2.
Sand pile sand pile is also known as sand pile compaction or sand pile compaction method.
That is, the soil layer within a certain range under the foundation shall be excavated, and then backfilled with sand, gravel or lime soil with high strength, and compacted to compactness.
There are two kinds of foundation overbreak: local overbreak and general overbreak.
According to the preloading method, the preloading method can be divided into surcharge preloading method and vacuum preloading method.
Because it is an overall backfill, as long as a single material (general materials can be used), such as sand, lime soil, silty clay, etc..
This method has a wide range of application, and has a large number of successful examples in sandy soil, silt, clay, muddy soil, miscellaneous fill and other foundations.
General backfilling ， general backfilling, that is, using certain backfilling materials, the whole can be backfilled to the base elevation.
The treatment depth of surcharge preloading method is generally about 10m, and that of vacuum preloading method is about 15m.
In this case, two treatment methods can be adopted: 1.
When the thickness of soft soil layer is less than 4m, natural foundation surcharge preloading method can be used.
The surcharge preloading method is divided into plastic drainage belt or sand well foundation surcharge preloading and natural foundation surcharge preloading.
Cement fly ash pile cement fly ash pile is a high bonding strength pile formed by adding water and mixing cement, fly ash, gravel, stone chips or sand, and forms a composite foundation together with the soil between piles and cushion.
5.
These two kinds of foundation overbreak should be treated separately.
Dynamic compaction method has the advantages of simple operation and fast construction speed.
If it is inconsistent with the actual situation, it is naturally caused by the investigation problem; or the measurement error in the actual construction).
It is mainly suitable for the treatment of soft foundation such as gravel soil, low saturated silt and cohesive soil, collapsible loess and so on.
For local overbreak, it is generally caused by bad foundation.
The cushion has the advantages of simple construction technology, short construction period and low cost.
Its definition refers to the method of strengthening the foundation by forming holes in the soft foundation by means of vibration, impact or water impact, and then squeezing the sand into the soil to form a large-diameter dense sand column.
4.
It is suitable for treating 1-4m thick soft soil layer, collapsible loess, miscellaneous fill, etc.
When it is used for the treatment of saturated clay, it is best to determine whether to use it after field test.
When the thickness of soft soil layer exceeds 4m, plastic drainage belt, sand well and other vertical drainage preloading methods shall be used.
3.
1) sand cushion and sand gravel cushion.
It is widely used in various projects.
Sand cushion and sand gravel cushion are to excavate a certain thickness of soft soil layer under the foundation, then backfill with strong sand or gravel, and compact it in layers as the bearing layer of the foundation.
For muddy soil, its applicability shall be determined according to regional experience or through field test.
The cushion replacement method is to excavate the soft soil layer within a certain range below the bottom of the foundation, and then backfill the materials with high strength, low compressibility and no corrosiveness, such as medium coarse sand, gravel or pebble, lime soil, plain soil, stone chips, slag, etc., and then tamp them in layers as the bearing layer of the foundation.
Its function is to improve the bearing capacity of the foundation, reduce the additional pressure borne by the natural soil layer under the cushion and reduce the settlement of the foundation through the stress diffusion of the cushion.
For the general overbreak, it is mainly caused by the inadequate or wrong investigation (the selection of bearing stratum and the buried depth of basement are obtained according to the geological report.
Sand pile belongs to a kind of loose pile composite foundation.
The preloading method is to pile soil or other heavy objects in the site before the construction of buildings, preload the foundation, make the foundation drain and consolidate under the preloading load, remove the load after the foundation strength is improved to meet the requirements, and then build buildings according to the design requirements, or use the load of the building itself for preloading.
Preloading method: preloading method is applicable to the treatment of all kinds of soft foundation, including natural sedimentary layer or artificial filling soil layer, such as swamp soil, silt, mucky soil and hydraulic filling.
For vacuum preloading works, drainage shafts must be set in the foundation.
Dynamic compaction method dynamic compaction method is to use the lifting machinery to lift the large tonnage rammer to a certain height, make the rammer fall freely, make the foundation soil bear a strong impact force, force the water in the soil to be discharged from the pores, rearrange the soil particles and reduce the compressibility, so as to improve the bearing capacity of the foundation soil.
Lime soil cushion is formed by excavating the soft soil layer within a certain range under the foundation bottom, mixing lime and cohesive soil mixed according to a certain volume ratio, and then backfilling, tamping or compacting in layers under the condition of optimal water content.
The replacement cushion can be divided into lime soil cushion, sand cushion, crushed (sand, stone cushion, etc.) according to the backfill materials.
This method has the advantages of wide applicability, large increase in bearing capacity, simple construction and short construction period.
There are five main treatment methods: 1.
Sand pile replacement can be used for projects with lax requirements on deformation control of saturated clay foundation.
Replacement method when the bearing layer under the building foundation is relatively weak and can not meet the requirements of superstructure load on the foundation, the soft foundation is often treated with soil replacement cushion.
Independent foundation, strip foundation and raft foundation are applied.
It is applicable to the treatment of weak cohesive soil foundation with strong water permeability, but it is not suitable for the reinforcement of collapsible loess foundation and impervious mature soil foundation, so as to avoid causing a large number of subsidence of the foundation and reducing its bearing capacity.
Sand pile method is suitable for compacting loose sand, silt, cohesive soil, plain fill, miscellaneous fill and other foundations.
it can also be used as an auxiliary anti-seepage layer of the structure.
Lime soil cushion is suitable for the reinforcement of general cohesive soil foundation with low groundwater level and dry foundation trench.
2) lime soil cushion.
Sand pile can also be used to treat liquefiable foundation.
The cushion has certain strength, water stability and impermeability, simple construction process, easy material acquisition and low cost.
