Evaluation of iron oxide impregnated filter paper method as an index of phosphorus availability in paddy soils of Tanzania

Phosphorus is a major yield limiting nutrient in rice production and yet most soil test methods for predicting P availability to plants have a number of shortcomings especially under flooded conditions. The objective of this study was to evaluate the iron oxide impregnated filter paper (Pi) method for assessing changes in P availability in soils subsequent to flooding and to determine the suitability of the method in assessing P status in paddy soils. The results indicated that available P increases considerably (between 34% and 256%) subsequent to flooding and this affected responsiveness of the soils to P application. Two versions of the Pi method namely; the Pi method used under flooded conditions (Pi-P_f) and Pi strips embedded directly in flooded soils (Pi-P_fe) were effective in assessing P availability in paddy soils. The two Pi methods were better correlated with rice dry matter yield than the traditional soil tests and are hence recommended for use in soil testing under flooded conditions. The tentative critical levels of P for the two procedures under pot conditions were 22 mg/kg for Pi-P_f and 15 mg/strip for Pi-P_ef.     

Pile Foundations in Earthquake-Resistant Construction

Experience with use of pile foundations is described for the construction of five-, nine-, and 12-story buildings under complex soil conditions in Georgia with consideration given to the differing seismicity of the regions. Deformations are cited for residential buildings erected on reinforced-concrete friction piles in weak clayey soils, and also buildings on piles situated in soils prone to slump-type settlement. The range of application of pile foundations is presented for these conditions.     

Numerical Analysis of a Tunnel in Residual Soils

This paper presents results of an elastoplastic finite element back analysis of a shallow tunnel through residual soils. The tunnel was constructed as part of the expansion of the underground transit system in the city of S?o Paulo, Brazil. A comprehensive laboratory testing program on undisturbed soil samples was performed in order to characterize the stress–strain–strength behavior of the residual soils. Results from this laboratory testing program were used to calibrate a nonassociated elastoplastic constitutive model utilized to reproduce the behavior of the residual soils under stress paths typical of underground excavation. A stress transfer method is proposed to simulate, using a two-dimensional finite element analysis, the response of the soil mass to the three-dimensional advancement of a tunnel excavation. Comparisons are presented between monitored displacements from an instrumented section of the Paraíso tunnel, empirical predictions, and the results of a finite element back analysis. Good agreement is achieved between the displacements obtained from field instrumentation data and the empirical and numerical results.     

Anisotropic Elastoplastic Bounding Surface Model for Cohesive Soils

The initial stresses existing in the natural ground are anisotropic in the sense that the vertical stress is typically larger than the lateral stresses. The construction activities, such as embankments and excavation, induce anisotropy in the stress system. The stress-deformation behavior and excess pore water pressure response of soils are affected by the inherent and induced stress anisotropy. This paper presents an improved soil model based on the anisotropic critical state theory and bounding surface plasticity. The anisotropic critical state theory of Dafalias was extended into three-dimensional stress space. In addition to the isotropic hardening rule, rotational and distortional hardening rules were incorporated into the bounding surface formulation with an associated flow rule. The projection center that is used to map the actual stress point to the imaginary stress point was specified along the K0 line instead of the hydrostatic line or at the origin of the stress space. A simplified form of plastic modulus was used and the proposed model requires a total of 12 material parameters, the same number as that of the single-ellipse time-independent version of the Kaliakin–Dafalias model. The model was validated against the undrained isotropic and anisotropic triaxial test results under compression and extension shearing modes for Kaolin Clay, San Francisco Bay Mud, and Boston Blue Clay. The effects of stress anisotropy and overconsolidation were well captured by the model. The time effect was not included in the formulations presented in this paper.     

Inter‐particle contact heat transfer model: an extension to soils at elevated temperatures

A simple ‘inter‐particle contact heat transfer’ model for predicting effective thermal conductivity of soils at moderate temperatures (0–30°C) has been extended up to 90°C. The extended model accounts for latent heat transport by water vapour diffusion in soil air above the permanent wilting point; below that point, the soil thermal conductivity is approximated by linear interpolation without latent heat effect. By and large the best results are obtained when the latent heat is used only in the ‘self consistent approximation’ model with an overall root mean square error of 35% for all soils under consideration or 26% when excluding volcanic soils. This option can also be applied to moderate temperatures at which the enhanced heat transfer is negligibly small. Copyright © 2005 John Wiley & Sons, Ltd.     

Limits on a Common Approximation for Layered Consolidation Analysis

A widely used procedure for solving the problem of vertical consolidation of layers with different properties is to transform the thicknesses of the layers in proportion to the square root of their coefficients of consolidation. However, the Gray–Barber closed-form solution shows that this procedure is not correct except under a restrictive set of conditions. The transformation method should not be used. When solutions are needed for layered systems, the Gary–Barber solution or numerical methods should be employed.     

Investigation of the Rheological Properties of Dense Clayey Soils

Results of experimental investigations are presented for rheological state equations of clayey soils in an axisymmetric stress state induced by two loading regimes. An approximation of rheological equations for shear and dilatational strains is given.     

Strengthening of a Damaged Multistory Building Constructed on a Slope Composed of Soil Prone to Slump-Type Settlement

The case of the deformation of a multistory tenement building on the slope of a ravine composed of soils prone to slump-type settlement is discussed. Measures taken to strengthen the foundations and slope, and results of observations on the effectiveness of their use are cited.     

非饱和土壤统计特征对宏观弥散度影响的分析

本文研究了重力为非饱和水分运动主要驱动力时，吸附溶质的宏观弥散度与孔隙介质统计特性和水力特性的关系，研究结果表明，宏观弥散度随溶质运移距离的增加而增加，并逐渐趋于一常数，宏观弥散度是土壤含水量、溶质吸附特性以及非饱和土体统计参数的函数，随平均含水量的增加而减少，随平均吸附因子和σｆ＾２、σα＾２、λｆ和λα的增加而增大。当溶质运移距离很大时，宏观弥散度为非饱和渗透系数的方差和相关距离的线性函数。