G W Clough

Design of a Large Calibration Chamber

The design and operation of a conceptually simple, low-cost chamber for calibration of cone penetrometers and other in situ devices is described. The chamber weighs over 5500 kg and houses a 4400-kg soil sample that is 1.5 m in diameter and height. Operations in the chamber are automated using a self-equilibrating hydraulic insertion frame, a soil pluviation system for sand placement, a vacuum unit for removing sand, and an automatic data acquisition system. The results from a series of cone penetration tests in Monterey No. 0/30 sand, using standard and miniature cones, are also discussed. These tests indicate that the chamber design was successful and also that nearly homogeneous samples could be prepared at different relative densities using interchangeable rainer plates.

Fabrication of Silty Sand Specimens for Large- and Small-Scale Tests

In the course of research concerning the relation of cone penetration results and liquefaction resistance, it was necessary to develop a reliable method for preparation of silty sand specimens for laboratory triaxial testing (3.6 by 7.1 cm in diameter) and for a large-scale calibration chamber (1.5 by 1.5 m in diameter). The objective was to simulate the in situ soil fabric and to allow for creation of a range of densities. Four alternate procedures were studied, including kneading compaction, pluviation through air, pluviation through vacuum, and consolidation from a slurry. The primary conclusions from the research were: 1. Kneading compaction is effective in producing laboratory specimens with a range of densities, but it is not an effective procedure for placing these materials in the large-scale calibration chamber. 2. Pluviation through air and vacuum creates specimens with unrealistically high void ratios. Obtaining a range of densities was not possible. 3. Slurry consolidation proved to be successful in creating specimens with a range of densities and was the technique chosen for the calibration chamber. Only vertical drainage was used in the calibration chamber to avoid formation of a specimen with a soft core surrounded by stiff sides. Eighteen to twenty days were required for consolidation, and the density of the specimens along a vertical profile varied by no more than 6% from the average density. There was little evidence of segregation of fines.

A Rational Procedure for Evaluating the Behavior of Impact-Driven Piles

A numerical solution has been developed using a finite difference formulation to simulate the one-dimensional impact wave propagation behavior and subsequent static load test performance. Based on this solution, the importance of residual driving stresses in properly interpreting pile behavior under axial loads is examined. This paper (1) briefly describes the analytical procedure developed by the authors to incorporate residual stresses explicitly, (2) applies the procedure to a documented pile load test to demonstrate the concepts developed, (3) examines the consequences of ignoring residual driving stresses in interpreting/predicting pile behavior under axial loads, and (4) demonstrates the influence of various parameters on the predicted pile performance.