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A thorough understanding of the hydro-mechanical behavior of rock joints is essential since joints typically serve as weak planes and fluid channels within rock masses. Joint roughness, among other factors, dominates the mechanical and hydraulic behavior of rock joints directly. Since 1970s, the joint roughness coefficient (JRC) has been used extensively to quantify joint roughness. As a result of using this variable in empirical equations, we can now anticipate the fluid flow characteristics under stresses. However, the validity of utilizing a single parameter to express the complicated geometry of joint surfaces should be testified. We used three-dimensional (3D) printers to produce a large number of joint samples with similar JRC (2 - 4) but varying surface geometry, including matched and mismatched joint surfaces. The mechanical and hydraulic apertures (E and e) of the printed joint samples were determined utilizing high confining pressure, permeability/porosity measurement equipment (YOKO2). The relationship between E and e can thus be quantified. The results indicate that the stress-dependent mechanical apertures of matched and mismatched joints with similar JRC is significantly different and result in the difference in e-E relationship. However, the measured e-E relationship is quite similar for matched or mismatched smooth joints regardless of joint surface geometry. To conclude, JRC is an appropriate index of smooth joint roughness for representing the stress-dependent e and E and accompanying e-E relationship.

The fragile geology, tectonically and active seismic mountain belt like Taiwan are exposed to numerous geological controls on development of landforms. Especially North-South elongated suture zone between Eurasian and Philippine sea plate formed a Longitudinal valley remarks very active seismic behaviors and bounded by west dipping Central Range Fault (CRF) and east dipping Longitudinal Valley Fault (LVF). Wuhe table land lies on the western side of central part of valley and approximately 200 meters elevated from Xiuguluan River bed. The unconsolidated Mud layers (>50 ka) with few carbonaceous materials of about ten meters’ thicknesses lies in thick conglomerates of tableland could be the lacustrine deposits based on sedimentary environment, which suggest that there was a short-term damming event which is inclined approximate 30 degrees towards northwest. Deformation of mud layer is further studied to analysis the active tectonics and structural controls on tableland. Numerous boreholes, geophysical prospecting, InSAR data, GPS data and past earthquake information are processed on this study as preparation of 3- dimensional geological model and deformation characteristics. Past earthquake behavior shows that CRF acts as blind strike slip movement and very less surface deformation or ruptures but small-scale fissuring on south along Yuli ruptures (Yuli fault trace from 1951 earthquake) from the tableland and the upliftment rate of tableland is slow approximately about >1mm/year. While there are debatable issues regarding to CRF mechanism but this research tries to correlate the active deformation behavior and preservation of Wuhe Tableland on the basis of fault characteristics in this region.

The Outer Western Carpathians represent an accretionary wedge of the Alpine-Himalayan orogenic zone in central Europe, where the Mesozoic and Cenozoic sedimentary (flysch) rocks were deformed and thrust over the European foreland during the Paleogene and Neogene. The thrusting processes terminated in the Upper Miocene, and the contemporary instrumental earthquake distribution records suggest that OWC are already stabilized and belong to the European Plate. This hilly to mountainous region has been intensively affected by various types of shallow slides, debris flows as well as deep-seated slope failures of different magnitudes. Due to the lack of direct evidence of intense seismicity, the permafrost thawing on a turn of the Pleistocene and intense rainfalls in the Holocene have been considered as their principal triggers. However, our current research revealed landforms attributed to the coseismic Holocene polyphase strike-slip faults´ surface ruptures. The associated coseismic sedimentary structures include injected sand and flame structures of fluviolacustrine sediments, large angular boulders in riverbed fluvial sediments, etc. Alongside with those structures and landforms, we documented also evidence for coseismic slope failures in the close surrounding of the faults near Lidečko Village and in the summit area of the Javorníky Mts. in the E part of the Czech Republic and north-western Slovakia, respectively. Several distinct faulting phases with offsets up to a few meters were dated from ca. 10.000 14C ka up to 1240 14C ka BP. Morphological analysis of LiDAR digital elevation models with a 1 m resolution revealed clustered populations of prehistoric presumably coseismic landslides that accompany the fault traces at both sites for a distance up to a couple of kilometres. Field inspections allowed description of their source zones, which were usually several meters up to first tens of meters deep and up to 500 m long. The landslide masses travelled for a distance up to 1-2 km, while being often transformed to debris flows and rock avalanches. They are characteristic with their distinctly depleted source zones at generally gentle slopes ranging from 8 to 20°. The contribution presents the faulting styles, particular events and associated coseismic landslide characteristics in detail and broader regional context, providing the first comprehensive evidence for possible coseismic origin of the deep-seated slope failures in the Outer Western Carpathians.The research was supported by the international bi-lateral project “Earthquake-triggered landslides in recently active and stabilized accretionary wedges” of the Czech Science Foundation (GAČR 22-24206J) and the Taiwanese Ministry of Science and Technology (MOST 111-2923-M-008-006-MY3).

