Dip Slope Research Articles

Spatial coupling relationship between faults and gold deposits in the Jiaodong ore concentration area and the effect of thermal doming-extension on mineralisation

As the third largest gold ore-forming province in the world, the deep metallogenic potential of and exploration strategies for Jiaodong gold deposits have attracted substantial attention. By applying three-dimensional (3D) geological modelling to these super-giant and giant gold deposits, this study reveals the 3D morphological characteristics of the ore-bearing faults and the ore-related granites, analyses the relationships between ore body locations and slope dip angle changes in the faults, and discusses the coupling relationships among gold mineralisation, ore-controlling faults, and magmatic activities. In the 3D model, the dip angles of ore-controlling faults gradually decrease downwards and alternate between steep and gentle along the fault dip direction. The ore bodies mainly occur in areas with relatively high fault-dip-angle change rates. Hence, positions with fault dip angles of 20°–50° and change rates of ≥0.91 should be considered as target areas for prospecting deep gold ore bodies. In-depth analysis suggests that the ore-hosting faults, granites, and gold mineralisation resulted from regional thermal doming and extensional movements. Gold ore bodies in the Jiaodong Peninsula occur inside or on the periphery of Mesozoic granite. Strong magmatic activities during the transition from enriched to depleted mantle provided the necessary metallogenic and thermal dynamic environment for gold mineralisation. In particular, the magmatic evolution provided abundant ore-forming materials. The detachment faults with varied dip angles provided favourable space for gold mineralisation, as the fluctuations of ore-forming fluid pressure caused by sudden changes in these dip angles served as the primary mechanism underlying the step-like gold mineralisation pattern.

Favorable reservoir prediction and connection model biulting of thick glutenite sediment in basin steep slope zone

The glutenite deposit in the Dongying basin's dip slope zone, which is influenced by Palaeogeomorphology, has a large deposit thickness, a diverse lithology that varies rapidly in the horizon, and a difficult sand body superposition. Due to the resolution of seismic data and the vast variances across sedimentary, the connection of sand bodies cannot be represented using a simple way, and it is difficult to analyze the link regulation between water injection and oil extraction. The seismic facies of distinct glutenite sediments may be determined using well data and the properties of glutenite deposits in nearshore subaquatic settings. Several inversion techniques are used to construct the low and high-frequency component, resulting in a high-quality sand prediction result with reasonably high resolution that adheres to sedimentary laws, using seismic facies analysis as a constraint and making full use of good data. The management of sand spread and connection may be defined based on the sand prediction result, and sand body connection models of different sedimentary surfaces can be created and used to change the well water intrusion.

Geology, geomorphology and geochronology of the coseismic? Emad Deh rock avalanche associated with a growing anticline and a rising salt diapir, Zagros Mountains, Iran

This work documents for the first time the prehistoric, but morphologically pristine, Emad Deh rock avalanche of the Zagros Mountains. The ca. 420 Mm3 rock avalanche was initiated as a rockslide on a dip slope affecting a weak unit of marls with interbedded limestones overlain by a thick and competent limestone formation. The slope is located on the northern limb of the growing Gavbast Anticline and at the edge of the inflating Gavbast Dome, related to a buried salt diapir of Hormuz salt. The unconfined rock avalanche deposits, covering 32 km2, were accumulated on coalescing alluvial fans and a floodplain environment. The depositional lobe shows sectors with distinctive morphological features attributable to the variable flow-depositional behavior of the debris stream, controlled by the nature of the substrate: (1) proximal continuous breccia flanked by levees; (2) intermediate depression; and (3) flat-topped polygonal hills and conical hills. A morphometric and spatial distribution analysis has been performed with the 550 conical hills (hummocks) mapped in the distal sector. The rock avalanche, with 914 m of maximal height drop (H) and 9280 m of runout (L), displays an extraordinarily high mobility (H/L index of 0.09), that can be attributed to the combined effect of dynamic rock fragmentation and basal lubrication by the soft substrate in the floodplain. Relief rejuvenation and slope over-steepening related to the growth of the anticline and the inflation of the Gavbast Dome are considered the main long-term preparatory factors that shifted the slope to a state of marginal stability. The slope failure was likely triggered by a large M ≥ 6.5–7 earthquake at ca. 5.4 ka, as indicated by OSL ages obtained from folded alluvium situated just beneath the rock avalanche deposit. The source of the earthquake was probably a blind reverse fault situated beneath the asymmetric Gavbast Anticline, as support the structural and geomorphic features of the fold. The identification and dating of large coseismic landslides in the Zagros Mountains, where large earthquakes are rarely accompanied by primary surface ruptures, could help to improve both landslide and seismic hazard assessments.

