A new transient method for determining soil hydraulic conductivity function

Instantaneous profile method (IPM) is a transient method for measuring a soil hydraulic conductivity function (SHCF), which relates soil hydraulic conductivity with suction. In the existing interpretation method of the IPM, boundary flux during testing must be known to integrate instantaneous profiles of water content for obtaining water flow rate. However, it is usually difficult and expensive to measure a boundary flux and if not known, assumptions that may not be easily justified (especially in the field condition) have to be made. In this study, a new method is proposed so that any boundary flux needs not to be measured, controlled or assumed during a test. The new method is evaluated through (i) hypothetical column tests using transient seepage analyses and (ii) five case studies. The new method is capable of determining a SHCF with good accuracy. Normalised root-mean-square deviation (NRMSD) for the old and new methods is less than 5% and 10%, respectively. The accuracy of the new method can be increased substantially (i.e., NRMSDThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

A new and simple water retention model for root-permeated soils

Vegetation can affect soil hydrology not only through evapotranspiration but also through changes in soil water retention curve (SWRC). Models that are able to predict root-induced change in SWRC are limited. Such models often contain many empirical parameters that are not easy to be obtained and calibrated. This letter proposes a new and simple model with only one root parameter, namely root volume ratio Rv, needed for predicting the SWRC of a root-permeated soil. The new model considers void ratio change through volume reduction of air void of soil due to the presence of roots. The modified void ratio of a root-permeated soil is then fed into a void-ratio-dependent SWRC model to predict any resultant change in SWRC. The performance of this new model is validated against three case studies. Good agreement between measurements and predictions is obtained, with discrepancies of degree of saturation &lt;13% for a given suction. </jats:p

Investigation of plant growth and transpiration-induced matric suction under mixed grass-tree conditions

Although evapotranspiration-induced matric suction for single species has been widely studied, little is known about how mixed-species planting would affect the plant growth and induced matric suction. This study aims to explore the effects of grass-tree interaction on their growth and induced matric suction during evapotranspiration (ET) and rainfalls. Field monitoring was carried out to measure matric suction responses in compacted soil that was vegetated with (i) single tree species, Schefflera heptaphylla and (ii) mixed species of the trees and a grass species, Cynodon dactylon. In each condition, three tree spacings (120, 180 and 240 mm) were planted. When tree spacing increased from 120 to 240 mm, the peak tree root area index (RAI, for fine roots with diameterThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

An evaluation of soil-structure interaction associated with a multi-propped excavation

SIGLEAvailable from British Library Document Supply Centre- DSC:DX173986 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Dynamic soil parameters and case damping for high-capacity long H-piles

Uncertainty exists in signal-matching techniques. The quake and damping obtained may not be the actual response of the soil. In this paper, the final sets, strain gauge readings, pile driving analyzer, and Case pile wave analysis program of 12 high-capacity long H-piles at the end of initial driving as well as two of them at restrike are studied. Measured and deduced data show that the soil response underneath the pile toes has limited movement and yielding despite the piles being set using very heavy hammer rams and large ram drops. The quake and damping decrease with increased shearing strain and shearing stress, but are influenced by pile whipping, rebounded stress wave, and load-transfer mechanism. The lumped Case damping factor decreases with increased side resistance to total resistance ratio. This factor can decrease or increase with time due to changes in the load-transfer mechanism after set-up, thus affecting the proportion of viscous damping of soil along the pile shaft and at the pile toe. A Case damping model is proposed that approximates the lumped Case damping factor as the sum of hysteretic damping of the pile and viscous damping of the surrounding soil. The effects of variation in load distribution and set-up along the pile shaft in layered soils and incomplete mobilization of soil at the pile toe on the Case damping factors are explained

Inherent anisotropic stiffness of decomposed tuff and alluvium

Recent advances in laboratory testing techniques enable accurate measurement of shear wave velocity in different planes for the determination of stiffness anisotropy of soils at very small strains. While most studies of elastic stiffness anisotropy have been conducted on sedimentary soils and clean sands, relatively little investigation into the anisotropic stiffness of decomposed materials has been reported. In this paper, a recent study of the degree of inherent stiffness anisotropy of natural completely decomposed tuff (CDT) and natural alluvium sampled from an excavation site in Hong Kong is discussed and reported. The shear moduli of CDT and alluvium at very small strains in the vertical and horizontal planes were determined by shear wave velocity measurements across specimen height and diameter using bender elements. The results are compared to the degree of inherent stiffness anisotropy of different materials. The effect of soil structure of natural material on stiffness anisotropy is highlighted