查看更多>>摘要：? 2022 Elsevier B.V.The high and steep anti-dip slopes at the dam site of the Miaowei Hydropower Station, located in the Lancang River valley in southwest China, are subjected to clusters of deep-seated toppling deformations (DSTDs). Geological mapping, exploratory adits, electron spin resonance (ESR) dating, and kinematic monitoring were conducted on the right bank slopes to explore the causes of failure and kinematic patterns of the DSTDs. The studied DSTDs formed in anti-dip metamorphic rock layers during the youngest terraces owing to the rapid incision of the V-shaped river valley under high tectonic stress. The maximum horizontal depth of toppling rocks on right bank slopes was greater than 200 m. Quantitative indices concerning the dip angle of the toppled rock layers, tensile aperture, and elastic wave velocity of rock masses, as well as qualitative indices including rock weathering and unloading, can be used as a comprehensive indicator system for characterizing the intensity of toppling. Toppled rock layers can be categorized into four zones according to toppling intensity: extremely intense, intense, moderate, and weak, as characterized by complete block detachment, composite tensile-shear fracture, tensile fracture, and reverse slip, respectively. Excavation at the slope toe triggered shallow sliding failures along the toppling-induced cataclinal discontinuities in zones of extremely intense and intense toppling, which seriously affected dam construction.
查看更多>>摘要：? 2022 Elsevier B.V.In the field of landslide monitoring, the assessment of the spatially-distributed three-dimensional surface displacement is crucial to understand the underlying mechanisms. Nevertheless, available technologies and techniques that provide such a datum are few and often suffer spatio-temporal resolution, logistic and/or financial limitations. In this framework, we developed a methodology that merges the three-dimensional measurements at specific points, acquired by a robotic total station (RTS), and the spatially-distributed data obtained with digital image correlation (DIC) of time-lapse camera photographs, to achieve the spatially-distributed three-dimensional surface displacement. The integration method follows this procedure: i) the DIC results are orthorectified on an existing digital elevation model; ii) the RTS data are rototranslated into the camera coordinate system; iii) the ratio α between displacement vertical component and module measured by the RTS is calculated and interpolated across the region of interest; iv) the orthorectified DIC results are rescaled according to α, obtaining the three surface displacement components; v) the displacement vector is rototranslated into the geographical coordinate system. The sensitivity analysis respect to α revealed that the integration method can be successfully applied even with a limited number of RTS measurement points. The developed methodology has been applied to the Mont de La Saxe rockslide case study, during a phase of strong acceleration. In this period, the displacement magnitudes varied between 0.1 m and 10 m, thus providing a stress-test input for methodology development and validation. The results have been compared with independent ground-based interferometric radar measurements, obtaining 0.99 linear correlation coefficient and median absolute deviation of 0.086 m, which is comparable with the DIC measurement uncertainty. The proposed method is based on the use of low-cost portable and commonly used field equipment, thus it can be easily implemented in existing monitoring networks without additional financial costs.
查看更多>>摘要：? 2022This study evaluates the feasibility of utilizing a hydroxyapatite-based binder (termed as SPC) stabilized contaminated soil in a decommissioned electroplating industry site as roadway subgrade material, where SPC is a mixture of superphosphate (SP) and calcium oxide (CaO) powders in a proportion of 3:1 by dry weight basis. Traditional Portland cement (PC) was used as a control binder for comparison purpose. The leachability of the stabilized soil was evaluated at 28 d. The engineering properties including dry density, soil resistance, and dynamic deflection modulus, were investigated at 1 d, 7 d, 28 d, and 600 d after construction. The results showed that stabilization using SPC is effective for immobilizing target contaminants of nickel (Ni) and zinc (Zn) in the contaminated soil and improving its mechanical properties including dry density, soil resistance, and dynamic deflection modulus. The SPC binder exhibited superior performance to PC in term of higher immobilization effectiveness of Ni and Zn, shorter curing time, and lower carbon footprint. The SPC-stabilized soil showed inferior strength, stiffness, and water sensitivity to those of the PC-stabilized soil.
