Raft foundation, also known as foundation, is understood as the bottom structure of a construction project that takes on the function of supporting the structure's load on the ground, helping the structure withstand the pressure of material blocks. located above. At the same time, it also has the function of ensuring the safety of the entire project.

In terms of application, raft foundations are called comprehensive foundations because they are shallow foundations and are mainly designed for use in places with weak ground, weak resistance whether with or without water, or due to The structural bridge of the project is suitable for projects with high load-bearing structures and high-rise housing projects. In addition, it is also suitable for projects with underlying structures such as basements, warehouses, tanks, swimming pools, toilets, etc.

This is considered a safe type of foundation and is widely applied because it is a safe and highly effective method of evenly distributing weight, helping to avoid subsidence. In particular, they are all developed into complete drawings for 2-story houses or similar.

2. Structure of raft foundation

The raft foundation is composed of many layers as follows:

• Concrete foundation layer: Average thickness of 100mm depends largely on the comprehensive foundation design on soft ground.
• Raft foundation height: about 3200mm according to engineers' calculations, suitable for most common housing projects.
• Dimensions of the complete foundation beam: approximately 300x700mn
• Foundation beam steel: Use the common form of longitudinal steel 6Φ(20-22), stirrup steel Φ8a150 to ensure safety for the whole project.
• Foundation plate steel: Use standard steel with 2 layers of steel Φ12a200.

(Illustration, source: Internet Collection)

3. Structure of raft foundation

If a construction project is 4mx4m in size and weighs 55 tons, the bearing capacity of the comprehensive foundation is calculated according to the formula: Construction weight/Construction area = 55 tons/16m=3.4 tons.
From there, it can be concluded that the comprehensive foundation structure can withstand forces of up to 3.4 tons/m². But the foundation structure will be divided and calculated depending on the specific characteristics of each area to ensure absolute safety and optimize construction costs.
In addition, in some projects, the comprehensive foundation is supported by columns, the bearing capacity will increase significantly.

(Illustration, source: Internet Collection)

4. Tiêu chuẩn thiết kế móng bè

Below are the comprehensive foundation design standards closest to reality, please refer to them to avoid risks during the foundation design process:

• Flat slab: The length of the slab is e=(⅙)l, the distance between columns l<9m and has a tonnage of about 1,000 tons/column.
• Inverted arch slab: This type of slab is often used by builders when the project requires high bending resistance. As for small projects, the arch can be made of brick, stone, concrete with e=(0.032 l + 0.03)m and the deflection of the arch is f=1.7 l ~ 1/10 l.
• Rib type: This type is structured in two types of ribs: the lower rib has a trapezoidal cross-section with the advantage of good anti-slip ability and an increasing trend. Next to that is the rib located on the village.
• Box type: This type of foundation is evenly distributed on the ground but the force is only concentrated on it. The box type foundation will be used for 2-story houses and multi-storey houses. The frame structure has good bearing capacity, great stiffness but quite light weight.

5. Advantages and disadvantages

- Advantage

• Raft foundations are especially suitable for projects with structures that are not too heavy such as level 4 houses or 1 to 3-storey houses because they have low cost and quick construction time.
• Comprehensive foundations are an effective solution chosen by many projects with designs for tanks, warehouses, swimming pools or basements, and toilets.
• Suitable for construction in places with low construction density and little two-way impact, including near neighboring buildings.

- Disadvantages

• Depending on the type of terrain and geology, raft foundations can be applied.
• The depth when placing the foundation is quite shallow, so it will lead to some problems such as stability due to environmental impacts such as underground drainage or earthquakes.
• Comprehensive foundations are susceptible to subsidence or deviation due to the impact of the underlying geological layers and can change at the locations of foundation drill holes, causing the project to crack and reduce its lifespan.

6. Comprehensive foundation construction process

The construction process includes the following steps:

(Illustration, source: Internet Collection)

Step 1: Construction preparation work
At this stage, you need to prepare tasks such as:

• Find a construction unit
• Prepare the construction site: clear and level the site.
• Prepare materials as well as machinery and equipment during construction.

(Illustration, source: Internet Collection)

Step 2: Dig the foundation hole
The construction area will be according to the construction drawings, on the leveled construction land area. The contractor needs to carry out the work of digging construction foundation holes on the entire land area specified in the drawings.

(Illustration, source: Internet Collection)

Step 3: Pour concrete to brace the foundation
Concrete needs to be mixed according to the correct standards for the quality of each component as well as carried out in accordance with  regulations on mixing and quality of concrete to ensure the quality of the project.
With a comprehensive foundation, concrete is poured in layers, each layer of concrete is about 20-30 cm thick. To ensure the connection of the concrete layers, the upper layer must overlap the lower layer when it begins to set.
Step 4: Acquisition and maintenance of the foundation
The raft foundation needs to be kept moist and watered to ensure standard humidity until the concrete adheres firmly and long enough to create the most stable finished product.

(Illustration, source: Internet Collection)

7. Note when constructing raft foundations

• Pay special attention to the care of the foundation, the comprehensive foundation must always be kept moist and avoid prolonged rain causing the cement to die, and avoid too much sun so that the concrete surface does not crack. Foundation preservation time will take about 1-2 days until the concrete really sticks.
• Although the raft foundation design on soft ground is appropriate, if the ground is unstable or at risk of subsidence, it will affect the project.
• During construction, piles are important points for transmitting forces, so it is necessary to pay attention to the appropriate arrangement of piles according to the requirements of the project to take full advantage of reducing internal forces in the foundation in an optimal way and the safest.

(Illustration, source: Internet Collection)

8. Introducing a reputable design & construction consulting service provider

The importance of construction units is undeniable because their reputation will ensure the quality and aesthetics of your project. Today, there are many units providing construction design services to meet the increasing construction demand in our country. Therefore, finding a reputable unit is not easy and requires you to spend time researching. During the selection process, you need to research carefully and ensure that the accompanying unit must have high professional qualifications, many years of experience, have a clearly signed contract, transparent costs,... Nowadays, according to feedback from some customers who have contacted Hung Nghiep Phu shows that there are currently many fraudulent units that are construction design consulting companies to scam people for many different purposes. To help customers save time searching, Công ty TNHH Đầu Tư Xây Dựng Hưng Nghiệp Phú is confident that it will be the best choice for you.

Hung Nghiep Phu Construction Investment Co., Ltd. with the mission of bringing the best solutions and services, together with customers to build a prosperous community, Hung Nghiep Phu is gradually asserting its brand through Sincere cooperation, with a team of leaders with ethical capacity, creativity, dedication to the profession, and strategic vision. Hung Nghiep Phu owns a team of skilled and highly qualified staff who will bring customers the best quality projects. 

Hung Nghiep Phu Construction Investment Company Limited - specializes in constructing civil and industrial projects. We look forward to accompanying customers in construction projects as well as legal procedures such as planning diagrams, applying for construction permits, completing processes, applying for fire prevention and fighting certificates, ... If you have any questions or are in need of designing and perfecting the process, please contact us immediately for a free consultation!

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Source: Collected Internet