Soil improvement via MICP (microbially induced carbonate precipitation) technologies has recently received widespread attention in the geoenvironmental and geotechnical fields. The durability of ...MICP-treated samples remains a critical concern in this novel method. In this work, fiber (jute)-reinforced MICP-treated samples were investigated to evaluate their durability under exposure to distilled water (DW) and artificial seawater (ASW), so as to advance the understanding of long-term performance mimicking real field conditions, along with improvement of the MICP-treated samples for use in coastal erosion protection. Primarily, the results showed that the addition of fiber (jute) improved the durability of the MICP-treated samples by more than 50%. Results also showed that the wet-dry (WD) cyclic process resulted in adverse effects on the mechanical and physical characteristics of fiber-reinforced MICP-treated samples in both DW and ASW. The breakdown of calcium carbonates and bonding effects in between the sand particles was discovered to be involved in the deterioration of MICP samples caused by WD cycles, and this occurs in two stages. The findings of this study would be extremely beneficial to extend the insight and understanding of improvement and durability responses for significant and effective MICP treatments and/or re-treatments.
On 30th October 2020, the eastern Aegean Sea was shaken by a Mw = 7.0 earthquake. The epicenter was located near the northern coasts of Samos island. This tectonic event produced an uplift of the ...whole island as well as several cases of infrastructure damage, while a small tsunami followed the mainshock. Underwater and coastal geological, geomorphological, biological observations and measurements were performed at the entire coast revealing a complex character for the uplift. At the northwestern part of the island, maximum vertical displacements of +35 ± 5 cm were recorded at the northwestern tip, at Agios Isidoros. Conversely, the southeastern part was known for its subsidence through submerged archaeological remains and former sea level standstills. The 2020 underwater survey unveiled uplifted but still drowned sea level indicators. The vertical displacement at the south and southeastern part ranges between +23 ± 5 and +8 ± 5 cm suggesting a gradual fading of the uplift towards the east. The crucial value of tidal notches, as markers of co-seismic events, was validated from the outcome of this study. The co-seismic response of Samos coastal zone to the 30th October earthquake provides a basis for understanding the complex tectonics of this area.
Two well-developed late Pleistocene dune fields have been identified on the western and eastern side of Akrotiri promontory (Lemesos, Cyprus). The dune fields extend immediately from the low level of ...their source beaches onto higher ground (>48 m amsl). Geomorphic observations supported by OSL dating and sedimentological data provided evidence of the dune development and for the palaeogeographic reconstruction of the area. Relative sea level changes and wave action during the upper Pleistocene and Holocene played an important role into the development of the palaeolandscape and affected the formation of the dunes. From the collected data the development of the western dune field started at 56.2 ± 5.5 ka when the relative sea level was at approximately −60 m and contributed to the development of the western tombolo of the area whereas the eastern dune field developed in the late Holocene, after the formation of the eastern spit that resulted in the formation of the Akrotiri Salt lake.
Coastal erosion is a major coastal hazard in Greece. This work aimed to assess the perceptions of citizens about coastal erosion. We developed a questionnaire containing 25 questions that was ...distributed online and filled out by 1636 respondents. A surprising find was that 33% of the respondents were not aware of the phenomenon of coastal erosion. On the other hand, among those respondents who are aware of coastal erosion, there is a basic understanding of the major factors promoting erosion and its impacts. Responses also highlighted a lack of information and awareness from the media and public authorities, while the vast majority considered that protecting the coast from erosion should be important or a priority. Our findings stress the need for awareness-raising activities about this important natural hazard.
The goal of our research is to educate students at primary schools in Greece on rapid ongoing natural disasters through the holistic-interdisciplinary science, technology, engineering, art, and ...mathematics (STEAM)-based method. As a learning tool, an integrated program was designed with a variety of actions and activities aiming to experientially educate students in a holistic-interdisciplinary STEAM-based way. These are based on science, technology, engineering, art, and mathematics. This three-month program was chosen to be conducted in a private school of Attica, Greece, for the course “skill laboratories”. It was conducted to students of the second (seven years old) and the fifth grade of primary school (10 years old). In the beginning and the end of the program, the 133 participating students were given questionnaires, in order for the program to be assessed as to whether it managed to accomplish the initial goals. A total of 266 digital questionnaires were collected through ArcGIS survey123 application (part of geospatial cloud by Esri), which is an integrated solution for the creation, distribution and analysis of survey data. From the statistical analysis of their answers, the conclusion was that the vast majority of the students felt stress, confusion, depression and shock when they saw a forest fire. Most kids stated that they have thought of the consequences of extended wildfires and the flood events that follow.
