Are you in need of improving the soil or ground for construction or using it as a construction material, then you are at the right place? But first, what does it mean by ground improvement.
There are a number of terms that have been used to describe making changes to the ground and/or soil to improve them for engineering purposes. Ground improvement is expressed by terms such as soil improvement, ground improvement, ground modification, soil stabilization, and so forth.
Even though there are different sorts of the definition of these terms but generally there is overlap between the applications that the terms are often used interchangeably
Ground improvement is the process of making the type of soil in the ground suitable for the intended purpose of its use. The intended purpose may be to support the loads from construction or to use the soil as construction material.
A construction site or soil is commonly labeled as hazardous, poor, or favorable based on several factors that affect the suitability for construction.
Hazardous soil: Totally unsuitable and hazardous, hence should be avoided – Locations close to faults, or seismically active regions – Loose to medium-fine sands subject to liquefaction – Any landfill of hazardous waste – Soils near volcanic active regions
Poor soil: Cannot be used in the in situ condition, but can be used after suitable treatment – Expansive soils – Organic soils – Loose sands and silts – Fissured rocks
Favorable soil: – Cohesive granular soils- sand-clay mixtures – Shallow rock without discontinuities
Normally the suitability of the soil in the ground is assessed for the capacity of bearing the construction over it or its properties in relation to water movement. The soil can be found to be inferior and in such case, there are several alternative solutions Such as:
(1) Abandon the project. This is a practical solution when the site’s location is the only alternative or changing location is highly expensive.
(2) Excavate and replace the existing “poor” soil.
This is a method that has declining application because it involves a high cost of excavation, hauling, and selected material. Nowadays also there is pressure from environmental concerns.
(3) Redesign the project or use structural members
In this case driven piles and drilled shafts bypass soft, weak, and compressible soils and transfer the loads to suitable bearing strata.
(4) Modify the soil (or rock) to improve its properties and/or behavior through the use of available ground improvement technologies.
Ground improvement is the application of soil or rock improvement methods that can be considered to fall into one of three categories:
(1) modification without the addition of any other material,
(2) modification including adding certain materials to the soil/ground, or
(3) modification by providing reinforcement or “inclusions” into the soil/ ground.
What is the purpose of ground improvement?
It is to improve the natural or geotechnical properties of soil or rock.
The targeted properties for improvement usually are
• Reducing compressibility to avoid settlement
• Increasing strength to improve stability, bearing capacity, or durability
• Reducing permeability to restrict groundwater flow
• Increasing permeability to allow drainage
• Mitigating the potential for (earthquake-induced) liquefaction
Types of ground improvement with respect to projects
There are different types of ground improvements and their applicability depends on the state of the project.
Generally, there are pre-construction, on-construction, and post-construction methods.
1. Preconstruction ground improvements
These are done during the planning and design stage and provide the preliminary and detailed design of how the site is going to be constructed. Since they are applied early phases of the project, the results are most desirable and cost-effective.
Examples of preconstruction improvements are ground densification, pre consolidation, drainage, dewatering and modification of hydraulic flows, planned underpinning, and various grouting techniques.
2. On-construction ground improvements
Those are soil improvement techniques that are carried out during the construction of the project. The soil improvement applications could become permanent parts of a project. Examples of on-construction improvements are compacted gravel columns, shallow soil treatment (including gradation control, shallow compaction, and treatment with admixtures), ground freezing, construction with geosynthetics, soil nails, tie-backs and anchors for cuts, excavation, lightweight fills (including geofoam), and so on.
3. Postconstruction ground improvements
These are remedial measures that are done after the completion of the construction phase of a project. These applications can be very costly but are used as last-choice alternatives to rectify problems encountered after (or long after) the completion of a project or to stabilize natural features that have failed or become hazardous.
Examples include methods to stabilize settlement problems, failed or near-failure slopes, seepage problems, and so forth. Processes used for postconstruction improvements include grouting, soil nails, drainage, dewatering and modification of hydraulic flows, and so on
What are the common Ground Improvement Techniques and Applications?
Generally, there are 4 categories of ground improvement techniques
Mechanical modification
This involves improving engineering properties by employing various methods of densification of soils. The methods that are used are such as compaction methods, by adding material to the ground, and reinforcement by using nonstructural members.
Hydraulic modification
The hydraulic characteristics of the water pertaining to the flow, seepage, and drainage are modified to result in the improved ground.
The methods that are used can be lowering the water table by drainage or dewatering wells, altering the permeability of soils, causing consolidation and pre-consolidation to reduce settlements, compressibility and increasing strength, filtering groundwater flow, controlling seepage gradients, and creating hydraulic barriers.