STABILITY ANALYSIS OF ROCK BLOCKS WITH ENTIRE SPHERE STEREOGRAPHIC PROJECTION BASED ON THE BLOCK THEORY: A CASE STUDY FOR A TUNNEL ENTRANCE PROJECT

This paper presents a static equilibrium kinematic analysis of rock performed in the tunnel entrance project using entire sphere stereographic projection under block theory. The objective of this study is to improve the predictive analysis of rock masses in terms of stability in rock masses area. Different key blocks with failure modes are determined. The conventional upper hemisphere stereographic projection is also employed for comparative analysis. Based on the findings, it was concluded that the planar failure is not probable in the case of the kinematic and block theory method in the tunnel entrance area. However, the wedge failure is more probable in both cases of analysis and the number of possible slide blocks in the case of kinematic analysis was found to be less than in the case of block theory; In these conditions, the support system should be provided for the reasons of safety. The comparative analysis shows that the results of block theory analysis are close to reality and provide more precision on the stable and unstable block than the results of kinematic analysis; Moreover, the block theory method using the entire sphere stereographic projection provides more precision on the sliding angle than the use of one sphere stereographic projection. Based on this study, the tunnel entrance is more stable for the dip slope face equal to 45 and not probable for slope face 60˚ and 85˚; but these results were limited in the case of stability analysis under gravitational loading.

Assessing the Stability of Dip Slopes Based on Analyzing the Stress at a Key Point on the Sliding Surface

Dip slopes are often encountered in deep-cut canyons and engineering projects. Such slopes, when they become unstable, commonly undergo bi-planar failure, and this mode of failure tends to produce the widest-ranging effects. In this work, a novel method is proposed for assessing the potential of a slope to undergo bi-planar failure based on a stress analysis at a key point on the sliding surface, namely, the point at which the two sections of the sliding surface are connected. Discrete-element simulations are first carried out to capture the essence of the penetration process of the bi-planar sliding surface based on displacement results, plastic failure, and principal stress development. Then, the key point on the sliding surface is skillfully selected according to the sliding surface penetration process, and the characteristics of the stress changes leading to slope failure are investigated using the stress analysis method. Subsequently, considering the stress states of this key point both in the overlying rock strata and in the intact rock at the toe of the slope, a novel method is proposed for assessing the stability of the dip slope and predicting the bi-planar failure surface formed. The stability of dip slopes was subsequently analyzed using both numerical and theoretical methods. The results obtained are highly consistent, confirming the feasibility and accuracy of the proposed method. The results also show that the bi-planar failure process is progressive and that the range of the failure is mainly located in the stress reduction zone. Moreover, the critical height of the dip slope remains approximately unchanged as the stratum thickness is changed. However, it decreases as the slope angle increases and increases linearly if the strength of either the rock or joints is increased. Additionally, if the joint strength is low, the dip slope undergoes buckling failure—increasing the joint strength, however, increases the likelihood of the occurrence of bi-planar failure. The proposed method offers a novel approach to assessing and designing dip slopes.

Three-dimensional reliability analysis of unsaturated soil slope considering permeability rotated anisotropy random fields

The spatial variability is an inherent characteristic of soils. In addition to isotropic and transversely anisotropic soils, rotated anisotropic soils can also be observed in nature owing to deposition and weathering. Recent studies revealed that the spatially variable soil strength parameters can significantly affect rotated anisotropically deposited soil slope stability. However, the influence of spatial variability of saturated water permeability (ks) on this type of slope stability has been not fully understood, especially for the three-dimensional (3D) slope analysis. This paper aims to investigate unsaturated soil slope reliability with 3D ks rotated anisotropy random fields under rainfall infiltration. Due to the low efficiency of the covariance matric decomposition method (CMD) in simulating large-scale 3D rotated anisotropy random fields, a modified CMD method is proposed to save the computational cost. Moreover, comparisons between 2D and 3D random finite element analyses are also discussed. The results indicate the modified CMD method can markedly improve computational efficiency by more than 3.3 times compared with the CMD method. Only applying variations of pore water pressure (PWP) of a section or groundwater table (GWT) cannot sufficiently account for the uncertainty of slope stability. The cross-dip slope, where the dip direction of the slope is perpendicular to the dip direction of strata, has a larger reliability index (1.3−3.0 times) than the dip slope and reverse slope at the same soil bedding plane orientation. The most unfavorable soil bedding plane orientation for the cross-dip slope and the dip/reverse slope is 0° (horizontally deposited) and 30° (slightly larger than slope angle), respectively. It is attributed to the relatively low ks along these two orientations being more likely to form the aquiclude, affecting overall variations of PWP, leading to a larger standard deviation of the factor of safety and a lower reliability index. Furthermore, the reliability of cross-dip slope can only be studied in 3D, while the dip slope and reverse slope reliability can be studied with 2D analysis to decrease computational burden when the slope length does not exceed 50 m.

