Effects of Stabilization on the Performance of Deltaic Lateritic Soils as a Road Pavement Material
Chapter One
AIM AND OBJECTIVES
The aim of this research study is to identify and examine the effects of Deltaic lateritic soils on the engineering properties of laterite and the possibility of improving these properties.
The objectives include:
- To collect samples of lateritic soil from a borrow pit at Abule-Ijoko Ogun
- To carry out index property test on the Lateritic soil with a view to identifying and
- To enhance the engineering properties of laterite used as base and sub-base course.
- To maintain and improve the standard and quality of our roads
- Stabilize the Laterite with Deltaic lateritic soils and determine the optimum binder (Superset in this case) content.
- To investigate the effect of temperature variations, pre-treatment conditions and testing
- To give recommendations, relating to the use of Deltaic lateritic soils, in the construction of flexible
CHAPTER TWO
REVIEW OF RELATED LITERATURE
HISTORY OF LITERATURE
From an engineering perspective, soil is any un-cemented or weakly cemented accumulation of mineral particles formed by the weathering of rocks and contains void spaces between particles, which are filled by water, and air (Craig, 1998). Also, Bell (1993) defined soil as a material having three components, which includes: solid particles, air and water. The geological formation is based on rock weathering which can occur either chemically when the minerals of a rock are altered through a chemical reaction with rain water, or mechanically through climate effects such as freeze – thaw and erosion. Soil is said to be residual soil, if the present location of the soil is that in which the original weathering of the parent rock occurred, otherwise, the soil is referred to as transported. Laterite is a soil group, which are formed under weathering systems productive of the process of laterization (decomposition of ferro alumino – silicate minerals, leaching of the combined silica and base; and the permanent deposition of sesquioxide within the profiles . The silica that is left unleached after laterization will form secondary clay silicate minerals. Laterites usually form a poor soil full of concretionary lumps and very unfertile because the potash and phosphate has been removed in solution, while only iron and silica are left behind . Laterites have been widely used for foundations and other construction purposes in subtropical and tropical regions, where they are deposited abundantly.
For any soil to be utilized for Civil Engineering works there is need for its investigation to enable the engineers to use the soil economically, to predict their engineering properties and their performance under field conditions, with a fairly good degree of accuracy.
Habeeb et all (2012) confirmed that the soil named “Laterites” was coined by Buchanan (1807) in India from a Latin word “Later” meaning brick. He described the material as “diffused in great masses, without any appearance of stratification, and is placed over the granite that forms the basis of Malayala (India). It is full of cavities and pores, and contains a very large quantity of iron in the form of red and yellow ochres. In the mass, while excluded from the air, it’s so soft that any iron instrument readily cuts it and its cut into square masses with a pick axe and immediately cut into the shape wanted with a trowel or large knife. It very soon becomes as hard as brick and resists the air and water much better than any bricks I have seen in India’’ (Charman, 1988).
Many definitions of laterite have been proposed in literature. Buchanan’s (1807) is the earliest and his definition is based on the ability of a soft red material to harden on exposure to air. Attempts at a more precise definition resulted in the application of chemical criteria to laterite, the potential of laterite as an iron or aluminium have helped to promote interest in their identification.
Lacroix (1913) divided laterite into true laterite, silicate laterite and lateritic clays, on the basis of the hydroxides content, and this was developed further by (Martin and Doyne, 1930) with the application of a silica-alumina ratio. Alexander and Cady (1962) reintroduced the concept of hardening and its relationship to the crystallization of iron oxides and dehydration. A silica sesquioxide ratio {SiO2 / (Al2O3 + Fe2O3)} with the ratio between 1.33 and 2 was therefore proposed for lateritic soils. Values greater than 2 indicated non-lateritic, tropically – weathered soils (Bell, 1993). Several attempts at a more useful definition based on morphology have also been made. Pendleton and Sharasuvana (1946) have defined laterite soils as profiles in which a laterite horizon is found, and lateritic soils as profiles in which immature horizons are found which develop under ‘appropriate’ conditions. None of the above definitions, however, helps the field identification of useful engineering material. Most researchers now prefer to use the definitions based on hardening, such as “Ferric” for iron – rich cemented crusts, “alcrete” or bauxete for aluminium–rich cemented crusts, “Calcrete” for calcium carbonate–rich crusts and “Silcrete for silica rich cemented crusts” (Fookes, 1997).
Laterite covers have mostly a thickness of a few meters but occasionally they can be much thicker. Their formations are favoured by a slight relief, which prevents erosion of the surface cover. Laterite occurring in non-tropical areas is products of former geological epochs. Lateritic soils from the uppermost part of the lateritic cover, in soil science are given specific names such as oxisol, latosol, ferallitic soil (Wikipedia, 2006).
Gidigasu (1972) worked extensively on lateritic soils of Ghana and concluded that laterite was derived from chemical and mechanical disintegration of the parent materials resulting into concentration of iron and aluminum oxides. Ola (1974) investigated stabilization problems associated with laterite and the modified result is used in production of blocks. Balogun (1982) investigated some physical, geochemical and geotechnical properties of laterite of Shagamu, Southwestern Nigeria; this he found to have significant difference in some index properties.
