SUMMARYThis paper extends the bounding surface, generalized plasticity, model of Part I to reproduce the behaviour of sands under both static and transient loading. Each of these modifications can be introduced separately in a hierarchical manner to model in an improved way the behaviour of sands. Good comparison with experimental observations is recorded. The simplicity of the original model is preserved with modifications being introduced progressively to model rising complexity of the phenomena.

SUMMARYSeveral models describing soil response under cyclic loading and the 'liquefaction' potential have been introduced in recent years with limited success. Most of these are over-complex for realistic parameter identification and have not been widely adopted for practical use. In this paper we introduce a relatively simple modification of the well-known critical state model which accounts reasonably well for the phenomena observed under cyclic tests and indeed improves the performance of critical state models in monotonic loading.This model is compared with experimental results and with the 'densification model' introduced earlier by the authors and shows good predictive capacity.The model is of a generalized plasticity-bounding surface type. In its simplest form, suitable for clay-like materials, it requires the identifications of a single parameter additional to those required for a standard, critical state model.

Tip screenout (TSO) fracturing is a means of creating greater propped fracture widths and hence fracture conductivities than can be achieved by conventional fracture treatments. This allows more cost-effective stimulations of higher-permeability reservoirs, especially where non-Darcy pressure losses are significant. This paper presents a procedure to design TSO schedules and reviews field results from the Ravenspurn South gas field, which was developed between 1988 and 1989. Evidence is provided to support the view that TSO pressure responses are-indeed the result of processes occurring close to the fracture tip, rather than slurry-enhanced viscosity effects along the fracture length.