Experimental study to investigate the effect of water impregnation on thermal performance of earth air tunnel heat exchanger for summer cooling in hot and arid climate

Effect of soil moisture contents on thermal performance of earth-air-pipe heat exchanger for winter heating in arid climate: In situ measurement

Due to world-wide distributions and extensively used as construction materials, geotechnical engineers are interested in understanding the mechanical behavior of residual soils which are sometimes referred in the literature as problematic soils. The climatic zones where residual soils occur are often experienced by many drying-wetting cycles due to seasonal variations. This seasonal variation in the water content termed as drying-wetting cycle is regarded as the most destructive environmental factor that may cause many foundation diseases. Considering these, the purpose of this study is to understand the effects of drying-wetting cycles on saturated shear strength characteristics of undisturbed residual soil. A series of consolidated drained (CD) triaxial tests are conducted on multiple drying-wetting soil specimens to analyze the saturated shear strength. The test results indicate that the stress-strain relationships appear to be strain-hardening. The deviatory stress and initial stiffness of saturated soils increase and the volume of soils becomes contractive as the net normal stress increases but decrease with increasing drying-wetting cycle numbers. The cohesion (cd) and internal friction angle (φd) decrease with increasing cycle number (N) but the attenuation rate of φd is less than cd. The variations of cd and φd with respect to drying-wetting cycles can be expressed by exponential function. The saturated shear strength and it’s attenuation rate due to drying-wetting cycles are analyzed. The effect is more significant for the first cycle and decreases with subsequent cycles and finally reaches to a constant state after 4 cycles. Furthermore, a mathematical function is proposed in this paper which can describe the saturated shear strength attenuation rate of drying-wetting cycle samples. Such studies are useful to understand the possible changes in shear strength behavior of residual soils below the engineering structures that are subject to periodic drying and wetting from climatic variations.

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Effect of Drying-Wetting Cycles on Saturated Shear Strength of Undisturbed Residual Soils

The strength deterioration of compacted loess caused by drying–wetting cycles is influenced by various factors. In this paper, the influence of dry density (ρ), drying–wetting amplitude (A), and lower bounds of drying–wetting cycles (wl) on strength deterioration of compacted loess due to drying–wetting cycles was studied through triaxial tests and environmental scanning electron microscope (ESEM). By fitting a hyperbolic function to the deterioration data, the influence of ρ, A, and wl on the maximum deterioration rate and the development speed of the deterioration of strength parameters were quantitatively analyzed. Accordingly, a compacted loess deterioration model (CLDM) that comprehensively considers the influencing factors was established. Finally, based on Python, the CLDM was applied to finite element software ABAQUS, and the stability of a loess fill slope after exposure to drying–wetting cycles was analyzed. Analysis results show that the CLDM is capable of simulating the effect of drying–wetting cycles on the stability of fill slopes.

Comprehensive strength deterioration model of compacted loess exposed to drying-wetting cycles

The main objective of this study is to evaluate the hysteresis of soil–water characteristic curves (SWCC) of highly expansive clay subjected to wetting and drying cycles. Variables considered included hysteresis suction range (i.e. low and high suction ranges), suction determination technique (vapour equilibrium technique, axis translation technique and contact filter paper technique) and initial specimen condition. Experimental results revealed that the degree of SWCC hysteresis was higher in the low hysteresis suction range (less than 1.5 MPa) than the high hysteresis suction range (greater than 1.5 MPa). The results further revealed notable difference between matric and total SWCCs of this expansive clay. Furthermore, a hysteresis was observed that is inherent to suction determination technique and is independent of soil characteristics. Also, it was concluded that initial specimen condition (i.e. as-compacted and saturated) had a significant impact on degree of hysteresis, especially in the low suctio...

Hysteresis soil-water characteristic curves of highly expansive clay

The wetting-drying effect of expansive soils plays an important role in slope stability analysis. According to the depth of atmospheric effect and the field observation data of moisture content, laboratory experiments on the strength of expansive soil with two wetting-drying cycle amplitudes were performed to discuss on the wetting-drying effect of expansive soil. The results show that the shear strength of expansive soil decreases with increasing number of cycles and finally reaches to a constant state. The value and cycle number of the constant state reduce with increase of amplitude of variation of water content. Furthermore, the stability analysis of expansive soil slope is studied with considering the wetting-drying effect. The results may provide the reference for the parameter selection in slope design.

Wetting-Drying Effect of Expansive Soils and its Influence on Slope Stability

In recent years, ground-source heat pumps (GSHPs) have been extensively used in engineering projects because of their ability to take advantage of geothermal energy and their subsequent ben...