Continuous 5-day (August 4–9, 2019) torrential rainfall in the monsoon season triggered more than 90 landslides on northwest-southeast extended mountain range of Mon State, Myanmar. In this study, remote sensing images, DEM, and limited fieldworks were used to create the landslide inventory. The topography features of these landslides are analyzed via ArcGIS. The largest one occurred on 9 August 2019 and caused 75 deaths and 27 buildings were damaged. This landslide occurred on gentle topography (slope angle, 23°) with long run-out, in which the angle of reach was relatively low (10°). The volume was 111,878 m3 was mainly composed of weathered granite and red soil and the sliding depth was approximately 7.5 m. Topographic characteristics including the relative slope height, angle of reach, and slope angle of source area of 35 landslides with areas > 4000 m2 were analyzed. The spatial distribution characteristics and topographic features of the 35 landslides below are distinguished: (1) the concentration of most of landslides on southwest-facing slopes showing the heterogeneous spatial distribution of landslide; (2) an uncommon landslide distribution in which more than half of landslide originates from upper slope; (3) the range of the angle of the source area (17°–38°) compatible with the internal friction angle of soils in tropical regions (17°–33°); and (4) the tangent of the angle of reach is generally smaller than 0.5 (angle of reach

A three-dimensional engineering geological model (EGM), which provides an approximation of the geological conditions, is a key element in any engineering project. The slope at Huafan University, Mt. Dalun, in the Western Foothills of northern Taiwan, is a dip slope that has been assumed to be unstable. The bedrock is mainly composed of intercalated sandstone and shale, where the thickness of the sandstone varies from thin to massive, interbedded with shale from the Miocene age. By interpolating the thickness of the colluvium derived from borehole data and analyzing the contours of the interpolation surface result, we find that the landslide material accumulates at the slope foot, towards the southwest in the direction of movement. Due to tectonic control—in particular, considering the two local faults that pass through the study area—the strata’s orientation significantly changes over the studied slope. As a basis for the 3D EGM, polynomial surface fitting is applied for detailed analysis of the sub-surface geological structure, as well as to compute the regressive orientation of the bedding plane derived from the borehole data. Based on the calculated regression plane passing through the elevations of the geological interface (key bed), the results indicate that the regression plane’s direction is consistent with the outcrop measurements. Moreover, several cross-sectional profiles are considered to visualize and clarify the 3D EGM. Finally, surface and sub-surface monitoring data are compared with the result, in order to refine the 3D EGM. The proposed geological model is expected to contribute to the comprehensive understanding of gravitational slope deformation, and may serve as a guideline to minimize potential disasters.

Site effect is one of the critical factors influencing the seismic hazard evaluation. Among others, the average shear-wave velocity of the upper 30 meters of a soil profile (Vs30) has been widely used for assessing the ground-motion amplification. However, spatial resolution of shear wave velocity data is usually poor for reginal- or national-wise evaluation. Standard Penetration Test N-value, the most abundant geotechnical data, was then used to estimate the shear wave velocity (Vs) empirically and the uncertainty of the Vs30 map can be reduced. In this study, we use the state variables of soils (void ratio and effective stress) to evaluate the shear wave velocity and to map the Vs30 in Taiwan. Engineering Geological Database for TSMIP (EGDT) comprises soil profile, shear wave velocity measurements, groundwater table, and soil physical properties (such as void ratio, water content, specific gravity, and unit weight), was used to construct the correlation between Vs, void ratio, and effective stress. The drilling database of Taiwan CGS was then used to estimate the spatial distribution of Vs30, where the Vs is un-available. The results were compared with the previous version of Vs30 map of Taiwan. The uncertainty of the new Vs30 map was evaluated and the propagation of uncertainty to the seismic hazard can be evaluated accordingly.

In this study, analysis results reveal two main deposition zones are located at the flank of upper Gaoping Submarine Canyon and Lower Fangliao Basin offshore SW Taiwan. The non-event related sediments deposited in past 150 years (i.e., 632 Mt km-2) was delivered and transported from Gaoping River by suspension process with tides and coastal currents and gradually spread out offshore. Meanwhile, the total mass of accumulation sediments is 1922 Mt km-2, accounting for 40% Gaoping Riverâs sediment load and suggesting that the deposition process is mainly controlled by natural hazards. Sedimentation rates in much of the study area, except in the main deposition zones, are less than 0.5 cm yr-1 (5 m kyr-1). Compared with the studies at the instability seafloor caused by high sedimentation rates (~30 m kyr-1), the offshore southwestern Taiwan is relatively stable. In this study, we also discovered a series of sediment waves located on the upper continental slope between Gaoping and Fangliao Submarine Canyons, which is related to the creeping process on seafloor. In summary, our results reveal the fluid activities, existence of weak layers and earthquake triggering are potential factors which might induced seafloor failures offshore southwestern Taiwan.

Submarine landslides frequently occur in passive continental margins or active margins (Hampton et al. 1996; Wynn et al. 2000; Mienert et al. 2002; Korup et al. 2007; Twichell et al. 2009; Cukur et al. 2016). Submarine landslides have been studied extensively not only for scientific research but also for submarine geohazards. Submarine landslides could jeopardize marine infrastructures, such as offshore drilling platforms or submarine telecommunication cables, and could even trigger disastrous tsunamis (Bondevik et al. 2005; Harbitz et al. 2006; Hornbach et al. 2007, 2008; Hsu et al. 2008; Su et al. 2012; Tappin et al. 2014; Li et al. 2015). For instance, one disastrous tsunami hitting the coastal area of southwestern Taiwan in 1781 or 1782 was reported (Chen 1830; Hsu 1983); the tsunami event was probably generated by submarine landslides in the offshore area of southwestern Taiwan (Li et al. 2015). Moreover, several submarine landslides triggered by the 2006 Pingtung earthquake have induced turbidity currents off southwest Taiwan and destroyed about 14 submarine telecommunication cables off SW Taiwan (Hsu et al. 2008). The area of southwest Taiwan currently has a dense population (more than 3 million people in total), one deep-water Kaohsiung Port, several tanks of liquefied natural gas and a nuclear power plant on the coast (Fig. 1). Numerous submarine telecommunication cables exist off SW Taiwan. If a considerable tsunami event would hit again the costal area of SW Taiwan, the damage could very serious. Likewise, there are two nuclear power plants on the coast of northern Taiwan (Fig. 2), and the population in northern Taiwan has more than 10 million people. Submarine telecommunication cables also exist off northern Taiwan. In any case, it is important to understand the status of seafloor stability in the offshore areas of SW and NE Taiwan. For that, this special issue of submarine geohazard records and potential seafloor instability is aimed to provide some research results, hoping to have a general reconnaissance of submarine landslide potential off Taiwan.

