What is soil plasticity ? How does it allow you to prevent slope failures ?
Inexpensive management of surface water could have prevented the slope failures illustrated in Figure 1. The slides occurred upon a creek escarpment on the east coast of Graham Island, Queen Charlotte Forest District. Since it was harvested in the early 1990’s this escarpment has produced an estimated 50 landslides, from 20 slide zones. Slope stability investigations have revealed that the escarpment is composed of medium plastic till. The till is among the most plastic (clay-like) of the soils a forestry worker can reasonably expect to encounter along coastal British Columbia. Inexpensive management of surface water would have prevented the worst of the slope failures upon the escarpment. Had the rock quarries in Figure 2 been built to be free draining, the slides in Figure 1 should not have occurred.
An Introduction to Geotechnical Engineering
This manual presents data on soil behaviour, with emphasis on practical and empirical knowledge, required by geotechnical engineers for the design and construction of foundations and embankments. It deals with: index and classification properties of soils; soil classification; clay minerals and soil structure; compaction; water in soils (capillarity, shrinkage, swelling, frost action, permeability, seepage, effective stress); consolidation and consolidation settlements; time rate of consolidation; the Mohr circle, failure theories, and stress paths; shear strength of sands and clays. Four appendices deal with the following: application of the "SI" system of units to getechnical engineering; derivation of Laplace's equation; derivation and solution of Terzaghi's one-dimensional consolidation theory; pore pressure parameters. (TRRL)
A single amino acid substitution in elongation factor Tu disrupts interaction between the ternary complex and the ribosome
Elongation factor Tu (EF-Tu).GTP has the primary function of promoting the efficient and correct interaction of aminoacyl-tRNA with the ribosome. Very little is known about the elements in EF-Tu involved in this interaction. We describe a mutant form of EF-Tu, isolated in Salmonella typhimurium, that causes a severe defect in the interaction of the ternary complex with the ribosome. The mutation causes the substitution of Val for Gly-280 in domain II of EF-Tu. The in vivo growth and translation phenotypes of strains harboring this mutation are indistinguishable from those of strains in which the same tuf gene is insertionally inactivated. Viable cells are not obtained when the other tuf gene is inactivated, showing that the mutant EF-Tu alone cannot support cell growth. We have confirmed, by partial protein sequencing, that the mutant EF-Tu is present in the cells. In vitro analysis of the natural mixture of wild-type and mutant EF-Tu allows us to identify the major defect of this mutant. Our data shows that the EF-Tu is homogeneous and competent with respect to guanine nucleotide binding and exchange, stimulation of nucleotide exchange by EF-Ts, and ternary complex formation with aminoacyl-tRNA. However various measures of translational efficiency show a significant reduction, which is associated with a defective interaction between the ribosome and the mutant EF-Tu.GTP.aminoacyl-tRNA complex. In addition, the antibiotic kirromycin, which blocks translation by binding EF-Tu on the ribosome, fails to do so with this mutant EF-Tu, although it does form a complex with EF-Tu. Our results suggest that this region of domain II in EF-Tu has an important function and influences the binding of the ternary complex to the codon-programmed ribosome during protein synthesis. Models involving either a direct or an indirect effect of the mutation are discussed.