[en] This paper discusses the geological and hydrogeological features of Quaternary deposits in Tianjin as well as the geohazards related to groundwater hydrology in this region. The soft soil deposits, comprising silt, sand, silty clay and clay, are composed of four aquifer groups. In the first aquifer group, one phreatic aquifer and two confined aquifers have relationships with underground construction in the urban area. These three aquifers are separated by two aquitards and collectively form a multi-aquifer system. During geotechnical construction, potential geohazards present are related to the groundwater, which include water-in-rushing, quicksand and piping hazards. To prevent the aforementioned geohazards, dewatering is conducted; however, groundwater pumping may result in large settlements of the surrounding ground. To reduce pumping-induced settlement, the dewatering–waterproofing system has been adopted. According to the characteristics of the subsoil, excavation depth and the surrounding environment, the dewatering system can be divided into five patterns. In the first four patterns, when pumping is conducted in the excavation pit, the groundwater head in the adjacent aquifers outside the pit decreases due to the leakage effect of the aquitards located between the aquifers. In the fifth pattern, waterproof curtain has cut off the aquifers completely and dewatering in the pit cannot result in settlement around excavation pit. To avoid geohazards related to groundwater hydrology, countermeasures recommended include construction of an effective waterproof curtain, selection of a reasonable excavation dewatering pattern and withdrawal of required groundwater.

[en] Highlights: • Ariake Sea has displayed signs of environmental deterioration in recent years. • Possible mechanism is decrease in tidal amplitude, tidal current and tidal flats. • The Isahaya Bay reclamation is one of the potential causes for environmental changes. • Dispute has arisen concerning opening the reclamation project dike's floodgates. • Countermeasures for reviving Ariake Sea as a sustainable ecosystem are suggested. - Abstract: This paper reviews the recent environmental deterioration in Ariake Sea, Japan, including an increased frequency of red tides and hypoxic waters and decreased fishery production. Analysis of the mechanisms of environmental deterioration suggests that it is possibly induced by the decrease in tidal flat area, decreases in the tide and tidal current and changes in the sediment environment. The Isahaya Bay reclamation project resulted in the loss of 1550 ha of tidal flats, and is one of the possible reasons for the decreases in the tide and tidal current. Therefore, some fishermen and researchers believe that opening the reclamation project dike's floodgates is an effective environmental restoration countermeasure for Ariake Sea. However, the central government decided not to open the floodgates at present due to strong opposition from local farmers, and some researchers believe that the influences of the Isahaya Bay reclamation project on the environmental changes outside of Isahaya Bay are minor. Several lawsuits regarding these relationships and the opening of the dike's floodgates are currently under dispute. To revive Ariake Sea as a sustainable ecosystem, other countermeasures for environmental restoration are suggested and discussed in this paper.

[en] Fire hazards are considered to be one of the most dangerous hazards in the world, which could lead to significant casualties and economic losses. This paper summarizes the fire hazards in China during the period from 2000 to 2016 in daily life, transportation, storages, industrial production, etc. In this research, the tempo-spatial distribution of fire hazards that result in fatalities, injuries and direct economic losses was studied. The place distribution of fire hazards was analyzed, and the primary causes of fire hazards were also discussed. In addition, an extensive fire hazard induced by an explosion incident at Tianjin harbor was studied and discussed. Linear regression relationships between the four indicators of fire hazard and the average gross domestic product were developed and analyzed. Based on the analyzed results, recommended mitigation measures against fire hazards were recommended.

