Effect of temperature on the soil–water retention characteristics in unsaturated soils: Analytical and experimental approaches

In unsaturated soil mechanics, the soil–water retention curve (SWRC) continues to play an important role, since it provides the necessary links between the properties and behaviour of unsaturated soils with a variety of engineering challenges. The temperature has been identified as the main factor influencing SWRC as compared to a variety of other parameters. The goal of this research is to describe theoretical and experimental aspects of the temperature effect on unsaturated soil water retention phenomena. Theoretically, a brief review of the constitutive laws governing the thermal-hydro-mechanical (THM) behaviour of unsaturated soils is presented, along with links between variations in suction with water content, temperature, and void ratio. It also provides a broad framework that would to be well adapted to describing many specific circumstances. Through a closed-form predictive relationship that is developed in this framework, the effect of temperature is examined. By using this relationship, the soil–water retention curve at arbitrary temperature could be determined from one at a reference temperature, therefore significantly decreasing the number of tests necessary to describe the thermo-hydro-mechanical behaviour of a soil. Besides, the SWRC of kaolinite clay was also measured at three different temperatures in an experimental program. The test findings reveal that when the temperature rises, the SWRC decreases significantly. The experimental results were then integrated with sixteen other available data sets covering a wide range of soil types, densities, and suction to create a complete verification program for analytical models. The proposed model has a good performance and reliability in forecasting the fluctuation of non-isothermal SWRC than any existing model, according to statistical assessment results. The analytical model can be used to examine the thermo-hydro-mechanical characteristics of unsaturated soils in numerical simulations.     

Effect of chemical erosion and freeze–thaw cycling on the physical and mechanical characteristics of granites

Bulletin of Engineering Geology and the Environment - Rocks in nature are very often subjected to weathering processes. The physical and mechanical properties of granites exposed to chemical...     

Influence of spark timing on the performance and emission characteristics of gasoline–hydrogen-blended high-speed spark-ignition engine

This article experimentally investigates the effect of spark timing on performance and emission characteristics of high-speed spark-ignition (SI) engine operated with different hydrogen–gasoline fuel blends. For this purpose, the conventional carbureted SI engine is modified into an electronically controllable engine, wherein an electronically controllable unit was used to control the ignition timings and injection duration of gasoline. The tests were conducted with different spark timings at the wide open throttle position and 3000 rpm engine speed. The experimental results demonstrated that brake mean effective pressure and engine brake thermal efficiency increased first and then decreased with the increase in spark advance. Peak cylinder pressure, temperature and heat release rate were increased until 20% hydrogen addition and with increased spark timings. NO_x emissions were continuously increased with the increment in both spark timings and hydrogen addition, whereas hydrocarbon emissions were increased with spark timings but decreased with hydrogen addition. CO emissions were reduced with the increase in spark timing and hydrogen addition.     

Effect of polyurethane on the stability of sand–clay mixtures

Three types of polyurethane were synthesized from mixtures of toluene diisocyanate, polyethylene glycol and polypropylene glycol for use in soil stabilization to improve the erosion resistance. The three polyurethanes were tested at different aqueous concentrations and sand:clay mixtures at weight ratios of 1:1, 1:3 and 1:5. The results of the rainfall simulation, unconfined compression and direct shear tests showed that the polyurethanes improve both strength and erosion resistance significantly. The observed improvement in soil erosion resistance is attributable to the physico-chemical interaction of the long-chain macro-molecules of polyurethane with the clay fraction of the soil.     

Acceleration generation due to strain localization of saturated clay specimen based on dynamic soil–water coupled finite deformation analysis

