查看更多>>摘要：? 2022 Elsevier B.V.In this work, we present the results of a rockfall trajectory study performed on the south-western slope of Mt. Catiello (Sorrento Peninsula, southern Italy). Such a study develops within a multi-methodological approach which integrates different types of remote sensing data and techniques. Specifically, ground-truth data (e.g., rock mass geo-structural information, rock block inventory) were generated by geologically-supervised interpretations of high-resolution virtual outcrop models (VOMs). These data were then used for reconstructing the in-situ fractured rock mass attributes of the Mt. Catiello peak, as provided by a Discrete Fracture Network (DFN) model, and to prepare the subsequent numerical simulations of rockfall trajectories. The resulting rockfall scenarios are consistent with the ground-truth data, both in terms of size and spatial distribution. Thus, we believe that the proposed approach can be effectively applied to other areas, characterized by similar geological features but higher levels of exposure and vulnerability.
查看更多>>摘要：? 2022 Elsevier B.V.The Bayu Tunnel is the most problematic tunnel project in the Lhasa-Nyingchi section of the Sichuan-Tibet Railway. Rockbursts have occurred frequently during the construction process, which has seriously threatened the safety of construction workers and equipment. Aiming at the rockburst hazard prediction problem of the Bayu Tunnel, in this paper an integrating method of combination weighting and matter-element extension theory is proposed. This method introduces the rock brittleness evaluation index BICSS, Russenes criterion and rock mass integrity coefficient as the main rockburst evaluation indexes, which characterized the control factors of rock physical and mechanical property, surrounding rock stress and rock mass integrity on rockburst tendency, respectively. Then the rockburst tendency evaluation index system is constructed. The weight of each rockburst control factor is determined by the combination weighting algorithm of triangular fuzzy number analytic hierarchy process (TFN-AHP), criteria importance though intercriteria correlation (CRITIC), and determination of comprehensive weight (MDI). The correlation degree between the rockburst sample and rockburst grade can be calculated using the matter-element extension theory, after which the prediction of rockburst grade is carried out. Finally, the applicability, superiority and the necessity of selected rockburst control factors in this method are verified and discussed further. The research results provide a new analysis method and technical means for rockburst tendency assessment of deep tunnel.
查看更多>>摘要：? 2022 Elsevier B.V.The motion of debris flows is controlled by the interaction of their fluid and solid components. In this work, a general two-phase model framework (Pudasaini, 2012) is adopted which captures the coupled effects of the individual phase dynamics to the overall mobility. While solving the model equations, the fluid phase is treated as a viscous Newtonian liquid while the solid phase is considered to be a granular material obeying a recently developed visco-inertial constitutive rheology. Solid and fluid components in the mixture are coupled through the interaction forces, namely buoyancy, drag, and virtual mass. The model is calibrated against results from instrumented flume experiments and from field measurements of saturated, channelized debris flows. The numerical model captures the enhanced mobility of debris flows due to the presence of interstitial fluid and provides better predictions of the flow dynamics relative to those obtained from single-phase frameworks. Better modeling agreement is obtained for granular-fluid flows with relatively high fluid content. The model is then used to simulate real debris flow events, including a case that occurred in the proximity of the Sichuan-Tibet Railway, where good agreement with reported field measurements is obtained. This modeling framework is expected to improve mitigation strategies for debris flows hazards.
查看更多>>摘要：? 2022 Elsevier B.V.A large-scale landslide in a deep valley often travels a long distance. The moving landslide debris impacts into the valley and interacts with the river and the opposite side of the valley. In the landslide movement process, energy, mass and momentum transfers inevitably take place. An in-depth study of energy and mass transfer mechanisms in various types of flow-like landslides will provide a scientific basis for developing energy criteria for evaluating landslide hazard chains and mitigation measures. In this study, a coupled DEM-ALE method is used to systematically evaluate the energy transfer mechanisms in landslides of various solid concentrations. The landslide dynamics involving river damming can be divided into three stages: the travel stage, the interaction stage, and the deposition stage. Kinetic energy is dominant in the travel stage but the frictional energy dissipation increases rapidly in the interaction stage. In the deposition stage, the kinetic energy changes to other energy components. The energy transfer mechanisms differ in different types of landslides. The kinetic energy of the fluid phase is mainly dissipated by viscosity shearing and turbulence, which is less efficient than internal and boundary frictional dissipations in the solid phase. The fraction of friction-dissipated energy increases with the solid concentration of the landslide mixture. Most of the remaining energy is dissipated by turbulence. Kinetic energy is the main energy transfer component during the landslide-river interaction. Flows of lower solid concentrations, e.g., debris flows, impact larger areas but are less likely to block a river.