The importance of the geological model in a geotechnical engineering project has long been recognized. However, the uncertainty associated with the geological model has rarely been quantified and explicitly considered in the geotechnical design. This paper explores the role of the geological model uncertainty and the benefit of reducing such uncertainty in a geotechnical design. To this end, the landslide that occurred on 25 April 2010 at 3.3 K of Freeway No. 3 in Northern Taiwan, referred to herein as NH-3 Slope, is re-analyzed with an assumed geological model (a dip-slope model in this case) under various uncertainty scenarios. Traditionally, the design (i.e., a choice of design parameters such as slope height, slope angle, and supporting anchors) of a rock slope seeks to satisfy a target factor of safety (FS). In the case of NH-3 Slope, the apparent dip angle of the slip surface along the dip direction of slope constitutes the geological model of concern. Different survey techniques produce data with varying degrees of error (or uncertainty) in the measured apparent dip angle. For example, data from a Regional Geological Map (RGM) typically yields an estimate of the bedding plane attitude with a significant level of uncertainty due primarily to low data density. In contrast, LiDAR can significantly reduce the uncertainty of the derived bedding plane attitudes. By lowering this uncertainty, the variation (or uncertainty) in the computed FS may be reduced, which tends to yield a lower failure probability (Pf), given other conditions being the same. The benefit of lowering the geological model uncertainty in a geotechnical design is demonstrated through a retrospective analysis of the NH-3 Slope.

We established a stress-history-dependent porosity model of potential target rocks for CO_2 geosequestration based on rock sample porosity measurements under various effective stresses (5 - 120 MPa). The measured samples were collected from shallow boreholes (＜ 300 m depth) drilled at the frontal fold in northern Taiwan. The lithology, density, and the stress-history-dependent porosity derived from shallow boreholes enabled us to predict the porosity-depth relationship of given rock formations at (burial depths of approximately 3170 - 3470 m) potential sites for CO_2 geosequestration located near the Taoyuan Tableland coastline. Our results indicate that the porosity of samples derived from laboratory tests under atmospheric pressure is significantly greater than the porosity measured under stress caused by sediment burial. It is therefore strongly recommended that CO_2 storage capacity assessment not be estimated from the porosity measured under atmospheric pressure. Neglecting the stress history effect on the porosity of compacted and uplifted rocks may induce a percentage error of 7.7% at a depth of approximately 1000 m, where the thickness of the eroded, formerly overlying formation is 2.5 km in a synthetic case. The CO_2 injection pressure effect on the porosity was also evaluated using the stress-historydependent porosity model. As expected, the pore pressure buildup during CO_2 injection will induce an increase in the rock porosity. For example, a large injection pressure of 13 MPa at a depth of approximately 1000 m will increase the rock porosity by a percentage error of 6.7%. Our results have implications for CO_2 storage capacity injection pressure estimates.

The critical taper model has been widely used to evaluate the strength contrast between the wedge and the basal detachment of fold-and-thrust belts and accretionary wedges. However, determination of the strength parameters using the traditional critical taper model, which adopts the Mohr–Coulomb failure criterion, is difficult, if not impossible. In this study, we propose a modified critical taper model that incorporates the non-linear Hoek–Brown failure criterion. The parameters in the proposed critical Hoek–Brown wedge CHBW model can be directly evaluated via field investigations and laboratory tests. Meanwhile, the wedge strength is a function of the wedge thickness, which is oriented from stress non-linearity. The fold-and-thrust belt in western central Taiwan was used as an example to validate the proposed model. The determined wedge strength was 0.86 using a representative wedge thickness of 5.3 km; this was close to the inferred value of 0.6 from the critical taper. Interestingly, a concave topographic relief is predicted as a result of the wedge thickness dependency of the wedge strength, even if the wedge is composed of homogeneous materials and if the strength of the detachment is uniform. This study demonstrates that the influence of wedge strength on the critical taper angle can be quantified by the spatial distribution of strength variables and by the consideration of the wedge thickness dependency of wedge strength.

A hydraulic tomography survey (HTS) is a conceptually improved technique that has been recognized to be efficient for estimating high-resolution aquifer parameters. Based on the concept of HTS, this study presents a modified stochastic inverse model for estimating hydraulic conductivity (K) and specific yield (Sy) in shallow and highly permeable unconfined aquifers. A well field with 15 fully screened wells was developed for the purpose of model implementations. In this study a synthetic example was first employed to assess the accuracy of the inverse model. We then implemented the model to field-scale, cross-hole injection tests in a shallow and highly permeable unconfined aquifer near the middle reach of the Wu River in central Taiwan. To assess the effect of constant head boundary conditions on the estimation results, two additional modeling domains were evaluated based on the same field data from the injection tests. Results for the synthetic example show that the modified inverse model can reproduce well the predefined geologic features of the unconfined aquifer. The inverse model can estimate accurately the ln K patterns and magnitudes. However, slightly fewer details of the ln Sy field are obtained due to the insensitivity of transient hydraulic stresses for specified sampling times. Model implementations of field-scale injection tests show that the model can estimate ln K and ln Sy fields with high spatial resolution. The estimated K and Sy values for the test site vary by one order of magnitude, indicating a relatively homogeneous aquifer for the tested well field. Results based on three different modeling domains show similar patterns and magnitudes of ln K and ln Sy near the well locations. This result suggests that the case with domain 40 m × 20 m should be sufficient for the injection tests at the well field.

