利用GPR天线-目标极化的瞬时属性分析方法探测LNAPL污染土壤

轻非水相流体(LNAPL)泄漏后会对土壤和地下水造成严重污染,为了准确探测出LNAPL泄漏范围,本文将GPR天线-目标极化的瞬时属性分析方法应用于轻非水相流体污染土壤探测的研究中。采用注入柴油的石英砂砂箱在实验室建立污染土壤模型,利用探地雷达对该污染土壤分别进行天线方位为0°、90°的测量。LNAPL土壤污染物形状、大小、结构并不规则,因此可以通过0°和90°方位天线测量来分析天线-目标极化特征,了解目标物的走向、形状等地下介质信息。通过对预处理后的包含天线-目标极化特征的信息进行瞬时属性分析,LNAPL污染范围可以被清晰地识别,提高了GPR探测能力。     

Seasonal variability of oxygen and hydrogen isotopes in a wetland system of the Yunnan-Guizhou Plateau,southwest China: a quantitative assessment of groundwater inflow fluxes

The Caohai Wetland serves as an important ecosystem on the Yunnan–Guizhou Plateau and as a nationally important nature reserve for migratory birds in China. In this study, surface water, groundwater and wetland water were collected for the measurement of environmental isotopes to reveal the seasonal variability of oxygen and hydrogen isotopes (δ¹⁸O, δD), sources of water, and groundwater inflow fluxes. Results showed that surface water and groundwater are of meteoric origin. The isotopes in samples of wetland water were well mixed vertically in seasons of both high-flow (September) and low-flow (April); however, marked seasonal and spatial variations were observed. During the high-flow season, the isotopic composition in surface wetland water varied from ?97.13 to ?41.73‰ for δD and from ?13.17 to ?4.70‰ for δ¹⁸O. The composition of stable isotopes in the eastern region of this wetland was lower than in the western region. These may have been influenced by uneven evaporation caused by the distribution of aquatic vegetation. During the low-flow season, δD and δ¹⁸O in the more open water with dead aquatic vegetation ranged from ?37.11 to ?11.77‰, and from ?4.25 to ?0.08‰, respectively. This may result from high evaporation rates in this season with the lowest atmospheric humidity. Groundwater fluxes were calculated by mass transfer and isotope mass balance approaches, suggesting that the water sources of the Caohai Wetland were mainly from groundwater in the high-flow season, while the groundwater has a smaller contribution to wetland water during the low-flow season.     

Characterizing groundwater/surface-water interactions in the interior of Jianghan Plain,central China

Hydrogeology Journal - Quantifying groundwater/surface-water interactions is essential for managing water resources and revealing contaminant fate. There has been little concern on the exchange...     

A non-hydrostatic model for the numerical study of landslide-generated waves

This paper proposes and demonstrates a two-layer depth-averaged model with non-hydrostatic pressure correction to simulate landslide-generated waves. Landslide (lower layer) and water (upper layer) motions are governed by the general shallow water equations derived from mass and momentum conservation laws. The landslide motion and wave generation/propagation are separately formulated, but they form a coupled system. Our model combines some features of the landslide analysis model DAN3D and the tsunami analysis model COMCOT and adds a non-hydrostatic pressure correction. We use the new model to simulate a 2007 rock avalanche-generated wave event at Chehalis Lake, British Columbia, Canada. The model results match both the observed distribution of the rock avalanche deposit in the lake and the wave run-up trimline along the shoreline. Sensitivity analyses demonstrate the importance of accounting for the non-hydrostatic dynamic pressure at the landslide-water interface, as well as the influence of the internal strength of the landslide on the size of the generated waves. Finally, we compare the numerical results of landslide-generated waves simulated with frictional and Voellmy rheologies. Similar maximum wave run-ups can be obtained using the two different rheologies, but the frictional model better reproduces the known limit of the rock avalanche deposit and is thus considered to yield the best overall results in this particular case.     

Development mechanism for the landslide at Xinlu Village,Chongqing, China

Due to the continuous and intense rainfall from June 26 to 28, 2016, Xinlu Village in Ganshui Town, Qijiang District, Chongqing, experienced a unitary-slip landslide at approximately UTC+8 19:30 on June 28. This landslide disrupted the Chuan-Qian railway and damaged four residential buildings. To analyze and rehabilitate the landslide, the engineering geology, hydrological conditions, and deformation instability mechanism of this landslide were investigated and comprehensively analyzed based on an in situ survey, geophysical drilling, and a laboratory quick-shearing test. The results show that the landslide is a typical gradual progressive landslide.     