查看更多>>摘要：? 2022 The AuthorsDespite some 9% of Norway's area being underlain by peat the geotechnical characteristics of the material have not been well documented. As peatlands form an excellent carbon sink there is much pressure on planning authorities to avoid the excavation of peat for infrastructure development. In engineering projects in peat often the resulting settlements both in the short and long term are of greatest concern. Because of the high variability of peat, several, largely empirically based, methods exist for predicting settlement on peat. These were often developed based on specific cases. These techniques have shown to be inadequate to generically predict long term creep settlements and the development of settlement with time. Here the engineering characteristics of peat from several sites in the Trondheim area of mid-Norway are studied using a series of field and laboratory tests including three types of oedometer test. The laboratory and field data, together with empirical correlations found in the literature, were used to provide input into the commercially available constitutive model Soft Soil Creep (SSC) in the computer code PLAXIS. The model was initially calibrated using the laboratory test results and then applied to the back-analysis of two full scale field trials in the Trondheim area, where the peat properties were significantly different. The modelling showed that SSC captured well the vertical settlement versus time behaviour of the peat. Guidance is provided for selecting the critical input parameters for SSC such as stiffness, yield stress and permeability. This work contributes towards efforts being made to bridge the gap between the numerical modelling community and practicing engineers.
查看更多>>摘要：? 2022 The Author(s)Compacted bentonite is considered as an engineered barrier in geological disposal of nuclear waste in fractured rocks. One concern with this concept is that the expansion of bentonite into fractures as the system saturates may lead to its erosion by flowing water. The loss of bentonite through erosion over long times may compromise the barrier. Commercial bentonite contains less soluble accessory minerals and experimental observations have shown that these are co-transported with clay minerals during expansion and form a mineral film at the eroding boundary. Quantifying the effects of the mineral film on the erosion rate is important for the assessment of the long-term sealing capacity of bentonite barriers. The paper presents a model for the extrusion of bentonite into fractures that considers key processes governing the co-transport of less soluble accessory minerals and explains why and where the mineral film forms and how it affects the erosion rate. The model is tested against two sets of published experimental data. It is demonstrated that the model predicts the phenomena observed in experiments: the build-up of a mineral film near the extrusion boundary; and the progressive growth of the mineral film thickness. Importantly, the model allows for investigating the effects of key environmental and material parameters – water chemistry, filtration coefficient, and mineral fraction – on the expansion and erosion. The results of such investigations are presented. It is shown that higher water ion concentration, larger filtration coefficient, and larger fraction of accessory minerals retard the swelling and extrusion of bentonite, thus reducing the overall erodibility. It is further shown that the presence of less soluble accessory minerals may reduce the loss of bentonite by a factor of 2 compared to a pure bentonite.
查看更多>>摘要：? 2022 Elsevier B.V.Chemical corrosion of rock masses commonly exists in natural environment (e.g., rock masses immersed in acidic groundwater) and in rock engineering practice (e.g., acid fluid injection in unconventional reservoirs). Rock fractures as the primary paths for fluid flow are susceptible to the chemical treatment, which may lead to geologic hazards (e.g., induced landslides and earthquakes). Here we show the transitional behaviors of rock fractures between stick-slip and stable sliding due to the chemical corrosion, which is characterized by a sequence of fast rupture followed by one or more slow ruptures. The chemical corrosion also modifies the frictional properties of rock fractures, in terms of friction rate parameters, characteristic weakening distance, stiffness ratio, and frictional property ratio. Our results indicate that the chemical corrosion essentially reduces the critical stiffness of the fracture and makes it approach the stiffness of the loading system, resulting in the occurrence of slip transition. The slip transition is strongly influenced by treatment duration and shear process, and the real area of contact density is a physical control linking fracture surface topography and frictional responses, such as AE energy and shear stress drop. The understanding of slip transition can improve our ability to interpret the seismic data and to predict the slip behaviors.
