An earth road is one whose wearing surface and foundation include specifically natural soil present on a given site during the construction by Civil Engineers. Soils can be categorized as cohesive soil and less cohesive soils depending on the engineering properties. It is noted that areas that are clayey periodically do not normally have sandy materials. Clays are considered as significant and normally determines the composition of the soil since it has dual qualities that are objectionable that make it the most upsetting of the materials to be handled during the construction of structures (Alfaro, 2009).
The clay soil swells when subjected to wetting and then shrinks during drying. It is for these reasons why the foundation soft structures built on top of the clay soil normally collapse during advanced weather conditions such as extreme rains and then followed by an extremely dry period. This research proposal is about the techniques that can be used to improve the soil when constructing and designing a foundation that would be used in the construction of structures such as roads, bridges, or other superstructures such as stadia (Bell, 2012).
The major objective of the during the construction of different research proposal is to propose the techniques of soil improvement that can be used during the initial construction of building foundations and also in the improvement of already existing foundations of structures such as bridges. This proposal also seeks to evaluate the impacts of all the techniques of soil improvement and then recommend the best soil improvement technique that can be applied by civil engineers during the process of designing numerous structures (Braja, 2015). Some of the soil improvement techniques that may be of significance in the field of civil engineering include soil reinforcement, chemical stabilization, grouting and injection, consolidation a precompression, vibration method, drainage method, and surface compaction (Choa, 2010).
The soil improvement process is a very significant step during the initial construction and also during the foundation improvement of the already completed structures. The general outcome of the soil improvement may be improved water condition, reduced permeability, reduced compressibility, and increased strength (Committee, 2009). The soil improvement techniques seek to enhance the soft soil conditions through fixing soil particles and masses, reinforcing, and compacting. There is also need for improving the soil under the heritage and historical buildings without affecting the already damaged foundation bearing capacity. These historic buildings form a major aspect of civilization hence cannot be demolished (Hansbo, 2010).
Some of the technical terms used in this research proposal include chemical stabilization, stone column, preloading, soil replacement, soil improvement, and jet grouting. Soil replacement involves the replacement of poor soil such as soft and medium clay or organic soils with a more competent material such as crushed stones, gravel, and sand. Precompression involves placing a surcharge fill on the top of the soil that needs consolidation settlement (Hawkins, 2009). Soil improvement involves the alteration of the property of soil so as to improve its engineering performance through either permanent measure to improve a structure already completed or temporary process to enable the construction of a particular structure. Stone columns are stone materials used in cohesive soils to speed up consolidation, minimize excessive settlement, and improve the shear strength of the soil (Johnson, 2011).
Silts and clay are construction materials of low-grade which find application in impervious elements like cut-off, dames (cores) since they are poorly drained, and they swell and shrink. Clay soil also loses its strength when wet and also is characterized by high compression strength and result in an undesirable settlement when used as highway subgrades. Sand despite having excellent drainage properties as also not appropriate since they do not have cohesion and laterally spread when vertical loads as applied. Therefore, these tow natural soils alone cannot be used as foundation materials in road construction or foundations basement.
A material that is stabilized may be considered as a combination of a given precise combination of aggregates and binder-soil obtained preferable neat or at the stabilization site, and then compacted so as to persist in its state of compaction without unfavorable change in volume or shape underexposure of adverse weather conditions or a weight of a structure or a force of traffic (Joshi, 2009). Numerous materials have been used as agents of soil stabilization. Out of these agents, the best stabilizer should be the one that provides a durable effect and involves low cost. Soil stabilization is normally applied in the soil of road construction and is known as granular stabilization or mechanical stabilization.
The mechanical stabilization process is applied in both surface-courses and also base-courses. A good mechanical stable surfacing or base is normally composed of a mixture of clay, silt, fine aggregates such as crushed or natural stone and sand, and coarse aggregates such as slag, crushed rock, and gravel compacted fully and correctly proportioned (Kamauchi, 2013).
The application of appropriately proportioned materials is of specific significance in the roads constructions. The principle of soil grading can be used for sub-grade soil improvement of low capacity bearing, through the addition of materials possessing lacking particles sizes such as clay sub-grades can be added to sand and also sand added to clay sub-grades. The methodology of the proposed soil improvement techniques that may be of significance in the field of civil engineering and are discussed below include soil reinforcement, chemical stabilization, grouting and injection, consolidation a precompression, vibration method, drainage method, and surface compaction (Kirsch, 2012).