Physical and chemical modification
This is achieved by what is called the “Stabilization” of soils. It is achieved by making physical or chemical changes in the soil structure by adding other materials.
Soil properties are modified with the addition of materials through physical mixing processes or injection of materials (grouting), or by thermal treatments involving temperature extremes.
The changes tend to be permanent (with the exception of ground freezing), resulting in a material that can have significantly improved characteristics.
Modification by inclusions, confinement, and reinforcement
Includes use of structural members or other manufactured materials integrated with the ground. These may consist of reinforcement with tensile elements; soil anchors and “nails”; reinforcing geosynthetics; confinement of (usually granular) materials with cribs, gabions, and “webs”; and use of lightweight materials such as polystyrene foam or other lightweight fills.
In general, this type of ground improvement is purely physical through the use of structural components. Reinforcing soil by vegetating the ground surface could also fall into this category
What are the factors affecting ground improvement methods?
The selection of the ground methods depends on several factors among them being soil type, economy, environmental considerations, Area, depth, and location of treatment required, the desired improved property, and availability of resources such as materials, skilled labor, and equipment.
What are the common ground improvement methods?
Soil densification
The oldest and most common method of all soil improvement methods. Densification consists of shallow compaction methods and deep (in situ) techniques.
Densification improves the properties of the soil in such a way that the characteristics of soil in responses to loading is improved.
densification will allow more efficient and cost-effective solutions for both the construction and remediation of civil engineering projects.
Drainage and filtering of fluids (usually water) through or over the ground
Geotechnical engineering legend Ralph Peck used to say, “Water in the ground is the cause of most geotechnical engineering problems.”
This ground improvement technique either facilitates drainage while preventing negative impacts such as erosion or increases the ground impermeability.
The aim of the Drainage applications is to reduce the soil’s weight and the excess water pressure and gives result in increased soil strength while reducing the load.
Drainage may also relate to
(1) dewatering for purposes of creating a (dry) workable construction site
(2) creating a situation that allows water to continually drain out and away from a structure such as a roadway or foundation.
(3) forcing the water out of saturated clayey soil in order to reduce compressibility, reduce settlement, and increase the strength of the clayey strata.
Proper drainage and filtering so as to ensure long-term stability is critical to water retention and conveyance structures
Drainage and filtering are achieved by using appropriate soil grain size and gradation control and the use of geosynthetic materials.
In the case of boosting the impermeability of soil techniques used include soil densification techniques, soil treatment with additives, and construction of soil structures or using geosynthetic materials.
Admixture stabilization
Admixtures or chemicals have been in use for a long period of time such as lime, cement, fly ash, and asphalts.
Proper application of admixture can improve the unwanted qualities of almost any soil type.
Much of the key to success with soil admixture improvement is the type and quality of the mixing process(s).
There are two types of mixing namely shallow and deep mixing. Shallow surface mixing is typically limited to the top 0.6 m. Deep mixing techniques go to depths of 30 m or more.
Soil reinforcement
Inclusions have been in use for a long time. For example, adobe bricks have been strengthened by straws from historic times until today. Modern-day applications use steel or geosynthetic reinforcements. Soil reinforcement is used for scour/erosion control and foundation support.
The geosynthetic reinforcement distributes the concentrated load and transfers it to a broader area. The resulting load over the weaker materials or to deep foundation support becomes lower and results in reduced settlement problems and higher capacity.
Inclusions are widely used for strengthening embankments, retaining walls, soil slopes, soil nail walls
Grouting
https://www.youtube.com/watch?time_continue=1&v=iHAEI8gZb4Q&feature=emb_title
The filling of voids in the soil by injecting materials like cement to modify the soil properties or ensure waterproofing.
grouting is applied to fill fissures and voids in rock, to fill voids between the ground and overlying structures, and to treat soils and rocks to enhance strength, density, permeability, and/or homogeneity.
The type of grouting method used depends on such considerations as the project’s specific requirements, the soil or rock type, and the ground’s amenability to different kinds of grout.
Lightweight fills
The reduction of the weight of soil above a load receiving area results in the increase of the laid carrying capacity of the soil. That is because the difference in the weight of the soil removed and the lightweight fills an additional load that can be supported by the application area. Hence, the various types of lightweight fills include as follows:
Granular Fills: Wood Fiber; Blast Furnace Slag; Fly Ash; Boiler Slag; Expanded Shale, Clay and Slate, Shredded Tires
Compressive Strength Fills: Geofoam; Foamed Concrete