation: Uses plain concrete.
- Reinforced Concrete Foundation: Incorporates steel reinforcement within the concrete.
By Depth of Burial
- Shallow Foundation: Buried to a depth of not more than 5 meters.
- Deep Foundation: Buried to a depth greater than 5 meters.
By Force Performance
- Rigid Foundation: Designed to bear loads without significant deformation.
- Flexible Foundation: Can accommodate certain degrees of movement and deformation.
By Construction Form
- Strip Foundation: Consists of a continuous strip of concrete that supports load-bearing walls.
- Independent Foundation: Supports individual columns or piers.
- Full Foundation: Spreads the load over a large area, typically used for heavy structures.
- Pile Foundation: Utilizes long, slender columns driven into the ground to support loads.
Ground Classification
Ground can be classified into natural ground and artificial ground based on its origin and treatment.
Natural Ground
Natural ground refers to soil layers that have sufficient bearing capacity without the need for artificial reinforcement. Buildings can be constructed directly on these soil layers. The types of natural ground used as building foundations include:
- Rock: The most stable and load-bearing natural ground.
- Gravel Soil: Composed of coarse-grained materials.
- Sand: Fine-grained and loose, yet can bear significant loads when compacted.
- Silt: Finer than sand, often requiring treatment to improve stability.
- Clay: Fine-grained with high plasticity, requiring careful assessment for load-bearing.
- Artificial Fill: Man-made deposits of materials, varying in stability.
Artificial Ground
Artificial ground is created when the natural ground lacks sufficient bearing capacity or the imposed loads are too large. The soil layer is reinforced through various methods to enhance its load-bearing capacity. Common reinforcement techniques include soil compaction, grouting, and pile installation.
Pile Foundation
Pile foundations are used for large industrial and civil buildings, especially when the natural ground consists of thick layers of soft soil. Pile foundations transfer the load to deeper, more stable soil layers or distribute it through friction along the pile’s length. Types of pile foundations include:
- Reinforced Concrete Precast Piles: Pre-made concrete piles driven into the ground.
- Grouted Piles: Formed by injecting grout into drilled holes to create a solid foundation.
Determination of Foundation Depth
Foundation depth refers to the distance from the designed outdoor ground level to the base of the foundation. Foundations are categorized into shallow and deep foundations based on this depth.
Shallow Foundation
A shallow foundation is one where the depth is less than 5 meters or less than four times the width of the foundation. These are commonly used for small to medium-sized structures.
Deep Foundation
A deep foundation has a depth greater than or equal to 5 meters or greater than or equal to four times the width of the foundation. These are used for larger structures or where the ground conditions require deeper support.
Determining Foundation Depth
The depth of the foundation is determined based on various factors, including soil type, load requirements, and environmental conditions. Shallow foundations are preferred when possible due to lower costs and simpler construction methods.
Foundation Reinforcement and Main Processing Methods
Foundation reinforcement is necessary when existing foundations are subjected to additional loads or environmental changes. Common scenarios include nearby construction, deep foundation pit excavation, new underground engineering, or natural disasters.
Foundation Grouting Reinforcement
This method is suitable for reinforcing foundations that have cracked due to uneven settlement, freezing, expansion, or other reasons. Cement slurry, with a water-cement ratio of 0.5 to 0.6, or epoxy resin is typically used for grouting.
Increasing the Base Area of the Foundation
When the existing foundation’s bearing capacity or base area size does not meet design requirements, the base area can be increased using concrete or reinforced concrete sets. This method distributes the load more evenly and enhances stability.
Anchor Static Pressure Pile
This technique involves pressing prefabricated piles into the soil using a static pile driver. The driver uses its own weight and additional counterweights to apply the necessary force. This method is effective for reinforcing foundations in various soil conditions.
Tree Root Pile Method
The tree root pile method uses small drilling rigs to create holes to the designed depth. Steel cages and grouting pipes are inserted, and cement slurry or mortar is injected. Combined with crushed stone aggregate, this forms robust piles. These piles can be vertical or inclined, single or bundled, depending on the reinforcement requirements.
Conclusion
Understanding the differences between foundation and ground, their classifications, and the methods used for their reinforcement is essential for anyone involved in construction. The foundation provides the critical support needed to ensure the stability and durability of a building, while the ground must have the capacity to bear these loads. By selecting the appropriate foundation type and reinforcement method, construction professionals can address various challenges and ensure the longevity and safety of structures.
