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Numerical simulation is important for the risk assessment of subaerial landslide-induced tsunami (SLIT) hazards; however, their predictive performances are thus far limited as these works fail to consider the involved uncertainties. We propose a novel probabilistic risk assessment framework for quantifying several uncertainties, such as the model parameters and bias. We successfully couple the numerical simulation and Bayesian-based back analysis method. The wave height and run-up are captured by a three-dimensional granular-flow landslide and renormalization group turbulence model in FLOW3D; furthermore, the relevant parameter information is calibrated using a Markov chain Monte Carlo algorithm with the differential evolution adaptive metropolis. In this framework, which incorporates the prior information of model parameters, and field observations, as well as numerical model bias, calibrated parameters exhibit a probability distribution with a small standard deviation, facilitating improved risk prediction capabilities; In addition, the optimized adaptive Kriging-based surrogate model with multiple outputs is established to reduce the computation cost of the framework with acceptable accuracy. The framework's outputs, including a spatial probability that tsunamis inundate elements at risk, and a hazard zonation map, contribute to the evaluation of SLIT hazards and prioritize mitigation measures. Our work introduces a paradigm for the application of the framework, demonstrated through studies of two landslides in Wu Gorge. Without loss of generality, the framework offers a novel perspective for the quantitative assessment of SLIT hazards. • Propose a Bayesian-based back analysis framework for assessing the subaerial landslide-induced tsunami hazard. • Successfully present the spatial probability and risk zonation maps considering multi-uncertainties. • Overcoming the computational cost problem in quantifying uncertainty. • This framework can combine various numerical methods. • Results can be utilized in the probability tsunami hazard analysis framework. [ABSTRACT FROM AUTHOR]

High-steep rock slopes are much more likely to collapse and form weir body due to earthquake. Converting the weir body to hydraulic engineering is a good way to deal with natural disasters. However, it is difficult to evaluate the stability of earthquake-induced rock slope due to the lack of shear strength parameters of rock mass. Based on three-dimension nonlinear finite elements, deformation reinforcement theory was adopted, in which plastic complementary is used to measure the global stability of slope, and unbalanced forces is utilized to identify the damage region. The shear strength parameters has been determined through back analysis based on stability and failure status before and after earthquake and monitoring data after earthquake. Then the stability evaluation under static conditions, dynamic conditions and rainfall conditions has been carried out respectively. The results show that failure mode of the slope under seismic load is consistent with the actual situation when the lowest material parameters are used. The major failure mode of the slope is sliding along the fault F5, and local collapse of the hanging body at the top of the slope under dynamic or rainfall load. The local stability can be improved effectively by excavating and taking bolt anchorages on the top of the slope. [ABSTRACT FROM AUTHOR]

On 30th July 2014, a devastating landslide resulted in the burial of a village called Malin in western India and led to about 160 deaths. The catastrophic failure was triggered by heavy rainfall over the last 3 days. Site investigation was conducted to obtain representative information about the area. To understand the relevant physics, which initiated landslide, seepage and back analysis of the unsaturated slope was performed. Transient seepage analysis was carried out using finite difference method to simulate the slope behavior during rainfall infiltration. A coupled fluid flow analysis was employed to capture the fluid/mechanical interaction in unsaturated soils accurately. The results show that antecedent rainfall played a role in slope instability; rainfall intensity and duration also have a big impact on slope instability. This paper presents a methodology to back analyse the slope so as to identify the mechanisms responsible for landslide initiation. Back analysis is performed using a probabilistic method based on Bayesian analysis. Probabilistic methods can back-analyse numerous sets of uncertain slope stability parameters. The uncertain parameters are imported as random variables in the analysis and are described by their probability distributions. Bayesian analysis updates these distributions based on the observed slope behavior. The method evaluates the reduction in matric suction which initiated landslide in Malin slope. The results show that the decrease in matric suction of about 100% in addition to the development of positive pore pressures is the main mechanism which has triggered the landslide. This amount of reduction in matric suction and the development of positive pore pressures decreases the mobilized shear strength in soil below the threshold value required to maintain equilibrium in the slope and hence the slope failed. [ABSTRACT FROM AUTHOR]

