Laboratory study in a calibration chamber of a pressuremeter test on silt

While a lot of attention has been devoted, in laboratory and field testing, to the determination of the mechanical properties of clays and sands, little attention has been given to the stress-strain-strength properties of silts.; Recent decades have seen a growing interest in the development of in-situ testing techniques. Of the many field tests available, the pressuremeter has a reasonably sound theoretical basis. However, different methods are used in performing pressuremeter tests, and there are inconsistencies in the pressuremeter test results.; This research includes a laboratory study to determine the stress-strain-strength/pore pressure behavior of reconstituted normally consolidated Silt, taken from Waterbury Dam, Vermont. A technique for forming a twelve inches (12") diameter by twenty four inches (24") high sample was developed. A series of model pressuremeter tests, with various stress increments and strain rates, and different drainage conditions, were performed on normally consolidated samples. The work involved the design and construction of a large slurry consolidometer, a large calibration chamber, and a miniature Menard type of pressuremeter. A new model for soil response, based on the Conlon (1965), and Bjerrum (1966) concept of an "open structure" was also developed.; In order to establish an independent set of engineering parameters for comparison, the laboratory pressuremeter tests on reconstituted large samples were complemented by a series of triaxial compression, and oedometer tests performed on normally consolidated conventional sized specimens tested at various rates of deformation.; The results obtained from both the laboratory pressuremeter tests and the triaxial tests showed that the shear strength of the low plasticity (I{dollar}sb{lcub}rm p{rcub}{dollar} = 4%) silt is rate independent. Loading rates as fast as 4.7% strain/min (10 min to double the initial volume of the pressuremeter) is found not fast enough to prevent drainage in the field. The drainage induces an increase in shear strength in the order of 40%.; The nonlinear model proposed assumes the existence of the pressure limit, and provides an excellent fit to the data of the laboratory pressuremeter test on silt. Its modified form provides an excellent fit to the data obtained from the triaxial tests. The model is very suitable for fitting stress strain curves having a very steep initial part, and show either strain softening or strain hardening behavior.