查看更多>>摘要：Chemical compaction dominated by clay mineral transformations, commonly develops in deeply buried mudstones, and prominently affects the petrophysical properties of mudstones and fluid flow. This paper takes the Neogene mudstones in the Ledong Slope of the Yinggehai Basin as research object, analyzes the relationship between chemical compaction and overpressure, establishes a new multisegment normal compaction trends (NCTs) and reevaluates the overpressure mechanisms. The results show obvious clay mineral transformation with increasing depth, and the top of the clay mineral transformations is approximately equal to the depth of the overpressure. The logging responses of overpressured mudstones are affected by clay mineral diagenesis, showing a 45% increase in the sonic transit time at 3500-5000 m and a 10% decrease in the density at the same interval, and the density response exhibits a relative lag. A method comprising an inversion algorithm calibrated by measured pressure data is proposed to establish multisegment NCTs. Furthermore, new loading-unloading curves comprising a mechanical loading curve and chemical loading curve are established to reevaluate the overpressure mechanisms. The loading-unloading curves show that the pressure gradient generated by mudstone compaction maybe less than 1.8. While the pressure data with pressure gradient larger than 1.8 fall on the unloading curve, indicating elevated sandstone pressures rather than in situ mudstone pressures. The multisegment NCTs were proven to provide a satisfactory overpressure estimate in the Ledong Slope as well as the relative contribution of different overpressure mechanisms. This paper provides new insight into mudstone compaction and overpressure responses, as well as a meaningful reference for the identification of multiple-overpressure generation mechanisms and the prediction of pore pressure in deeply buried formations.
查看更多>>摘要：Rainfall reservoir-induced landslides in the Zigui Basin, China Three Gorges Reservoir (CTGR) area, exhibit typical step-like deformation characteristics with mutation and creep states. Previous landslide displacement forecasting models yielded low prediction accuracy especially for mutational displacements. Coupled with the lack of monitoring sites and data limitations, it is extremely difficult to obtain accurate and reliable early warnings for landslides. The multi-feature fusion transfer learning (MFTL) method proposed in this paper applies the knowledge and skills obtained from the Baijiabao landslide scenario and sufficient monitoring data to improve the prediction capacity for other landslides, such as the Bazimen and Baishuihe landslides. The model barely relies on the long-time continuous monitoring process, and it can not only fill gaps in data when monitoring is interrupted, but also provide real-time displacement predictions based on accurate weather forecasting and periodic reservoir scheduling. In addition, the non-uniform weight error (NWE) evaluation method is proposed in this paper to focus more on the mutation state prediction accuracy because landslide instability is most likely to occur in this stage. Compared with other intelligent algorithms, the results indicate that the MFTL method owns low prediction error and high reliability, as well as the positive generalization ability in landslide prediction. This study paves the potential way for realizing the real-time, whole-process and accurate landslide forecasting.
查看更多>>摘要：Site investigation is an important step of geotechnical projects. Previous studies have investigated the benefits of undertaking site investigation for differing scopes by assuming the measurements obtained from site investigation tests are “true” measurements without measurement errors. However, measurement errors are inevitable in all types of site investigation testing methods which cannot be neglected. This paper attempts to quantify the effects of measurement errors on the optimal number of site investigation tests and optimal testing methods. Monte Carlo simulations, random field theory and Kriging fitting method are utilised to incorporate the uncertainties due to soil variability and measurement errors in the slope reliability analysis process. Results indicate that there are significant benefits from increasing the number of site investigation tests in terms of the risk reduction of slope design. By taking the cost of site investigation into account, the optimal number of site investigation tests can be identified by balancing the risk and the cost.
查看更多>>摘要：Site effect is considered a critical component affecting ground motions, and the shallow velocity structure is a primary factor for determining the site effect. The shallow velocity structure should be carefully evaluated to mitigate earthquake hazards. Thus, we use microtremor array measurements as well as the inversion of microtremor horizontal-to-vertical spectral ratios (MHVSRs) to investigate shallow S-wave velocity (Vs) profiles in Taiwan, which is one of the most seismically active areas of the world. On the basis of the diffuse field assumption, Vs profiles can be efficiently inverted. To reduce the nonuniqueness of MHVSR inversion, Vs profiles obtained using microtremor array measurements and from an engineering geological database were adopted as model constraints. Finally, this study included 3587 inverted MHVSR Vs profiles and 65 inverted Vs profiles from microtremor arrays. The results were used to create a detailed updated VS30 map of Taiwan and to map the depth contours of Z1.0; thus, the relationship between VS30 and Z1.0 was determined. We proposed a new parameter, HR, as a proxy for VS30, that is defined as a ratio of the average MHVSR across high- and low-frequency bands. This parameter was correlated to the predominant frequency without subjective selection. Moreover, we constructed a pseudo-three-dimensional shallow Vs model of Taiwan, which describes main shallow structural features and provides complete details for plain areas.
