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1. Bearing capacity of foundations on sand
Journal of Terramechanics, 1971, Vol. 8, No. 1, pp. 73-77, Pergamon Press. Printed in Great Britain.
ABSTRACTS 1.
Abdul-Baki Assad and Lewis A. Beik. Bearing capacity of foundations on sand. J. Mech.
Fdns. Div. ASCE, March (1970). The subject of bearing capacity of foundations on sand has been studied extensively by investigators. Although different approaches have been presented, a few points remain to be clarified, as for example the effect of footing roughness on the bearing capacity in the case of surface and shallow footings. In this study, the writers attacked the problem by finding the most critical slip surface that holds equally well for friction effect and surcharge. The solution proved to be very simple to apply with the help of a set of graphs. The results obtained were compared with those of other investigators and proved to be very encouraging. Also it was observed that for a surface footing the angle that the static wedge makes under the footing is somewhere between q5 and 45-t-~b/2 and that the angle approaches the upper limit when D/B almost reaches the ratio 3. (Authors' Summary.) 2.
A . W . Bishop and V. K. Garga. Drained tension tests on London clay. Geotechnique 19 (2) 309-313 (1969). Authors have developed an ingenious experimental setup to perform tension tests on soils. A specimen with a reduced central section is mounted in a triaxial cell and subjected to an all round pressure; an axial tensile force is then applied to the sample. Due to the difference in area between the central section and the bases of the specimen, tensile failure may be induced in the central section while the effective stress at the top and bottom bases of the specimen is still compressive; the end caps, therefore, will not become detached from the ends of the specimen, and no clamping is needed. A suitable choice of the ratio of end section to midsection areas and of cell pressure permits tension tests of this type to be performed on materials having tensile strengths of any magnitude. It is important to point out that, according to Griffith's theory, the tensile stress at failure is independent of the value of the compressive stress provided the latter does not exceed three times the tensile stress. The results of a series of tests on intact samples of London clay are presented. The tensile stress at failure, in drained conditions, lies in the range 0"27 to 0"34 k g / c m ~ and is very close to the value predicted from the compression strength by the modified Griffith theory. In reviewer's opinion, the paper presents an ingenious and useful experimental technique that will make easier the study of tensile strength of soils, a matter of considerable practical interest. (Appl. Mech. Rev.)
3.
G. Das. Some two dimensional mixed boundary-value problems of a semi-infinite mass of sandy soil (in English). Rev. Roumaine Sc. Tech. 13 (6) 1149-1152 (1968). An analytical solution for two problems in plane stress is derived for which the normal displacement at the boundary of a semi-infinite mass is defined. The media is defined with the peculiar property that the shear modulus /~ is smaller than the usual elasticity relation involving the modulus of elasticity E and Poisson's ratio tr, namely E / 2 ( l + t r ) . It is argued that the assumption may be justified for sand. The cases deal with the normal stresses to produce localised depressions at the boundary. (Appl. Mech. Rev.)
4.
M . J . Dwyer. The braking performance of tractor-trailer combinations. J. Agric. Engng Res. 15 (2) 1970. Equations are derived for the maximum decelerations which can be obtained with balanced and unbalanced trailers with and without trailer brakes. The equations are used to produce graphs showing the maximum decelerations of trailers having typical dimensions, of different weights relative to the towing tractor on surfaces of different adhesion coefficients and with different types and degrees of braking on the trailers. Results measured during braking tests on tractors and trailers are given. Unbalanced trailers are shown to have a better braking performance than balanced trailers and it is, therefore, recommended that trailers should be designed to carry the maximum permissible proportion of their weight on the tractor. Both over-run and power brakes on trailers are shown to provide 73
ABSTRACTS 1.
Abdul-Baki Assad and Lewis A. Beik. Bearing capacity of foundations on sand. J. Mech.
Fdns. Div. ASCE, March (1970). The subject of bearing capacity of foundations on sand has been studied extensively by investigators. Although different approaches have been presented, a few points remain to be clarified, as for example the effect of footing roughness on the bearing capacity in the case of surface and shallow footings. In this study, the writers attacked the problem by finding the most critical slip surface that holds equally well for friction effect and surcharge. The solution proved to be very simple to apply with the help of a set of graphs. The results obtained were compared with those of other investigators and proved to be very encouraging. Also it was observed that for a surface footing the angle that the static wedge makes under the footing is somewhere between q5 and 45-t-~b/2 and that the angle approaches the upper limit when D/B almost reaches the ratio 3. (Authors' Summary.) 2.
A . W . Bishop and V. K. Garga. Drained tension tests on London clay. Geotechnique 19 (2) 309-313 (1969). Authors have developed an ingenious experimental setup to perform tension tests on soils. A specimen with a reduced central section is mounted in a triaxial cell and subjected to an all round pressure; an axial tensile force is then applied to the sample. Due to the difference in area between the central section and the bases of the specimen, tensile failure may be induced in the central section while the effective stress at the top and bottom bases of the specimen is still compressive; the end caps, therefore, will not become detached from the ends of the specimen, and no clamping is needed. A suitable choice of the ratio of end section to midsection areas and of cell pressure permits tension tests of this type to be performed on materials having tensile strengths of any magnitude. It is important to point out that, according to Griffith's theory, the tensile stress at failure is independent of the value of the compressive stress provided the latter does not exceed three times the tensile stress. The results of a series of tests on intact samples of London clay are presented. The tensile stress at failure, in drained conditions, lies in the range 0"27 to 0"34 k g / c m ~ and is very close to the value predicted from the compression strength by the modified Griffith theory. In reviewer's opinion, the paper presents an ingenious and useful experimental technique that will make easier the study of tensile strength of soils, a matter of considerable practical interest. (Appl. Mech. Rev.)
3.
G. Das. Some two dimensional mixed boundary-value problems of a semi-infinite mass of sandy soil (in English). Rev. Roumaine Sc. Tech. 13 (6) 1149-1152 (1968). An analytical solution for two problems in plane stress is derived for which the normal displacement at the boundary of a semi-infinite mass is defined. The media is defined with the peculiar property that the shear modulus /~ is smaller than the usual elasticity relation involving the modulus of elasticity E and Poisson's ratio tr, namely E / 2 ( l + t r ) . It is argued that the assumption may be justified for sand. The cases deal with the normal stresses to produce localised depressions at the boundary. (Appl. Mech. Rev.)
4.
M . J . Dwyer. The braking performance of tractor-trailer combinations. J. Agric. Engng Res. 15 (2) 1970. Equations are derived for the maximum decelerations which can be obtained with balanced and unbalanced trailers with and without trailer brakes. The equations are used to produce graphs showing the maximum decelerations of trailers having typical dimensions, of different weights relative to the towing tractor on surfaces of different adhesion coefficients and with different types and degrees of braking on the trailers. Results measured during braking tests on tractors and trailers are given. Unbalanced trailers are shown to have a better braking performance than balanced trailers and it is, therefore, recommended that trailers should be designed to carry the maximum permissible proportion of their weight on the tractor. Both over-run and power brakes on trailers are shown to provide 73