Comparison of Different Foundation-Supporting Forms

Time:2023-01-06From:sinorock View:

The main forms of foundation support are Steel Sheet Piles, Diaphragm Walls, Concrete Piles, Soil Nailing Walls, Gravity Retaining Walls, SMW, Slope Excavation, etc. The comparison and analysis of these common foundation support forms will be introduced in this article.

1. Steel Sheet Piles

steel sheet piles

source:civil knowledges

Applicable conditions

Steel sheet pile support is generally used for foundation support with a depth of no more than 5m. When the excavation depth of the foundation is greater than 5m, it is generally combined with the internal support system to form a combined support structure.

Advantage

l The structure itself has strong rigidity and strength. It is also waterproof for the tightness between the structural steel sections

l The construction of structural steel is simple and fast, which can greatly shorten the construction period, and is conducive to the implementation of construction mechanization and drainage system;

l After the foundation support completes, the structural steel can be pulled out and reused.

Shortcoming

l Steel sheet pile support requires a large amount of specific steel, which is expensive and longer manufacturing time;

l During the process of mechanical driving, the structural steel is easy to deviate from the axis, and it is not easy to correct;

l The piling work is easily suspended by obstacles, and the obstacles must be removed to continue construction.

2. Diaphragm Walls

diaphragm walls
source:sciencedirect

Applicable conditions

l It is suitable for deep foundation excavation, generally used for foundation depths greater than 10m;

l Suitable for softening rock or gravel soil;

l Suitable for supporting projects with high protection requirements buildings around;

Advantages

l The diaphragm wall is a reinforced concrete structure with high rigidity and high safety performance during foundation excavation;

l It has strong impermeability and good waterproof performance. When the drainage in the foundation pit has little impact on the groundwater level around the foundation, it can be used as the outer wall of the basement structure to achieve the purpose of saving costs;

l The total construction period is relatively short, and the excavation volume of earthwork is relatively small, which is conducive to the control of the total construction period and cost.

Shortcoming

l It is difficult to control the quality of joints between continuous wall segments, and it is easy to form weak points in the structure

l High technical requirements for construction

l The grout storage and grout production site covers a large area, which is easy to cause pollution.

3. Concrete Piles

Applicable conditions

l The general cantilever concrete pile structure is suitable for the support of the foundations whose excavation depth is not greater than 5 m in the soft soil layer;

l In the design of foundation support for basements with two or more floors, the combined foundation support structure composed of row piles and an internal support system is often used, which is generally suitable for foundation excavation depths of 5-20 m.

Advantages

l Applicable to different soil layers;

l The pile length can be changed due to geological conditions;

l The reinforced concrete of the pile body has high rigidity, good stability, and small deformation;

l Hole forming can be more selective according to the soil layer and construction period requirements.

Shortcoming

l High cost and long construction period. It is necessary to wait for the pile body and the internal support system to reach a certain strength before excavating the earthwork. Reinforcement measures are required between the piles;

l The gaps between piles are likely to cause water and soil loss, especially in sandy soil areas with high water levels. Water-stopping measures should be taken according to the soil conditions on site;

4. Soil Nailing Wall

soil nail wall

Applicable Conditions

l Applicable to foundations whose excavation depth is not greater than 15 m;

l Applicable to site restrictions requiring vertical excavation areas.

Advantage

l The structure is light, flexible, and has good earthquake resistance;

l The construction equipment is relatively simple, with no need to occupy a separate site;

l Low project cost;

l With the self-drilling anchor bolts, the drilling and grouting can be completed at one time without casing, which improves the anchoring effect and construction efficiency;

Shortcoming

l It may damage the underground pipelines or the original building foundations

l Durability issues such as corrosion of anchor rods should be considered in permanent structures;

l It is necessary to excavate and construct in layers, reserve an operation platform, and wait for the support structure to reach a certain strength before continuing to excavate.

5. Gravity Retaining Wall

gravity walls

source: tensar.co.uk

Applicable conditions

It is suitable for the site where the ground is stable and the excavation of earthwork will not cause damage to adjacent buildings.

Advantage

l Local materials, easy construction, low project cost

Shortcoming

l Large volume and heavy weight, which require a high bearing capacity of the formation;

l Consume more materials

6. SMW Construction Method

Commonly known as a new type of cement-soil mixing pile, that is, inserting H-shaped steel into the cement mixing pile to make it a support structure with both rigidity and impermeability.

Applicable conditions

l Suitable for muddy soil, silt, clay, sandy soil, sand, gravel, pebbles, and other soil layers;

l Projects that require waterproofing for foundations

Advantage

l Small disturbance to the soil;

l There is basically no mud pollution, and the site occupies a small construction site;

l The vibration and noise of construction machinery are small, and construction can be carried out at night;

l The water-stop performance of the structure is better;

l After the supporting structure has completed its function, the H-shaped steel can be recycled and reused after taking certain measures, and the project cost is relatively low.

Shortcoming

l Cement and soil curing takes a long time;

l H-shaped steel should be inserted when the cement mixing soil is not completely hardened.

7. Sloped Excavation

Applicable Conditions

l It is suitable for projects with open sites, no important buildings (structures) and underground pipelines around;

l It is generally suitable for foundation projects with an excavation depth not greater than 5m.

Advantage

l The project cost is low, the construction process is simple, and the construction period is relatively short.

Shortcoming

l Only suitable for shallow foundation support;

l It is easy to cause the foundation collapse after soaking in the rainy season; in areas with groundwater around, drainage measures should be considered.

The above are a comparative analysis of common support forms for foundation support. In actual engineering, the conditions are more complicated, and two or more types of foundation support are often used to form a combined support structure. Because of the large economic loss and social impact caused by accidents in foundation engineering, it needs to be treated with caution and safety first.

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