查看更多>>摘要：? 2022 Elsevier B.V.Reconstructing the ages and magnitudes of prehistoric extreme events that are recorded in landforms and sediments allows us to capture the full range of frequency-magnitudes and estimate the expected time for the repetition of a catastrophic event. The Eastern Himalayan Syntaxis and its surrounding areas are highly prone to the occurrence of river blocking. Previous studies have re-established three glacier-dammed lakes in the valley of Yurlung Tsangpo, namely, Gaga Lake, Dazhuka–Yueju Lake and Jiedexiu Lake. Here, we identified a series of sedimentary evidence containing offshore clay or silt varve, nearshore vaguely stratified silty sand and subaqueous foresets, which are associated with five landslide-dammed lakes in the lower reach of Purlung Tsangpo, including Lulang (LLDL), Dongjiu (DJDL), 102 (102DL), Jialong (JLDL) and Zedang (ZDDL). By assuming an initial catastrophic drainage, the highest elevation of exposures and original dam heights derived from dam morphology were used to represent the minimum and maximum estimates of lake levels of individual lakes. The maximum estimate of lake volume ranges from 4.3 × 109 m3 (LLDL) to 1.1 × 108 m3 (ZDDL). The 14C dating results provide the chronology of the LLDL from 24.2 ka BP to 15.4 ka BP. DJDL from 11.5 ka cal. BP to 7.0 ka cal. BP, JLDL from 4.9 ka cal. BP to 2.7 ka cal. BP. ZDDL from early Holocene to 5.8 cal. BP. Most of them occurred during deglaciation. We further used low-temperature thermochronological data to illustrate the spatial pattern of fluvial incision rates. Overall, climate-driving factors, such as rainfall intensity along with enhanced river incision post LLGM, preconditioned the occurrence of the abovementioned landslides.
查看更多>>摘要：? 2022 Elsevier B.V.The construction and operation of the Sichuan-Tibet railway require constructing extensive supporting facilities along its route. Sichuan-Tibet transportation corridor features high mountains and deep valleys where land resources suitable for such purposes are very limited. As a result, safe utilization of the torrential fan along the railway becomes essential. Focus on buildings at the torrential fan, this paper aims to develop a vulnerability model that can assess their maximum potential damage and support the planning and development of the torrential fan. The model was developed based on 51 building damage data collected at 11 torrential fans. The hazard intensity was defined by the geometric configuration of torrential fans and the location of assessed buildings. In addition, a physical experiment was carried out to study the shielding effect of building groups. The results show that the shielding effect range is about 25 times the building size, and the maximum reduction in impact force can reach 60%. The advantage of the proposed vulnerability assessment model is that it only requires the spatial information of the site that can be easily derived from the satellite image. In addition, the model can reflect the complex torrential process and the shielding effect of building groups. This study provides an alternative approach to building vulnerability assessment. It supports the planning and development of torrential fans when constructing the supporting facilities for the railway construction and operation.
查看更多>>摘要：? 2022 Elsevier B.V.Many uncertainties exist in geotechnical engineering. Spatial variability is a type of uncertainty that has received more and more attention in recent years. Scale of fluctuation (SOF) is a parameter for measuring the spatial variability of soil properties. To investigate the proper method for computing the SOF of soil properties, two types of methods (auto-correlation function method (ACM), and variance reduction method (VRM)) are compared theoretically and numerically, and the influence factors, such as number of data points involved in curve fitting for the auto-correlation function (ACF) or variance reduction function (VRF) and sampling interval, on the SOFs are analyzed. To improve the accuracy of curve fitting for the ACF or VRF, a weighted least squares (WLS) method is proposed, in which the weight of each data point of sample function decreases with the increasing of lag distance between two points in a random field. Three types of soil parameters, including the CPT, the physical, and the hydraulic parameters, are tested by in-situ and laboratory tests, and the SOFs of these parameters are computed. Computation of the SOFs proves that the VRM combined with the suggested WLS is a good method for computing the SOFs of soil properties. Comparison of the SOFs shows that there are negligible differences among the three types of soil parameters of clay layers in Hefei, which is further proved by the Wilcoxon test from a statistical point of view. By using the VRM combine with WLS, the SOFs of clay are computed based on 509 sets of CPT data from 34 sites in Hefei. The statistics of SOFs can give a reference for the selection of SOF for reliability analysis or reliability-based design of geo-structures with spatial variability.
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