Abstract:
A study on the behavior of a centrally loaded
artificially prepared air dry sand layer is
thesis. The study is concerned with the
apparatus to study the bearing capacity
constituted of selected sands of Bangladesh.
strip footing
reported in
development
of sand
on an
this
of an
layers
A bearing capacity testing apparatus was designed and constructed
in the laboratory. The apparatus mainly consist of a model tank
of dimensions 57 cm x 85.5 cm x 60 cm, a sand spreader, a
levelling apparatus, a strip footing and a loading rig having a
capacity of 27 kN.
Plane strain model tests were carried out using a rough based
footing resting on dense, (Dr = 80%to92%), semi-infinite (H/B~3)
layer of sand collected from different locations of Bangladesh.
The mechanical sand spreader was used to form the sand bed.
Strain controlled'loads were applied and the plane strain
conditions were carefully maintained. The bearing capacity tests
were carried out for surface (D/B=O) and shallow (D/B=0.5,1.0)
depth footing using four selected soil samples having different
angle of internal friction. The load, settlement and rotation
measurement were taken using load and strain dial gauges. Basic
computer programs were developed to analyze the data and present
the results. The effects of angle of internal friction(~) and depth of
surcharge on bearing capacity, angle of internal friction on
bearing capacity factors Ny, Nq and Nyq are studied. The results
are compared with those predicted by the existing methods. It is
observed that for a surface strip footing the bearing capacity
results are in good agreement with that given by the empirical
relation of Feda (1961) and Abdul Baki and Beik (1970) whereas
for a shallow depth footing the results are in satisfactory
agreement (Varying from 68% to 102%) with the results of Abdul
Baki and Beik (1970). It is further noticed that when the footing
depth closes to the width of footing the bearing capacity
predicted by Terzaghi has excellent agreement (within a range of
90% to 95%) with the experimental results particularly for higher
values of ~.It is, however, observed that,in general,the
predicted results are on the safe side in almost all the cases.
The experimental results show that the predicted values of Ny by
existing formulas are highly conservative,the exception being
that of Feda (1961), which is on the unsafe side. Terzaghi's
(1943) formula predicts bearing capacity factor for surcharge,Nq,
very closely while D/B is approximately 0.5. The reasonable
agreement for Nq was also observed while using the formulas of
Meyerhof (1955) and Br. Hansen (1961).
Statistical analysis of the experimental results yield good
correlations between ~ and the bearing capacity factors. And as
such, these relations are proposed to estimate the bearing
capacity of strip footing resting on Bangladesh sands.
