Recovery of Excavated Materials as an Alternative Solution to Earth Building Materials

The tunnel excavation works generate huge quantities of earth. These excavated materials are primarily stored in landfills. This paper proposes an alternative solution for valorizing excavated earth in earthen constructions. Firstly, the excavated earth was characterized using differential and gravimetric thermal analysis (DTA / TGA), infrared spectra (FTIR), and X-ray diffraction. Hence, sand, fine particles, and water extracted from excavated earth are used to elaborate mortars’ stabilized with cement, lime, and slag. Short hemp fibers were also used to diminish shrinkage cracks. The quantity of stabilizers was fixed to 5% by weight of the excavated earth while the water/solid ratio was maintained constant and equal to 0.45. Five different mortar formulations were performed using excavated earth and were cured for 28 days in a controlled environment before testing. Compressive and three-point flexural tests were carried out to determine specimens’ mechanical properties. The characterization results show that the excavated earth are mainly composed of dolomite, calcite, quartz, and clay. While, the mechanical results show that the stabilized excavated earth with cement additive presents higher mechanical properties relative to the other additives.

The role of concentrations variability of organic matter in kerogenic shale defluidisation on the catagenic depths

The Baltic kerogenic shale – kukersites (О2kk) were considered high-carbon marls which consist of three rock-forming components: organic matter (kerogen), carbonates and terrigenous material. As example used are data of the other high-carbon rocks. It is shown that increased concentrations of organic matter predetermine a number of features of these rocks (reduced density, reduced strength, etc.). The concentrations variability of the organic matter makes conditions the heterogeneity of the intraformational space, the anisotropy of many parameters, as well as the manifestation unevenness of the fluid-generation and evacuation capabilities. It was found that in kukersite shales fluid-generating properties can appear at the earliest stages of catagenesis. The role of areas with the maximum qualities of organic matter in the defluidisation of the shale coals is emphasized: here the more intensive generation of gas-liquid products and increased strength contribute to the earlier formation of drainage microcracks and fluid fractures. The appearance of shrinkage cracks due to catagenic losses of organic matter and usually uneven volume contraction and due to fluidgenerating shale coals is substantiated. The possibility of fluid-generating shale coals losing it lithological individuality during of it defluidisation is found out. Keywords: organic matter; oil shale; kukersite; defluidization; catagenesis; hydrocarbons.

Construction And Test of An Instrumented 2D Channel With Rainfall And Insolation Control.

This paper presents the construction and testing of a large instrumented 2D channel for the simulation of the performance of compacted barriers under controlled conditions of insolation and rainfall. Details of the main apparatus devices and capabilities and the results of a long-term test performed on a capillary barrier (CB) are presented. The performed test aimed to simulate the CB behavior over a period of one year in typical semi-arid conditions. The channel behavior was considered very promising with its components functioning as expected and providing the desired information. Concerning the CB performance, it is shown that the upper clayey layer of soil presented undesirable shrinkage cracks that impacted the CB performance, mainly at the end of the period of evaluation. The obtained results point to the need to use of silty or low plasticity clayey soils in the CB design, despite the higher expected values of hydraulic conductivity, as well as the adoption of layers thicker than usual in order to preserve the integrity of the clayey soil near the interface with the bottom coarse soil layer.

Unsaturated Hydraulic Conductivity Variation of Expansive Yazoo Clay with Wet-Dry Cycles

Expansive soils are subjected to shrink-swell behavior with moisture variation in Mississippi, United States. With successive moisture and temperature variations over the seasons, the hydraulic conductivity of expansive soil is subjected to change because of the development of shrinkage cracks, which can be as large as as 1.2 cm wide and 1.5 m deep in the field, affecting the vertical hydraulic conductivity (Kv), whereas the horizontal hydraulic conductivity (Kh) remains fairly constant. The current study intends to investigate the hydraulic conductivity of highly expansive Yazoo clay at different wet-dry cycles. To observe the changes in the hydraulic conductivity with different wet-dry cycles in the laboratory, an instantaneous profile method to measure the permeability was utilized. Compacted Yazoo clay samples at different initial moisture content instrumented with moisture sensors at different depths to monitor changes in the moisture content were investigated. The samples were subjected to one, two, and three numbers (1N, 2N, and 3N) of wetting and drying cycles. For the drying process, testing chambers are kept in a controlled high-temperature booth of about 37°C simulating high summer temperatures in Mississippi. After the end of the wet-dry cycles, the test is performed to investigate the changes in the hydraulic conductivity of soil with the presence of shrinkage cracks. The hydraulic conductivity of highly plastic clay is very low at a fully compacted state and was observed to be (1.0×10-8 cm/s) at the 1N wetting phase. However, with an increment in the wet-dry cycles, the Kv of Yazoo clay increases (3.70×10-4 cm/s) after the sample is exposed to three wet-dry cycles. Even though the changes in the Kv of highly plastic clay define the infiltration behavior, which mostly controls the slope failure and pavement distress, consideration of the climatic loads is ignored in the design phase of the highway embankment and levees. By inclusion of the climatic variation, and evaluating the performance, the design life and resilience of the structures can be significantly increased