Electrical Resistivity Imaging (ERI) was carried out continuously for 10 days to map the subsurface resistivity distribution along a potentially hazardous hillslope at the Jieshou Junior High School in Taoyuan, Taiwan. The reliability of the inverted resistivity structures down to about 25 m depth was examined with synthetic modeling using the same electrode arrangements installed on land surface as in field surveys, together with a DOI (depth-of-investigation) index calculated from the ERI data. The subsurface resistivity distribution is consistent with results from well logging. These ERI recordings were taken daily and provided highly resolved imagery of the resistivity distribution underground and illustrated the dynamical fluid-flow behavior due to heavy rainfall infiltration. Using Archie’s law, the resistivity distribution was transformed into a map of relative water saturation (RWS), which is strongly correlated with the rainfall infiltration process. We then found that the averaged RWS is significantly correlated with daily precipitation. Our observations indicate that time-lapse ERI is effective in monitoring subterraneous rainfall infiltration; moreover, the preferential flow paths can be delineated according to the changes in averaged RWS derived from the ERI data.

Earthquakes can generate seismic disturbances that propagate vast distances and trigger landslides that can achieve high-speeds. It remains difficult to identify the co-seismic ground motion of these landslides and their triggering earthquakes. In this paper, we report on the analysis of co-seismic ground motions generated by the initiating fracture and deposition impact of the Tsaoling landslide. The landslide, with a source volume of 125 × 10 6 m 3 , was triggered by the 1999 Chi-Chi earthquake in Taiwan. The ground motion was recorded by a strong ground motion station, CHY080, near the scar area. The polarization of the seismic waves indicates that the peak acceleration was parallel to the dip direction. Modified ensemble empirical mode decomposition (EEMD), with additional clustering analysis, was applied to decompose the seismic signals. Two instances were found in the seismic records of a series of peculiar wave packets, with the first being associated with the landslide initiation and the second the landslide impact on the deposit valley. To confirm the first landslide breakage, the decomposed signals were compared with the predictions of the analytic elastic wave model and Newmark analysis. The landslide impact was verified with a computational fluid dynamic simulation. Comparison between the EEMD decomposed signals, elastic wave theory, Newmark rigid body analysis, and numerical simulation demonstrates the claimed landslide motion.

Tsaoling landslide is the largest and best documented landslide among several large landslides induced by the 1999 Taiwan Chi-Chi earthquake. Pliocene sedimentary rocks of about 125 Mm 3 in volume slid along very flat bedding planes dipping by 14° with an average speed of 35–40 m/s for about 1650 m, before hitting the bank of the Chinshui River during the landslide. Detailed analysis of DTMs before and after the earthquake using a GIS software leads to an accurate determination of the locations of the centroids of landslide mass, revealing the horizontal and vertical displacements of the 2524 m and 524 m, respectively. Those displacements and landslide mass give an apparent friction coefficient of 0.21 and the release of the potential energy of 1.6 × 10 15 J. We conducted rotary-shear high-velocity friction experiments on fault gouge from bedding-parallel faults under semi-wet conditions and at 3 MPa normal stress corresponding to the overburden pressure of the landslide mass. We also compiled reported data on the frictional properties on shale powders and fault gouge from the landslide site under both dry and wet conditions, and proposed a velocity–displacement dependent friction law that can describe most experimental data. Newmark analysis of landslide motion with six scenarios for different landslide materials and conditions, assuming a simple rigid block sliding and using measured frictional parameters, revealed that the landslide did not occur with dry frictional properties, and that the landslide occurred at 38–39 s with accumulated displacements of 0.62 m–1.09 m and reached at the river bank at 82–87 s after the generation of Chi-Chi earthquake at its epicenter. Those timings are consistent with high-frequency signals at 32–40 s and at 76 s recorded at a nearby seismic station and with a survivor's witness that the landslide initiated 10 s after he felt strong ground motion, possible S wave arrival at 25.2 s. Slip-weakening is essential in initiating the landslide and low friction coefficient (0.08–0.1) allowed high-speed of the landslide possible. The landslide was caused by a few peaks of northeast-oriented strong accelerations of the ground motion. Frictional work during the sliding of the landslide mass was estimated to be of about 23% of potential energy, and the rest of the released energy is likely to have been consumed during the stopping phase of the landslide after hitting the river bank in complex processes such as fragmentation, heat dissipation, and spreading of the landslide deposits.

Pliocene sedimentary rocks of about 130 Mm3 in volume slid along bedding planes dipping by 14°, with an average speed of about 35 m/s, during the Tsaoling landslide. We conducted friction experiments to reproduce the initiation processes of this landslide, by idealizing landslide movements during the earthquake as accelerating/decelerating motion. Experiments were done on shale from the field, at 3 MPa normal stress corresponding to the overburden pressure. Results indicate that the accelerating/decelerating motion causes weakening and strengthening at each oscillation cycle and results in overall slip weakening which can be approximated as an exponential slip weakening. Behaviors during oscillatory slip are fairly similar to those during sliding at constant slip rates. Newmark analysis with measured frictional properties reveals that the landslide can be triggered with wet gouge properties, but the landslide motion stops with parameters for dry shale gouge. Delayed initiation of the landslide is consistent with a survivor's witness.

