EJERS, European Journal of Engineering Research and Science
Vol. 3, No. 12, December 2018
a lower unit with fine to coarse sandstone and averages obtained from each point of measurements in the
intercalations of calcareous shales and thin shaly study area. Table II and Fig. 3 showed the GPS coordinates
limestone. and sampling locations in the study area.
d) The Ogwashi-Asaba Formation: This was deposited
during Tertiary-Oligocene-Miocene age [37]. It is Penetration index (PR) = ∆𝐷𝑝 ÷ ∆𝐵𝑐 (1)
made up of variable succession of clays, sands and
grits with seams of lignite. Uma and Egboka [37] where
reported this formation to be made up of PR = DCP penetration index in unit of length divided by
unconsolidated sand with lignite at various layers. blow counts
e) The Benin Formation: This was deposited during ∆𝐷𝑝 = Penetration depth
Miocene-Recent age [37]. The Benin Formation ∆𝐵𝑐 = blow counts corresponding to penetration depth
consists of coarse-grained gravelly sandstones with ∆𝐷𝑝
minor intercalations of shales and clays. The sand
units which are mostly coarse grained; pebbly and
poorly sorted contain lenses of fine grained sands
[28]. The sands and sandstones are coarse to fine,
partly unconsolidated with thickness ranging from 0
to 2100 m [10]. Benin Formation is in part cross-
stratified with the forset beds alternating between
coarse and fine-grained sands. The petrographic
study on several thin sections shows that quartz
makes up more than 95 % of all grains [28].
III. MATERIALS AND METHODS
A. Field Measurements and Sample Collection
Dynamic cone penetrometer Test (DCPT) method as
designated in ASTM D 6951/D 6951 – 09 [9], covers the
measurement of the penetration rate of the dynamic cone Fig. 3. Performing Dynamic Cone Penetration Test in the Study Area
penetrometer with 8 kg hammer through undisturbed soil to TABLE II: SAMPLE LOCATION POINTS WITH GPS COORDINATES IN THE
the depth of 6 m in the study area. DCP measurements were STUDY AREA
done in parts of Owerri, and average of four readings taken Sample Label Location Coordinates
from each test location was recorded as one measurement 05˚ 22.2ʹ 0ʺ N
Sample 1 (Sp1) Obinze
06˚ 55.5ʹ 0ʺ E
for the area. Six (6) DCP testing were measured, samples 05˚ 23ʹ 32ʺ N
Sample 2 (Sp2) Ihiagwa
collected and Global Positioning System (GPS) coordinates 06˚ 57.5ʹ 44ʺ E
taken at the same locations with sample numbers: Sp1, Sp2, 05˚ 30ʹ 02ʺ N
Sample 3 (Sp3) Irete
06˚ 55.5ʹ 0.25ʺ E
Sp3, Sp4, Sp5 and Sp6 (Table II and Fig. 3). The DCP 05˚ 28ʹ 12ʺ N
Sample 4 (Sp4) Egbu
testing readings were recorded at intervals of 0.5 m to 6 m 07˚ 01ʹ 31ʺ E
depth. 05˚ 26.9ʹ 0ʺ N
Sample 5 (Sp5) Avu
06˚ 54.5ʹ 1ʺ E
In the field, the number of blows required to advance the 05˚ 25.4ʹ 05ʺ N
cone by 0.5 m depth into the soil is what was measured and Sample 6 (Sp6) Naze
07˚ 02ʹ 0.3ʺ E
recorded. DCP testing are expressed in terms of the
penetration index or resistance (PR), which is defined as
downward vertical movement of the DCP cone produced by
one drop of the sliding hammer (inch/blow or mm/blow).
DCP testing consists of using the DCP’s free-falling
hammer to strike the cone, causing the cone to penetrate the
Sp4
base or subgrade soil, and then measuring the penetration
per blow, also called the penetration rate in mm/blow. This
measurement denotes the stiffness of the tested soil layers,
with a smaller penetration index or resistance (PR) number
indicating a stiffer material. In other words, the PR is a
measurement of the penetrability of the subgrade soil.
Fig. 4. Sampling Locations in the Study Area
Results are processed as graph of penetration index (PR) in
mm/blow versus penetration below the surface (m). The
The CBR of the undisturbed soil in the study area was
graphs would show a profile of different strength layers and
calculated from the empirical method in equation (2) as
PR would represent DCP test characteristic at certain depth.
stated by the U.S Army Corps of Engineers (USACE) and
Kleyn et al. [20] equation (1) was used to calculate the
Webster et al. [38].
penetration index (PR) (mm/blow) of the subsurface soils in
the study area. The results were interpreted based on the
log(𝐶𝐵𝑅) = 2.465 − 1.12 log(𝑃𝑅) (2)
DOI: http://dx.doi.org/10.24018/ejers.2018.3.12.973 3