No abstract available

[en] In this research, a low-carbon stabilization method was studied using Recycled Asphalt Pavement (RAP) and Fly Ash (FA) geopolymers as a sustainable pavement material. The liquid alkaline activator (L) is a mixture of sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH), and high calcium FA is used as a precursor to synthesize the FA-RAP geopolymers. Unconfined Compressive Strength (UCS) of RAP-FA blend and RAP-FA geopolymer are investigated and compared with the requirement of the national road authorities of Thailand. The leachability of the heavy metals is measured by Toxicity Characteristic Leaching Procedure (TCLP) and compared with international standards. The Scanning Electron Microscopy (SEM) analysis of RAP-FA blend indicates the Calcium Aluminate (Silicate) Hydrate (C-A-S-H) formation, which is due to a reaction between the high calcium in RAP and high silica and alumina in FA. The low geopolymerization products (N-A-S-H) of RAP-FA geopolymer at NaOH/Na₂SiO₃ = 100:0 are detected at the early 7 days of curing, hence its UCS is lower than that of RAP-FA blend. The 28-day UCS of RAP-FA geopolymers at various NaOH/Na₂SiO₃ ratios are significantly higher than that of the RAP-FA blend, which can be attributed to the development of geopolymerization reactions. With the input of Na₂SiO₃, the highly soluble silica from Na₂SiO₃ reacted with leached silica and alumina from FA and RAP and with free calcium from FA and RAP; hence the coexistence of N-A-S-H gel and C-A-S-H products. Therefore, the 7-day UCS values of RAP-FA geopolymers increase with decreasing NaOH/Na₂SiO₃ ratio. TCLP results demonstrated that there is no environmental risk for both RAP-FA blends and RAP-FA geopolymers in road construction. The geopolymer binder reduces the leaching of heavy metal in RAP-FA mixture. The outcomes from this research will promote the move toward increased applications of recycled materials in a sustainable manner in road construction. - Highlights: • Environmental evaluation of fly ash (FA) based geopolymer stabilized Recycled Asphalt Pavement (RAP). • Microstructural development was examined via XRD and SEM analyses. • UCS of RAP-FA geopolymers and RAP-FA blends were compared with road authorities' requirements. • The leachability of the heavy metals is measured by TCLP and compared with international standards.

[en] Highlights: • Regional flood risk level was evaluated using both AHP and I-AHP methods. • Flood risk level of metro system was evaluated based on flood risks within 500 m range from metro lines. • Comparative results between AHP and I-AHP assessment results were analyzed. • Results were validated using the observed flood hazards on May 10, 2016, in Guangzhou, China. Metro system is a vital component of mass transportation infrastructure, providing crucial social and economic service in urban area. Flood events may cause functional disruptions to metro systems; therefore, a better understanding of their vulnerability would enhance their resilience. A comparative study of flood risk in metro systems is presented using the analytic hierarchy process (AHP) and the interval AHP (I-AHP) methods. The flood risk in the Guangzhou metro system is evaluated according to recorded data. Evaluated results are validated using the flood event occurred in Guangzhou on May 10, 2016 (hereinafter called “May 10th event”), which inundated several metro stations. The flood risk is assessed within a range of 500 m around the metro line. The results show that >50% of metro lines are highly exposed to flood risk, indicating that the Guangzhou metro system is vulnerable to flood events. Comparisons between results from AHP and I-AHP show that the latter yields a wider range of high flooding risk than the former.

[en] Highlights: • Evaluation of Fly Ash (FA) based geopolymer stabilized lateritic soil/GBFS blend. • Role of L, NaOH/Na₂SiO₃, GBFS content, and curing time were investigated. • Microstructural development was examined via XRD and SEM analyses. • UCS of FA geopolymer stabilized blends was compared with road authorities requirements. - Abstract: Granulated Blast Furnace Slag (GBFS) was used as a replacement material in marginal lateritic soil (LS) while class C Fly Ash (FA) was used as a precursor for the geopolymerization process to develop a low-carbon pavement base material at ambient temperature. Unconfined Compression Strength (UCS) tests were performed to investigate the strength development of geopolymer stabilized LS/GBFS blends. Scanning Electron Microscopy and X-ray Diffraction analysis were undertaken to examine the role of the various influencing factors on UCS development. The influencing factors studied included GBFS content, Na₂SiO₃:NaOH ratio (NS:NH) and curing time. The 7-day soaked UCS of FA geopolymer stabilized LS/GBFS blends at various NS:NH ratios tested was found to satisfy the specifications of the Thailand national road authorities. The GBFS replacement was found to be insignificant for the improvement of the UCS of FA geopolymer stabilized LS/GBFS blends at low NS:NH ratio of 50:50. Microstructural analysis indicated the coexistence of Calcium Silicate Hydrate (CSH) and Sodium Alumino Silicate Hydrate products in FA geopolymer stabilized LS/GBFS blends. This research enables GBFS, which is traditionally considered as a waste material, to be used as a replacement and partially reactive material in FA geopolymer pavement applications.