Engineering behaviour of jointed rocks is substantially incompetent as compared to intact rocks due to the presence of joints. Rock bolts are routinely used to reinforce jointed rocks at project sites. The assessment of the strength behaviour of bolt-reinforced jointed rock is a challenging task due to the complex interaction between the joints and the bolts. The present paper attempts to resolve this issue through an experimental study. Natural rock cores with a natural joint, and synthetic rock cores with smooth joint have been tested under uniaxial compression. The tests have been performed on specimens without and with bolt. Grouted steel bolt was used to reinforce the rock. Results from the tests indicate that the provision of the bolt alters the failure mode of jointed rock, and enhances the strength and modulus values. Strength and modulus of the reinforced rock were found to be correlated with each other. It is proposed that the strength of reinforced rock can be obtained from strength and modulus of the intact rock and the modulus of the reinforced rock. The intact rock strength and modulus may be obtained from laboratory tests and the modulus of the reinforced rock may be obtained by back analysing the deformations observed in the field. Sakurai's critical strain concept has been analysed and it is observed that the correlations suggested through proposed empirical approach closely commensurate with critical strain approach and hence give scale free results. [ABSTRACT FROM AUTHOR]

Long-term settlement data of a thick soft clay deposit improved by vertical drains frequently shows different field settlement behaviors from laboratory-driven predictions by conventional theories due to the variability and uncertainty of the soil properties, modeling simplifications, and types of prediction methods. This paper presents the field application of a back-analysis method based on a genetic algorithm (GA) to evaluate the performance of a new settlement prediction method compared with conventional graphical settlement prediction methods, such as the hyperbolic method and the Asaoka method. The GA back-analysis method shows better flexibility in modifying surcharging plans and adaptability to multi-layered thick soft soil deposits at the early stages of post-construction settlement. Thus, this new settlement prediction method enables geotechnical engineers to subsequently modify the heights of surcharge fills in accordance with field settlement data monitored in the interim for rapid and cost-effective construction. The comparative results show that the GA back-analysis method is capable of superior field performance in settlement predictions compared with two conventional graphical methods, within a margin of less than 200 mm in a thick soft clay deposit with multiple layers under complex loading conditions. [ABSTRACT FROM AUTHOR]

Abstract: This study presents results of numerical back analysis for estimation of strength and modulus parameters of gravelly cobble deposit through various laboratory and field tests. A non-linear and stress dependent stiffness soil model implemented in the finite element software was used to simulate four conventional triaxial compressive (CTS) tests, two pure shear triaxial (PS) tests, one field plate load (PL) test, one field direct shear (FDS) test, and one natural slope stability (NSL) analysis. The internal friction angle ϕ and stress dependent stiffness modulus E 50 ref back analyzed from those various tests were summarized and evaluated considering the load conditions and stress states. Results show that the strength parameter ϕ tends to decrease linearly with an increase of the minor principal stress σ 3′ when they were plotted in a semi-logarithmic graph. The stiffness moduli evaluated from the back analysis, cyclic triaxial test, and downhole test are compared and discussed. In addition, results of numerical analysis of the recent excavation case history in Taichung gravelly cobble deposit are presented to verify the summarized parameters, which are selected with respect to the in-situ stress state. [Copyright &y& Elsevier]

Abstract: A variety of structural discontinuities crossing the slopes of Alipasa feldspar open pit mine, in western Turkey, caused different types of slope failures which led to interruptions in ore production. Thereupon, extensive geotechnical investigations, including geological characterization, in-situ and laboratory geotechnical testing, long-term movement monitoring, back-analyses and possible remedial measures, were conducted. Field observations and subsequent analyses suggested that the failures were limited to benches and the movement developed down-slope along discontinuities due to the following reasons: (i) unfavorable orientations of the foliation planes and joints, (ii) low shear strength along discontinuities and (iii) exceptionally heavy rains filling the tension cracks prior to failure. Comparisons between movement vectors and orientation of discontinuities showed a good agreement that indicates two types of instability, namely, planar and wedge failures. A back analysis procedure for the assessment of failures along the rough discontinuities, with non-linear failure envelopes, was successfully applied to the unstable slopes in the pit. The results of the 2-D limit equilibrium back-analyses and movement monitoring data suggested that the wedges and/or planar blocks formed at the uppermost benches tended to move down to fill the gap which resulted from the previous movement of the blocks in the benches. Remedial measures such as dewatering and reduction of height of the benches were suggested. Results of stability analyses conducted for possible remedial measures were presented and discussed. [Copyright &y& Elsevier]

