Soil column infiltration tests on biomediated capillary barrier systems for mitigating rainfall-induced landslides

Rainfall-induced landslide is a common geohazard in tropical and humid regions. Capillary barrier system (CBS) is a popular and widely studied mitigating measure for rainfall-induced landslides. However, several previous studies have shown that the performance of the conventional CBS under intense rainfalls has not been particularly convincing. This paper aims to explore the feasibility and effectiveness of a newly proposed system, known as “biomediated capillary barrier system” (B-CBS) in minimizing water infiltration into soil. A one-dimensional soil column was used to investigate the infiltration characteristics of the proposed system. The results showed that the B-CBS of biomediated residual soil overlying original residual soil (Test IV) could effectively control the infiltration into soil by taking advantage of the less-permeable biomediated soil cover. The B-CBS of biomediated residual soil overlying gravelly sand (Test V) and the three-layered B-CBS of fine sand overlying gravelly sand and biomediated residual soil (Test VI) showed the best performance in terms of minimizing the water infiltration. A suction of about 5 kPa still remained in the soil column after 60 min of infiltration from the ponded water on the soil surface.     

Up-to-date urban rainstorm intensity formulas considering spatial diversity in China

With accelerating urbanization in China, urban waterlogging has had a serious impact on urban sustainable development and citizen welfare. Simple urban rainstorm intensity formulas with a monotonous frequency distribution type cannot meet the practical needs of urban drainage planning and design. This study focuses on the development of urban rainstorm intensity formulas based on spatial diversity in China. Using the annual maximum sampling method, rainstorm data of 607 cities throughout China were collected into a database, with a total of 24,933 rainfall samples (annual observations) under various specified precipitation durations. The database was used to verify that integrating the Pearson III and Gumbel distributions would constitute an optimal theoretical distribution type, owing to its small error and increased fitting precision. Modification and coordination of four important parameters in the rainstorm intensity formula were done using a digital elevation model, which improved the accuracy of the formula. In addition, precipitation distributions in China were treated from the perspective of topographic features to validate the calculations from up-to-date formulas. Accuracy assessment was accomplished using a national code (GB-50014-2006), GIS-based isograms, and authoritative results from the Hydrological Bureau of the Ministry of Water Resources. This work provides a comprehensive foundation for the establishment of an up-to-date rainstorm intensity formula for China, which can be used widely in different cities.     

Satellite altimetry for measuring river stages in remote regions

The advent in satellite altimetry with the most accurate satellite radar altimeter since 1992 and its successive missions have enabled the routine global monitoring of water-level (or stage) for surface waters and changes in the quantities of dammed water reservoirs. However, satellite altimeter measurements typically have spatial resolution capable of observing only large water bodies, such as major lakes and rivers. This paper addresses the challenges of how to investigate water levels in medium (~?1 km in width) to small (~?100 m and narrower) rivers. Comparisons between the ENVISAT altimetry ICE-1 waveform retracking height and standard water-level measurements for multiple sections of Ohio River, Columbia River, and Red River of the North in the United States (US) reveals that the satellite altimetry measured water levels agree well with those observed at nearby US Geological Survey gaging stations over the 10-year period starting from 2002. The significant results include those obtained at Thompson, North Dakota (ND, correlation coefficient or R value of 0.76 between satellite and in situ water-level measurements) and Fargo, ND (R?=?0.74), where the stream channels of Red River are merely?~?50 m and ~?40 m wide, respectively, under normal climatic conditions. In addition, demonstrations of the approach over largely inaccessible portions of Tigris–Euphrates Rivers and Helmand River in the Middle East aided in understanding hydrology in these systems. This study demonstrates the ability of satellite radar altimetry to characterize rivers in these study regions which are much narrower than 100 m in width.     