Performance of a Ground-Source Heat Pump System and the Heat-Moisture Migration of Surrounding Soils in Karst Areas

Swell-shrink clays are widely distributed in the Guangxi province of southern China in the form of expansive soils and lateritic clays. They have high particle dispersion, poor permeability, and significant swell-shrink properties. In recent decades, a series of problems closely related to the physical-mechanical properties of the swell-shrink clays have been encountered in various engineering projects. Mineral composition is a critical factor affecting the physical-mechanical properties of these clays. However, determining accurately their mineral compositions is difficult because the analytical methods available are expensive, time consuming, and have a high possibility of errors. Therefore, identifying a method suitable for quantitatively analyzing the mineral composition of the swell-shrink clays is necessary. In the current study several swell-shrink clays, including two expansive soils and four lateritic clays, from the Guangxi region were investigated. Qualitative analytical methods such as differential thermal analysis (DTA) and X-ray diffraction (XRD) were conducted to identify the mineral composition of the soils. The results indicated that the expansive soils were composed mainly of quartz (Qz), montmorillonite (Mnt), illite (Ilt), and kaolinite (Kln). The Baise specimen also contained a certain amount of calcite (Cal), while the lateritic clays primarily contained Kln and goethite (Gth) as well as lesser amounts of Qz and gibbsite (Gbs). On the basis of the aforementioned results, rough quantitative analyses of the mineral compositions were conducted using X-ray fluorescence (XRF) and the Bogue method. The results indicated that the lateritic clay samples from Wuming, Guilin, and Liuzhou contained 70–80% Kln, while the Laibin lateritic clay was 50% Kln. The lateritic clays contained ~10% Gth. The expansive soils were 30–40%, 25–30%, and 10–15% of Ilt, Qz, and Mnt, respectively. Finally, the relationships between the mineral compositions, zeta potentials, and free swelling ratios are discussed briefly. This investigation indicated that the zeta potential was mainly related to the type and content of clay minerals in the soil when neutral water was used as the free solution (pH = 7). The correlation between the swelling index and the zeta potential of the expansive soils was greater than that of the lateritic clays, which indicated that the swelling properties of expansive soils were more affected by the clay mineral composition than those of the lateritic clays. The results provide a systematic method for the qualitative and quantitative analysis of the mineral composition of swell-shrink clays and primary data for studying how mineral composition affects the physical properties of swell-shrink clays in the study area.

Analysis of the mineral compositions of swell-shrink clays from guangxi province, china

The shear strength of expansive soil has the obvious varying property with the changing of seasonal climatic. Based on Palmgrem-Miner linear accumulative damage theory, laboratory experiments on the strength of expansive soil combining with different wetting-drying cycle amplitudes were performed to discuss on the fatigue accumulative damage of expansive soil in the alternation of wetting-drying environment. The results show that：(1)The applying sequence of high (low) cycle amplitudes have significant effect upon the fatigue accumulative damage of expansive soil, and the strength attenuation of expansive soil is mainly controlled by the high circulate amplitude. (2) The Palmgrem-Miner linear accumulative damage criterion can basically reflect the fatigue accumulative damage process of expansive soil in the alternation wetting-drying environment, and the value of damage score “D” is close to 1 when the strength of expansive soil is stabled.

Research on Fatigue Accumulative Damage of Expansive Soil in the Alternation of Wetting-Drying Environment

Effects of two sample preparation methods on tensile strength of red clay are studied. The first method adopts standard layered-bumping to make sample whose layer interfaces are vertical to tensile force. The second method uses compaction apparatus to prepare big sample and the big sample is cut to prepare triaxial sample whose layer interface is parallel to tensile force. Test results indicate that the layer interfaces of soil sample have large influence on the single axle tension test, because the results of the sample prepared by 1st method have large dispersion and low strength, while the results of the sample prepared by 2nd method are just the opposite.Moreover,the layer interfaces of soil sample have little influence on the unconfined compressive strength test, and the results of the tensile test and unconfined compressive strength test of the samples prepared by 2nd method meet with the Griffith Criterion, so the samples of uniaxial tension test should be prepared by 2nd method.

Hai Bo Lu

Papers

Wetting-Drying Effect of Expansive Soils and its Influence on Slope Stability

Performance of a Ground-Source Heat Pump System and the Heat-Moisture Migration of Surrounding Soils in Karst Areas

Analysis of the mineral compositions of swell-shrink clays from guangxi province, china

Research on Fatigue Accumulative Damage of Expansive Soil in the Alternation of Wetting-Drying Environment

Effects of Sample Preparation Methods on Tensile Strength of Red Clay