The grouting technology has become a common method of ground improvement and is normally used for underground and foundation constructions of structures such as houses and bridges. The grouting process involves filling cavities and pores in rock or soil with a material that is liquid in nature so as to improve the shear strength by improving the cohesion and minimize the permeability (Kwong, 2011). Some of the classifications of grouting technique include jet grouting, grouting of voids, compaction grouting, displacement grouting, and penetration grouting as shown in the figure below:
Figure 1: Modes of grouting (Lambe, 2011)
This is a method of ground treatment in which grout is injected into a medium that is porous without disturbance of the initial structure. Any material of grout can be used during permeation grouting, however, there should be a limit of the mixture of grout applied for a given rock o soil type. This method of grout technique is applied to enhance the liquefaction potential, improvement of excavation character in sands, and improvement of the value of foundation bearing (Maity, 2017).
This is a technique of ground treatment that entails injection of soil cement grout of thick-consistency under pressure into the mass of soil, then consolidation, and densifying the soils surrounding. The grout mas injected conquers space produces by the pressure-densification. When injected into bedrock or soils which is very dense, there will be confinement of compaction grout since the material surrounding is dense. This method is normally applied in pile repair, augmentation pile capacity, easing of liquefaction potential, relieving and raising of foundation and structure elements, and also densification of foundation soil (Moseley, 2013).
This is an erosion-based system where grout and soil are hydraulically mixed to produce situ geometries of silcrete. Granular soils are known to be the most plastic and erodible clays. The rotary drill is applied so as to attain the design depth required and at that point, air or water and grout are pumped to the drill rig (Nicholson, 2014). There are three different systems of the traditional jet, these include a triple-fluid system, double-fluid system, and single-fluid system as shown in the figure below:
Figure 2: System of jet grouting (Purushothama, 2008)
Sand drains as established by drilling holes through the layer of clay by the use of continuous flight auger or rotary drilling. The holes are then filled by the use of sand. When a surcharge is applied at the surface of the ground, the pressure of pore water in the clay will rise, and it will be distributed by drainage in both horizontal and vertical directions. Hence accelerating the settlement (Purushothama, 2014). The rand drains reinforce the soft soil in which they are installed in. The figure below shows the schematics of sand drains:
Figure 3: Sand drains (Raj, 2012)
This sand drains technique has numerous disadvantages such as budget and construction problems due to huge sand drains diameter, there can be cavities during bulking and filling of sand, and also there may be surrounding soil disturbances during the installation of the sand drains (Raison, 2012).
The stone columns are commonly used in speeding up the consolidation through reducing the horizontal drainage paths for the flow of pore-water, reducing the excessive settlement, and also improving the shear strength. The figure below shows the construction of stone columns through the drilling of holes which extend through clay to a soil that is more firm. These stone columns can be installed as either panel of columns, or continuous walls, or independent columns. These columns of stones are commonly preferred than san drains because its granular nature which gives extra strength to the soils surrounding (Raison, 2012).
Figure 4: Stone column process (Maity, 2017)
The stone granules minimize settlements through the promotion of soil arching which transfers the loads to the stiffer columns from the soil surrounding. The system of the stone column can provide an efficient and economical solution for the bridges and dams constructed on top of clay soil. This type of reinforcement transfers stress to the stone column from the clay soil because of the difference in stiffness between the soil and stone column, and this may avert large displacement and minimize the differential and also total settlement (Braja, 2015).
In this technique, the stabilization of soil depends on the chemical reactions between the natural soil and the additives such as fly ash, cement, or lime to attain the effect desired. The major reason for soil stabilization includes reducing the soil compressibility, increasing the durability and strength, and also accelerating soil settlement (Committee, 2009).
Soil stabilization with coal flies ash in an expanding alternative currently. These binders cannot realize the effect desired on its own, hence the stabilization of clay by the use of fly ash should be accompanied by the use of cement and lime (Johnson, 2011).
Lime involves an economical method of stabilization of clay soil. The selection of an appropriate clay stabilization concentration depends on attaining the pH value targeted. This method can be unsuitable in case the admixture concentration is not sufficient to ensure durability and strength which usually range from to 5 to 10%. Lime is normally mixed with the soil either at the site of construction or in the plant, or by use of lime slurry which injects lime into the clay. The soil properties improvement is attributed to the reaction between soil and lime where monovalent cations in the soil are substituted with divalent ions (Maity, 2017).
This method is normally used in wide range soil stabilization, in case enough quantity of the cement is added. As the content of clay increases, soils become more problematic to work and pulverize. The reaction of cement does not depend on the minerals of soil, and the major role is its reaction with available water in the clay. In this method, water and soils are mixed with cement at the site by special equipment. The chemical and physical reactions within the soil and cement take place. The cement setting will cover the soil as a glue, however, it will not alter the soil structure. The cemented soil hardening depends on the degree of compaction, curing temperature, and water-cement, soil ration (Kwong, 2011).
