The application of vapour equilibrium technique to control suction to study the shrinkage and water retention of compacted Claystone-Bentonite mixtures

Understanding soil shrinkage and retaining water is essential for learning more about the possibility of cracking of liner. Moreover, the factors that influence it are also important to know to improve the material tested as hazardous waste liners. The vapour equilibrium technique is widely used to control suction of compacted soils experiencing drying-wetting phenomena. It is considered to be inexpensive, simple, and has the ability to adequately control the suction applied to soil samples. This paper, therefore, describes its application in studying the shrinkage and water retention in compacted claystone-bentonite mixtures. This involved using five saturated salt solutions including potassium sulphate (K2SO4), potassium chloride (KCl), sodium chloride (NaCl), potassium carbonate (K2CO3), and magnesium chloride (MgCl2.6H2O). The sample was allowed to be in equilibrium with the relative humidity salt solution and a calliper was used to measure the dimensions every day up to when this was achieved. The results showed the bentonite in the mixture affects the amount of shrinkage and water retention while the sample’s initial moisture content was also found to be very influential on the magnitude of the primary and residual shrinkage. Moreover, the sample’s ability to hold water was almost the same without differentiating the initial water content at a total suction of more than 41084.91 kPa.

Assessment of Various Methods to Measure the Soil Suction

The foundation of the lightweight structures is commonly in unsaturated state conditions because located above the ground-water table. The matric suction governs the hydro-mechanical behaviour of unsaturated soils. Soil suction estimation is challenging both in the field and lab. The indirect and direct techniques are utilized to measure the soil suction. Several types of equipment utilized to measure the soil suction have been developed with innovative technology. However, there are constraints on reliability, suction range estimation, application, etc. The primary objective of this study is to review, describe the working principle, report limits, and benefits of various techniques utilized to measure the soil suction and select the cost-effective. A comparative study on direct and indirect technique of soil suction estimation is conducted base on recent literature, with a focus on suction range, procedure, type of suction, processing time, and application (lab/field). The apparatus utilized to measure directly or indirectly the matric suction found in the literature displays the highest range in the order of 1500 kPa except for the filter paper. The thermocouple psychrometer and the transistor psychrometer can measure a maximal total suction of 8000 kPa. The chilled-mirror hygrometer can measure a maximal total suction of 30000 kPa in the laboratory. The filter paper technique and the chilled-mirror hygrometer are cost-effective techniques. However, the filter paper technique is likely the easiest and low-cost technique to measure the matric suction and total suction for the full range with extreme care in the test procedure both in the field and lab.

The effect of microbial calcite precipitation on the retention properties of unsaturated fine-grained soils: discussion of the governing factors

In recent years, biogeotechnology has been introduced as a novel and environmentally friendly technique for soil improvement. The need to address global warming and the adverse environmental effects of the chemical additives have led to the emergence and development of the techniques which use calcite producing microorganisms in order to improve soil mechanical properties. While the effects of microbial induced calcite precipitation (MICP) on the hydraulics and mechanics of saturated coarse-grained soils have been well examined and studied, there is not yet much information on the effects these microorganisms would have on the unsaturated soil mechanical behaviour. The first step, in this regard, is to understand the effect of the processes involved in the MICP on the soil retention properties. Soil water suction is a key factor controlling soil hydraulic and mechanical behaviour. In this study, the influence of MICP on the soil total suction in an unsaturated fine-grained soil sample has been explored using filter paper experiment. The results of this study revealed that by increasing the amount of bacterial solution, the soil saturation-total suction curves are significantly affected. The soil water retention changes are attributed to the change in double layer thickness as well as the precipitation of calcite crystals.

Predicting aphid abundance on winter wheat using suction trap catches

The relationship between the number of cereal aphids in flight (recorded by a national grid of suction traps in the Czech Republic) and their occurrence on winter wheat (in Prague) was established between 1999–2015. The flight of all the species was bimodal. Except for Rhopalosiphum padi, whose flight activity peaked in autumn, > 80% of individuals were trapped during April to mid-August. The species frequency was different between the winter wheat and aerial populations. R. padi, the dominant species in the trap catches, formed a small proportion of the aphids on the winter wheat, while Sitobion avenae and Metopolophium dirhodum, which were underrepresented in the suction traps, alternately dominated the populations on the wheat. The aphid abundance in the wheat stands was correlated with the suction trap catches in the “spring” peak (April to mid-August), and the maximum flight activity occurred 4–10 days after the peak in the number of aphids on the wheat. In contrast, the prediction of the aphid abundance in the wheat stands using the total suction trap catches until the 15th of June (the final date for the application of crop protection actions) was reliable only for M. dirhodum. Its maximum abundance on the wheat exceeded 40 aphids per tiller if the total suction trap catch until the 15th of June was ≥ 60 individuals per trap. The prediction of R. padi and S. avenae abundance using the suction trap catches was not reliable.

Experimental Study on Comprehensive Performance of Sintering Biporous Wicks Prepared by Salt Dissolution and Cold Pressing Process

Porous wicks are a key component of loop heat pipes (LHPs). In order to enhance the antigravity and long-distance operation ability of the LHP, a porous wick is required to have the characteristics of high permeability and high capillary suction capability. In this paper, biporous wicks were prepared by salt dissolution pore-forming technology, and a gas resistance testing platform and a capillary suction testing platform were setup to test the samples. The current research studies the effects of different pore-forming agent mass ratios (10%, 30%, and 40%) and different cold pressing pressures (30 kN, 40 kN, 50 kN, and 60 kN) on the porosity, permeability, and the suction speed. The study finds that the porosity, permeability, and the total suction mass of the porous wicks all increase when the NaCl mass increases; the increase of the suction speed is proportional to the increase of the porosity and the permeability, and hence, proportional to the increase of NaCl mass. The total suction mass and suction speed is inversely proportional to cold pressing pressure.

FRACTAL MODEL FOR THE CORRELATION RELATING TOTAL SUCTION TO WATER CONTENT OF BENTONITES

Great efforts have been made to determine total suction using elaborate laboratory tests, because there is no a specific correlation relating the total suction to the water content of bentonites. However, elaborate laboratory tests are difficult and time consuming to perform on bentonites. Thus, a theoretical equation is a necessary choice to correlate the total suction to the water content. A simple method is proposed to calculate the total suction from the water content based on the surface fractal model for bentonites. The correlation relating the total suction to the water content is expressed by a power-law function with the exponent of [Formula: see text] is the surface fractal dimension of bentonites. The surface fractal dimension can be determined using the nitrogen adsorption isotherm tests. The total suction of bentonites calculated from the proposed method is in satisfactory agreement with the experimental data found in the literature. In addition, the correlation of the total suction to the water content also offers another method to determine the surface fractal dimension of bentonites.