查看更多>>摘要：In recent decades, the number of tunnels has increased within city centres worldwide due to the construction of new underground train lines, thus instigating subsequent issues related to an increase in the amount of vibrations affecting pre-existing buildings and infrastructures; therefore, more studies have been devoted to investigating the interactions between underground train lines and buildings within the framework of a site-city interaction (SCI) scheme. The already designed layout of line C of the Rome Metro was chosen as the research object of a case study focusing on underground train-induced vibration propagation in the city centre of Rome (Italy). Numerical modelling was carried out to analyse the propagation of future vibrations within the large buried alluvial valley and to assess the spatial extension of the induced vibration resentment. Two different subsoil models were considered for this study area: i) a homogeneous model (HoM), in which a homogeneous filling of Tiber alluvia was considered, and ii) a heterogeneous model (HeM), where the Tiber alluvia was distinguished within various lithotechnical units. Specific geophysical measurements were performed to i) record vibrations induced by accelerating, braking and regularly transiting trains to provide input for numerical modelling and ii) define the typical ambient vibration noise of the investigated area. Numerical modelling was then performed using the CESAR-LCPC code, which adopts a finite element method (FEM) solution in the time domain, to simulate the propagation of train-induced vibrations within the Tiber River valley in both the HoM and HeM simulations. The simulation outputs reveal a negligible deamplification effect up to approximately 2 Hz with respect to the considered solicitation in the area located above the tunnels and a maximum effect with respect to the reference ambient vibration noise within 5 and 10 Hz along the valley. The vibrations induced by the accelerating trains can be associated with the highest resentment at the free surface of the valley. A more intense effect generally results in the HeM simulation, which highlights the nonnegligible role of the heterogeneities present within the Tiber alluvia in propagating train-induced vibrations. The numerical outputs highlight that the train-induced vibrations can propagate hundreds of metres away from the underground train location, i.e., up to 400 m astride the axis of the designed tunnels in the case study considered here, and can be distinguished with respect to the regular ambient vibration level.
查看更多>>摘要：The Horizontal-to-Vertical Spectral Ratio (HVSR) obtained from microtremor data recorded at three test sites are analyzed in order to highlight some issues related to the computation of the SESAME criteria that define the statistical robustness of possible peaks. In case of multiple-peak HVSR curves, it is shown that to properly assess the statistical properties of a peak and avoid the problem of multimodal data distribution, it is crucial to isolate each peak by reducing the frequency range around it. It is also shown that, while the standard approach used to obtain a homogeneous data set is represented by the removal of large-amplitude transient events before the computation of the HVSR, the removal of outlier HVSR curves can be a more effective way to obtain such a goal, being outlier HVSR curves not necessarily associated to large-amplitude transient events. It is eventually briefly discussed the problem of the proper management of multi-peak HVSR curves in microzonation studies while defining the so-called soil frequency maps. It is argued that to focus these maps just on the lowest-frequency (f0) value is questionable because higher-frequency peaks can be much more important when the local urban landscape is characterized by low-rise buildings.
查看更多>>摘要：The pore structure of soils and rocks plays a crucial role in geotechnical, geo-environmental and geological engineering, as it dominates the hydro-mechanical behaviour, gas- and liquid-permeability as well as material transport property of soils and rocks. A large amount of pore size distribution (PSD) data of porous materials have been experimentally determined in the past decades and are currently available in the literature. However, a general expression to parameterize these PSD curves is still missing. In this study, a general multimodal PSD model is developed based on the probability theory, which is a strong tool to quantify the complex soil microstructure precisely. The parameters in the model possess a clear physical meaning. The model is validated by reproducing the PSD curves of two clays and a sand-clay mixture having a complex pore structure. The parameterized PSD curves demonstrate a strong consistency with the measurements. In addition, the model is applied to predict the PSD evolution under hydro-mechanical processes (e.g., compaction, saturation- swelling-process), the water content – soil suction – dry density relationship of Boom clay after compaction and the time-dependent PSD evolution of MX80 Bentonite. Beside soils, the proposed general multimodal PSD relationship can describe the pore structure of any other porous and granular material, as all the underlying physics is the same for all of them. The proposed model can be incorporated into the existing effective stress parameter formulation, permeability models and constitutive models of unsaturated multimodal soils.
