Manuel J. Mendoza

Quick and Reliable Procedure for Liquid Limit Determination of Fine-Grained Soils

This paper describes comparative results of liquid limits for fine-grained soils, determined by the percussion-cup standard procedure and alternative techniques with penetrating cones. Microwave oven drying is used as a complement to fall-cone tests. In this way, the liquid limit for a soil sample can be accurate and reliably obtained in about 45 min. The studied cones were the pioneer Swedish cone with 60° angle and 60 g mass, and the English cone with 30° and 80 g. Percussion liquid limits differ from those obtained with the cones; however, results of a comprehensive experimental program evince that there exist linear correlations between their liquid limits.

Modeling soil-pile interaction under axial loading using a bilinear Mohr-Coulomb based model

It is common practice to rely on traditional relationships to compute the bearing capacity of deep foundations. In particular, when dealing with piles is essential to calibrate the load-displacement response, both for axial and lateral loading and to define the load transfer mechanism at the pile tip and along the shaft. These calibrations allow to reduce uncertainties and to design less expensive and safer foundations. The objective of this paper is to simulate the mechanical response obtained from a load test performed in a real scale cast in place concrete pile embedded in alluvial sand, using a 3D finite differences model. The pile was instrumented to monitor directly the reaction along its shaft and tip. The interface was modeled using a shear coupling-spring with frictional resistance. Both the soil and the pile were represented with four nodes axi-symmetric elements. The stress-strain behavior of the soil and soil-pile interface was described with a bilinear MohrCoulomb constitutive law. Although the simplicity of the bilinear model, good agreement was observed between the measured and computed responses when monotonic increasing loading was applied (i.e. static conditions). However, the bilinear constitutive model largely underestimates the measured permanent deformations prevailing in the pile-soil system after unloading. This should be accounted for when analyzing the dynamic response of the soil-pile system.