查看更多>>摘要：? 2022 The AuthorsTailings dams are commonly built incrementally to increase the storage capacity of the Tailings Storage Facility (TSF), usually without interrupting the mining activities. Dam management practices, lack of knowledge on tailings behaviour and the poor performance of monitoring and management processes have resulted in disastrous tailings dam failures with human and economic losses, as well as huge environmental consequences to ecosystems and local communities. In the literature, correlation analyses have been carried out considering different variables: stored volume, released volume, runout distance, dam height, peak discharge. Several databases of tailings dam failure are available online, each with different levels of detail. This paper computes the statistics of tailings dam failures using an up-to-date database on failures and a catalogue of existing TSF. The existing correlations between stored and released volumes have been verified using a larger database. The new proposed regression analysis considers the functional relationship between released volume and characteristics of the dam such as height and stored volume (i.e., dam factor). The effect of construction type, fill material and failure mode on the released volume has also been evaluated as well as the frequency of tailings dam failure as function of the construction method. Tailing dams built using the upstream construction method turn out to be more prone to failure, and more susceptible to static and dynamic liquefaction. The new correlation provides more reliable estimates of the expected released volume as a function of dam height and stored volume and should prove useful for runout analyses and risk assessment of tailings dam failure. Finally, the analyses carried out show that there is no correlation between the water pond extension and the released volume.
查看更多>>摘要：? 2022 Elsevier B.V.While it is widely acknowledged that interparticle bonding due to free iron oxide (FIO) dramatically affects the behavior of natural clay, the exact role of FIO in determining soil physicochemical and mechanical properties and the underlying mechanism remain unknown. In response, this study removes FIO from natural Zhanjiang clay, a structured marine clay with cementation, to investigate how FIO affects the physicochemical and mechanical behaviors of soil. The immersion method and leaching method (with dithionite-citrate-bicarbonate solution) are used for FIO removal. The test results indicate that the removal of FIO significantly changes the soil physical indices and degrades the mechanical properties. The effects of FIO removal are explained from the perspective of microstructural alterations as revealed by scanning electron microscopy (SEM) observations, mercury intrusion porosimetry (MIP) tests, energy-dispersive X-ray spectroscopy (EDS), and zeta potential measurements. FIO is distributed at the contacts between soil particles and exists in the bridging form. Due to the attraction between the positively-charged FIO and the negatively-charged clay mineral surfaces, soil particles are bounden to form larger soil aggregates with enhanced stability. The removal of FIO leads to the breakdown of soil aggregates and the generation of large pores, thereby increasing soil compressibility and decreasing the shear strength. This study provides some new micro-level understandings of how FIO affects the behavior of natural clay.
查看更多>>摘要：? 2022Rapid sliding in a rock avalanche may occur from strain- and strain-rate- weakening of the rupture-surface strength. However, existing research on rock-avalanche dynamics pays little attention to rupture-surface weakening. In this paper, we used high-speed-friction tests on limestone and shale of the Qixia Formation to determine strain- and strain-rate- weakening of the rupture surface of the Jiweishan rock avalanche. The strain- and strain-rate- weakening model inferred that the friction coefficient of the rupture surface decreased rapidly to a residual value of <0.1 within a short interval after rock-avalanche failure, which was collectively determined by shear rate and shear displacement. We used this rate-weakening in a numerical model to investigate the dynamics of the rock avalanche, and compared it with another model that used a constant value of friction. Our model results suggested that rupture-surface weakening could cause the disintegration of the sliding body and influence the post-failure motion of the Jiweishan rock avalanche. With strain- and strain-rate- weakening, a larger sliding-out velocity (~ 13–27 m/s) of the rock mass was modelled due to reduction of frictional energy consumption causing by rupture-surface weakening. Hence a strain and strain-rate- weakened rock mass could both fly farther in the air and strike the ground at a lower angle maintaining more kinetic energy. The transport distance of such a sliding rock mass would have been ~50–500 m longer than in a model without weakening. Our study suggested that strain- and strain-rate- weakening behavior of a rupture surface would significantly increase the rock-avalanche transport distance. Use of such a model might provide more accurate prediction of the disaster reach of rock avalanches.
查看更多>>摘要：? 2022 Elsevier B.V.During the downslope long-distance movement of debris avalanches, particles interact with each other in various modes, by rolling, sliding and colliding with each other. During transport, grains may undergo breakage, changing in size and shape. However, research on debris avalanches at the grain scale remains limited, in particular, the evolution of grain morphology at different scales, from the overall form down to surface roughness, with runout distance. This paper investigates the evolution of particle morphology of granite gravel particles during long distance travel using a rotating drum, Micro-Deval apparatus, together with three-dimensional (3D) image analysis with a 3D laser scanner. The effects of particle shape and pore fluid (dry, saturated with water or slurry) on the evolution of particle morphology during transport were investigated. It was found that while the gravel was strong enough to resist the fragmentation that could be induced by the inter-particle actions during testing, the corners and edges became rounded, and the general form and surface roughness remained unaffected by the particle interactions. The more angular the grains, the easier the corners to be abraded during interaction. The change of local roundness of the grains was amplified in water-saturated conditions and suppressed in a slurry-saturated medium. The viscosity of the pore fluid, rather than initial particle shape, was critical in controlling the particle morphology evolution.