Dynamic Analysis of the Seismo-Dynamic Response of Anti-Dip Bedding Rock Slopes Using a Three-Dimensional Discrete-Element Method

Earthquakes are a major external factor that induce landslides. In order to systematically study the dynamic effects and failure mechanism of anti-dip bedding rock slopes (the slope trend is the same as the joint trend, while the slope dip direction is opposite to the joint dip direction) under seismic action (as well as the spatial effects of the structural planes in the anti-dip bedding rock slopes), three-dimensional (3D) discrete-element numerical calculations were performed to analyze anti-dip bedding rock slopes with different slope angles, joint angles, and joint trends subjected to the action of natural seismic and sinusoidal waves. The results were analyzed to investigate the amplification effect, change in Fourier spectrum, failure mechanism, and permanent displacement of the slope under the applied seismic action. The permanent displacement of the slope was calculated using Newmark’s method and the results obtained were discussed and compared with those obtained from a dynamic analysis performed using the 3D discrete-element method. The results showed that the regularity of the spatial distribution of the amplification effect was less clear than that encountered in the planar problem (unidirectional or bidirectional dynamical loading), and this leads to the effect of having an overall rhythmical nature. The seismic wave decays in the high-frequency part from the bottom up of the slope, while the dominant frequency of the seismic wave decreases. The value of the permanent displacement obtained using Newmark’s method is much smaller than that obtained using the dynamic 3D discrete-element analysis approach. The angle between the joint and slope trends has a significant effect on the amplification effect, failure mode, permanent displacement, and stability of slopes subjected to seismic action.

Model test on deformation and failure behaviour of arching-type slope under excavation condition

Excavation is one of the common triggers for slope failures. Loss of support at the toe of a slope due to mining excavation can cause unloading of geomaterials close to the excavated area and stress redistribution. The deformation behaviour of arching-type slopes is different from the deformation behaviour of common dip slopes. Therefore, it is necessary to study the deformation and failure mechanism of slopes under excavation conditions. In this study, a series of physical model tests was conducted on arching-type slopes with different slope angles and relative densities. The physical models were monitored by various instrumentation, such as a digital camera, a high-speed camera, earth pressure gauges, and a multi-smartphone measurement system. The deformation characteristics during excavation were analysed by using particle image velocimetry (PIV). The results show that the yielding area, including the arch-shaped large deformation area and upper small deformation area, and two sides of unyielding areas were clearly observed and considered features of arching-type slope deformation related to the arching effect. In arching failures, slopes with higher relative densities can generate larger initial kinetic energy. Toe failure, sliding failures, tension cracks, and bulking failure subsequently occur in the final failure. The equations for the maximum excavation width and the curve of the stable arch of arching-type slopes are verified.

Channel incision into a submarine landslide on a Carboniferous basin margin, San Juan, Argentina: Evidence for the role of knickpoints

AbstractEmplacement of submarine landslides, or mass‐transport deposits, can radically reshape the physiography of continental margins, and strongly influence subsequent sedimentary processes and dispersal patterns. Typically, progressive healing of the complicated relief generated by the submarine landslide occurs prior to progradation of sedimentary systems. However, subsurface and seabed examples show that submarine channels can incise directly into submarine landslides. Here, the evolution of a unique exhumed example of two adjacent, and partially contemporaneous, submarine channel‐fills is documented. The channels show deep incision (>75 m), and steep lateral margins (up to 70°), cut into a >200 m thick submarine landslide. The stepped basal erosion surface, and multiple terrace surfaces, are mantled by clasts (gravels to cobbles) reflecting periods of bedload‐derived sedimentation, punctuated by phases of downcutting and sediment bypass. The formation of multiple terrace surfaces in a low aspect ratio confinement is consistent with the episodic migration of knickpoints during entrenchment on the dip slope of the underlying submarine landslide. Overlying sandstone‐rich channel‐fills mark a change to aggradation. Laterally stacked channel bodies coincide with steps in the original large‐scale erosion surface, recording widening of the conduit; this is followed by tabular, highly aggradational fill. The upper fill, above a younger erosional surface, shows an abrupt change to partially confined tabular sandstones with normally graded caps, interpreted as lobe fringe deposits, which formed due to down‐dip confinement, followed by prograding lobe deposits. Overlying this, an up‐dip avulsion induced lobe switching and back‐stepping, and subsequent failure of a sandstone body up‐dip led to emplacement of a sandstone‐rich submarine landslide within the conduit. Collectively, this outcrop represents episodic knickpoint‐generated incision, and later infill, of a slope adjusting to equilibrium. The depositional signature of knickpoints is very different from existing models, but is probably reflective of other highly erosional settings undergoing large‐scale slope adjustment.