In the article “Engineering geology-A fifty year perspective”(Juang et al., 2016), which celebrated the 50th anniversary of Engineering Geology, the authors described Engineering Geology for Engineering Projects (EGEP) together with Geological Engineering and Geotechnical Engineering (GEGE) as important elements of Engineering Geology. For example, four-hundred and twelve papers were published in Engineering Geology from 1986–1995. Among which, one-hundred and twenty (about 30%) were related to EGEP. The research topics mainly included design and construction of foundations, tunnels, and slopes (eg dams, embankments, landslides). However, the papers published on EGEP and GEGE declined significantly from 2006 to 2015. It was speculated that the worldwide economic recession that began in 2008 might have contributed to the decline of infrastructure development and the number of …

Carbon dioxide geological sequestration (CGS) has been recognized as one of the potential solutions for reducing anthropogenic CO2 emissions. The Changhua Coastal Industrial Park (CCIP) in central Taiwan has been preliminarily evaluated as a potential site for CGS. The CCIP site possesses sloping and layered heterogeneous formations with stagnant groundwater flow. Previous geophysical investigations of seismic reflection survey have found no significant faults near this site. Prior to the actual application of CGS in the field, it is important to carry out numerical simulations to predict the short- and long-term evolution of injected CO2 into deep geological formations. In this study, the TOUGHREACT/ECO2N simulator is employed in order to conduct comprehensive CGS assessments at the CCIP site. Field scale CGS simulations are utilized to capture the details of the physical features, such as the displacement of saline brine by the injection of CO2, buoyancy/gravity convection, and salt precipitation due to pore water dry-out, in the vicinity of the CO2 injection well. Simulation results show that (1) the migration of CO2 plume did not penetrate the low permeability formation at 500 years, (2) formation tilting caused a slightly asymmetric CO2 plume oriented toward the up-tilt direction, and (3) the amount of solubility and residual gas trapping accounted for 26.8% and 19.0%, respectively, of injected CO2 by weight at 500 years.

The critical displacement is referred to as a threshold for slope failure, compared with the calculated permanent displacement under seismic load using Newmark displacement analysis. The critical displacement, usually obtained from laboratory shear tests under low and constant shear rates, is defined as the coseismic displacement beyond which strength of sliding surface reach residual values. The typical value ranges a few centimeters, depending on the frictional characteristics of sheared materials. However, this definition of the critical displacement might be oversimplified since the strength of sliding surface is velocity-dependent. Therefore, we collected the shear tests results of different materials under different shear velocities to evaluate the velocity-displacement dependency. Besides, we redefine the critical displacement of catastrophic landslide (D cr ) as the accumulated permanent displacement before rapid slide occurred. The influence of the strength and seismic parameters on the newly defined critical displacement is assessed using Newmark displacement analysis incorporating velocity-displacement dependent friction law. The dip angle of sliding surface is assumed as 15°. The synthetic seismic load is simplified as sinusoidal wave with peak ground acceleration of 600 gal. Different seismic frequencies of 0.5, 1.2, 2.0 Hz are used to evaluate the influence of frequency on D cr . The results show that the range of D cr is much higher than few centimeters, and D cr is highly related to frictional characteristics of sheared materials, especially within the slip-weakening distance. Moreover, D cr is also influenced by frequency rather than peak ground motion acceleration of the sinusoidal wave. This study highlights that the initiation of landslide are extremely complex, which can be function of frictional law, seismic frequency, and geometry of sliding plane. The reasonableness of the velocity-displacement dependent friction law and the representative of the seismic wave should be considered for evaluating the initiation of catastrophic, rapid moving landslide.

To characterize the hypermobility mechanism of rock avalanches, a series of rotary shear tests at different shearing velocities (Veq) ranging from 0.07 m/s to 1.31 m/s and at a normal stress of 1.47 MPa were carried out on soil sampled from the basal facies of the Yigong rock avalanche that occurred in the Tibetan plateau in China. Through conducting these tests, the macroscale and microscale features of the deformed samples were analyzed in detail with the following valuable conclusions being reached: (1) soil subjected to rotary shear exhibits a clear velocity-dependent weakening characteristic with an apparent steady state friction of 0.13 being reached at Veq ≥ 0.61 m/s, (2) high-temperature rises and layers with high porosity were observed in the samples sheared at Veq ≥ 0.61 m/s, and (3) the cooperation of thermal pressurization and moisture fluidization induced by friction heating plays an important role in explaining the marked frictional weakening of the soil. In addition, the appearance of nanoparticles due to particle fragmentation should facilitate the weakening of the soil but is not the key reason for the marked frictional weakening.

Dam-breaches that cause outburst floods may induce downstream hazards. Because landslide dams can breach soon after they are formed, it is critical to assess the stability quickly to enable prompt action. However, dam geometry, an essential component of hazard evaluation, is not available in most cases. Our research proposes a procedure that utilizes post-landslide orthorectified remote sensing images and the pre-landslide Digital Terrain Model in the Geographic Information System to estimate the geometry of a particular dam. The procedure includes the following three modules: (1) the selection of the reference points on the dam and lake boundaries, (2) the interpolation of the dam-crest elevation, and (3) the estimation of dam-geometry parameters (i.e., the height, length, and width), the catchment area, the volumes of barrier lake and landslides dam. This procedure is demonstrated through a case study of the Namasha Landslide Dam in Taiwan. It was shown the dam-surface elevation estimated from the proposed procedure can approximate the elevation derived from profile leveling after the formation of the landslide dam. Thus, it is feasible to assess the critical parameters required for the landslide dam hazard assessment rapidly once the ortho-photo data are available. The proposed procedure is useful for quick and efficient decision making regarding hazard mitigation.

