Nonlinear Consolidation Theory Research Articles

Air-boosted vacuum preloading method for land reclamation with vertical drains: Numerical and analytical solutions

As an emerging ground treatment technique, the air-boosted vacuum preloading method accelerates the consolidation process of soils with vertical drains and enhances the bearing capacity and stability of grounds. This improvement is achieved by augmenting the horizontal pressure differential between the drainage body and the surrounding soils. In the realm of existing theories, consolidation models are primarily established under the assumption of linear characteristics of soils. Nonetheless, for marine sedimentary soft soils characterized by high compressibility, the application of nonlinear consolidation theory becomes more appropriate. The well resistance effect of the drainage body over time is also considered in this study, and a comprehensive consolidation model tailored to soft soils with air-booster pipes and vertical drains is proposed. Subsequently, the analytical and numerical solutions for this consolidation model are derived, respectively. Comparisons are made with existing conventional linear consolidation models to substantiate the validity of the proposed consolidation model. This investigation delves into the influence of nonlinear compressibility and permeability of soils, variable well resistance, and drain spacing ratio, on consolidation behaviors. Particular emphasis is placed on the determination of the startup time for the air-boosted system. Finally, the proposed consolidation model is applied to the actual field prediction, affirming the accuracy and applicability of the developed consolidation model in practical soft soil treatments.

Determination of hydraulic parameters of non-linear consolidation clay layers by type curve method

The consolidation of clay layers is of great significance for groundwater environmental protection, groundwater storage utilization, and land subsidence. In this study, the governing equation for the excess pore water pressure during the non-linear consolidation process of clay layers under load conditions is obtained based on the one-dimensional non-linear consolidation theory. Analytical solutions are then derived for clay layers with single or double drainage caused by the dissipation of the excess pore water pressure. With these analytical solutions, the groundwater dynamics and deformation of the clay layer are analyzed. Correspondingly, a type curve method is proposed to calculate the hydraulic parameters of the clay layer through laboratory experiments, which verifies the reliability of the analytical solutions. The study results show that the deformation of the clay layer predicted by the non-linear consolidation theory is smaller than that predicted by the linear consolidation theory. The deformation of the clay layer increases with the increase in the thickness of the clay layer, the compressive index, and the overburden load, while it decreases with the increase in the initial void ratio and the initial effective stress. The stable time, at which the consolidation of the clay layer is completed, increases with the increase in the compression index and the thickness of the clay layer, while it decreases with the increase in the initial void ratio, the initial effective stress, and the initial hydraulic conductivity. It does not vary with the load pressure. Conclusively, the deformation prediction based on the non-linear consolidation theory is more accurate and applicable to further load pressures.

Geotechnical performance of fine tailings in an oil sands pit lake

Syncrude Canada Ltd.’s Base Mine Lake (BML), the first commercial-scale demonstration of an oil sands pit lake, was commissioned in December 2012, following in-pit deposition of fine tailings (FT) between 1995 and 2012. The geotechnical design basis for the FT in BML is that it will consolidate and densify over time, contributing to fines sequestration below the water cap. This paper presents the geotechnical performance of the FT in BML within the context of this geotechnical design basis. The FT has settled from 196.0 to 171.6 Mm3 by 2019, with cumulative settlement varying spatially between 0.3 and 6.7 m. FT settlement is consistent with the expected self-weight consolidation as modeled by finite-strain non-linear consolidation theory, and is reflected as temporal increase in the profiles of solids content and effective stress. Sonar surveying, profile sampling, shear strength, and underwater photography show that the transition of geotechnical properties at the mudline becomes increasingly distinct over time. These observations support the geotechnical design basis for BML and indicate the fines continue to be sequestered below the water cap.

Nonlinear consolidation theory for prefabricated vertical drains with elliptic cylindrical assumption

Based on the influence of the non-linear change in the consolidation process of permeability coefficient and compressibility of soft soils and the theory of elliptic cylinders, derived the control equation of the nonlinear consolidation of the vertical foundation of the strip plastic drainage board. Further, according to the complete orthogonal space theory, the equivalent polynomial analytical expression of the nonlinear term is given. Then, the analytic solutions of the nonlinear consolidation are given, and through numerical calculation and verification analysis, it is considered that the Indrarantna (2005) approximation has a relatively small error at Cc/Ck (close to 1) and Nu (<4), but when Cc/Ck (difference from 1) and Nu are large (>4), the error is large.

A computation model for pile-soil stress ratio of geosynthetic-reinforced pile-supported embankments based on soil consolidation settlement

The pile-soil stress ratio (PSSR) is the key to the design and construction of geosynthetic-reinforced pile-supported (GRPS) embankments. However, the computation models for the PSSR which takes account of the effect of consolidation settlement of soil among piles (SAP) is not complete. This paper splits the piles and the SAP into multiple small elements for iterative calculation, according to the principle of the collaborative actions between pile, soil, embankment and reinforcement. The calculation method for pile-soil interaction was improved by Davis’ 1D nonlinear consolidation theory, and the hyperbolic load transfer model of pile-soil interface proposed by Wong and Teh. Then, a novel computation model for the PSSR of GRPS embankments was established, under the joint impact of soil arching effect, tension membrane effect and improved pile-soil interaction. Finally, this proposed computation model was proved reasonable by the comparison with tests and other methods, and the effects of key parameters were investigated. The results show that the settlement difference between piles and SAP increased with the degree of consolidation of the SAP and the elapse of time; the PSSR below the reinforcement net (RN) is slightly higher than that above the RN; the PSSRs above and below the RN are both positively correlated with the degree of consolidation and initial bulk compressibility of the SAP.