Graphical charts for onsite Continuous Slope Mass Rating (CoSMR) classification using strike parallelism and joint dip or plunge of intersection

We propose the new continuous slope mass rating (SMR) charts for easy calculation of SMR class of rock slopes in the field. SMR class can be determined by plotting the parallelism between dip directions of slope and discontinuity (slope dip direction and trend direction of intersection line in case of wedge failure) (A) in the x-axis and discontinuity dip amount (βj) (plunge amount in case of wedge failure (βi)) in the y-axis using SMR charts. We apply the proposed SMR charts to an assumed rock slope consisting of four joint sets and a basic Rock Mass Rating (RMRb) value of eighty. SMR class for the assumed rock slope was calculated using proposed SMR charts and by the existing Graphical Slope Mass Rating (GSMR) method. After comparing both the methods, we demonstrate, the proposed SMR charts prove to be simpler and take less time to evaluate SMR class as compared to the GSMR method. The GSMR method requires matching six stereonets for a single rock slope, whereas by using proposed SMR charts minimal use of stereonet is required to calculate trend and plunge of intersection. Proposed SMR charts incorporate the continuous functions (F1, F2, and F3) for SMR calculation, whereas a discrete rating system is used in the GSMR method. This study suggests, the proposed SMR charts are easy to use, more efficient, and can be adopted as a valuable tool for the preliminary rock slope stability assessment in mountainous areas like the Himalayas, where within a few meters joints and slopes geometries changes.

High-resolution sequence stratigraphy in continental lacustrine basin: A case of Eocene Shahejie formation in the Dongying Depression, Bohai Bay Basin

Approximate 500 m deltaic-lacustrine successions were formed within 2 Ma in the Liangjialou area of the Dongying Depression in the Bohai Bay Basin (eastern China). However, few studies on sequence stratigraphy were previously conducted in the east of Liangjialou. In the present study, we integrate high-resolution three-dimensional (3D) seismic data with well-logging data to study the sequence stratigraphy and the depositional system.Our study shows that: (1) Four systems tracts have been identified in the study interval, they are HST, FSST, LST and TST. The HST has an ascending shelf-edge trajectory and aggradation to progradation stacking pattern. FSST has a descending shelf-edge trajectory and progradation to degradation stacking pattern. LST has a low-angle ascending shelf-edge trajectory and progradation to aggradation stacking pattern. TST has a backstepping shelf-edge trajectory and retrogradation stacking pattern. (2) Five high-resolution sequences (equal to 4th-order sequence), HRS1∼HRS5, were further subdivided within the 3rd-order LST. In addition, the depositional systems of HRS1∼HRS5 are significantly variable in 3D space. The delta and deep-water deposits in the north are larger than those in the south. (3) The formation of the sequence is controlled by both tectonics and dry-wet climatic cycles. The tectonic subsidence and high sediment supply in overall wet climate play a major role in the formation of the 3rd-order sequence. The higher frequency dry-wet climatic cycles dominate the formation of internal systems tracts. We further divide the climate of study interval into three stages that are excellent correlated to the specific systems tracts: Stage 1 (evaporation < precipitation) corresponds to HST; Stage 2 (evaporation > precipitation) corresponds to FSST; Stage 3 (evaporation < precipitation) corresponds to LST. (4) The basin morphology and source location mainly control the lateral variability of the depositional system of LST. Low paleotopography, narrow shelf width and steep slope dip in the north cause a large accommodation, and promote the development of the deltaic and deep-water deposits. In contrast, a high relief, wide shelf width and gentle slope cause only minor accommodation in the south, and limit the development of the deltaic and deep-water deposits.

