Iris Publishers- Open access Journal of Civil & Structural Engineering | Geotechnical Indications and Shallow Bearing
Capacity Analysis within Lekki Peninsula, Lagos using
Direct Shear Analysis
Authored by HO Nwankwoala
It has become imperative for a review of the subsurface engineering
properties of the Lekki Peninsula due to increase in
urbanization. The study focuses on the shear strength parameters and
ultimately the shallow bearing capacity of the subsoil using
the direct shear method. With methods based on CPT, SPT, Particle Size
Distribution and Direct Shear Analysis, an underlying loosed
sandy layer of about 4m thick overlying a medium dense sand was
revealed. Plot from direct shear analysis reveals zero cohesion
and phi values = 170 indicative of a loosed soil. This loosed property
of the soil was also revealed by the non-peaked plot of the
direct shear test and the particle size distribution plot. Based on
correlation for non-cohesive soils using N-values, compressibility
parameters for the loosed sandy layer (N values=5) indicates Elastic
Modulus < 3500Kpa, while the Medium dense sandy layer
(N values=17) indicates values of about 13000Kpa. This implies high
compressibility is expected within the loosed sandy layer.
Settlement predictions based on a loading of 200KN/m2
indicated a settlement of 74mm. Recorded Water level is less than 1m.
Based on a shallow bearing capacity of 55kpa and intolerable settlements
and CPT values within the study area, a raft foundation is
most appropriate for multistory building while a deep foundation is apt
for higher loads.Geotechnical site investigation is the process of collecting
information and evaluating the conditions of the site for the purpose
of designing and constructing the foundation for a structure, such
as a building, plant or bridge [1,2]. Foundation studies usually
provide subsurface information that aid in the design of structures
[3,4]. Good planning for and management of a geotechnical site
investigation is the key to obtaining sufficient and correct site
information for designing a structure in a timely manner and with
minimum cost for the effort needed [5,6]. The effort and detail of
the geotechnical site investigation to obtain sufficient and correct
site information to select and design a foundation for a building is
complex [7]. It depends on the following: (a) design criteria of the
proposed structure; (b) historic knowledge of general site conditions
and building performance; (c) drilling equipment availability;
(d) time of year the work needs to be done may determine the
geotechnical site investigation method and finally; (e) the overall
costs. With the increasing population growth in Lagos State, Nigeria,
development activities have been on the rise around the coastal
areas of the state. One of such cities is the Lekki Peninsula. The area
of the city is about 800km2 with a Population greater than
400,000
(Wikipedia). The review of the Subsoil is penitent in view of the
high rate of urbanization within the area. This Study is to review
the stratigraphy of the superficial deposit underlying the area to
a depth of 10m, to determine relevant engineering characteristics
of the deposits, to enable appropriate foundation design of the
structure and ultimately estimates its Shear Strength parameters/
shallow bearing capacity using the Direct Shear method. [8,9] states
that the shear strength parameters (angle of internal Friction and
cohesion) is the principal engineering property that determines the
stability of soils under structural load. Investigative procedures
comprise of one (1No.) boring and two Cone Penetrometer.
To read more about this Article...Journal of materials in civil engineering asce
Please follow the URL to access more information about this article
To know more about journals...Iris Publishers
No comments:
Post a Comment