【Excerpts】Foundation uneven settlement, how to treat?

       There are various reasons for the settlement of foundation. The even settlement will bring huge impact to the building, and the damage to the building is irreparable. Settlement and uneven settlement will occur during the construction of the building and after the completion of the building. If it is a uniform settlement, the damage may not be great. But if it is uneven settlement, it will lead to structural changes of the building. So that the building collapse, can not continue to use. Therefore, it should be concerned in the initial design.

The cause of the uneven settlement of the foundation

1、Geological factors

       Due to the fluctuation of bedrock, the local soil is uneven and the thickness of the soil layer is different, so one part of the building foundation is often placed on the hard bedrock, and the other part of the foundation is placed on the hard soil layer. Or in the foundation soil is soft, the foundation of the soft soil thickness is large, soil compression is larger, there are dark ditches, caves and so on. The water content of the foundation is not normal, and the building foundation will produce uneven settlement after compression.

2、Survey factors

       The investigation unit does not operate according to the regulations, such as the hole in drilling is not accurate or the hole depth is not in place, resulting in the accuracy of geological report and authenticity is not high. In the actual construction, some projects even do not carry out effective geological investigation and blind construction.

3、Design factors

       The length of the building is too long; the building is complex, with many concave and convex corners, or height difference and load; settlement joints are not set in appropriate parts; insufficient overall stiffness of foundation and building; improper foundation treatment, unreasonable foundation design; the influence of composite foundation of adjacent buildings.

4、Construction factors

       No serious groove inspection; construction drainage scheme is unreasonable; arbitrary reconstruction and expansion of buildings; low mortar strength, ash joint is not full, and tie bars are not set according to the prescribed standards.

5、Other factors

       Large exploitation of groundwater, improper use of buildings. Change the use of the house at will, increase the load or increase the vibration, damage the wall, lead to the uneven settlement of the building, wall cracking, structural damage.

Specific measures to prevent the uneven settlement of the foundation

1、 Architectural design measures:

（1） Construction measures

       The plane shape of the building should be made to be simple, regular and neat, and try to avoid complex shape, too many Yin angles, and significant height difference or load difference of the building. Crack accidents in soft soil areas are often common in buildings with different height or load, especially when high, low or light and heavy units are connected into one and the settlement joint is not set.

（2）Ensure quality

       Strengthen the on-site acceptance of raw materials, and prohibit unqualified materials from entering the construction site. In the bricklaying, we should follow the masonry method of upper and lower wrong joints and inside and outside. And pay attention to the reliable connection of masonry and non-structural components, to improve the integrity of the wall.

（3）Set the ring beam

       At the foundation and the top floor of the building, a reinforced concrete ring beam should be set up for each building. Other layers can be set by layers, its main function is to enhance the integrity of the building. It can prevent or reduce the occurrence of cracks in a certain procedure, even if the cracks can prevent its development.

（4）The height height ratio of the building and the reasonable layout of the vertical and horizontal walls

       The vertical and horizontal walls of the masonry structure building shall be connected as far as possible, and an appropriate distance shall be kept between the horizontal walls and the horizontal walls, generally not more than 1.5 times of the width of the building. Vertical and horizontal walls keep as straight as possible, reduce turning points, so as to maximize the integrity of the building.

（5）Set up the settlement joint

       The settlement joint can be used to effectively divide the building, and then realize the unit body. Thus, the settlement between each unit body can be complementary to reduce the adverse impact of uneven settlement on the building. For the longer length of buildings and different building periods or different parts of the same building period should be carried out settlement joint construction, and ensure the width of the settlement joint requirements.

（6） The influence of two adjacent buildings

       Buildings not only deform the foundation of the building, but also causes the deformation of the adjacent soil layer due to the diffusion of pressure. Therefore, in the construction of buildings, a certain safe distance should be maintained between the two buildings.

2、Structural design measures:

（1）Reduce the load of the building

       In the architectural design as far as possible to reduce the self-weight stress, the use of building materials measurement selection of light weight, high strength of materials. At the same time, the measures of building a basement or semi-basement can also be adopted to reduce the settlement of the building.

（2）Increase the strength and stiffness of the building

       Control the height ratio of the building as much as possible, and the number of transverse walls can be appropriately increased, which helps to increase the integrity and stiffness of the building. In addition, we can start from the structure of the building to enhance the integrity of the building. Even if large settlement occurs, large deflection deformation can be avoided. To a certain extent, reduce the occurrence of cracks, even if the cracks, can also prevent the cracks continue to expand and develop.

（3）The superstructure of the building shall adopt the building system of static structure

       For buildings and industrial plants with weak foundation, the structural system of static structure can be considered, so as to reduce the consequences of uneven settlement.

（4）Set up the construction post-pouring belt

       Set up the construction post-pouring belt, which is a kind of "release" before "resistance" method. The parts of the post-pouring belt are usually set in the main building of the building and the structure of the secondary building with relatively small stress. In the construction of the main building and the auxiliary building of the building, the place for the pouring belt should be reserved in advance from the foundation beam, wall, foundation roof to the beam and plate of the superstructure. After waiting for the completion of the main building and the secondary building, the reinforced concrete to strengthen the main and secondary buildings, so that the whole structure into a whole. In this way, the settlement of the building can be "put", so that part of the building settlement and then pouring belt construction, and then "resistance". That is, through the structural measures, improve the strength of the masonry, strengthen the integrity and crack resistance of the wall, reduce the deformation of the wall.

3、Foundation design measures:

（1）In the foundation design, the deformation of the building should be mainly controlled. The designing unit shall effectively check the final settlement and the eccentric distance of the foundation.

（2）In the design of foundation foundation, designers should consciously strengthen the stiffness and strength of the building. Use various forms to reduce or eliminate the flexible deformation of the foundation.

（3）When the mechanical properties of the low level itself can not meet the support needs of the building, certain technical measures must be taken to deal with it.

（4）For the same building, the same foundation should be used as far as possible, and the foundation should be buried in the soil layer of the same thickness. If different foundation forms are used, the superstructure of the building must be disconnected, especially in the seismic area.

——Source: Civil Engineering Inspection

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