In the conventional bifurcation and strain localization analyses of geomaterials, the inertia forces are generally ignored, based on the quasi-static equilibrium equation. Even though a great deal of literature exists on dynamic strain localization analyses, information on acceleration generation during the formation of shear bands has not been emphasized. Inspired by the acoustic emission phenomenon in laboratory tests and the seismic acceleration related to the slippage of faults, a dynamic soil–water coupled strain localization analysis is performed in the present paper on a saturated rectangular clay specimen subjected to constant cell pressure under plane strain conditions, employing the SYS Cam–clay model as the elasto-plastic constitutive model for the soil skeleton. An initial geometrical imperfection was introduced to the specimen to trigger one single shear band, and the following results were found: (1) Two types of oscillation occurred within the specimen during acceleration when the specimen was subjected to compression deformation at a constant rate, namely, (a) one caused by the sudden external compression and (b) the second induced by the formation of strain localization/a shear band. With the occurrence of the shear band, if, for example, the vertical rate was equivalent to about 10 cm/s, the accelerations that occurred within the specimen were in the order of several thousand gal, which is similar to those measured during earthquakes; (2) The effects of the time increment, the mesh division, the initial confining pressure, the OCR and the stress-control loading on the generated acceleration in (b) were investigated in detail. It was found that under stress control, even though the formation of the shear band was similar to that under displacement control, the induced acceleration behaved quite differently.     

Effect of silica fume and expanded perlite addition on the technical properties of the fly ash–lime–gypsum mixture

The main objective of this research was to investigate the effect of different type of pozzolan additions to cement free lightweight block made from fly ash–lime–gypsum mixture and observe the changes in physical, mechanical, thermal properties and microstructure. Thermal conductivity of the fly ash–lime–gypsum mixture was improved by the addition of the expanded perlite. Optimal strength-thermal conductivity combination was obtained by the usage of silica fume and expanded perlite together. Improved strength properties were obtained by using hydrothermal curing conditions and superplasticizer addition.     

Analysis of the effect of freeze–thaw cycles on the degradation of mechanical parameters and slope stability

Bulletin of Engineering Geology and the Environment - The changes that occur to the physicomechanical features of rocks during freeze–thaw cycles are crucial to research on the stability of...     

Aquifer characteristics and water quality of Miocene–Pleistocene sediments, Kuwait

Al-Atraf is one of the water well fields of Kuwait supplying Kuwait City with the brackish groundwater obtained from the Kuwait Group aquifer of Miocene–Pleistocene age. The study determined the hydrogeological and hydrochemical characteristics of the groundwater in order to identify the major chemical processes that influence the groundwater quality of the study area. The results of the aquifer test analyses indicate that the Kuwait Group is a confined to semi-confined aquifer, with a transmissivity ranging between 62 and 321 m²/day. The flow net analysis implied that the groundwater moves from southwest to northeast. The estimated transmissivity values agree well with those calculated from the aquifer test. The results of the chemical analyses data of the Al-Atraf field show that the groundwater is mainly brackish, of NaCl and Na₂SO₄ water types. The groundwater is undersaturated with respect to halite, gypsum and anhydrite and supersaturated with respect to quartz, dolomite and calcite in the direction of groundwater flow. The average Pco₂ of the groundwater is higher than the Pco₂ of the earths atmosphere indicating that the groundwater is supplied with CO₂ during the infiltration processes and dissolves the carbonate minerals under closed-system conditions.     

Effect of sepiolite on retention and drainage of suspensions of fiber–reinforced cement

This research is focused on the study of the effect of rheological grade sepiolite on flocculation, retention and drainage of fiber–cement suspensions by using a focused beam reflectance measurement probe and a vacuum drainage tester. Results show that the sepiolite could be used in the manufacture of fiber–cement to increase the retention of solids and the drainage rate especially in mixtures containing poly(vinylalcohol) fibers.     

The effect of styrene–butadiene–rubber/montmorillonite modification on the characteristics and properties of asphalt

In order to study the effect of styrene–butadiene–rubber/montmorillonite (SBR/MMT) modification on the characteristics and properties of asphalt, modified asphalts were prepared by incorporating MMT into SBR and mixing this into asphalt. The X-ray diffraction (XRD) results show that SBR/MMT composites may form an intercalated structure and SBR/MMT modified asphalts may form an exfoliated structure. The morphologies of the samples have been characterized by fluorescent microscopy. The results indicate that SBR/MMT modified asphalts formed an ideal fine network structure. The addition of SBR/MMT to asphalt increased both the softening point and viscosity and decreased the penetration of the modified asphalts at high temperatures. High-temperature storage stability tests indicated that the modified asphalts are very stable in some SRB/MMT, SBR/MMT content range. Especially, the modified asphalts exhibited higher complex modulus (G¹) and lower damping factor (tan δ). It implies that SBR/MMT displays improved viscoelastic properties, resulting in enhancing its resistance to rutting at high temperature.     

