Before starting any flooring project, contractors need to ensure that they commence construction project on hard ground. If the construction of the building is not done on solid ground, then it may lead to repairs and instability later on. Besides, many of these soils are collapsible, i.e., when the soils are under load and in case of a significant increase in the moisture content or saturation of the soil, the structure collapses, thus producing unacceptable displacement values for the buildings.
Because of these characteristics, problems often occur in industrial floors, pavements and other types of slabs on ground and shallow foundations.
Factors affecting the soil choice for improvement method
Several factors are affecting the soil choice for the improvement method, each of them is given below.
1. Soil type – This is one of the most important parameters that will control what approach or materials will be applicable to only certain types of soil types and grain sizes
2. Area, depth and location of treatment required – Many ground improvement methods have depth limitations that render them unsuitable for applications for deeper soil horizons.
3. Desired/required soil properties – Different methods are used to achieve different engineering properties, and certain methods will provide various levels of uniformity to improved sites.
4. Availability of materials – Depending on the location of the project and materials required for each feasible ground improvements approach.
5. Availability of skills, local experience, and local preferences – While the engineer may possess the knowledge and understanding of a preferred method.
6. Environmental concerns – With a better understanding and a greater awareness of effects on the natural environment, more attention has been placed on methods that assure less environmental impacts.
The concept of sub-base, subgrade and base
American Concrete Institute’s defines sub base, subgrade and base as following;
- Subgrade-this is the native soil (or improved soil), usually compacted
- Subbase-this is a layer of gravel on top of the subgrade
- Base (or base course)-this is the layer of material on top of the subbase and directly under the slab
The only layer that is required is the subgrade—you have to have ground to place a slab on the ground on top of. If the natural soil is relatively clean and compactable, then you can put a slab right on top of it without any extra layers. The problems with that are that the soil may not drain well and it can be muddy during construction if it gets wet, it may not compact well, and it can be difficult to get it flat and to the proper grade. Typically, the top of the subgrade should be graded to within plus or minus 1.5 inches of the specified elevation.
A sub base and base course, or both, provide several good things. The thicker the subbase, the more load the slab can support, so if there are going to be heavy loads on the slab-like trucks or forklifts-the designer will probably specify a thick subbase. A subbase can also act as a capillary break, preventing water from wicking up from the groundwater table and into the slab. The subbase material is usually reasonably low-cost gravel without a lot of fines.
A base course on top of the subbase makes it easier to get to the proper grade and to get it flat. If you use some sort of a choker course of finer material on the top of the subbase, it will support your people and equipment during concrete placement. It will also keep your slab thickness uniform, which will save money on concrete-the most expensive part of the system. A flat base course will also allow the slab to slide easily as it shrinks, reducing restraint and the risk of cracks as the concrete contracts after placement (drying shrinkage). The weight of the slab and anything on top of it is going to eventually be supported by the soil. When a building site is excavated, usually the soil gets moved around-high spots are cut and low spots are filled. Everything then should get compacted before you place the concrete, subbase and base.
Soil improvement techniques for industrial flooring
There are various controlled manners to improve the supporting soil of shallow foundations, industrial floors and pavements on collapsible soils by increasing resistance, rigidity and stability against collapse, and reducing both strain and permeability.
Given below are a few techniques to improve soil foundation in flooring. Some of them are analysed below.
Grouting
The grouting is one of the best methods where some kind of stabilizing agent inserted into the soil mass under pressure. The pressure forces the agent into the soil voids in a limited space around the injection tube. The agent reacts with the soil and /or itself to form a stable mass. The most common grout is an admixture of cement and water, with or without sand. Various chemicals can be used as grouting agents. Chemical agents are the most expensive foundation treatment of all.
Jet Grouting
For a strong basement, ground improvement is necessary, because it reduces the risk of any damage later on. Today, jet grouting technique is used on various grounds for hardening them. This technique involves high-pressure system through which fluid is injected into the soil. Later, these liquids spread and break up within the soil, thus creating a uniform mixture, which then solidifies and settles. This is one of the basic processes, which is used for solidifying construction ground.
Dynamic Compaction
Another way to improve the solidity of the ground is dynamic compaction. It is the procedure of compressing soil by dropping huge steel rigs from a specific height of about 40 to 80 feet. This compresses loose soil and fills the dugout areas.
