When you start your home building journey, one of the first technical terms you may hear is “strip foundation”. So what is it? What is strip footing? and why is it commonly used in civil works in Vietnam? Let's find out more about this type of foundation with XHOME Saigon!
What is a strip foundation?
Strip Foundation is a type of shallow foundation, in the form of a long, continuous strip or can intersect (like a checkerboard) running along the foot of a wall or row of columns. The main task of a strip foundation is to receive the load from the structure (roof, floor, wall, etc.) and distribute it evenly to the ground below, helping to stabilize the structure and avoid uneven subsidence.
In simple terms, a strip foundation acts as a solid “road” that supports the entire weight of the house and spreads that pressure over a larger area of land, ensuring that the ground can bear the load without excessive deformation.
History of strip foundation development
Understanding the history gives us insight into current applications and limitations. Strip footings have evolved from simple forms using local materials to the more complex and load-bearing reinforced concrete strip footings of today. This progression reflects advances in construction techniques and materials, meeting the ever-increasing demands for durability and scale of construction.
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Classification of popular strip foundations today
To choose the right type of strip foundation, engineers often rely on many different criteria. Below are common ways to classify strip foundations:
1. Classification by configuration (load bearing direction):
- One-way strip foundation: The foundation strips are arranged parallel in a certain direction (usually the length or width of the house), without intersecting each other. This type is suitable for townhouses and tube houses with load-bearing walls in one main direction.
- Two-way strip footing (interference strip footing): The foundation strips are placed in both directions, intersecting each other to form a grid like a chessboard. This type helps distribute the load more evenly, increasing the stability and strength of the structure, suitable for more complex house plans or those requiring large loads in both directions.
2. Classification by nail hardness:
- Hard ice foundation: Usually made of reinforced concrete, has very small deformation, ensuring stability and high durability for the project.
- Soft (flexible) ice nails: Calculated to have a certain deformation, materials such as bricks, rubble concrete, or even wood (melalwood piles) can be used for temporary or light-duty constructions on ground that is likely to sink.
- Combined strip foundation: It is a combination of hard and soft foundations, or a combination of strip foundations with other types of foundations (eg single foundations) to optimize load-bearing capacity and cost.
3. Classification by construction method
Besides the above classifications, in practice there are also variations such as:
- Deep Strip Foundation: When the good soil layer is deep.
- Wide Strip Foundation: For weak soil, need to spread the load.
- Trench Fill Foundation: Fill the trench with concrete.
- Stepped Strip Footing: For steep terrain.
Outstanding advantages of strip foundation
Strip foundations are trusted because they possess many outstanding advantages:
- Cost Effective: Compared with raft foundations or pile foundations, strip foundations often have lower costs due to savings in materials (concrete, steel) and labor.
- Simple construction: Construction techniques are not too complicated, suitable for many construction teams in Vietnam.
- Good load distribution: Helps the load of the building to be transferred evenly to the ground, reducing the risk of subsidence and wall cracking.
- Even settlement: Especially important for the long-term stability of the structure.
- Flexible: The design can be adapted to suit a variety of terrains (e.g. stepped strip footings for sloping ground) and soil conditions.
Disadvantages and limitations to note
Besides the advantages, strip foundations also have limitations:
- Limited load capacity: Not suitable for large projects, high-rise buildings (usually over 3-4 floors) or heavy concentrated loads.
- Not ideal for soft ground: On soft clay, mud, or soil with poor bearing capacity, strip footings may not be safe.
- Sensitive to uneven settlement: Especially in areas with high water tables, expansive soils or seismic activity.
- Anti-rollover stability, limited sliding: Because the foundation is shallow, the ability to resist large horizontal loads may be limited.
When to use strip footings? Practical applications
Strip footings are the optimal choice for the following cases:
- Civil works: Townhouses and villas from 1 to 3 floors (or more depending on land conditions and design).
- Small and medium scale projects: Low-rise schools, hospitals, small factories with moderate loads.
- Structures with load-bearing walls: Strip footings run along the wall for efficient load transfer.
- Relatively good ground: Soil has stable bearing capacity.
- House with basement: Strip footings can be combined as retaining walls for basements.
Ice nails should not be used when:
- The project has very large loads, super high-rise buildings.
- The ground is too weak, prone to subsidence, mud, peat.
- The terrain is too steep and complex without a suitable stepped strip foundation design solution.
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Technical standard strip foundation construction process at XHOME Saigon
To ensure the quality and durability of the project, the strip foundation construction process must be strictly implemented through the following steps:
- Site preparation:
- Site clearance: Clear trees, trash, and obstacles.