Evaluating igneous sources of the Taveyannaz formation in the Central Alps by detrital zircon U–Pb age dating and geochemistry

Late Palaeogene syn-tectonic volcanic products have been found in the Northern Alpine foreland basin and in the South Alpine hemipelagic basin. The source of abundant volcanic fragments is still in debate. We analyzed the geochronology and geochemistry of detrital zircons, and evaluated their temporal and genetic relationships with potential volcanic sources. The study shows that the detrital zircon U–Pb age patterns have two major age groups: a dominance (ca. 90%) of pre-Alpine zircons was found, as commonly observed in other Alpine flysch formations. These zircons apparently derived from erosion of the early Alpine nappe stack in South Alpine and Austroalpine units. Furthermore, a few Neo-Alpine zircons (ca. 10%) have ages ranging from Late Eocene to Early Oligocene (~ 41–29 Ma). Both source materials were mixed during long riverine transport to the basin margins before being re-deposited by gravity flows. These Palaeogene ages match with the activity of Peri-Adriatic magmatism, including the Biella volcanic suite as well as the Northern Adamello and Bergell intrusions. The values of REE and ¹⁷⁶Hf/¹⁷⁷Hf_(t) ratios of the Alpine detrital zircons are in line with the magmatic signatures. We observe an in time and space variable supply of syn-sedimentary zircons. From late Middle Eocene to Late Eocene, basin influx into the South Alpine and Glarus (A) basins from the Northern Adamello source is documented. At about 34 Ma, a complete reorganisation is recorded by (1) input of Bergell sources into the later Glarus (B) basin, and (2) the coeval volcaniclastic supply of the Haute-Savoie basin from the Biella magmatic system. The Adamello source vanished in the foreland basin. The marked modification of the basin sources at ~ 34 Ma is interpreted to be initiated by a northwestern shift of the early Alpine drainage divide into the position of the modern Insubric Line.     

Deformation mechanism of strain localization in 2D numerical interface tests

Heterogeneity arises in soil subjected to interface shearing, with the strain gradually localizing into a band area. How the strain localization accumulates and develops to form the structure is crucial in explaining some significant constitutive behaviors of the soil–structural interface during shearing, for example, stress hardening, softening, and shear-dilatancy. Using DEM simulation, interface shear tests with a periodic boundary condition are performed to investigate the strain localization process in densely and loosely packed granular soils. Based on the velocity field given by grains’ translational and rotational velocities, several kinematic quantities are analyzed during the loading history to demonstrate the evolution of strain localization. Results suggest that tiny concentrations in the shear deformation have already been observed in the very early stage of the shear test. The degree of the strain localization, quantified by a proposed new indicator, α, steadily ascends during the stress-hardening regime, dramatically jumps prior to the stress peak, and stabilizes at the stress steady state. Loose specimen does not develop a steady pattern at the large strain, as the deformation pattern transforms between localized and diffused failure modes. During the stress steady state of both specimens, remarkable correlations are observed between α and the shear stress, as well as between α and the volumetric strain rate.     

A simple approach to evaluating leakage through thin impervious element of high embankment dams

Internal erosion is the most common reason which induces failure of embankment dams besides overtopping. Relatively large leakage is frequently concentrated at defects of impervious element, and this will lead to eventual failure. The amount of leakage depends not only on integrity of impervious element, but also on dam height, shape of valley, shape of impervious element and water level in reservoir. The integrity of impervious element, which represents the relative level of seepage safety, is not easy to be determined quantitatively. A simple method for generalization of steady seepage state of embankment dams with thin impervious element is proposed in this paper. The apparent overall value of permeability coefficient for impervious element can be obtained by this method with reasonable accuracy and efficiency. A defect parameter of impervious element is defined as an index to characterize seepage safety of embankment dams. It equals the ratio of the apparent overall value of permeability coefficient to the measured value in laboratory for intact materials. Subsequently, seepage safety of three dams is evaluated and the evolution of defect level of impervious element of dams is investigated. It is proved that the newly proposed method in this paper is feasible in the evaluation of relative seepage safety level of embankment dams with thin impervious element.     

Study on the quantitative relationship between soil in situ strength and drilling parameters

The rational use of drilling parameters is a hot issue in the field of geotechnical engineering and geological engineering. A new method, for evaluating the bearing capacity of soils using drilling parameters was proposed. First, through the mechanical analysis of the drill bit, the preconditions and theoretical formulas for calculating the bearing capacity of soils using the bit’s torque are clearly defined. Next, drilling tests and dynamic cone penetration tests were performed on miscellaneous fill, silty clay, sandy clay, medium coarse sand and gravel sand, and the empirical formula for calculating the bearing capacity of these soils were given. Then, using the new method and the empirical formula, the bearing capacity of the soil under the roadbed was examined. The test results show that the bit’s torque is a good parameter for the evaluation of the bearing capacity of the soil. Finally, the application scope of the new method and the empirical formula is discussed, and the subsequent research directions are pointed out.     

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.