Ground deformation can cause serious environmental issues such as infrastructure damage, ground compaction, and reducing the ground capacity to store water. Mashhad, as one of the largest and most populated cities in the Middle East, has been suffering from extreme subsidence. In the last decade, some researchers have been interested in measuring land subsidence rates in the Mashhad valley by InSAR techniques. However, most of those studies were based on inaccurate measurements introducing uncertainties in the resulting subsidence rates. These researches used a small number of EnviSat data with long perpendicular and inhomogeneous temporal baseline. This paper seeks to determine the subsidence rate in urban areas of Mashhad in recent years, the threat that was neglected by the city managers and decision-makers. For this purpose, the Persistent Scatterer inSAR technique was applied in the study area using two time-series of descending and ascending Sentinel-1A acquisitions between 2014 and 2017. The results demonstrated the maximum line-ofsight deformation rate of 14.6 cm/year and maximum vertical deformation (subsidence) rate about 19.1 cm/year which could have irreversible consequences. The results were assessed and validated using piezometric data, GPS stations, and geotechnical properties. This assessment confirms that the main reason for subsidence in the interested area is groundwater over-extraction. Also, investigation of geotechnical properties shows that thick fine-grained layers in the northwest of the city could strongly affect the results. At the end of this paper, a new simplified method was proposed to estimate specific storage in special cases to predict the subsidence rate. Ground deformation has been reported as one of the severe geological hazards around the world 1. It is mainly due to the fact that anthropogenic activities such as fluid extraction or injection, underground excavations, and expanding construction have been increased in many regions as a forthcoming problem 2-5. Multiple studies have reported that several areas are suffering from land subsidence as a result of fluid overextraction. These areas include but are not limited to cities in
Sand pluviation is a method used to prepare a model sand specimen to carry out some particular laboratory tests such as static and dynamic tests on footings, retaining walls, piles, as well as calibration of static and dynamic penetrometers. Preparation of uniform reconstituted sand specimens of required density is a prerequisite for obtaining reliable results. In this paper, two rainer systems, which are capable to prepare homogeneous sand specimens, are introduced. The first is a rainer system with a perforated plate and the second is a portable curtain rainer system. The portable curtain rainer system essentially consisting of a sand storage, flexible hose, a hopper, rigid tubes, and curtain with different opening widths. This study aims to reach a better understanding of the effects of deposition intensity (DI) and height of fall (HF) on the relative density (RD) of reconstituted sand specimens. The uniformity of the sand bed is verified by measuring the relative densities of 20 samples at different locations of the tank. By using a portable curtain rainer system, large uniform sand specimens with a wide range of RD ¼ 23-96% can be achieved. The results demonstrate that at a lower value of HF, the variation of RD is significant, while it has an insignificant effect on RD for values of HF ≥ 600 mm. Furthermore, in order to achieve a dense to very dense sand bed, the DI should be controlled. It was also observed that both systems significantly improve the horizontal and vertical homogeneities of the sand specimens. With an increase in the RD of reconstituted sand specimens, higher repeatability of uniform pluviation was achieved.
Volcanic ashes (VA) are one of the by-products of explosive volcanic eruptions. They can be used as a soil stabilizer due to their cementitious properties as an eco-friendly soil stabilization approach. In this study, the impact of VA as an additive material (up to 20%) was investigated on the behavior of a clayey soil under one-dimensional compression tests and uniaxial compression tests. To this aim, the VA percentage effect, curing conditions, i.e. the optimum moisture content (OMC) and saturated sample, and curing time, on the oedometer modulus, and the uniaxial compression strength (UCS) are investigated. Results show that the addition of VA increases the UCS continuously in saturated conditions. However, this improvement is considerable for 5% additional VA at the OMC state and it induces 325% improvement in UCS. The maximum improvement of UCS occurs at 20% addition of VA in saturated condition. It was also revealed that VA-soil mixtures are more sustainable at low stress levels and the oedometer modulus increases with the VA addition. A long-term curing time leads to an increase of the fabricated bonds due to the pozzolanic reaction. Additional VA has no significant effect on the consolidation parameters specifically for short-term curing time.
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