Composite foundation is a kind of artificial foundation which is formed by the reinforcement or displacement of some soils.

According to the concept of the generalized composite foundation and composite foundation can be respectively is vertical (pile) composite foundation and the level to enhance body (reinforced foundation), which can be divided into the medium material pile composite foundation pile composite foundation in the upper structure and foundation stiffness is bigger, the ground stress spread down the base, bearing properties and shallow foundation near, Including gravel pile, sand pile and slag, etc.), and the bonding material pile composite foundation, pile has the strong cohesive force, but small modulus and rigidity than concrete, under large load can excessive deformation and broken pile, including soil pile, lime soil pile, lime pile and cement-soil mixing pile, powder jetting mixing pile and jet grouting pile, roots, etc.).

According to the classification of foundation cushion stiffness, the composite foundation can be divided into the composite foundation under rigid foundation and composite foundation under flexible foundation. The BEARING behavior of composite foundation under rigid foundation and FLEXIBLE foundation is different: THE pile-soil load sharing of composite foundation under flexible foundation is smaller than that of composite foundation under rigid foundation, while its settlement is larger than that of rigid foundation.

Action mechanism of composite foundation:

1, the role of pile body

The pile stiffness in composite foundation is large, and the stress in the foundation will be distributed according to the material modulus when the pile deformation is equal under the rigid foundation. Therefore, stress concentration occurs in the pile body, most of the load is borne by the pile body, and the stress on the soil between piles decreases accordingly. As a result, the bearing capacity of the composite foundation is increased and the settlement is reduced.

2, compaction effect

Sand pile, soil pile, lime pile, gravel pile and so on in the construction process, because of vibration, compaction, soil discharge and other reasons, can play a certain role in the compaction of soil between piles. Lime pile has the characteristics of water absorption, heating and expansion, and also plays the role of compaction of soil between piles.

3And accelerate consolidation

Gravel piles and sand piles have good water permeability, which can accelerate the consolidation of the foundation. Cement soil piles and concrete piles can also accelerate the consolidation of the foundation to a certain extent.

4, cushion function

The composite foundation or composite layer formed by the combination of piles and soil between piles is superior to the original natural foundation because of its performance, which can play the role of soil exchange similar to cushion, uniform foundation stress and increase stress diffusion Angle. In the foundation where the pile does not run through the whole soft soil layer, the cushion plays an important role.

All kinds of composite foundation have cushion function. The horizontal reinforcement composite foundation and the loose material pile composite foundation have more obvious effect.

5, reinforcing effect

Reinforcement mainly refers to the soft soil layer with small thickness, and the pile body can pass through the whole soft soil layer to reach the hard layer under it. At this time, the pile body will produce certain stress concentration phenomenon under the action of external load, so that the soil between piles will bear the Pressure decreases, and the results compared with the natural foundation, composite foundation bearing capacity increases, the compression quantity decreased, the stability is enhanced, the sedimentation rate will accelerate, also can be used to improve the soil shear strength, reinforcement of composite pile soil layer can improve the stability of the slope, the reinforcement effect known as reinforcement effect.

At present, the test data obtained in engineering practice are obtained under the rigid foundation, so the building foundation on the composite foundation should have good stiffness generally, in order to give full play to the bearing capacity of the composite foundation.

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