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Some Geotechnical Properties of Two Foundation Soils from Malete, Central Nigeria

von Olubunmi Owoyemi (Autor) M.O Awojobi (Autor)

Wissenschaftliche Studie 2016 17 Seiten

Geowissenschaften / Geographie - Geologie, Mineralogie, Bodenkunde

Leseprobe

ABSTRACT

Malete is a fast growing rural area with new buildings springing up daily in it. There is presently no research on the geotechnical properties of the foudation soil in the area. This research aims at determining the suitability of some soil samples from Malete as infrastructure foundation. Bulk samples taken from two selected locations at varrying depths of trial pits were tested in the laboratory for their shear strengths and index properties. Cone penetration resistance, Carlifornia bearing ratio, compaction, consolidation and permeabilty charcteristics were also assessed.

The physical properties measured, varied significantly with depth except for specific gravity which does not vary sigficantly with depth. Soil samples from all pits consist mostly of poorly graded gravely sands with little fines containing a percentage of coarse to medium grained sand fractions averagely above 85%. Penetration resistance values gotten from hand penetrometer range between 700KN/m2 and 950KN/m2. The average safe bearing capacity estimated for strip footing using a factor of safety of 3 at depth of one meter is not less than 473KN/m2 anywhere in the study area. Samples from the two locations generally exhibit good compaction parameters, high to medium permeability and low compressibility. The highest bearing capacity values were gotten at the lateritized basement top.

Key Words: Foundation, Bearing capacity, Shear strength, Index properties

Corresponding Author:

Tel: 2347036761892

E-mail:lade.owoyemi@gmail.com

1. INTRODUCTION

Recently, cases of collapsed buildings in Nigeria has been on the rise. This calls for detailed geotechnical investigations of foundations soils so as to guard against re-occurrence of such ugly incidents. Material study of foundation soils to a large extent, serves as preventive measure for foundation failures. Nwankwoala and Warmate (2014), studied the foundation geotechnical properties of a site in Port Harcourt, Adunoye and Agbede (2014) used Terzaghi’s equations to determine the bearing capacity of soil samples from Obafemi Awolowo University Campus. He found correlations between angle of internal friction and bearing capapcity of the studied soils. Other researchers such as Ola (1988), Ogunsanwo (2002), Ige and Ogunsanwo (2009), Oyedele et. al. (2011), Avwenagha, et al. (2014), have worked on the geotechnical properties of foundation soils in Ngeria, however there is no documentation of the geotechnical characteristics of the foundation soils in the study area.

Malete is there about the fastest growing village near Ilorin. This is due to the establishment of Kwara state university campus in this rural area. Many new structures are springing up daily in the area. Most of these building owners do not pay attention to the geotechnical properties of foundation soils in the area. This paper investigate the geotechnical properties of two foundation soils in Malete using samples taken at varying depths and chainage within an average area of about 8,000m2 at each location.

2. LOCATION OF STUDY

The study area is located within the Kwara State University Campus. Two locations where rapid infrstructural developments are taking place were delinated. The two locations are underlain by migmatitic - gneisses belonging to the migmatite-gneiss complex of Southwestern Nigeria. The area is on a watershed shedding its storm water into the Apodu River as shown in Fig. 1. The vegetation of Malete area is that of woody savannah. Table 1 shows the location coordinates of the trial pits.

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Fig 1. Geological map of Malete area showing the location of the study area. ( Modified after Geological survey of Nigeria 1973)

Table 1. GPS Coordinates of trial pits

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3. Methods

Ten trial pits were dug at each location. Disturbed and undisturbed samples were taken at intervals where changes in soil characteristics were observed along the soil profile up to 1.65 m depth where lateritized basement rock were encountered. Classification tests including sieve analysis, consistency limits, specific gravity and natural moisture content were carried out on samples. Cone penetrometer test, shear box test, consolidation, compaction and permeability tests were also carried out on these samples. The shear strength parameters were estimated from shear box test.

Cone Penetrometer tests performed were by using 20 tones capacity penetrometer. With this arrangement, it was possible to measure both the point and frictional resistance of the soil to the point of hardpan basement encountered at a depth of 0.4m, 1.0m and 1.65m that gave stiff and constant resistance. The dial gauges used in carrying out the tests were calibrated prior to commencement of the test. All laboratory tests performed on the soil samples collected are in compliance with the specifications contained in BS 1377, methods of testing of soils for civil engineering purposes and ASTM standards.

The bearing capacity paprameters were gotten from shear box test. The bearing capacities were calculated using Terzaghi’ bearing capacity equation for shallow strip footing ( Equation 1). The safe bearing capacities were calculated using a factor of safety of 3 and equation 2. The depths used in the calculation of the bearing capacities are generally higher than the width used.

Qu = c Nc + γDNq + 0.5γ BNγ (1)

QS = Abbildung in dieser Leseprobe nicht enthalten (2)

Where; Qu ; ultimate bearing capacity, QS; safe bearing capacity, c = cohesion of soil (kN/m2), γ = effective unit weight of soil (kN/m3); D = depth of footing (m), B = width of footing (m). Values of bearing capacity factors Nc, Nq, and Nγ for different angles of internal friction,φ, as proposed by Terzaghi.

4. RESULTS AND INTERPRETATION

4.1.Classification Tests

This category of tests were carried out on samples taken from 20 trial pits at varying depths from the two locations. The results show that these samples consist mainly of Poorly graded gravely sands with little fines and a percentage of coarse to medium grained sand fractions averagely above 85%. At deeper depths, however samples contain more gravels. Fig 3 shows the distribution of grain sizes in the investigated samples. The specific gravity ranges between 24.0 and 2.75 for location one, it ranges between 2.64 and 2.67 for the second location. For location one, the natural moisture content range between 1.5 % and 6.8%, the range for location two is between 1.1 % and 8.1%. Only the few samples with appreciable amount of fines were tested for their consistency limits because of the granular nature of the soil. For location one, the liquid limit range between 29% and 34% while plastic limit ranges between 18% and 25%. Plasticity index averages 10.5%. The liquid limit for location two ranges between 32% and 34% while plastic limit ranges between 22% and 23.5%. Plasticity index averages 10%. Casagrande plasticity chart classify soils from the two locations as inorganic low to medium plasticity soil.

Most soil samples from both locations classify as A-2 4 under the AASHTO classification system, rating as good subgrade materials. Bulk density, dry density, specific gravity and natural moisture content increases with depth. While the values of these parameters vary significantly with natural moisture content and dry density exhibiting the strongest correlation with sampling depth. The correlation of some index properties with depth is shown in fig 4.

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Fig 2: Grading curves of some soil samples from the study area

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Fig 3: Bar chart showing the grain size distributions of samples from both locations.

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Details

Seiten
17
Jahr
2016
ISBN (eBook)
9783668337008
ISBN (Buch)
9783668337015
Dateigröße
1003 KB
Sprache
Englisch
Katalognummer
v341599
Institution / Hochschule
Kwara State University
Note
Schlagworte
some geotechnical properties foundation soils malete central nigeria

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Titel: Some Geotechnical Properties of Two Foundation Soils from Malete, Central Nigeria