In some islands of the Aegean, there is evidence of the occurrence of repeated rapid subsidences during the Late Holocene. In this paper, the shape of tidal notches that may be well-preserved ...underwater is recalled in order to reconstruct sequences of coseismic subsidences and other relative sea-level changes, which occurred during, at least, the last few millennia. A reanalysis of the published measurements of submerged tidal notches in several islands reveals that subsidence trends in many areas of the Aegean are not continuous with gradual movement but, also, are the result of repeated coseismic vertical subsidences of some decimetres at each time. The estimated average return times are of the order of approximately some centuries to one millennium. Although the results cannot be used for short-term predictions of earthquakes, they may provide useful indications on the long-term tectonic trends that are active in the Aegean region.
Remains of past sea levels such as tidal notches may provide valuable information for the investigation of relative sea-level changes (RSL) of eustatic/tectonic origin. In this review, we focus on ...case studies of coastal changes from the Corinth Gulf, where impacts of past earthquakes can be traced through various indicators. The southern coast has undergone a tectonic uplift during the Holocene, whereas the northern coast has undergone subsidence. The magnitude of RSL fall in the south Corinth Gulf is larger than RSL rise in the north. Exploiting previous measurements and datings, we created a geodatabase regarding the relative sea-level changes of the whole gulf, including geodetic data based on permanent GNSS observations. The combination of geomorphological (long-term) and geodetic (short-term) data is a key advance for this area, which is characterized by fast rates of N-S crustal extension and strong earthquakes. The joint dataset fits the tectonic model of an active half-graben where the hanging wall (northern coast) subsides and the footwall (southern coast) is uplifted. The highest uplift rates (3.5 mm/year) are near Aigion, which indicates an asymmetric localization of deformation inside this active rift.
In recent years, traditional material for coastal erosion protection has become very expensive and not sustainable and eco-friendly for the long term. As an alternative countermeasure, this study ...focused on a sustainable biological ground improvement technique that can be utilized as an option for improving the mechanical and geotechnical engineering properties of soil by the microbially induced carbonate precipitation (MICP) technique considering native ureolytic bacteria. To protect coastal erosion, an innovative and sustainable strategy was proposed in this study by means of combing geotube and the MICP method. For a successful sand solidification, the urease activity, environmental factors, urease distribution, and calcite precipitation trend, among others, have been investigated using the isolated native strains. Our results revealed that urease activity of the identified strains denoted as G1 (Micrococcus sp.), G2 (Pseudoalteromonas sp.), and G3 (Virgibacillus sp.) relied on environment-specific parameters and, additionally, urease was not discharged in the culture solution but would discharge in and/or on the bacterial cell, and the fluid of the cells showed urease activity. Moreover, we successfully obtained solidified sand bearing UCS (Unconfined Compressive Strength) up to 1.8 MPa. We also proposed a novel sustainable approach for field implementation in a combination of geotube and MICP for coastal erosion protection that is cheaper, energy-saving, eco-friendly, and sustainable for Mediterranean countries, as well as for bio-mediated soil improvement.
Many issues arise from the recession of sea cliffs, including threats to coastal communities and infrastructure. The best proxy to study cliff instability processes is the cliff face evolution. ...Unfortunately, due to its verticality, this proxy is difficult to observe and measure. This study proposed and compared three remote sensing methods based on structure-from-motion (SfM) photogrammetry or stereorestitution: boat-based SfM photogrammetry with smartphones, unmanned aerial system (UAS) or unmanned aerial vehicle (UAV) photogrammetry with centimetric positioning and Pléiades tri-stereo imagery. An inter-comparison showed that the mean distance between the point clouds produced by the different methods was about 2 m. The satellite approach had the advantage of covering greater distances. The SfM photogrammetry approach from a boat allowed for a better reconstruction of the cliff foot (especially in the case of overhangs). However, over long distances, significant geometric distortions affected the method. The UAS with centimetric positioning offered a good compromise, but flight autonomy limited the extent of the monitored area. SfM photogrammetry from a boat can be used as an initial estimate for risk management services following a localized emergency. For long-term monitoring of the coastline and its evolution, satellite photogrammetry is recommended.
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