Title | Effects of Fe-oxides cementation on the deformation characteristics of a highly weathered old alluvium in San Juan, Puerto Rico |
Publication Type | Journal Article |
Year of Publication | 2003 |
Authors | Zhang G, Germaine JT, Whittle AJ |
Journal | Soils and Foundations |
Volume | 43 |
Issue | 4 |
Start Page | 119 |
Pagination | 119-130 |
Date Published | 08/2003 |
ISSN | 1341-7452 |
Keywords | weathering |
Abstract | The old alluvium formed in early Pleistocene in San Juan, Puerto Rico has undergone substantial post-depositional weathering in the tropical marine climate, resulting in a special combination of mineralogy and microstructure, The stiff intact material consists of interconnected silt-sized aggregates, which in turn comprise groups of clay platelets containing smectites. Finely divided Fe-oxides act as coatings over clay platelets and bridge connections between aggregates so that a stiff network of aggregates is formed in the intact material. Such microstructure with Fe-oxides cementation renders this soil unusual deformation characteristics. The consolidation behaviour differs significantly from that of common sedimentary soil : (1) the coefficient of consolidation decreases from 0.1 to 10-5cm2 / s by four orders of magnitude as the soil is compressed to 20 MPa ; (2) the swelling strain increases significantly with the maximum past consolidation stress ; (3) the intact soil exhibits exceptionally high yield stresses (e. g., 0.8 MPa and 6 MPa for the upper and lower layers, respectively) ; and (4) the normal compression strain can be completely recovered upon unloading when samples are pre-compressed beyond the yield stress. Results of triaxial drained shear tests suggest that the intact soil possess isotropic Mohr-Coulomb strength parameters and a nearly constant cohesion over depth, despite variations in mineralogy and density with depth. Such abnormal deformation characteristics are the macroscopic exhibitions of microstructure alteration caused by stresses. |
URL | http://doi.org/10.3208/sandf.43.4_119 |
DOI | 10.3208/sandf.43.4_119 |