查看更多>>摘要：Optimal whole-life design for marine structures requires an accurate assessment of how their underlying geo-materials respond to various static and cyclic loads. This study experimentally investigates the undrained shear behavior and stiffness characteristics of intact, soft marine clay that outcrops an offshore wind farm in southeast China. A series of monotonic and cyclic triaxial tests were conducted on the highly compressible marine clay, and the test results were interpreted within the critical state framework. The elastic shear modulus measured using bender elements in triaxial tests was compared with the secant modulus that gradually degraded with the strain during monotonic and cyclic loading. An interesting finding was that the elastic stiffness measured at various loading stages increased exponentially with the mean effective stress; a power-law increasing trend was also observed in the secant modulus normalized by the void ratio at various strain levels. It was also demonstrated that the intact sample under cyclic loading is stiffer than that under monotonic loading at the same strain level. Furthermore, a close correlation between the nonlinear undrained shear stiffness and the elastic stiffness measured during monotonic or cyclic loading was observed, which is of vital importance when evaluating the stiffness degradation behavior of natural soils over strain ranges relevant to major engineering works.
查看更多>>摘要：As the mining depth increases year by year, the geological environment of the coal seam becomes more complex. Coal rocks are vulnerable to damage from high temperature, immersion, high ground stress and other factors. This study is aimed at realizing the monitoring and early warning of coal rock dynamic disasters in complex environments such as high temperature and immersion. Firstly, mechanical properties of coal rocks after high temperature and immersion treatment were tested through experiments. It was found that both high temperature and immersion can cause mechanical damage to coal rock. In addition, the acoustic emission (AE) and electromagnetic radiation (EMR) signals generated by coal rock samples during failure were collected in real time. The following conclusions were drawn: All these signals are closely related to the damage degree of coal rock. The AE and EMR signals generated by coal rock under load after different temperature treatments were different, and their intensity decrease after immersion treatment. Furthermore, the damage of coal samples caused by high temperature and immersion was explored through quantitative analysis, and the evolution law of crack propagation during coal rock failure was discussed. The mechanical properties of coal rock after the damage of high temperature and immersion and the mechanisms of AE and EMR signal generation and variation during deformation and failure were revealed. This study provides theoretical guidance for the monitoring of coal rock dynamic disasters.
查看更多>>摘要：Events characterized by widespread landslides provide rare but valuable opportunities to investigate the spatial and size distributions of landslides in relation to seismic, climatic, geological and morphological factors. This study presents a unique event inventory for the co-seismic landslides induced by the February 25, 2018 Mw 7.5 Papua New Guinea earthquake. The mainshock rupture was dominated by reverse fault motion, and this was also the case for the aftershocks. The latter also triggered widespread landslides in combination with rainfall during the period between February 26 and March 19. We mapped approximately 11,600 landslides of which, more than 10,000 were triggered by the mainshock, with a total failed planimetric area of about 145 km2. Such a large area makes this inventory the world's second-largest recorded landslide event after the 2008 Mw 7.9 Wenchuan earthquake, where the motion changed from predominantly thrust to strike-slip. Large landslides are abundant throughout the study area located within the remote Papua New Guinea Highlands. Specifically, more than half of the landslide population is larger than 50,000 m2 and overall, post-seismic landslides are even larger than their co-seismic counterparts. To understand the factors controlling the distribution of landslides' occurrence and size, we combine descriptive statistics as well as more rigorous bivariate and multivariate analyses. We statistically show that the 15-day antecedent precipitation plays a role in explaining the spatial distribution of co-seismic landslides. Also, we examine four strong aftershocks (Mw ≥ 6.0) within 9 days after the mainshock and statistically demonstrate that the cumulative effect of aftershocks is the main factor disturbing steep hillslopes and causing the initiation of very large landslides, up to ~5 km2. Overall, the dataset and the findings presented in this paper represent a step towards a holistic understanding of the seismic landslide hazard assessment of the entire Papua New Guinea mainland.
NSTL
Elsevier