The method of soil compaction is simple, as by adopting the right technique, ground improvement can be done successfully. Once the compacting is done, the compacted area is again dugout for about 10 to 20 feet. This is done for assuring the hardness of the ground. After the completion of this process, the area is prepared for any construction work.
However, for ground improvement, a combination of binder and water is essential, because this can break up the soil and hardens the ground. Thus, with the help of these techniques, you can turn any soil for construction. Each technique has its drawbacks and benefits thus, using it on the requirement of the project can improve the stability of the ground. Thus, the improvement of the ground is essential if you want your building to a long lasting.
Soil stabilization and sealing by injection
Soil stabilization and sealing by injection is performed to strengthen and seal soil/rock substrate. Such operation prevents e.g. settlement of soil, which can lead to an accident or a construction disaster. Soil stabilization is executed mainly in hardly accessible areas of application, where an accumulation of heavy machinery is impossible due to technical or economic reasons. In such situations injection replaces jet grouting effectively. It is inseparably linked with terms such as deep foundations, micro tunneling, strengthening embankments and excavation pits. A broad range of injection materials and equipment allows for quick selection of effective technology, tackling causes and consequences of an accident. We specialize in stabilization of soils by injection, i.a. in stabilization of structure underpinning (heads, foundations, bottom slabs), stabilization of slabs and floors, improvement of the load-bearing capacity of soil – soil consolidation, filling voids and caverns – foundation underpinning, soil sealing – anti-filtration barriers in soil, stabilization of quicksand. For more details go injections in geoengineering.
Soil compaction
Soil compaction produces an increase in soil density and a decrease in air volume without producing a decrease in water content. It can improve shear strength, stiffness, bearing capacity and stability, reducing settlement and frost heave. This may be necessary for a suitable level base for the construction of a building. Existing soil can be compacted, or layers of new soil can be compacted, taking a site to the required level.
Vibro-compaction
Vibro-Compaction uses company-designed probe-type vibrators to densify soils to depths of up to 120 feet. Vibro-Compaction increases bearing capacity for shallow-footing construction reduces settlements and also mitigates liquefaction potential in seismic areas.
Vibro concrete columns
Very weak, cohesive and organic soils that are not suitable for standard Vibro techniques can be improved by the installation of Vibro Concrete Columns. Beneath large area loads, Vibro Concrete Columns reduce settlement, increase bearing capacity, and increase slope stability.
Dynamic deep compaction
Dynamic Deep Compaction is an economic site improvement technique used to treat a range of porous soil types and permit shallow spread footing construction. Soils are densified at depth by the controlled impact of a crane-hoisted, heavy weight (15-35 tons) on the ground surface in a predetermined grid pattern. Dynamic Deep Compaction is also successful in densifying landfill material for the highway construction of recreational landscaping.
Soil mixing
Typically used in soft soils, the soil mixing technique relies on the introduction of an engineered grout material to either create a soil-cement matrix for soil stabilization, or to form subsurface structural elements to support earth or building loads. Soil mixing can be accomplished by many methods, with a wide range of mixing tools and tool configurations available.’
Geotextiles
Geotextiles are typically made using synthetic fibres such as polyester or polypropylene which create a flexible and porous fabric capable of providing strength and stability. Geotextiles can reinforce, protect, filter, drain and separate, and many applications use them alongside soil, placed at the tension surface for strength purposes.
Cement/lime stabilisation
This involves the addition of a binder product such as hydrated lime or quicklime to the soil which reduces moisture and improves stability. Soil modification and stabilisation involves the addition of lime or cement to a soil to improve its strength and render it acceptable as an engineering fill. Quicklime (calcium oxide) is used with fine or cohesive soils, while cement is primarily used with granular soils. Cement increases the bearing ratio (CBR) and achieves higher strengths. Some cohesive soils do not achieve the required long-term strengths, therefore a two-stage process is adopted (i.e. lime followed by cement). .
Conclusion
There are ground improvement or ground modification techniques that can be used to stabilise or improve the condition of an area of ground before construction work takes place. This may be necessary to improve or modify the ground shear strength, stiffness, and permeability.
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