Investigation of the effects of wetting–drying and freezing–thawing cycles on some physical and mechanical properties of selected ignimbrites

This study was performed to investigate the changes in the physical and mechanical parameters of ignimbrites of different colors (black, red, yellow, gray) from Central Anatolia under the influence of wetting–drying and freezing–thawing cycles. For this purpose, 96 NX-size core samples were prepared. The unit weight, specific gravity, apparent porosity, water absorption by weight, slake durability index, uniaxial compressive strength, and P-wave velocity of each ignimbrite sample before conversion were determined. All of these parameters were then redetermined every 10 cycles (for a total of 50 cycles) for each sample. The changes in the values of the parameters after these set numbers of cycles were evaluated statistically. The petrographic and chemical compositions of the volcanic rocks influence their physical and mechanical properties, so some changes were also observed in the ignimbrite samples after these physical processes. Freezing and thawing cycles were observed to have an obvious impact on the physical and mechanical properties of the samples. The greatest changes were observed in black ignimbrite (with ferromagnesian minerals).     

Effect of ethanol on the performance,emission and combustion characteristics of a compression ignition engine fuelled with vegetable oil–diesel blend

Experimental work had been carried out to analyse the effect of ethanol on the performance, emission and combustion characteristic of vegetable oil–diesel blend (50% vol. rapeseed oil and 50% vol. diesel fuel). The vegetable oil–diesel–ethanol blended fuels were prepared by using microemulsification technique and the main properties were measured. The results showed that, with the increase in ethanol volume fraction in the blends, the viscosity and density were decreased and close to those of diesel fuel. The combustion started later; the peak cylinder pressure, peak heat release rate varied significantly under different operating conditions and the corresponding crank angles of the peak values were retarded. There were slightly higher brake-specific fuel consumptions. Smoke and nitrogen oxide emissions were observed to reduce, but carbon monoxide and hydrocarbon emissions were found slightly higher with the increase of ethanol volume fraction under all ranges of engine operating conditions.     

Impact of pre‐construction planning and project characteristics on performance in the US electrical construction industry

The mild recession experienced in the early part of this decade forced many US electrical contractors to reduce their profit margins as a way to win jobs and survive economically. However, to make up for lower profit margins, contractors turned to ‘better planning’ as a method for improving their efficiency and increasing their profitability. In general, contractors believe that better planning contributes to better project performance, but the evidence has been mostly anecdotal. A study was conducted recently that transformed anecdotal evidence about the impact of pre‐construction planning on performance into quantitative evidence. The research resulted in the development of a model pre‐construction planning process that was based on outstanding projects that were well planned and performed well. The study quantified the relationship between pre‐construction planning activities, project characteristics and performance, and a separate validation study found that those projects that performed a comprehensive planning process similar to the model planning process were more likely to achieve their estimated work hours, profit, budget and completion goals.     

The effect of silica fume and high-volume Class C fly ash on mechanical properties,chloride penetration and freeze–thaw resistance of self-compacting concrete

In this study, cement has been replaced with a Class C fly ash (FA) in various proportions from 30% to 60%. Durability properties of various self-compacting concrete (SCC) mixtures such as, freezing and thawing, and chloride penetration resistance have been investigated besides mechanical properties within the scope of this study. Similar tests were carried out with the incorporation of 10% silica fume (SF) to the same mixtures. Test results indicate that SCC could be obtained with a high-volume FA. Ten percent SF additions to the system positively affected both the fresh and hardened properties of high-performance high-volume FA SCC. Although there is a little cement content, these mixtures have good mechanical properties, freeze–thaw and chloride penetration resistance.     