This paper presents a 2D numerical technique based on the boundary element method (BEM) for the analysis of linear elastic fracture mechanics (LEFM) problems on stress intensity factors (SIFs) involving anisotropic bimaterials. The most outstanding feature of this analysis is that it is a singledomain method, yet it is very accurate, efficient, and versatile (i.e., the material properties of the medium can be anisotropic as well as isotropic). A computer program using the BEM formula translation (FORTRAN 90) code was developed to effectively calculate the stress intensity factors (SIFs) in an anisotropic bi-material. This BEM program has been verified and showed good accuracy compared with the previous studies. Numerical examples of stress intensity factor calculation for a straight crack with various locations in both finite and infinite bimaterials are presented. It was found that very accurate results can be obtained using the proposed method, even with relatively simple discretization. The results of the numerical analysis also show that material anisotropy can greatly affect the stress intensity factor.

This study aims to quantify the tectonically induced thrusting and erosion. Here, we propose and evaluate a laboratory-based method for determining the maximum effective stress ever sustained by a sedimentary-rock formation. The porosities of nineteen samples collected from two deep boreholes of the Taiwan Chelungpu-Fault Drilling Project were measured under different confining stresses. The relation between measured porosity and confining pressure (compaction curve) is bilinear in log–log scale. The maximum effective stress of the tested rocks was determined from the intersection point of the two straight lines of the compaction curve. The maximum effective stresses of the rocks below the Sanyi Fault (reverse fault) are close to the in-situ vertical effective stress. Above the Sanyi Fault (hanging wall), where the rocks have been thrust, the maximum effective stresses of the rocks are significantly greater than the in-situ stress with an average value of 29.48 MPa. That is, the eroded thickness of the formation on the hanging wall of the Sanyi Fault is 2482 m, a value close to that determined from the geological profile (2773 m). It is inferred that the total displacements along the thrust Sanyi Fault is 11.5 km, a value close to that determined from the geological profile (14–16 km). These results indicate that the proposed laboratory-based method is potentially useful for determining the thrusting and erosion in a fold–thrust belt and the total displacements along a thrust fault.

Inundation caused by landslide dams may occur in the upstream and downstream of the dams. A proper flooding hazard assessment is required for reaction planning and decision-making to mitigate possible flooding hazards caused by landslide dams. Both quick and detailed procedures can be used to evaluate inundation hazards, depending on the available time and information. This paper presents a systematic approach for the assessment of inundation hazards and risks caused by landslide dam formation and breaches. The approach includes the evaluation of dam-breach probability, assessment of upstream inundation hazard, assessment of downstream inundation hazard, and the classification of flooding risk. The proposed assessment of upstream inundation estimates the potential region of inundation and predicts the overtopping time. The risk level of downstream flooding is evaluated using a joint consideration of the breach probability of a landslide dam and the level of flooding hazard, which is classified using a flooding hazard index that indicates the risk of potential inundation. This paper proposes both quick and detailed procedures for the assessments of inundation in both the upstream and downstream of a landslide dam. An example of a landslide dam case study in southern Taiwan was used to demonstrate the applicability of the systematic approach.

This paper presents a numerical procedure to explore how hydraulic conductivity anisotropy and strength anisotropy affect the stability of stratified, poorly cemented rock slopes. The results provide information about the anisotropic characteristics of the medium, including the orientation of bedding planes, the anisotropic ratios of the hydraulic conductivity and the geological significance of the hydraulic conductivity anisotropy on the pore water pressure (PWP) estimation of finite slopes. Neglecting the hydraulic conductivity anisotropy of a slope with horizontal layers leads to a 40% overestimation of the safety factor. For a dip slope with inclined layers with θ = 30°, including the strength anisotropy caused a 25% reduction of the safety factor compared to the cases which isotropic strength is assumed. This paper highlights the importance of the hydraulic-conductivity anisotropy and the strength anisotropy on the stability of stratified, poorly cemented rock slopes.

Typhoon Morakot (2009) caused serious damage in southern Taiwan due to intensive rainfall with long duration. The issue of greatest concern arising from the disasters brought about by this extreme event was the burying of the entire village of Hsiaolin by a massive debris flow and landslide. Based on seismological and near-surface magnetic data, this tragic scenario arose due to a combination of events, a massive landslide, the formation of a landslide dam, and the consequent debris flow when this dam was breached. The objective of this part of the study is to investigate the spatial and temporal characteristics of the debris flow induced by the landslide breach. The US National Weather Service BREACH model and the Federal Emergency Management Agency approved FLO-2D model are integrated to facilitate the investigation of this catastrophe. A series of simulations including a 2D rainfall-runoff simulation over the Cishan River basin, landslide dam breach routing, and 2D debris flow simulation around the Hsiaolin Village were conducted. Hydraulic calculations were performed to determine the equivalent top elevation of the landslide dam based on inflows computed from the 2D rainfall-runoff simulation in association with the Digital Terrain Model (DTM) and upstream constraint of the backwater inundation areas. The hydrograph of the upstream inflow which induced overtopping failure was provided by a 2D rainfall-runoff simulation using the FLO-2D model calibrated by comparison with the downstream discharge record. The longevity of the landslide dam was less than 1 h, and it took only about 8 minutes to completely breach. The peak discharge rate of this massive landslide dam breach was 70,649 m3/s. The dam break hydrograph was then used for upstream inflow to drive the FLO-2D debris flow simulation. The average sediment concentration by volume was 0.362. The simulated deposited sediment depth showed a reasonable match to the differences of DTMs before and after the disaster.

