What is the underlayment and where is the location

1. Overview. The cushion is the intermediate layer of the reinforced concrete foundation and the foundation soil, the function is to make its surface smooth and convenient to bind the steel bar on it, and also play the role of protecting the foundation, all of which are plain concrete, without adding reinforcement. If there is a reinforcement, it cannot be called a cushion and should be regarded as a foundation slab.

About the thickness of the cushion is described in the Code for the Design of Building Foundations

GB50007-2002 stipulates in the section: The thickness of the cushion of the extended foundation should not be less than 70mm, and the strength grade of the cushion concrete.

It should be C10. An extended foundation refers to a reinforced concrete independent foundation under a column.

and reinforced concrete strip foundations under the walls.

It is not necessary to use underlayment in unreinforced extended foundations. Unreinforced extended foundation refers to a foundation made of brick, rubble, concrete or rubble concrete, plaster and triad.

and other materials composed of strip foundations under walls or independent foundations under columns.

This paragraph. Second, the role.

It plays the role of leveling, isolation and transition. 1. It is convenient for the construction of pay-off and support of foundation formwork. 2.

Ensure the effective position of the foundation bottom plate reinforcement and the protective layer is well controlled; Isolate the bottom reinforcement and soil from contamination. 3.It is convenient for the bottom surface of the foundation to be used as an anti-corrosion layer.

4.Leveling, by adjusting the thickness to make up for the error of earthwork excavation, so that the bottom plate is stressed in a plane, and the high-grade concrete of the foundation is not wasted. Mattress is a method to solve the unevenness of the foundation in CFG composite foundation.

For example, when the building is on a rocky foundation and clay on the other, it is solved by adding a bedding layer (graded sand) to the rocky foundation. The bedding layer is a necessary condition for the formation of a pile composite foundation.

Without the cushion layer, the soil between the piles can not give full play to its bearing capacity, so it can not form a pile composite foundation; The underlay refers to the structural layer located below the base layer. Its main function is water insulation, drainage, and anti-freezing to improve the working conditions of the base and soil foundation. The material can be sand, ceramsite.

Mortar, concrete, etc. Essentially, the cushion is the force transmission layer, and the cushion is the protective isolation layer.

Adjust the stress distribution of the load on the foundation to prevent stress concentration. The cushion layer can ensure that the foundation always transmits a part of the load to the soil between the piles through the cushion layer, and adjusts the sharing of the load between the pile and the soil.

Your questions are not asked all, so it's not good how. Generally speaking, there are two types of underlayments. One is pavement cushion and the other is structural cushion. Not sure which one you asked. Give a link for your reference, I don't know if it can help.

Pavement underlayment. foundation cushion.

The cushion layer is the structural layer of its lower part relative to the surface layer, which plays the role of filling the appropriate height, ensuring that the base layer is flat and firm, and the internal buried pipeline is played.

The cushion refers to the structural layer located below the base layer, and its main role is water insulation, drainage, and anti-freezing to improve the working conditions of the base and soil foundation, and its water stability requirements are good.

The cushion position is between the structural layer between the base and the soil foundation, and when the water temperature of the soil foundation is poor, it is used to improve the water temperature of the soil foundation, improve the water stability and frost heave resistance of the pavement structure, and can diffuse the load to reduce the deformation of the soil foundation.

Mattress cushions. It is the force transmission layer, and the cushion is the protective isolation layer, adjust the stress distribution of the load to the foundation, prevent the stress concentration, and the cushion can ensure that the foundation always transmits a part of the load to the soil between the piles through the cushion layer, and adjusts the sharing of the pile and soil load. Slouch shouted.

It is not necessary to use cushion in unreinforced extended foundations, which are made of brick, rubble, concrete or rubble concrete.

Ash and triple soil.

and other materials composed of strip foundations under walls or independent foundations under columns.

Conditions of use:

1. Cushions should be provided for road sections where the roadbed is often in a wet and over-wet state, as well as road sections that produce freezing hazards in seasonal freezing areas.

2. There are two types of cushion materials: granular material and inorganic binder stabilized soil, granular material includes natural gravel, coarse sand, slag, etc., when coarse sand and natural gravel are used, the particle content of less than 5% should be less than 5%; When using slag, the particle content of less than 2mm should be less than 20%.

3. The thickness of the cushion should be determined according to the local experience, and when the total thickness of the pavement in the seasonal freezing area is less than the minimum thickness of the anti-freezing, the cushion material should be supplemented.

The underlay refers to the structural layer located below the base layer. Its main function is to improve the working conditions of the base and soil foundation by water insulation, drainage and anti-freezing, and its water stability requirements are good.

The cushion is located in the structural layer between the base layer and the soil foundation, and when the soil foundation water stability is poor, it is used to improve the water stability of the soil foundation, improve the water stability and frost heave resistance of the pavement structure, and can diffuse the load to reduce the deformation of the soil foundation. Therefore, it is usually set when the soil base is wet and the temperature condition is poor. The strength of the cushion material is not necessarily high, but its water stability must be good.

The underlayment is usually concrete.

Concrete cushion is the intermediate layer of reinforced concrete foundation and foundation soil, the function is to make its surface smooth and convenient to bind steel bars on it, and also play the role of protecting the foundation, all are plain concrete, no need to add reinforcement. If there is a reinforcement, it cannot be called a cushion and should be regarded as a foundation slab. Protective layer of stressed reinforcement of reinforced concrete foundation:

40mm when there is a cushion; 70mm without underlayment.