A Refined Formula for the Allowable Soil Pressure Using Shear Wave Velocities
Bogazici University, Istanbul, TurkeyThe Open Civil Engineering Journal 01/2011; 511(1):1-8. DOI: 10.2174/1874149501105010001
Based on a variety of case histories of site investigations, including extensive bore hole data, laboratory testing and geophysical prospecting at more than 550 construction sites, an empirical formulation is proposed for the rapid de-termination of allowable bearing pressure of shallow foundations in soils and rocks. The proposed expression corroborates consistently with the results of the classical theory and is proven to be rapid, and reliable. Plate load tests have been also carried out at three different sites, in order to further confirm the validity of the proposed method. It consists of only two soil parameters, namely, the in situ measured shear wave velocity and the unit weight. The unit weight may be also determined with sufficient accuracy, by means of other empirical expressions proposed, using P or S -wave velocities. It is indicated that once the shear and P-wave velocities are measured in situ by an appropriate geophysical survey, the allowable bearing pressure as well as the coefficient of subgrade reaction and many other elasticity parameters may be determined rapidly and reliably.
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ABSTRACT: The bearing capacities and coefficient of subgrade reaction of sand and shale lithologies of Niger Delta sedimentary basin, Nigeria have been computed from shear wave velocities using a relatively simple formula. The shear velocities were obtained from five oil exploratory wells. The computed ultimate bearing capacities of the sand ranges from 3141.755 to 5593.447 kN mm -3 with an average of 4367.601 kN mm -3 while, that of the shale ranges between 2487.786 and 6335.588 kN mm -3 with an average of 4411.687 kN mm -3. The computed allowable bearing capacity of the sand varies from 1047.252 to 1864.482 kN mm -3 while that of the shale lithology is from 829.262 to 2111.863 kN mm -3. Furthermore, the estimated subgrade reaction for the sand varies between 41890.07 and 74579.29 kN mm -3 while that of the shale is from 33170.48 to 84474.5 kN mm -3. The results show that the bearing capacities of the sand and shale lithologies are very high. This may be attributed to high consolidation and compaction of the formations in the subsurface and thereby resulting in the stability of most foundations in the area. Although, the shale lithology has a high bearing capacities and coefficient of subgrade reaction yet it is not advisable to put foundation on it whenever it is close to the earth surface because when it has the ability to swell/contract whenever it absorb or looses water it.
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ABSTRACT: This paper promotes the further development and adoption of infinite elements for unbounded problems. This is done by demonstrating the ease of application and computational efficiency of infinite elements. Specifically, this paper introduces a comprehensive set of coordinate and field variable mapping functions for one-dimensional and two-dimensional infinite elements and the computational steps for the solution of the affiliated combined finite-infinite element models. Performance is then benchmarked against various parametric models for deflections and stresses in two examples of solid, unbounded problems: (1) a circular, uniformly-distributed load, and (2) a point load on a semiinfinite, axisymmetrical medium. The results are compared with those from the respective closed-form solution. As an example, when the vertical deflections in Example 2 are compared with the closed form solution, the 45% error level generated with fixed boundaries and 14% generated with spring-supported boundaries is reduced to only 1% with infinite elements, even with a coarse mesh. Furthermore, this increased accuracy is achieved with lower computational costs.