查看更多>>摘要：? 2022 Elsevier B.V.Geotechnical parameters of linear earth structures, such as embankments and earth dams, are usually obtained from point-wise investigations through drilling or penetration tests, commonly time and cost consuming. Non-invasive geophysical investigations can be considered alternative for a preliminary screening of earth structures physical properties, given their surveying speed and their depth and length of investigation. Seismic and electrical methods can be also used, through specific correlations, for the estimation of geotechnical soil characteristics. Several methodologies have been developed over the years combining two or more geophysical techniques for the estimation of geotechnical parameters. In this paper, data from geophysical surveys were used for the comparison of geotechnical parameters forecasted with three different methods (with theoretical, statistical, and field based approaches respectively). Their strongpoints and limitations were also evaluated by comparison with available direct geotechnical investigations. Integrated seismic and electrical data from extensive surveying performed over seven retaining structures located in Piedmont Region (NW Italy) were used to forecast their fine content and hydraulic conductivity distributions. Geophysical data were acquired using seismic and electric streamers, useful for the simultaneous execution of the surveys in motion along the earth structures. The results of this study show the effectiveness of the proposed data acquisition approach and elaboration procedures as a first screening tool for earth retaining structure safety assessment. The increased capability of the theoretical method to better predict geotechnical parameters with respect to the other methodologies is also reported.
查看更多>>摘要：? 2022 Elsevier B.V.Rockburst is a difficult problem that restricts the development of deep rock mass engineering technology, and the warning of rockburst occurrence time remain a common challenge worldwide. This paper presents geological information and rockburst occurrence time in different drilling & blasting procedures collected in detail from a deep tunnel. A characterization method of MS (Microseismic) sequences has been designed to characterize the evolution law of microseismicity in the blasting cycle. An LSTM (Long Short-Term Memory) model is established to construct and augment the MS sequence samples, and a database was established based on information such as geology, excavation, support, MS sequence, and rockburst. Based on the information in 600 blasting cycles of the database, a multisource data mining method for analyzing the MS sequence formation mechanism is established. The relationship between the characteristics of rockburst occurrence time and MS sequence is established, and the formation mechanism of the MS sequence is used to interpret the potential rockburst type and occurrence time affected by geological conditions and drilling & blasting procedures. The results show that the number and spacing of structural planes have an important influence on the frequency, intensity and type of rockbursts. Rockburst may occur in each procedure of the blasting cycle. The frequency of rockburst during the danger elimination and support stage is the highest, during the drilling and charging blasting stage is the lowest. The MS sequence in blasting cycle is divided into four types, which have a good relationship with the rockburst occurrence time in blasting cycle procedures. Rockburst type and occurrence time in different procedures is mainly controlled by the rock mass structure, excavation footage, excavation rate and blasting time interval. The results have important reference value and guiding significance for rockburst time warning and hazard control.
查看更多>>摘要：? 2022 Elsevier B.V.Offshore groundwater (OG) systems are widely distributed in the coastal areas, where nearshore land reclamation projects are constructed for seaports, airports, and urban other infrastructures. However, there is almost no study on the interaction between these projects and the OG system. This paper presents the first such an effort using the Hong Kong International Airport near Lantau Island, as a case study by developing a three-dimensional density-dependent flow and transport model to investigate the interaction between the reclaimed airport and the OG system. Results show that the offshore relatively fresh groundwater may flow from the nearby Lantau Island through the submarine confined aquifer. The higher pore water pressure in the basal aquifer beneath the airport is generated by the regional groundwater system of the nearby Lantau Island. Besides, the reclaimed airport also serves as extra aquifer space for the storage of fresh groundwater resources. The expansion of the 3rd runway will further increase the water table and move the center of the water mound toward the 3rd runway area. The groundwater system in the airport will reach a new steady state 50 years after the expansion, and the volume of the fresh groundwater lens is calculated to be ~5.2 × 107 m3 with a maximum water table of 1.4 m above mean sea level. The findings of this study have implications on the large-scale nearshore land reclamation which may be affected by the OG system in other coastal areas.
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