Groundwater is one of the most difficult problems during the work of foundation construction. The existence of water decreases the shear strength and increases the pressure of pore water. Heavy water inflow is also likely to result in collapse and erosion of the sides of the structure. There numerous methods that can be used to regulate the groundwater and ensure economical and safe scheme of construction. These methods include vacuum dewatering system, deep-well drainage, and well-point systems. During the construction of bridges, the civil engineers should first divert the flow of the water to another location, and then drain the areas by use of the above techniques before commencing the process of construction (Nicholson, 2014).
This is the simplest and the oldest technique of improving the conditions of soil bearing. The condition of the foundation can be improved by substituting poor soil such as soft clay or organic soils with more proficient materials such as crushed stone, gravel, or sand. The application of soil replacement under the shallow foundation can increase the soil of soil bearing and minimize the consolidation settlement. The advantage of this technique is that it requires less delay during construction and it is more economical (Raj, 2012).
In this research of the proposed soil improvement technique in different ground characteristics, the results of the findings can be disseminated to other interested peoples majorly civil engineers, construction companies, and landscape designers through numerous channels that can be accessed by these targeted groups. The proposed method of dissemination is through writing the findings of the research and then publishing them in peer-reviewed journals in the engineering fields so as to target a large number of interested people (Kirsch, 2012).
This proposal on evaluation and determination of the best technique for improving the soil during construction is expected to take approximately 18 months. There will be need of visiting numerous construction sites to view the foundations of structures under constructions or already completed to determine the type of soil improvement techniques that are being used and the reason why that technique was chosen for the particular structure. Depending on the speed of the research team, the time lime for this research as shown in the figure below:
Figure 5: Gantt chart for the project research
Conclusion
Soil improvement can be defined as the alteration of the property of soil so as to improve its engineering performance through either permanent measure to improve a structure already completed or temporary process to enable the construction of a particular structure. This research proposal proposes the techniques that can be used to improve the soil when constructing and designing a foundation that would be used in the construction of structures such as roads, bridges, or other superstructures such as stadia by considering the cost of the technique, method of installation, and their functions. Some of the soil improvement techniques that may be of significance in the field of civil engineering include soil reinforcement, chemical stabilization, grouting and injection, consolidation a precompression, vibration method, drainage method, and surface compaction. The general outcome of the soil improvement may be improved water condition, reduced permeability, reduced compressibility, and increased strength.
References
Alfaro, M., 2009. Improvement Techniques of Soft Ground in Subsiding and Lowland Environment. London: CRC Press.
Bell, F., 2012. Engineering Treatment of Soils. New York: CRC Press.
Braja, M., 2015. Firewall Media. Michigan: Cengage Learning.
Choa, V., 2010. Soil Improvement: Prefabricated Vertical Drain Techniques. Sydney: Thomson.
Committee, J., 2009. In Situ Soil Improvement Techniques. California: American Association of State Highway and Transportation Officials.
Hansbo, S., 2010. Foundation Engineering. s.l.: Newnes.
Hawkins, B., 2009. Ground Chemistry: Implications for Construction. Ontario: CRC Press.
Johnson, S., 2011. Precompression for improving foundation. New York: Proc. American Society of Civil Engineers.
Joshi, R., 2009. Soil improvement by lime-fly ash slurry injection. California: Soil Mechanics and Foundation.
Kamauchi, H., 2013. Improvement of soft ground bearing capacity using synthetic meshes. Colorado: Journal of Geotextiles and Geomembranes.
Kirsch, K., 2012. Ground Improvement, Third Edition. Melbourne: CRC Press.
Kwong, L., 2011. Soft Soil Engineering. Perth: CRC Press.
Lambe, W., 2011. Soil Mechanics. Toledo: John Wiley & Sons.
Maity, J., 2017. Ground Improvement Techniques. Kolkata: PHI Learning Pvt. Ltd.
Moseley, M., 2013. Ground Improvement, Second Edition. Michigan: CRC Press.
Nicholson, P., 2014. Soil Improvement and Ground Modification Methods. Perth: Elsevier Science.
Purushothama, P., 2008. Soil Mechanics and Foundation Engineering. Mumbai: Pearson Education India.
Purushothama, R., 2014. Ground Improvement Techniques. New York: Firewall Media.
Raison, C., 2012. Ground and Soil Improvement. Melbourne: Thomas Telford.
Raj, P., 2012. Ground Improvement Techniques. Colorado: Firewall Media.
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