Effect of freeze–thaw and thermal shock weathering on the physical and mechanical properties of an andesite stone

Natural stones are exposed to physical weathering due to freeze–thaw (F–T) and thermal shock (TS) when they are used as pavement, cladding and masonry material. In this study, the deterioration of andesite was investigated by determining the physical and mechanical properties of andesite samples after each 10 cycles of F–T and TS up to 50 cycles. It was found that the P-wave velocity, Schmidt hardness and compressive strength decrease to different extents with F–T and TS while porosity and water absorption increase with F–T cycles but decrease with TS cycles. The results showed that F–T has a more destructive effect on the studied material than TS, although abrasion loss measurements suggest that the effect on the surface of the material is greater with TS. An exponential model is proposed to predict the variation of material properties with F–T and TS cycles.     

Influence of initial dry density and water content on the soil–water characteristic curve and suction stress of a reconstituted loess soil

In the northwest of China, many loess landslides have occurred without clear triggering factors (i.e., rainfall, earthquake, human activities, etc.). To better understand and analyze the hydro-mechanical properties of these slopes and then provide evidence for their stability analysis subjected to matric suction, it is essential to clarify the soil–water characteristic curve (SWCC). In this study, we conducted a set of experimental trials to examine the influences of initial dry density, water content upon the SWCCs of a loess soil taken from a loess landslide area, by using a conventional volumetric pressure plate extractor. Two common SWCC models have been investigated to evaluate which one is better for loess soil. The suction stress characteristic curves (SSCCs) were also estimated and analyzed. We found that behaviors of SWCCs would be different when the matric suction was greater than a certain value. The two SWCC equations have approximately the same performance in describing the SWCC. The rates of desorption decrease and residual water content increases with increasing the initial dry density, while the initial dry density has little, if any, influence on the air-entry value (AEV). The specimen compacted under higher initial water content would exhibit a higher AEV value and residual water content but lower rate of desorption as compared with the lower initial water content. The magnitude of suction stress had an approximately linear relationship with matric suction before the AEV value, the SSCC shapes will be markedly varied with the initial dry density and water content.     

Effects of water content and interface roughness on the shear strength of silt–cement mortar interface

Although the shear behaviors of silt–structure interfaces are critical in engineering practice, they have not been extensively investigated systematically. In this study, the influence of the silt water content and interface roughness on the shear behaviors of silt–cement mortar interfaces is investigated. Forty–eight silt–cement mortar structure interface tests and 18 silt direct shear tests were carried out. The results indicated that as the water content of the silt gradually increased to saturation, the interface shear stress–displacement curves changed from strain softening to strain hardening, and the interface shear strength decreased significantly. The shear strength of the rough interface was found to be significantly greater than of the silt, and the shear strength of the smooth interface was found to be lower than that of the silt. The interface shear strength gradually increased with the surface roughness, but the increase tended to be gentle. A large shear deformation was observed, and this increased with the decrease in soil water content and the increase (up to a point) in interface roughness. A model of the interface shear strength between unsaturated soil and structures considering the influence of water content and interface roughness was established and verified.     

A study on the mechanical behaviour of cement–bitumen treated materials

Full depth reclamation (FDR) of asphalt pavements has gained general appreciation because of its technical, economical and environmental advantages. Along with FDR, the use of cement–bitumen treated materials (CBTM) rapidly increased over the last 10 years even if the lack of well-established technical specifications and reliable in situ control procedures hinder the cost-effective use of this material. Specifications for CBTM are currently based on experience and do not consider all the relevant parameters that affect the mixture behaviour. In this study the influence of curing conditions, temperature and moisture on the mechanical behaviour of CBTM is investigated. The recycled material was sampled during the FDR operations carried out on the Italian A14 motorway. The effect of curing and temperature on stiffness, and resistance to repeated loading were evaluated using cyclic indirect tensile tests. Moisture susceptibility was assessed by means of indirect tensile strength tests. Results showed a temperature-dependent behaviour of CBTM and allowed to define a simple model to predict the stiffness modulus based on curing time and temperature. In addition, the resistance to repeated loading proved to be a significant factor for the mechanical characterization of tested materials. Finally, regardless of curing conditions, the mixtures showed good moisture resistance.