In this paper, technologies from multiple disciplines are used to reconstruct the shape of the Hsiaolin landslide dam, a short-lived landslide dam (SLD), that was triggered by Typhoon Morakot. Here, the formation, failure mode and breaching process of this SLD are investigated. The results indicate that the overtopping time and the debris budget constrained the dam geometry. The inferred volume of the Hsiaolin landslide dam (15.4 million m3) is much smaller than the actual landslide volume (25.2 million m3) even considering the rock-mass dilation and debris entrainment. Meanwhile, a 46% error could be induced if an over-simplified equation (a function of the dam height, length and width) is used to calculate the dam volume. The saddle of the dam crest, which is where overtopping occurred, could be used as a reference to measure the dam height and length. Accordingly, the determined dam dimensions of height (44 m), length (370 m) and width (1500 m) are suggested to be the representative geometrical indices that influenced the stability of the Hsiaolin landslide dam. The flow rate of the dammed river, another variable relevant to dam stability, was determined from a run-off simulation. It is suggested that, instead of the peak flow before the dam formation, the flow rate during the blockage period (2974 m3/s) should be used as the training data for building a statistical model for stability predictions. Finally, the low hydraulic gradient at the toe of the dam's surface and the high safety factor of the dam slope indicate that the piping and slope instability were irrelevant to the failure of the Hsiaolin short-lived landslide dam. It is postulated that overtopping (about one hour after the blockage) dominated the failure process of this heavy-rainfall-induced landslide dam.

Typhoon Morakot caused serious damage to southern Taiwan. Almost all major mountain highways located in the affected region suffered severe damage from landslides, rock falls, and debris flows. Among these highways, Ali Mountain Highway is one of the most severely affected. Ali Mountain Highway, i.e., T18 route, was constructed in the early 1980s. For the past 30 years of operation, it has suffered substantial damage from different natural hazards. The continued damage–rehabilitation cycle is implemented to maintain the serviceability of this highway. Ali Mountain Highway was seriously damaged by the strike of typhoon Morakot on August 8, 2009. Traffic through this highway was interrupted for over 3 months until temporary rehabilitation was completed. This paper provides a summary of the damage suffered along the Ali Mountain Highway and presents suggestions for mitigation strategies to minimize the likelihood of similar levels of damage during other extreme typhoons such as the typhoon Morakot. The manuscript summarizes extensive field surveys and aerial photo analysis carried out by the authors to investigate the mechanisms of typical slope failures along the Ali Mountain Highway. The engineering geology perspectives are emphasized in the analyses. Geological and hydrogeological features for the sites in this study were found to be the most influential factors dominating the failures. The fault-related weak zones and impermeable layers dominated the global stability of the slopes. In summary, geotechnical engineers should consider carefully the characteristics of geological structures for mitigation and rehabilitation of landslides. Extreme scenarios, such as typhoon Morakot, should also be considered.

A large and deep-seated landslide at Hungtsaiping was triggered by the 1999 Chi-Chi earthquake with the magnitude of 7.3. Extensive site investigations for the landslide were conducted including field reconnaissance, geophysical exploration, borehole logs, and laboratory experiments. Thick colluvium was found around the landslide area and indicated the occurrence of a large ancient landslide. The Hungtsaiping area involves at least two large landslides events, an ancient rockslide and the 1999 colluvium slide. With the consideration of a source collapse mass, the two landslides in sequence are reasonably reproduced by the distinct element modeling. The modeling is calibrated by rock mass strength behavior through a procedure with the Hoek–Brown failure criterion, statistical experimental design, and optimization techniques. The mechanism of the 1999 landslide that cannot be revealed by the underground exploration data alone is clarified. The proposed procedure enables a rational and efficient way to determine micro-parameters for the distinct element modeling of landslides.

Landslides may obstruct river flow and result in landslide dams; they occur in many regions of the world. The formation and disappearance of natural lakes involve a complex earth–surface process. According to the lessons learned from many historical cases, landslide dams usually break down rapidly soon after the formation of the lake. Regarding hazard mitigation, prompt evaluation of the stability of the landslide dam is crucial. Based on a Japanese dataset, this study utilized the logistic regression method and the jack-knife technique to identify the important geomorphic variables, including peak flow (or catchment area), dam height, width and length in sequence, affecting the stability of landslide dams. The resulting high overall prediction power demonstrates the robustness of the proposed logistic regression models. Accordingly, the failure probability of a landslide dam can also be evaluated based on this approach. Ten landslide dams (formed after the 1999 Chi-Chi Earthquake, the 2008 Wenchuan Earthquake and 2009 Typhoon Morakot) with complete dam geometry records were adopted as examples of evaluating the failure probability. The stable Tsao-Ling landslide dam, which was induced by the Chi-Chi earthquake, has a failure probability of 27.68% using a model incorporating the catchment area and dam geometry. On the contrary, the Tangjiashan landslide dam, which was artificially breached soon after its formation during the Wenchuan earthquake, has a failure probability as high as 99.54%. Typhoon Morakot induced the Siaolin landslide dam, which was breached within one hour after its formation and has a failure probability of 71.09%. Notably, the failure probability of the earthquake induced cases is reduced if the catchment area in the prediction model is replaced by the peak flow of the dammed stream for these cases. In contrast, the predicted failure probability of the heavy rainfall-induced case increases if the high flow rate of the dammed stream is incorporated into the prediction model. Consequently, it is suggested that the prediction model using the peak flow as causative factor should be used to evaluate the stability of a landslide dam if the peak flow is available. Together with an estimation of the impact of an outburst flood from a landslide-dammed lake, the failure probability of the landslide dam predicted by the proposed logistic regression model could be useful for evaluating the related risk.