- Leveling: Create flat surface, preliminary compaction.
- Locating the foundation axis: Use machines and stakes and wires to accurately determine the location of the foundation axes.
- Check neighboring structures (if any) for protection.
- Digging foundation pit:
- Excavate according to the dimensions (width, depth) and shape approved in the design drawings.
- The bottom of the foundation pit must be flat.
- Treat groundwater (if any) by pumping or creating a sump.
- Formwork work:
- Install formwork (wood or steel) according to the correct shape and size of the foundation.
- Make sure the formwork is tight, sturdy, and not deformed when pouring concrete.
- Steel work:
- Fabricate, bend and install steel bars according to design drawings (steel type, diameter, distance, position).
- Tie steel joints properly, ensuring strong joints.
- Place concrete spacers to create a protective layer for the steel, avoiding direct contact between the steel and the ground or formwork.
- Steel must be clean, free of dirt and grease.
- Pouring concrete foundation:
- Final check of formwork and reinforcement before pouring.
- Mix concrete according to design grade, ensuring quality.
- Pour concrete continuously and regularly, avoiding interruptions.
- Use a rammer to compact the concrete, remove air bubbles, and help the concrete become solid.
- Concrete curing and formwork removal:
- Keep the concrete moist (water, cover with tarpaulin) for at least the first 7 days to allow the concrete to gain strength.
- Remove formwork when the concrete has reached the required strength (usually after 24-48 hours depending on conditions).
- Filling the foundation pit:
- Fill the voids around the foundation with excavated soil or suitable material.
- Compact in layers to ensure tightness.
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Golden notes when designing and constructing strip foundations
To maximize the effectiveness of strip foundations and ensure safety for the project, it is necessary to pay attention to:
- Thorough geological survey: This is the first step, helping to determine the soil type, load-bearing capacity, groundwater level... from which to decide on the appropriate foundation type and design parameters.
- Calculate the exact load: Including static load (self-weight of the structure) and live load (people, furniture, wind, snow...).
- Determine the optimal nail size:
- Width of foundation slab: Usually 2-3 times the wall width, minimum as specified (eg 900-1200mm).
- Foundation depth: Depending on soil type, load, usually equal to or greater than wall width, minimum 450mm-1m to avoid frost or weak surface soil effects.
- Height (thickness) of foundation beam/foundation slab: For example, 350mm foundation slab, 500-700mm foundation beam
- Standard steel design: The quantity, diameter, and position of steel (for example, plate steel Φ12a150, longitudinal beam steel 6Φ(18-22), stirrup steel Φ8a150) must ensure the ability to withstand tensile and bending forces of the foundation.
- Comply with Vietnamese standards (TCVN): Especially TCVN 9362:2012 (Design of house and building foundations), TCVN 4453:1995 (Concrete construction), TCVN 5574 (Design of reinforced concrete structures).
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Compare strip foundations with other types of foundations
| Characteristics | Ice Nails | Single Foundation (Cup Foundation) | Mong Be | Pile Foundation |
| Shape | Continuous strip, or grid | Individual blocks under the column | Large panels cover the entire area of the building | Piles driven deep into the ground |
| Application | Low-medium-rise house, load-bearing wall | Single column, light load | Weak soil, heavy load, multi-storey building | Very weak soil, very heavy load, high-rise buildings, bridges |
| Treatment cost | Medium | Low | Cao | Very high |
| Construction | Relatively simple | and | Complicated | Very complicated, requires specialized machinery |
| Force-resistance | Good for evenly distributed loads | Good for small concentrated loads | Very good, evenly distributed over a wide area | Excellent, transmits to deep hard soil layers |
| Land suitability | Good to average soil | Good land | Weak, expansive soil | The soil is very weak and unstable. |
Strip footings are an effective, economical and popular foundation solution, especially for homeowners who want to build a house, suitable for low to mid-rise residential buildings built on relatively good ground. Simplicity in construction and load distribution are the main advantages that make this type of foundation popular.
However, the selection and design of strip foundations requires careful calculation, based on geological survey results and compliance with technical standards.
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Are you planning to build and need expert advice on foundation solutions for your project? Our team of experienced engineers XHOME Saigon ready to support you. We provide complete design and construction services, ensuring a solid foundation for your dream home.
Contact XHOME Saigon now for free consultation!
- Hotline: 0899.199.786
- Website: xhomesg.com.vn
- Address: 1st Floor, Orient Building, 331 Ben Van Don, Ward 1, District 4, HCMC