Preparation of integrative cubes as a novel biological permeable reactive barrier medium for the enhancement of in situ aerobic bioremediation of nitrobenzene-contaminated groundwater

Recent studies have indicated that in situ aerobic bioremediation is one of the most effective methods for remediating groundwater contaminated with nitrobenzene (NB). Aerobic bioremediation is largely dependent on the maintenance of adequate dissolved oxygen (DO) levels in the groundwater. Traditional in situ aeration has various disadvantages, such as high operational costs and nonuniform aeration. In this study, integrative cubes were prepared and utilized as a novel biological permeable reactive barrier (bio-PRB) medium to enhance the aerobic bioremediation of NB-contaminated groundwater. The results revealed an NB removal rate greater than 98.68% after 15–20 days of continuous oxygen release from the bio-PRB medium. DO concentrations reached 8.0 mg/L during treatment, and NB-degrading bacteria were able to tolerate a range of pH conditions. This multifaceted bio-PRB medium can simultaneously adsorb and biodegrade NB, release oxygen, and neutralize the pH with phosphate buffer. The results of this study suggest that this bio-PRB medium represents a highly effective in situ bioremediation method for NB-contaminated groundwater.     

An insight into the surface velocity of Inylchek Glacier and its effect on Lake Merzbacher during 2006–2016 with Landsat time-series imagery

Mountain glacier is one of the extremely sensitive indicators for climate change, and its surface motion distribution and corresponding variation are valuable information for understanding ice mass exchange and glacier dynamics. This paper presents the long-term ice velocity distributions of Inylchek Glacier in the Tianshan region by pixel-tracking algorithm with time-series Landsat imagery acquired during 2006–2016. Then the monitored ice motion fields of Inylchek Glacier were carefully analyzed and revealed a generally similar spatial distribution characteristic. Most of the ice of the North Inylchek Glacier remains in a stagnant state except for the upstream part, but a relatively high velocity of 20–40 cm/day with an RMSE of 3 cm/day was observed on most part of the South Inylchek Glacier, except for the slow-moving glacier terminus. We also state the glacier dynamics around Lake Merzbacher and their possible effect on its glacier lake outburst flood (GLOF) risk. Besides, the surface velocity distribution on South Inylchek Glacier surface during the ablation period from 2014 to 2016 was also established and also compared with annual velocity. The corresponding difference yields that there is a positive relation between ice motion and temperature variation. Therefore, the time-series ice surface motion yielded by the Landsat imagery thus could provide us an efficient and low-cost way to analyze the current state and changes in glaciers, thanks to the continuous and regular spaceborne observations provided by the Landsat satellites.     

Development and verification of the comprehensive model for physical properties of hydrate sediment

Natural gas hydrate is widely distributed all over the world and may be a potential resource in the near future, whereas hydrate dissociation during the development affects wellbore stability and drilling safety. However, the present modeling of hydrate reservoir parameters ignored the influence of effective stress and only considered the hydrate saturation. In this paper, a series of stress sensitivity experiments for the unconsolidated sandstone were carried out, and the influence of mean effective stress on physical parameters was obtained; a comprehensive model for the physical parameters of hydrate reservoir was developed subsequently. With the help of ABAQUS finite element software, the established comprehensive model was verified by the use of the wellbore stability numerical model of hydrate reservoir. The verification results show that ignoring the effect of mean effective stress on the parameters of hydrate formation aggravates the invasion of drilling fluid into the hydrate formation. Besides, ignoring the stress sensitivity of reservoir physical parameters will underestimate the wellbore instability during hydrate drilling, which will be a threat to the safety of gas hydrate drilling. At the end of the drilling operation, the maximum plastic strain of the model for considering and not considering stress sensitivity was 0.0145 and 0.0138, respectively. Therefore, the established comprehensive model will provide a theoretical support for accurately predicting the engineering geological disasters in hydrate development process.     

Use of photo-based 3D photogrammetry in analysing the results of laboratory pressure grouting tests

This paper presents a non-destructive, low-cost, photo-based, 3D reconstruction technique for characterizing geo-materials with irregular shapes of a relatively large size. After being validated against two traditional volume measurement methods, namely the vernier caliper method and the fluid displacement method for regular and irregular shapes, respectively, 3D photogrammetry was used to analyse the grout bulbs formed in laboratory pressure grouting tests. The reconstructed 3D mesh model of the sample provides accurate and detailed 3D vertex data, which allowed the volume, densification efficiency and bleeding behaviour of the grout bulbs to be analysed. Comparing the bulb section views at different grouting pressures also offers an intuitive observation of the grout development and propagation process. Moreover, the 3D vertex data and surface area included in the model are of great importance in validating numerical predictions of the pressure grouting process and analysing the interface shear resistance of grouted soil nails or anchors. Compared to existing approaches, the new 3D photogrammetry method possesses several key advantages: (a) it does not require expensive, specialized equipment; (b) samples are not destroyed or modified during testing; (c) it allows to reconstruct objects of various scales and (d) the software is public domain. Therefore, the adoption of this 3D photogrammetry method will facilitate research in the pressure grouting process and can be extended to other problems in geotechnical engineering.     

