Two-phase Soil Research Articles

Direct measurements of oxygen microprofiles and distribution of phospholipid-P in a two-phase soil—manure system

Concentrations of phospholipid-P (Plip-P) were used as an estimate of biomass in soil. Plip-P was correlated with biomass-C, as determined by chloroform fumigation-direct extraction, in soil from a fertilizer experiment, although a background of non-biomass Plip-P was suggested. The distribution of Plip-P was followed during three weeks in a two-phase model system designed to study microbial processes in and around a manure-saturated zone. Concentrations of Plip-P in the soil were unaffected by the presence of manure at ⩾ 4 mm distance from the soil-manure interface. A sharp gradient between manure and soil phases was maintained throughout the three weeks. Oxygen microelectrodes (i.d. ca. 5 μm, o.d. 150–200 μm) were used for direct measurements of oxygen penetration into the manure-saturated zone. No decrease in oxygen concentration was recorded in the soil phase. By Day 1 oxygen penetrated only 0.15 mm into the manure, increasing to 2-2.5 mm after 21 days. During this period the diffusive flux of oxygen decreased five-fold. Aerobic decomposition of dissolved C in the manure was apparently restricted to a thin layer of 0–2 mm thickness below the soil-manure interface.

Nonlinear seismic response analysis of earth dams

The objective of this paper is to propose a general and efficient numerical procedure for analysing the dynamic response of geotechnical structures, which are considered as both nonlinear and two phase systems. In Section 2, the appropriate coupled dynamic field equations for the response of a two-phase soil system are briefly reviewed. The finite element spatial discretization of the field equations is described and time integration for the resulting nonlinear semi-discrete finite element equations is discussed. In Section 3, iterative techniques are examined for the solution of the global nonlinear system of finite element equations. A large amount of computational effort is expended in the iterative phase of the solution and so the iterative procedure used must be both reliable and efficient. The performance of three iterative procedure is examined: Newton Raphson, Modified Newton Raphson and Quasi-Newton methods, including BGFS and Broyden updates. Finally, in Section 4, the elasto-plastic earthquake response analysis of a two phase nonhomogeneous earth dam is presented. Extensive documentation exists 1 for the particular problem selected including recorded earthquake motions at the base and crest of the dam. The results of the numerical calculations are compared to the recorded response of the dam.

Elasto-plastic consolidation of soil

A theory of the behaviour of an ideal mass of two-phase soil is developed. This theory unites the usually separately considered aspects of analytical soil mechanics of settlement and deformation; time dependent consolidation; and yielding leading to collapse of the mass. The theory assumes the soil to be an elasto-plastic permeable material and a finite element approximation of the resulting equations is derived through the principle of virtual work. Two example problems are treated numerically.