Abstract: Design and construction of underground structures are usually being performed based on an approximate understanding of geotechnical parameters, which are essential for selection of construction method and support system. The main purpose of this study is to determine the geotechnical parameters using back analysis based on convergence data, and also to adopt an appropriate primary support system. By installation of suitable support structure, the amount of tunnel ceiling''s settlement was reduced to a number lower than the allowable limits. Back analysis was conducted throughout the alternative univariate method by PLASIX 3D Tunnel. The research showed that performed analysis based on convergence data and back analysis can be utilized as a more economical and time-saving method in comparison to consultant Engineers design based on soil mechanic tests. In addition, the parameters obtained from back analysis were greater than soil mechanic test method. Thus, the evaluations show that measurement error in soil mechanic tests is likely the source of this difference. [Copyright &y& Elsevier]

Abstract: On 30 January 2009, a rock slide involving approximately 0.23Mm3 of highly jointed gneiss from the local Ercinic substratum was recorded in southern Italy. The landslide occurred after exceptional autumnal rainfalls and involved a quarry whose activity has been documented over the past 10years by aerial images. An engineering-geology model of the slope involved in the landslide was developed based on the geomechanical classification of the outcropping rock masses, the ISRM (2007) indexes Ib (the block size index) and Jv (the volumetric joint count), and the observed geological setting of the slope. An equivalent continuum approach was adopted to attribute strength and stiffness parameter values to the different classes of jointed rock masses. A simplified evolutionary model of the slope was developed, starting from 300ka (i.e., from the erosional phase following the deposition of the 300-m-a.s.l. marine terrace deposits overlaying the gneiss substratum) to 30 January 2009. The model took into account the main depositional phases as indicated by the Pleistocene marine terrace deposits and the documented stages of quarry activity. Time-dependent stress–strain numerical modelling was performed by the FDM software FLAC 6.0. A visco-plastic Burger model was used to back-analyse the landslide event and to define the values of the rheological parameters for the jointed gneiss. The results, which were strongly constrained by the geomorphological evidences and by the displacement field observed before and after the landslide, demonstrated a combination of i) time-dependent gravitational slope deformation and ii) anthropogenic release due to quarry activity, which induced a progressive failure process and an increase in the jointing within the gneissic rock mass located behind the cut-wall of the quarry. Failure was ultimately triggered by intense rainfalls that occurred in the 3months before the landslide. The stress–strain numerical modelling demonstrated the reliability of visco-plastic rheology for simulating the rock mass creep in this case history: viscosity values in the range of 1019–1023 Pa·s were derived. [Copyright &y& Elsevier]

Abstract: Case histories of the Tsaoling landslide and the Chiu-fen-erh-shan landslide, both located in Taiwan, are used in this study to validate the procedure proposed for the dynamic back-calculation of the shear strength parameters of the sliding surfaces of large landslides. This new procedure uses the Newmark sliding model while simultaneously considering the critical displacement concept. The premise of the new procedure is that, in a stable slope, back-calculation tends to underestimate the shear strength; however, as the intensity of earthquake shaking increases and the slope approaches failure, the back-calculated shear strength will approach to the “true” value. Based on this concept, the new procedure (method) is developed and validated with the two well-documented case histories. The shear strength parameters back-calculated using the proposed method agree well with those reported in the literature. The new dynamic back-calculation procedure is especially suitable in the situation where groundwater monitoring data are unavailable. Thus, the new method is complementary to the traditional groundwater-based limiting equilibrium back calculation approach. [Copyright &y& Elsevier]