Soil wettability in ground engineering: fundamentals,methods, and applications

Wettability is a fundamental property controlling the extent of wetting in flat and granular solids. In natural soils, wettability affects a wide variety of processes including infiltration, preferential flow and surface runoff. In mineral processing, wettability is paramount in enhancing the efficiency of separation of minerals from gangue. The manipulation of surface wettability is equally crucial in many industrial applications. For instance, superhydrophobic surfaces are those on which water drops roll off easily and as such are used for self-cleaning applications. Therefore, while wettability is strongly cross-disciplinary, its evolution has been discipline-specific with a direct extrapolation or transfer of concepts, approaches, and methods to ground engineering unlikely to remain valid. This paper synthesizes relevant aspects from surface chemistry, materials science, mining engineering, and soil science, and discusses their implications within the context of new granular materials that resist wetting, for use in barriers or ground improvement and, in unsaturated soils, where the effects of wettability have been documented.     

Study on the natural radioactivity level of stone coal-bearing strata in East China

Based on γ-radiation dose rate and radon concentration measurements and ²³⁸U, ²³²Th, ²²⁶Ra, and ⁴⁰K radionuclide testing, this study identifies the radioactive anomalies of stone coal-bearing strata in East China and evaluates the natural radioactivity levels in the air, solid, water and plant media in the typical area of the regional stone coal-bearing layers. The stone coal-bearing strata in East China occur in the lower Cambrian system along the margin of the Yangtze block; additionally, the radioactive anomaly area is sporadically distributed in the stone coal-bearing layers. The background values of ²³⁸U, ²³²Th, ²²⁶Ra, and ⁴⁰K are higher in the stone coal-bearing areas, and the spatial distribution of these natural radionuclides shows significant variability. ²³⁸U and ²²⁶Ra clearly accumulate in the coal, coal gangue and soil and are the main sources of the environmental radiation in coal mines. The γ-radiation shows a higher background value in the stone coal-bearing area, and this radioactive pollution cannot be ignored. Typically, the effective dose of γ-radiation exceeds the limit value of 5 mSv/a, and the total α and total β concentrations of the groundwater are 10–30 times the limit value at some points. The residents near the mining area are subjected to a higher radiation dose, and the groundwater, building materials, and plants have been contaminated by the radioactive pollution sporadically through time. It is necessary to strengthen the monitoring work of radioactive environments and to take appropriate control measures.     

Effect of climate change on water resources in the Yuanshui River Basin: a SWAT model assessment

The Yuanshui River Basin is one of the most important river basins ensuring food production and livelihoods in the Hunan and Guizhou Provinces of China. Based on digital elevation model, land use, soil, and meteorological data, the soil and water assessment tool was used to analyze the response of water resources in the basin to climate change. Specifically, the monthly runoff from the Yuanshui River Basin was simulated. Runoff measurements from the 1961–1990 series were used to calibrate model parameters, and measurements from the 1991–2010 series were used for model validation. The Nash–Sutcliffe efficiency coefficient, correlation coefficient, and water balance error were used to evaluate the simulation results; the values obtained for these parameters were 0.925, 0.929, and 2.0%, respectively, indicating that the established model can be applied successfully to runoff simulations. To evaluate the effects of climate change and human activities on runoff, 24 different climate scenarios were modeled. By comparing the model simulation results with the baseline scenario, the effects of climate change were analyzed by year, during the dry season, and during extremely dry conditions. The results showed that runoff decreased with increasing air temperature and decreasing precipitation, and that the effects of rainfall on runoff were greater than those of air temperature. Under the same baseline conditions, the effects of climate change on runoff were most pronounced during extremely dry months.