This study investigated the effect of two types of fibers (natural and synthetic) on the swelling properties of clayey soils. Nylon and palmyra fibers with different aspect ratios (L/d ) were mixed with three types of expansive soils that had different physical properties. Four aspect ratios (25, 50, 75, and 100) and five different amounts of fiber (1, 2, 3, 4, and 5%) were used in the study and both swelling pressure and swell potential were evaluated for each combination. The results of the study showed that an increase in the percentage of both types of fiber reduced the swelling pressure and swell potential of the clayey soils significantly. It was also noted that the palmyra fibers had a greater effect than the nylon fibers in reducing the swelling pressure of the expansive soils that included the same amount of the fiber. The lower aspect ratio (L/d ) appeared to have a greater effect in reducing the swelling pressure for the two types of fibers. The impact of mixing the fibers with the clayey soils increased as the clay fraction increased.

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This study investigated the effect of wheat straw ash (WSA) on the performance of concrete in response to thermal cycling, which was evaluated by measuring the compressive strength and electrical resistivity and by visual inspection of cracks in the concrete specimens. Three levels of WSA replacement—5, 10 and 15% by weight of sand—were utilised. The other experimental parameters investigated in the study were: aggregate type (volcanic tuff and crushed basalt), water-to-cement ratio (w/c; 0·5 and 0·7) and air entrainment (non-air-entrained and air-entrained). After an initial moist curing period of 90 days, the concrete specimens were subjected to thermal cycling over the range 30–150°C for a period of 24 h using an electric furnace. The results of the study showed that thermal cycling of WSA concrete induced many cracks that were dispersed over the surface of the specimens. The WSA concrete was found to be more resistant to the effects of thermal cycling in comparison with plain concrete and furthermore, the performance of WSA concrete in response to thermal cycling improved with increasing WSA content. WSA concrete containing tuff aggregate showed more resistance to thermal cycling than that containing basalt aggregate. In response to thermal cycling the WSA concrete at a w/c ratio of 0·5 was observed to show better performance in comparison with WSA concrete at a w/c ratio of 0·7. The air-entrained WSA concrete showed a greater improvement in response to thermal cycling in comparison with non-air-entrained WSA concrete.

Over the past few decades the country of Qatar has been one of the fastest growing economies in the Middle East; it has witnessed a rapid increase in its population, growth of its urban centers, and development of its natural resources. These anthropogenic activities compounded with natural forcings (e.g., climate change) will most likely introduce environmental effects that should be assessed. In this manuscript, we identify and assess one of these effects, namely, ground deformation over the entire country of Qatar. We use the Small Baseline Subset (SBAS) InSAR time series approach in conjunction with ALOS Palsar-1 (Jan. 2007 to Mar. 2011) and Sentinel-1 (Mar. 2017 to Dec. 2019) synthetic aperture radar (SAR) datasets to assess ground deformation and conduct spatial and temporal correlations between the observed deformation with relevant datasets to identify the controlling factors. The findings indicate: (1) the deformation products revealed areas of subsidence and uplift with high vertical velocities of up to 35 mm/yr; (2) the deformation rates were consistent with those extracted from the continuously operating reference GPS stations of Qatar; (3) many inland and coastal sabkhas (salt flats) showed evidence for uplift (up to 35 mm/yr) due to the continuous evaporation of the saline waters within the sabkhas and the deposition of the evaporites in the surficial and near-surficial sabkha sediments; (4) the increased precipitation during Sentinel-1 period compared to the ALOS Palsar-1 period led to a rise in groundwater levels and an increase in the areas occupied by surface water within the sabkhas, which in turn increased the rate of deposition of the evaporitic sediments; (5) high subsidence rates (up to 14 mm/yr) were detected over landfills and dumpsites, caused by mechanical compaction and biochemical processes; and (6) the deformation rates over areas surrounding known sinkhole locations were low (+/−2 mm/yr). We suggest that this study can pave the way to similar countrywide studies over the remaining Arabian Peninsula countries and to the development of a ground motion monitoring system for the entire Arabian Peninsula.

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