Effect of freeze-thaw cycle on hydraulic conductivity of compacted clayey soil

When filling embankment dams in cold regions,engineers must solve two freeze–thaw cycle(FTC)-induced soil problems.First,compacted soil constituting the dam is subjected to the FTC during dam construction.Second,loose soil material(LSM),which is subjected to the FTC,fills the dam.To investigate the effects of the aforementioned two problems on the hydraulic conductivity of compacted clayey soil,a series of permeation tests on clayey soil compacted before and after FTC were conducted in this study.The results showed that for the first problem,the hydraulic conductivity of compacted clayey soil subjected to one FTC significantly increases by two to three orders of magnitude because FTC-induced cracks can cause preferential flow in the permeation process.For the second problem,when the FTC number is less than a critical number,the FTC of the LSM may result in the development of united soil particles,thereby increasing the effective porosity ratio and hydraulic conductivity of the compacted soil.It was discovered that the hydraulic conductivity of compacted soil can increase by one to three times when the LSM is subjected to 10 FTCs.When the FTC number exceeds a critical number,the effective porosity ratio and hydraulic conductivity of the compacted soil may decrease with the FTC of the LSM.This should be investigated in future studies,and the results can be used to improve engineering management processes when filling embankment dams during winter in cold regions.

Elastic Modulus Prediction of Three-dimension-4 Directional Braided C_f/SiC Composite Based on Double-scale Model

Double-scale model for three-dimension-4 directional（3D-4d） braided C/SiC composites has been proposed to investigate its elastic properties. The double-scale model involves micro-scale that takes fiber/ matrix/porosity in fibers tows into consideration with unit cell which considers the 3D-4d braiding structure. Micro-optical photographs of composites have been taken to study the braided structure. Then a parameterized finite element model that reflects the structure of 3D-4d braided composites is proposed. Double-scale elastic modulus prediction model is developed to predict the elastic properties of 3D-4d braided C/SiC composites. Stiffness and eompliance-averaging method and energy method are adopted to predict the elastic properties of composites. Static-tension experiments have been conducted to investigate the elastic modulus of 3D-4d braided C/SiC composites. Finally, the effect of micro-porosity in fibers tows on the elastic modulus of 3D-4d braided C/SiC composites has been studied. According to the conclusion of this thesis, elastic modulus predicted by energy method and stiffness-averaging method both find good agreement with the experimental values, when taking the micro-porosity in fibers tows into consideration. Differences between the theoretical and experimental values become smaller.

Wave propagation in liquid-saturated porous solid with micropolar elastic skelton at boundary surface

The present study is concerned with the reflection and transmission of plane waves at an interface between homogenous invisicid liquid half space and a micropolar liquid-saturated porous solid half space. The reflection and transmission coefficients of various reflected and transmitted waves with the angle of incident have been obtained. Numerical calculation has been performed for amplitude ratios of various reflected and transmitted waves. Micropolarity and porosity effects on the reflection and transmission coefficients have been depicted graphically. Some particular cases have been deduced from the present formulation.

Performance Analysis of Thermoacoustic Refrigerator of 10 W Cooling Power Made up of Poly-Vinyl-Chloride for Different Parallel Plate Stacks by Using Helium as a Working Fluid

Refrigerants are usually provided in the conventional refrigeration system although the refrigerants produce Chlorofluorocarbons(CFCs)and Hydro-chlorofluorocarbons(HCFCs),which are hazardous to the environment.However,these disadvantages can be overcome by using air or inert gas in the thermoacoustic refrigeration system.In the present experimental work,helium is used as a working gas with an operating pressure range of 0.2 MPa to 1.0 MPa in order to study the performance of thermoacoustic refrigerator(TAR)which is fabricated using Poly-Vinyl-Chloride(PVC).The parallel plate stacks with different porosity ratios have been considered to study the performance of TAR.The temperature difference between the hot and cold heat exchanger and acoustic dynamic pressure were recorded by using Bruel and Kjaer data acquisition system under different operating conditions.The effect of different operating parameters such as operating frequency(200 Hz to 600 Hz),cooling load(2 W to 10 W)and drive ratio(0.6%to 1.6%)have also been considered to study the performance of TAR.The TAR also modeled in DeltaEC software and the results are compared with the experimental outcomes and found to be in good agreement.The experimental results show that-2.1℃is the lowest temperature measured at cold heat exchanger by achieving the highest temperature difference of about 32.9℃.An improvement is around 36%as compared to that of previous experiments that used aluminium TAR.The highest Coefficient of Performance(COP)and the Relative Coefficient of Performance(COPR)are found to be 2.024 and 0.217,respectively.