Abstract: Decomposed granites are often found in Galicia, Spain, where they are referred to as jabres. Similar decomposed granites are also found in many other parts of the world. Granite weathering rarely produces an homogeneous altered rock mass with all material decomposed to the same degree – or even a simple weathering profile where the degree of alteration decreases progressively with depth. This paper presents an empirically based approach that allows estimation of the shear strength of this type of materials in terms of Mohr–Coulomb cohesion and internal friction angle values. The approach is based on back analysis of failed slopes in decomposed granites, and it is implemented through simple in-situ testing and classification of the weathered granite, treating it as a soil material. An advantage of the used approach is that it allows prediction of shear strength values at different locations within the deposit in a quick and economical way, from which average values of shear strength parameters can be computed. This is particularly important when considering the heterogeneous nature of decomposed granite formations in relation to the scale of the engineering work involved. Analysis of three slopes instability cases in jabres in Galicia, illustrating the approach are described in detail. These correspond to a road cut, a natural slope and the wall of an open pit mine. [Copyright &y& Elsevier]

Abstract: Deformability of rock masses influencing their behavior is an important geomechanical property for the design of rock structures. Due to the difficulties in determining the deformability of jointed rock masses at the laboratory-scale, various in-situ test methods such as pressuremeter, dilatometer, plate loading tests etc. have been developed. Although these techniques are currently the best and direct methods, they are time-consuming and expensive, and present operational difficulties. In addition, the influence of the test volume on deformation modulus depending on the method employed is also important. For these reasons empirical equations to indirectly estimate the deformation modulus have also been recommended by several investigators as an alternative approach. In this study; the geomechanical quality of weak, heavily jointed, sheared and/or blocky greywacke rock masses, on which very concentrated civil works are continuing at the southern and southwestern parts of Ankara (Turkey), was assessed. The deformation modulus was determined by pressuremeter tests, the possible effects of variables on the derived deformation modulus from the pressuremeter test were evaluated by numerical methods, and the comparisons between the deformation modulus of the greywackes obtained from the pressuremeter tests and their geomechanical quality (GSI and RMR) were made. Numerical simulations revealed that the presence of a disturbed annulus around the borehole causes underestimation of the deformation modulus, while the effect of length to diameter ratio of the pressuremeter probe on the deformation modulus is minor. Based on the geo-engineering characterization assessments, mainly two greywacke rock masses with different geomechanical qualities were identified. Geotechnical quality of one of these rock masses was verified by the back analysis of two slope failures. The empirical equations to indirectly estimate the deformation modulus of the greywackes using their GSI and RMR values yielded high coefficients of correlation. [Copyright &y& Elsevier]

Abstract: In this study, a complex landslide, which occurred on 17 March 2005 near Koyulhisar town of Sivas Province of Turkey, is presented. The landslide resulted in 15 deaths and the destruction of about thirty houses at Kuzulu village. The main aims of this study are to assess the landslide in terms of engineering geology and geotechnics, to back-analyze the landslide in the source area, and to estimate its motion and destructive forces on structures. Furthermore, the effect of a future earthquake on stability condition of the mobilized but not completely failed mass adjacent to the right flank of the landslide is also investigated. Field observations, eyewitnesses, geomechanical laboratory tests, interpretations on pre-event aerial photographs and analyses using different approaches have been fundamentals of this study. Site observations indicate that the initial landslide in the source area occurred in highly weathered volcanics along a failure surface passing through the volcanics and along the interface between the volcanics and underlying limestone. Then the movement transformed into an earth flow and moved down through a V-shaped channel in the underlying limestone about 2 km until it stopped at a small settlement, which is called Kuzulu. Site observations and back-analysis of the initial slide suggest that the most likely cause should be water pressure increase as it is the season of snow melting and thawing of the groundwater. Interpretations on pre-event aerial photographs and the information obtained from eyewitnesses indicated that slope movements in the study area, where old landslide topography is evident, were continuing for many years. The simulation of the landslide with consideration of Bingham type yielding criterion together with water pressure variation suggested that the maximum velocity of the earth flow was 14.4 m/s and 13.6 m/s when it reached Kuzulu. Furthermore, this evaluation showed that the earth flow reached Kuzulu after 300 s, which is consistent with the information obtained from local people. The impact of the earth flow on the structures could be about 170 kPa against which only reinforced concrete structures may resist. Dynamic analyses suggested that a future earthquake, which may occur in the region, may result in a complete failure of the unstable mass remaining at the source area. [Copyright &y& Elsevier]

