Solute Removal Analysis of a Large-Scale Fracture Plane Considering Different Flow Paths and Different Hydraulic Head Differences

An experimental and numerical study was carried out to investigate the solute removal process through a large-scale fracture plane considering different flow paths and hydraulic head differences.The visualization techniques were utilized in the experiment to capture the removal process images,which were then transferred to binary images.The variations in dimensionless concentration,which is defined as saturation of solute phase,were analyzed.With increasing hydraulic head difference,the speed of solute removal increases and the dimensionless concentration decreases.The flow paths result in different solute distribution patterns and different mechanisms for solute removal such as advection and diffusion,thus the curves of dimensionless concentration versus time are different.The dimensionless concentration over time decreases from approximately 1,which is smaller than 1 due to the existence of bubbles,to approximately 0,which is larger than 0 because the folds of the background are dealt as“solute”.A significant longer time is needed to achieve a certain fixed dimensionless concentration for a smaller hydraulic head difference.With the finite element software COMSOL multiphysics,the solute removal process,flow velocity fields,flow streamlines,as well as the hydraulic pressure fields were analyzed,which shows a good consistency with the experimental results.In practical engineering,when the solute pollutes the underground environment,the removal ability can be more significantly enforced by immediately applying a larger hydraulic head difference along a longer distance between the inlet and outlet boundaries.

Hydraulic head difference at two sides of suspended waterproof curtain during multi-grade dewatering of excavation

This paper proposes an approach to calculate the head difference at two sides of suspended waterproof curtains during multi-grade dewatering.The seepage during the dewatering process can be subdivided into three regions:(i)seepage in pit,(ii)seepage between cur-tains,and(iii)seepage outside the pit.The flow rate of the first region is equal to the pumping rate,and the flow rate of the second and third regions can be obtained by numerical analysis.A numerical model is established to simulate the seepage in the second and third regions and its performance is validated by using the measured data of a series of field tests.The flow rate of each region is then used to derive formulae for the head difference in conventional dewatering,which can be used to determine the head difference at two sides of each waterproof curtain during multi-grade dewatering.The proposed formula expresses the head difference as a function of the relative depth of the curtain inserted into the confined aquifer,the thickness of the aquifer,the distance between two curtains,and the anisotropy of the hydraulic conductivity of the aquifer.The proposed numerical approach is further validated by using data derived from numerical analysis.The validation results demonstrated that the predictions of the proposed approach are acceptable and convenient.