Analysis Of Steel-Rcc Composite Deck Bridge

: In the literature, provisions for analysis and design of steel-RCC composite deck type truss and cable-stayed bridges do not exist. A composite deck type truss bridge model is analyzed using STAAD Pro V8i software and a model with the same dimensions is tested in the laboratory. The experimental test results are used to validate the STAAD analysis results. Bottom chord strain and mid-span deflection of the composite bridge model as found from the STAAD analysis and the laboratory experiment closely tally with each other. This validates the standard STAAD analysis results. However, in the top chord member, due to shrinkage cracks in the deck slab concrete, the experimentally recorded strain is higher by about 100% than the STAAD analysis result. Shear force in studs is considerably large near supports and joints as compared to the midsection. Therefore, the design of shear studs may be carried out based on the shear forces in the studs found from the STAAD analysis. Thus it is recommended that STAAD or any other standard finite element analysis software can be used for analysis and design of the composite bridges.

Effect of Alkali Pollutant in Influencing Crack Propagation in Soils

Shrinkage, deformation, and cracking will occur under extreme climate conditions such as drought, due to the accumulation of salt inside the soil during the evaporation of water on the surface of the soil. In this study, the image processing method was used to quantitatively analyze the dehydration cracking process of clay polluted by alkaline pollutant sodium carbonate on the basis of experiments. The mechanism of the effect of sodium carbonate concentration on the shrinkage cracks of clay was discussed through the analysis and comparison of different concentrations of sodium carbonate samples. The results showed that the water loss and shrinkage cracks of alkaline contaminant clay were developed in different stages. Firstly, first-level cracks developed diagonally or parallel to the edge of the container, and then second-level cracks developed along the main cracks with an angle of close to 90°. Most of the third-level or higher-level cracks were approximately perpendicular to the second-level cracks or the edge of the container and developed in parallel. In the cracking stage, the water loss ratio of the sample had a good positive correlation with the surface crack ratio. The slope of the fitted curve increased with the increase of the sodium carbonate concentration. With the increase of sodium carbonate concentration, the water loss ratio and the width of first-level cracks of clayey soil decreased, and the total length and the number of cracks increased, while the surface cracking ratio increased first and then decreased.

Hydrogen gas bubble nucleation from corrosion of steel in compacted bentonite

<p>The reference concept for the deep geological disposal of spent fuel and high-level radioactive waste in Switzerland foresees carbon steel disposal canisters surrounded by compacted bentonite buffer material. In support of performance assessments, long-term in-situ corrosion experiments were conducted in Opalinus Clay at the Mont Terri Underground Research Laboratory (URL) in Switzerland, wherein carbon steel coupons were embedded in MX-80 bentonite. The preparation of the steel specimens and bentonite, the exposure in a sealed borehole in the URL, and the retrieval, dismantling and imaging of specimens were conducted under strictly anoxic conditions. Samples were removed for analysis after exposure durations of 372, 628, 1024, and 2008 days. A key finding was the development of visible reddish-brown corrosion fronts around the metal surfaces and along shrinkage cracks that extend up to approximately 0.5 cm into the bentonite. Iron that originated from the corroded surface was transported along the cracks and precipitated as Fe-hydroxides due to oxygen sorbed on bentonite.</p><p>The formation of shrinkage cracks is thought to result from a local desaturation of the bentonite near the steel surface. To test this hypothesis i.e., to test the likelihood of a separate gas phase forming in addition to hydrogen mass dissolved in liquid water, it is necessary to evaluate the fate of hydrogen in the bentonite adjacent to the steel surface. For this, a flow and transport numerical model of the steel coupon surface and surrounding bentonite was implemented for the simulation of hydrogen release with the simultaneous consumption of water at the steel surface. The effect of single- and (potentially) two-phase flow with the diffusive and advective transport of the hydrogen and water components in the gas and liquid phases were modelled in a fully coupled manner. The numerical simulations were performed probabilistically in a Monte Carlo framework to account for parametric uncertainty, comprising 1’000 perturbations of all flow and transport parameters used in the model for the bentonite.</p><p>Overall, the simulation results are consistent with the hypothesis of a link between cracks observed in the bentonite and a temporary formation of a gas phase that results in preferential pathways for the transport of iron corrosion products.  The probability of gas formation in the model lies between 89% and 94% at the steel-bentonite interface and decreases significantly at distance of 1 cm from the steel coupon. Peak gas saturation at the steel-bentonite interface ranges up to approximately 1% with a mean value of approximately 0.18%. In all simulations, any gas phase forming in the bentonite dissolves back into the liquid phase within 300 days.</p>