The large landslides along the Black Sea shore in Turkey are well-known instability phenomena and responsible for considerable economic losses each year. The severity of the problem increased particularly in recent years as increased scarcity of land forced utilization of inherently unstable areas. In 1988, severe rainstorms at the city of Sinop on the Black Sea shore triggered ground movements on a gentle coastal slope subjected to building loads and caused extensive damage to buildings founded on the slope. Comprehensive investigations of the failure were carried out and used to establish a geotechnical model for the slide. The model allowed consideration of building loads and different groundwater conditions. In addition, the model studies were complimented by limit-equilibrium and finite-element stress analyses. The results indicated movements on a circular sliding surface through stiff clay. The toe of the landslide is located at the shoreline and remains active. The failure was probably initiated by rising groundwater level combined with surcharge loads imposed by buildings on the slope. Other contributing factors include sand extraction and coastal erosion. Remedial works are recommended involving a rockfill buttress at the toe of the slide and drainage improvements on the surface of the slope. [Copyright &y& Elsevier]

A disastrous earthquake rocked Taiwan on September 21, 1999, with magnitude ML=7.3 and an epicenter near the small town of Chi-Chi in central Taiwan. The Chi-Chi earthquake triggered landslide on the dip slope at the Chiufengershan. In this study, a review of the topography and geology of this area was followed by field investigations. Laboratory testing was applied to understand the geomaterial composing the slope. Then, based on a series of limit equilibrium analyses, the failure mechanism of this landslide and the risk of the residual slope were studied.According to the stability analyses, the pre-quake slope is quite stable, with factor of safety of 1.77 (dry) to 1.35 (full groundwater level); explaining why there is no written record of a landslide here for the past 100 years. In contrast, a back analysis shows that the Chi-Chi earthquake-induced dynamic loading is far more than the dip slope can sustain, due in part to the short distance to the epicenter. A Monte Carlo type probability analysis suggests that the residual slope is more dangerous than the pre-quake slope and needs more attention. [Copyright &y& Elsevier]

Landslides in the vicinity of reservoirs are prone to generate deadly waves as in the infamous Vajont case. There are more than 3800 landslides in the Three Gorges Reservoir area through detailed geological investigations, which constitutes a serious tsunami threat to the population and properties nearby. The Liangshuijing landslide, a very large creeping landslide located in the region and characterized by a complex morphology of multiple time varying failure mechanisms, is here investigated. Currently comprehensive measurements taken by ground monitoring network, inclinometric readings, in situ and laboratory geotechnical tests were analyzed to build a conceptual model for the landslide's drivers and its kinematics. The cumulative displacement time series were decomposed into trend and periodic components to reliably establish the relationship between displacements and reservoir behavior. A series of numerical slope stability analyses employing finite element limit analysis was performed to identify the material properties compatible with the observed landslide kinematics. Our results shed light on how reservoir behaviors drive landslide development, on how the identified failure mechanisms affect the observed terrain displacements and on which failure mechanism turns out to be dominant as reservoir conditions change. Our findings provide new insight for hazard assessment and mitigation of landslides near reservoirs: considerably smaller local failure mechanisms may cause a tsunami almost severe. Therefore, a single stability analysis may not be adequate but a full suite of analyses probing the range of possible conditions is required. • Modelling and monitoring identify reservoir controls on landslide displacement. • Landslide velocity is more sensitive to reservoir level than to change in level. • Changing reservoir conditions drive time sequencing of the landslide mechanism. • Much smaller landslides do not necessarily result in much smaller tsunamis. [ABSTRACT FROM AUTHOR]