How to hit the foundation of rural self-built houses? You have to know!

Building houses in rural areas will encounter foundation problems more or less. If you want to build a safe and comfortable house, you must lay a solid foundation. The following small series gives some methods on how to lay a solid foundation.

Basic classification of foundation:

(1) According to the materials used, it can be divided into lime-soil foundation, brick foundation, rubble foundation, concrete foundation and reinforced concrete foundation.

(2) According to buried depth, it can be divided into shallow foundation and deep foundation. The buried depth less than 5M is called shallow foundation, and the buried depth greater than 5M is called deep foundation.

(3) According to mechanical properties, it can be divided into rigid foundation and flexible foundation.

Rigid foundation: refers to the foundation built with materials with high compressive strength and low bending and tensile strength. The materials used are concrete, brick, crushed stone, lime soil, concrete, etc. Generally, it can be used in civil buildings with six floors or less and light factory buildings with wall bearing.

Flexible foundation: A foundation made of materials with high tensile and bending strength is called a flexible foundation. Usually made of reinforced concrete. This kind of foundation is suitable for the situation that the load of the superstructure is relatively large, the foundation is relatively soft and the rigid foundation cannot meet the requirements.

(4) According to the structural form, it can be divided into strip foundation, independent foundation, full-house foundation and pile foundation.

Strip foundation: when a building is supported by a brick wall, the foundation under the wall is often set continuously to form a strip foundation.

Independent foundation: when the upper part of the building is a frame structure or a single column, independent foundation is often used; If the column is prefabricated, a cup-shaped foundation is used.

Whole house foundation: When the load transmitted by the superstructure is very large, the bearing capacity of the foundation is very low, and the independent foundation cannot meet the requirements of the foundation, the lower part of this building is often made into a whole reinforced concrete foundation, which becomes the whole house foundation. According to the structure, it can be divided into cutting foundation and box foundation.

Pile foundation: If the soft soil layer of the foundation is thick and the shallow foundation cannot meet the requirements of foundation strength and deformation, pile foundation is often used. The function of pile foundation is to transfer load to hard soil layer through pile. According to the construction method, it can be divided into reinforced concrete precast pile and cast-in-place pile.

Deformed foundation: it is suitable for basements or foundations with low bearing capacity and large upper load.

Box foundation: In order to increase the rigidity of the foundation, the bottom plate, top plate and wall of the basement are cast into a whole, and the box-shaped internal space constitutes the basement, which has great strength and rigidity and is mostly used in high-rise buildings.

Precast reinforced concrete pile: this kind of pile is prefabricated in the construction site or component yard, driven into the soil with a pile driver, and then the reinforced concrete cap is poured on the top of the pile. It has large bearing capacity, is not affected by the change of groundwater level, and has good durability.

Reinforced concrete cast-in-place piles can be divided into casing cast-in-place piles, bored cast-in-place piles and explosive cast-in-place piles.

2. Buried depth of foundation: The distance from outdoor design ground to the bottom of foundation is called buried depth of foundation.

When determining the buried depth of building foundation, the following conditions should be considered:

(1) Influence of soil structure: Building foundation should be set on solid and reliable foundation, not on soft soil with low bearing capacity and high compressibility. The buried depth of foundation is closely related to soil structure.

(2) Influence of groundwater level: Groundwater has great influence on the bearing capacity of some soil layers. The strength of cohesive soil decreases with the increase of water content; When the groundwater level drops, the soil water content decreases, and the foundation will drop.

(3) Influence of freezing line: The dividing line between frozen soil and unfrozen soil becomes freezing line. When the building foundation is in the frozen soil layer, the frost heave of the soil in winter will make the building arch upwards; When the soil layer thaws, the foundation sinks again, leaving the house in an unstable state.

(4) Influence of adjacent buildings: If there are old buildings around the newly-built houses, besides determining the buried depth of the foundation according to the above conditions, the influence of the newly-built houses on the old buildings should also be considered.

3. At the same time, increase the foundation treatment method and application scope.

(1) soil replacement cushion method

The basic principle of cushion method is to dig out shallow soft soil or bad soil and roll it by layers. According to the backfill materials, it can be divided into sand, crushed stone, pulverized coal, dry slag, soil (lime soil, lime fly ash) and so on. Mechanical rolling, plate vibration and heavy hammer tamping are commonly used in construction. It is used for earthwork backfilling with large area of foundation pit and large amount of excavated earthwork, and is generally suitable for filling in shallow soft soil layer and low-lying areas.

Dynamic compaction and silt squeezing method adopts dynamic compaction, gravel filling and silt squeezing methods to form gravel piers in the foundation. Suitable for silt and muddy soil foundation with small thickness.

(2) Vibration compaction method: The principle of vibration compaction method is to reduce the void ratio of foundation soil and improve the strength through vibration and extrusion, so as to achieve the purpose of foundation treatment.

(3) Drainage consolidation method: Its basic principle is that under the action of additional load, pore water is gradually discharged, resulting in consolidation deformation. Drainage consolidation method is mainly composed of drainage system and pressurization system.

(4) Sand drain method: in soft clay foundation, set a series of sand drains, and lay sand cushion or sand ditch on the sand drains to shorten the drainage distance, thus accelerating consolidation and strength growth. Sand drain method is usually supplemented by surcharge preloading.

(5) Laying a sand cushion on the clay layer by vacuum preloading method, then sealing the sand cushion with a thin film, and pumping the sand cushion and sand drain with a vacuum pump to reduce the groundwater level and accelerate the foundation consolidation under the action of atmospheric pressure. It is suitable for soft soil foundation with stable negative pressure boundary conditions in the reinforcement area.

(6) Vacuum-surcharge preloading method: when vacuum preloading can't reach the required preloading load, it can be used in combination with surcharge preloading, which is suitable for soft clay foundation.

(7) Method of lowering groundwater level: By lowering groundwater level, the pore water pressure in soil is reduced, thus increasing effective stress. It is suitable for projects with underground water level close to the ground and small excavation depth, especially for saturated silt and fine sand foundation.

(8) Insert the metal electrode into the soil by electro-osmotic drainage method, and apply direct current. Due to the effect of DC electric field, water in soil flows from anode to cathode, and then water is discharged from cathode. With the help of electroosmosis, the water in the soil can be gradually removed. Suitable for saturated soft clay foundation, which is not much different from houses.