This study proposes a sediment-budget model to predict the temporal variation of debris volume stored in a debris-flow prone watershed. The sediment-budget is dominated by shallow landslides and debris outflow. The basin topography and the debris volume stored in the source area of the debris-flow prone watershed help evaluating its debris-flow susceptibility. The susceptibility model is applied to the Tungshih area of central western Taiwan. The importance of the debris volume in predicting debris-flow susceptibility is reflected in the standardized coefficients of the proposed statistical discriminant model. The high prediction rate (0·874) for the occurrence of debris flows justifies the capability of the proposed susceptibility models to predict the occurrence of debris flows. This model is then used to evaluate the temporal evolution of the debris-flow susceptibility index. The analysis results show that the numbers of watershed which are classified as a debris-flow group correspond well to storage of sediment at different time periods. These numbers are 10 before the occurrence of Chi-Chi earthquake, 13 after the occurrence of Chi-Chi earthquake, 16 after the occurrence of landslides induced by Typhoon Mindulle (Typhoon M), and 14 after the occurrence of debris flows induced by Typhoon M. It indicates that the occurrence of 7·6 Chi-Chi earthquake had significant impact on the debris flow occurrence during subsequent typhoons. Copyright © 2009 John Wiley & Sons, Ltd.

article i nfo Landslides can cause the formation of dams, but these dams often fail soon after lake formation. Thus, rapidly evaluating the stability of a landslide dam is crucial for effective hazard mitigation. This study utilizes discriminant analysis based on a Japanese dataset consisting of 43 well documented landslide dams to determine the significant variables, including log-transformed peak flow (or catchment area), and log- transformed dam height, width and length in hierarchical order, which affect the stability of a landslide dam. The high overall prediction power (88.4% of the 43 training cases are correctly classified) and the high cross- validation accuracy (86%) demonstrate the robustness of the proposed discriminant models PHWL (with variables including log-transformed peak flow, and log-transformed dam height, width and length) and AHWL (with variables including log-transformed catchment area, and log-transformed dam height, width and length). Compared to a previously proposed "DBI" index-based graphic approach, the discriminant model AHV - which uses the log-transformed catchment area, dam height, and dam volume as relevant variables - shows better ability to evaluate the stability of landslide dams. Although these discriminant models are established using a Japanese dataset only, the present multivariate statistical approach can be applied for an expanded dataset without any difficulty when more completely documented worldwide landslide-dam data are available.

On September 20, 1999, the M s 7.6 Chi-Chi earthquake ruptured the Chelungpu fault in central Taiwan. After the earthquake, two deep boreholes cutting the fault were drilled. The seismic velocities (P- and S-wave velocities denoted by v p and v s ) were well-logged at a 2000-m deep hole. The values of density, porosity and permeability of ten rock samples obtained at different depths were measured in the laboratory. Well-logged and measured results are used to study the following problems: (1) the depth variations in seismic velocities, porosity, and permeability; (2) the relationship between P- and S-wave velocities; (3) porosity-dependence of P- and S-wave velocities and their ratio; and (4) porosity-dependence of density. Results show that the polynomial can describe the depth variations in seismic velocities. The porosity slightly decreases with increasing depth. The permeability is depth-dependent and can be described by a polynomial, but the functions are different for different rock types. The porosity and permeability in the fault zone cannot be evaluated from the related depth-dependent functions inferred from wall rocks. A linear relationship, which is different from v s = 0.58 v p for the perfectly elastic materials, exists between v s and v p . Seismic velocities linearly decrease with increasing porosity. The ratio of v p to v s slightly depends on the porosity. The porosity-dependent functions of bulk and shear modulus are constructed and their values for dry rocks are also evaluated.

The Chi-Chi earthquake (Mw = 7.6) of September 21, 1999 triggered many landslides in central Taiwan. Two of these landslides, Hungtsaiping (HTP) and Jiufengershan (JFES) were situated as close as 2 km from each other but had significant differences in their kinematics. JFES landslide was a catastrophic rockslide-avalanche and the HTP landslide was relatively slow-moving. The authors conducted a study to explore the reasons for such differences. Factors such as the characteristics of strong ground motion, sliding direction of landslide, and friction angle of the sliding surface were considered in the study. An analysis of 12 strong-motion records collected in the study area showed that the distribution of horizontal pseudostatic coefficients, earthquake energy ratio and permanent sliding-block displacements (Newmark displacement) were anisotropic with their predominant direction mostly in the E/W–ESE/WNW trending. This direction is perpendicular to the axis of the main geological structures of the studied area. The computed Newmark displacement in the sliding direction of the JFES landslide is larger (44%) than that of the HTP landslide with sliding surface inclination of 21° and friction angle of 28° We can conclude that the seismic anisotropy and the corresponding sliding direction are important contributing factors to the kinematics of studied landslides. The back-calculated friction angle of the sliding surface that corresponds to a critical Newmark displacement for the JFES landslide is about 3.5° higher than that of HTP landslide. The material (colluvium) on the sliding surface in HTP should be less velocity-dependent than that of the JFES landslide (rock) according to the back calculations. The importance of seismic anisotropy, sliding direction, and mechanical properties of sliding surface on the kinematics of deep-seated landslides is demonstrated.