Modelling consolidation accelerated by vertical drains in soils subject to creep

Abstract

The settlement of embankments and reclamations over soft soils is frequently accelerated by the use of vertical drains. The magnitude of long-term settlement is sometimes reduced by the use of surcharge, although there is often uncertainty about how long the surcharge should be maintained to minimise creep movement. The design of vertical drains is generally based on closed-form solutions of Terzaghi's consolidation equation, and rarely takes into account non-linear stiffness and creep of the soil. In this paper a one-dimensional finite difference consolidation analysis is outlined showing how vertical and radial drainage of a multi-layer soil profile in the zone of influence of a vertical drain may be modelled. The analysis allows inclusion of a zone of peripheral smear around the drain and drain resistance, permeabilities may be varied with void ratio, and creep is modelled both during and after primary consolidation. The application of the model is illustrated with back-analysis of field data from construction of an embankment with temporary surcharge over estuarine alluvium.

Consolidation analysis for soft soil with non‐Darcian flow considering variable discharge capacity of prefabricated vertical drain

“…To incorporate flexibility in considering boundary conditions and variations in permeability coefficients, this study adopts the FDM as utilized by Nash and Ryde. 39 Figure 3 shows the grid distribution after spatial discretization, and the pore pressure gradient i T , i B , i L , i R are defined in Equation (5).…”

“…k T k B k L and k R are the boundary permeability coefficient, which are calculated in the same way of Nash & Ryde. 39 𝑢 * 𝑚,𝑛 =…”

Consistent Implicit Time Integration for Viscoplastic Modelingof Subsidence above Hydrocarbon Reservoirs

“…τ, µ * , λ * , and κ * are material parameters with a clear physical meaning and easily identifiable through standard laboratory tests, such as odometric tests. τ is a characteristic time, usually set equal to 24 h. µ * is the modified creep index (modified because it is expressed in terms of the volumetric strain rather than the void ratio), which can be obtained in the long term from: (i) the slope of volumetric strain v versus the logarithm of time [11] (see Figure 2a), (ii) the slope of the inverse of volumetric strain rate versus time (see [28]), and (iii) the slope of logarithm of strain rate versus strain (see [29]), while λ * is the modified compression index, measuring the slope of the normal consolidation line in the v − log p plane (see Figure 2b), and κ * is the modified swelling index, measuring the slope of the unloading or swelling curve in the same plot. The parameters λ * and κ * should not be confused with the more commonly used λ and κ (without the * at the apex): Equation ( 31) in [11] states their relationships (it is λ * = λ/(1 + e) and κ * = κ/(1 + e), where e is the void ratio).…”