CHAPTER THREE
METHODOLOGY
SAMPLING
The soil was collected from a borrow pit at Abule-Ijoko Ogun State. Top soils of the sampling area were removed. Experimental samples were collected and packed in sack bags. Each bag was properly packed, sealed and labeled appropriately. They were promptly transferred to the laboratory for testing in accordance to the available standard procedures by The American Society of Testing and Materials (ASTM) or American Association of State Highway and transportation Officials (AASHTO) or based on the literature review. For the laboratory testing program, Deltaic lateritic soils was considered as a candidate stabilizer to treat the soil type.
ANALYSIS OF LABORATORY TESTS
Prior to commencement of any construction project whether on road or building involving site formation work, site investigation is carried out to establish the geological profile. Very often for road construction project, samples are taken by borehole drilling for tests including, particle size distribution, moisture content and triaxial tests etc. The results are useful for engineering design e.g. slope stability analyses. For pavement design, soil properties at subgrade level are required. It is recommended that samples from the designed subgrade level should be taken for CBR evaluations. This is considered appropriate for design purpose. Other than for road construction projects, CBR tests and other associate tests are also required for the design of structural maintenance treatments for existing roads. Discussed herein are the different laboratory tests to be performed on the collected lateritic soil sample.
CHAPTER FOUR
RESULTS, ANALYSIS AND DISCUSSION
PRESENTATION OF RESULTS
The result of the preliminary tests (sieve size analysis, natural moisture contents, specific gravity and Atterberg limits) as well as the strength tests (compaction, Californian Bearing Ratio-CBR, Unconfined Compressive Strength- UCS), are presented. The summary of the results of the preliminary analysis on the sample is shown in Table 1 below:
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS
CONCLUSION
From the results of the investigation carried out within the scope of the study, the following conclusions can be drawn:
The laterite was identified to be a silty-clay classified as an A-6(0) soil type based on AASHTO (1986) classification system. From the results achieved from the CBR test, we noticed that soaked sample had a higher CBR value as the percentage of Deltaic lateritic soils increased when compared to un-soaked
From the strength tests (Compaction, CBR, UCS), Considering the minimum CBR and UCS values for base course for a lightly trafficked road according to Federal Ministry of Works General Specification for Bridges and Road works; (1997) which is 180% for CBR, and 1500 – 3000 KN/m2 for UCS, it can be concluded that for strength consideration, Deltaic lateritic soils at 10% content satisfy the requirements
In summary, the addition of Deltaic lateritic soils as stabilizer increases the Unconfined Shear Strength and reduces the Permeability of the lateritic soil. Thus, it will be important in highway improvement in Nigeria.
RECOMMENDATIONS
In order to improve the state and condition of Nigeria highways, the following recommendations are made:
- The soil sample classified as A-6(0) could be recommended as silty-clay and could be rated generally as good base course soil material. It can also be recommended that Deltaic lateritic soils Stabilization of this soil would yield appropriate base & sub base materials for road pavements in Nigeria due to relatively high C.B.R Values as specified by The Federal Ministry of Works and Housing of Nigeria.
- PowerMax is recommended as a stabilizer for lateritic soils as it reduces the level of permeability with reduces in replacement as displayed in Figure 30
- Deltaic lateritic soils is highly recommended for stabilizing lateritic soils as it yields relatively high UCS values of cured lateritic soil samples as shown in Figure 29
- The use of Deltaic lateritic soils is hereby recommended as a laterite soil stabilizer particularly for use on natural soil such as A-6(0) to improve it capacity subbase material in highway pavement
REFERENCES
- AASHTO T 88 (2013): Standard Method of Test for Particle Size Analysis of Soils, American Association of State Highway and Transportation Officials.
- AASHTO T 89 (2013): Standard Method of Test for Determining the Liquid Limit of Soils, American Association of State Highway and Transportation Officials.
- AASHTO T 90 (2008): Standard Method of Test for Determining the Plastic Limit and Plasticity Index of Soils, American Association of State Highway and Transportation Officials.
- AASHTO T 99 (2010): Standard Method of Test for Moisture Density Relations of Soils, American Association of State Highway and Transportation Officials.
- AASHTO T 193 (2007): Standard Method of Test for the California Bearing Ratio, American Association of State Highway and Transportation Officials.
- Akanbi, E. O. (2006): Geotechnical assessment of the coastal plain sands of south western Nigeria as highway construction material, Unpublished dissertation, Department of Civil & Environmental Engineering, University of Lagos, Nigeria, 224pp.
- Alayaki, F. M. (2002): An examination of the engineering characteristics of lime, cement, and terralite stabilized laterite base course. Unpublished dissertation, Department of Civil &Environmental Engineering, University of Lagos, Nigeria.
- Akiije, I. (2014): “Strength and Permeability Characteristics of Selected Laterite Stabilized Using Deltaic lateritic soils”, International Journal of Scientific & Engineering Research, Volume 5, Issue 12