One-dimensional non-linear consolidation theory of soft ground coupled with thermal effect

Temperature has an important effect on the consolidation of soft soil. Considering current experimental data, a compression model for soft soil considering the influence of temperature is discussed. At the same time, a new expression for the permeability of soft soil considering the effect of temperature is presented. On the basis of the two models, a one-dimensional non-linear consolidation equation considering the effect of temperature on soft ground is established. Following the classical solution method of Davis and Raymond, the equation is solved analytically. After that, the influence of temperature on the consolidation process of soft ground is analysed. The results show that the higher the temperature, the faster will be the consolidation rate; the influence of temperature on consolidation rate is not a simple linear relationship.

One-dimensional nonlinear consolidation theory for soft ground considering secondary consolidation and the thermal effect

Based on the assumption that the change of the void ratio is caused by effective stress, creep effect and temperature, a one-dimensional nonlinear consolidation theory considering the thermal effect is established that contains the heat balance equation and the continuity equation. Verification and calculation examples are performed. The results show that the dissipation rate obtained using the present method is slower than that obtained using the traditional method. The pore water dissipation rate or consolidation rate considering the secondary consolidation and temperature is higher than that when only considering secondary consolidation. Heating accelerates the dissipation rate of pore water, especially in the early stage of consolidation.

Development of negative skin friction on single piles: uncoupled analysis based on nonlinear consolidation theory with finite strain and the load-transfer method

The development of negative skin friction (NSF) on single piles is investigated based on an uncoupled method of analysis with the Mikasa (1963) generalized nonlinear consolidation theory in terms of finite strain and the nonlinear load-transfer method. Predicted results are compared with results based on the conventional linear consolidation theory with infinitesimal strains. It is found that predicted development of dragload using the conventional consolidation theory is slightly greater and conservative compared to that using the nonlinear consolidation theory based on effective stress (β method). Effective stress predictions using the conventional theory are larger due to the faster dissipation of excess pore pressures, with the assumption of constant coefficient of consolidation and permeability. However, since the relative displacements required to mobilize the ultimate skin friction are small, and piles are usually installed near the final stages of soil consolidation, the differences in the predictions for the development of dragload on piles between the two consolidation theories are overshadowed. Using the uncoupled model for pile NSF, it is therefore found that the most significant factor for the estimation of dragload and downdrag is the proper selection of the β value rather than the consolidation theory used.

Influences of soil consolidation and pile load on the development of negative skin friction of a pile

Negative skin friction (NSF) along a pile caused by soil consolidation is of great concern to engineers. The development of NSF is time-dependent because soil consolidation is also time-dependent. In this paper, a numerical solution is provided for the development of negative skin friction of a pile in nonlinear consolidated soil under different loads on a pile top. A hyperbolic interface model is also developed. This model considers the development of shear strength during soil consolidation and loading–unloading scenarios at the pile–soil interface. One-dimensional nonlinear consolidation theory is invoked to estimate the soil settlement and shear strength. The distributions of NSF and the axial force along the pile are obtained using the differential quadrature method (DQM). The influences of soil consolidation and different pile loads on the negative skin friction of a pile are discussed.

Solution to 1-D consolidation of non-homogeneous soft clay *

In this work, semi-analytical methods were used to solve the problem of 1-D consolidation of non-homogeneous soft clay with spatially varying coefficients of permeability and compressibility. The semi-analytical solution was programmed and then verified by comparison with the obtained analytical solution of a special case. Based on the results of some computations and comparisons with the 1-D homogeneous consolidation (by Terzaghi) and the 1-D non-linear consolidation theory (by Daviset al.) of soft clay, some diagrams were prepared and the relevant consolidation behavior of non-homogeneous soils, is discussed. It was shown that the result obtained differs greatly from Terzaghi’s theory and that of the non-linear consolidation theory when the coefficients of permeability and compressibility, vary greatly.

Nonlinear Consolidation Theory for Nonhomogeneous Clay Layers and its Application

The first author derived a generalized one-dimensional consolidation theory in 1961 involving strain that takes into account the changes in mv, k, consolidation pressure and the depth of the clay layer (finite strain), during the consolidation process, and the effect of the selfweight of clay. This theory, however, applies only to clay layers with uniform consolidation properties; it has limited applicability to clay layers in the field, which are usually composed of different soils. The consolidation theory was thus amended to account for the continuous change in consolidation properties along the depth. The derivation of this consolidation theory is detailed, and two examples of application to thick alluvial clayey layers in the Osaka Port area together with comparisons with field observations are presented.