Abstract:
This study deals with the behaviour of reinforced sand beds in
relation to bearing capacity of footing foundation resting on
these. The sand beds consist of layer of sands of varying
thickness,with horizontally placed jute cloth reinforcement
inclusion. Model tests were conducted to investigate the bearing
capacity, settlement and rotation of rough based strip, square and
circular footings.
Tests were carried out in a tank on beds of sand having relative
densities varying from 73 to 88 percent. The triaxial angle of
internal friction of the sand was approximately in the range of 34°
to 390. The sand bed thickness was maintained to three times the
least dimension of the footing. Strain controlled vertical loads
were applied on the footing placed on the surface of sand bed.
The effects of angle of internal friction of sand and the depth of
reinforcement, on bearing capacity are studied. The results are
established, discussed and compared with those predicted by the
existing methods.
It is observed that bearing capacity factors predicted by Terzaghi
(1943), Meyerhof (1963), Hansen (1970) and Vesic (1973) are all
conservative even if the plane strain angle of shearing resistance
is considered in estimating the bearing capacity. The variation is within 32 per cent to 62 percent of the experimental results. The
observed ultimate bearing capacity shows reasonable agreement with
the predicted value given by Feda (1961), Abdul Baki and Beik
(1970)_ and Quadir (1990). Statistical analysis of the experimental
results yield good correlations between ~ and the bearing capacity
factors. As such, these relations are proposed to estimate the
bearing capacity of strip footing resting on Bangladeshi sands.
The results also indicate that shape factors for square and
circular footings vary with the angle of internal friction of soil.
In general, shape factors found to have larger values than those
suggested by Terzaghi (1943). The observed values of shape factors,
for foundations in dense sand (~ = 39.2o)are found to agree with
values predicted by Terzaghi (1943).
For the case of reinforced sand bed, it is observed that the
bearing capacity of the sand layer increases significantly while
compared to an unreinforced bed. This is also found to be true if
a particular settlement is considered for a comparison of bearing
pressure. This increase of bearing capacity is found to be in the
range of 160 percent to 270 percent.
The reinforcement depth in the foundation sand bed has also a
significant influence on bearing capacity. In general, the bearing
capacity increases with the decrease of top layer thickness. The
experimental values of bearing capacity are found to have good
agreement with the predicted values of Binquet and Lee (1975b). For unreinforced bed, failure outcrop arises on all sides. It is at
a distance of 2B to 3B from the edges of the footing. Nearly
circular failure outcrop arises when the bed was loaded with
circular footing. Failure of reinforced bed was either by tie
pullout after overcoming frictional resistance or by shear failure
above the reinforcement.
