6.9 SUMMARY AND CONCLUSIONS

The upper-bound technique of limit analysis is used herein to develop approximate solutions for the bearing capacity of cohesive soils with weight. Solutions are presented for smooth and rough and surface, shallow and deep footings. Soil is treated as a perfectly plastic medium with the associated flow rule. The limit analysis solutions for smooth surface footings are shown to compare favorably with slipline solutions. Meyerhof's solutions and the limit analysis solutions for rough, shallow and deep footings are shown to agree remarkably well.

It has been shown that the upper-bound technique of limit analysis can predict bearing capacities of cohesive ponderable soils with internal friction to within a reasonable degree of accuracy, for ? ranging from 0 to 40 and G ranging from 0 to 5. At the least, it can be said that the results compare favorably with existing limit equilibrium solutions.

The most forceful argument for the adoption of the limit analysis method is the fact that its rational basis allows it to be conveniently extended to more complex bearing capacity problems. For example, as demonstrated here, the limit analysis method can be easily adopted to the solution of layered soils. More important, the method can be used to obtain upper- and lower-bound solutions of the three-dimensional bearing capacity problem where exact solutions of the equations of plasticity are all but impossible except for the most elementary of problems. The application of the limit analysis method to some three-dimensional bearing capacity problems...