Equivalent fracture network model for steady seepage problems with free surfaces

Based on the back analysis of equivalent continuum theory in frcatued media by Snow (1969), an equivalent fracture network model is proposed to evaluate steady seepage problems with free surface in porous media. In contrast to the continuum-based approaches on seepage flow, the continuum is replaced by an artificial fracture network system formed by two sets of fractures. The relationships between the permeability coefficients of porous media and equivalent parameters of fracture dip, spacing and aperture are deduced. The corresponding governing equations and finite element procedure according to the variational inequality theory are developed. Through good agreements of free surface locations between the proposed method, numerical data and field measurement in four typical examples, the proposed equivalent fracture network model is validated in modelling free surface flow in porous media. The solutions on the isotropic and anisotropic rectangular dams show that the proposed model has weak sensitivity of the fracture dip and mesh size, and its equivalence to the continuum-based method is also proved. In addition, the proposed model can be successfully used for the fractured media as well as porous media, the fracture direction has a significant impact on the free surface flow behavior in the fractured media, in which the fracture directions are negative for the antidip slope and positive for the dip slope to drain ground water. Finally, the results from the zoned dam with clay core and sand shell and the left bank abutment demonstrate the feasibility of the proposed model in complex dam engineerings with isotropic and anisotropic heterogeneity media.

Seasonal Surface Fluctuation of a Slow-Moving Landslide Detected by Multitemporal Interferometry (MTI) on the Huafan University Campus, Northern Taiwan

A slow-moving landslide on the Huafan University campus, which is located on a dip slope in northern Taiwan, has been observed since 1990. However, reliable monitoring data are difficult to acquire after 2018 due to the lack of continuous maintenance of the field measurement equipment. In this study, the multitemporal interferometry (MTI) technique is applied with Sentinel-1 SAR images to monitor the slow-moving landslide from 2014–2019. The slow-moving areas detected by persistent scatterer (PS) pixels are consistent with the range of previous studies, which are based on in situ monitoring data and field surveys. According to the time series of the PS pixels, a long period gravity-induced deformation of the slow-moving landslide can be clearly observed. Moreover, a short period seasonal surface fluctuation of the slow-moving landslide, which has seldom been discussed before, can also be detected in this study. The seasonal surface fluctuation is in-phase with precipitation, which is inferred to be related to the geological and hydrological conditions of the study area. The MTI technique can compensate for the lack of surface displacement data, in this case, the Huafan University campus, and provide information for evaluating and monitoring slow-moving landslides for possible landslide early warning in the future.

Feasibility of Artificial Slope Hazards Identification in Regional Mountainous Highway Using SBAS-InSAR Technique: A Case Study in Lishui, Zhejiang

Safety status of artificial slopes is significant for the operation and maintenance of highway to mitigate the risk; thus, slope hazard identification is necessary. In order to realize large-area and low-cost application for regional highway, taking the Longqing Highway (length of 55 km) as a case study, the SBAS-InSAR (Small Baseline Subset-Interferometric Synthetic Aperture Radar) technique is adopted to detect the ground deformation and conduct hazard identification based on slope dip, aspect, geological data and historical hazard record. Field survey is carried out to verify the identified potential hazards. Results show that the detected potential hazards are distributed mainly in the areas consisting of granite residual and the Quaternary soil. Six potential hazards identified by the SBAS-InSAR-based method are roughly in accordance with the on-site verification. It is suggested that the SBAS-InSAR technique has the ability to obtain the slope deformation accurately and reveal the safe condition of the slopes. The SBAS-InSAR technique can be suitable for assistance in regional highway slope inspection.

Classification of slope area types and hydrocarbon accumulation rules in Wuerxun-Beier Depression

After more than 50 years of exploration and development, Wuerxun-Beier depression has entered a high exploration stage. It is more and more difficult to find large-scale structural reservoirs. Therefore, structural-lithologic reservoirs in slope areas have gradually become the focus of exploration. Based on the overall study and dissection of the depression, the geological differentiation characteristics of the large-scale slope area are discussed. According to the occurrence of the slope, the intensity of tectonic activity, the intensity of source supply and the pattern of synsedimentary fault combination, the slope zone in the study area can be divided into six types, namely, the steep slope with strong source along the fault step type, the compound fault step type of medium slope with strong source, the reverse fault step type of the gentle slope with strong source, and the weak supply type. Different types of slope have different sand control mechanisms and reservoir forming characteristics, such as the source gentle slope forward fault terrace type, the weak source gentle slope reverse fault terrace type and the weak source middle slope forward fault terrace type. Source supply intensity and slope dip control the development type of sedimentary system, the combination of synsedimentary faults and valleys controls the distribution characteristics of sedimentary system. Through exploration practice, significant discoveries have been made on the southwestern, southeastern and northern slopes of Beixi, Wuerxun-Beier depression, which confirms that the slope area is the main breakthrough direction for oil and gas exploration and large-scale reservoir increase in continental fault-depression lake basins.

Slope Stability Analysis of Haibat Sultan Road Cut, Kurdistan Region, Iraq Using a Field Method

The road that crosses the Haibat Sultan Mountain in the northern part of Iraq; is one of the dangerous roads in this region. To perform a slope stability analysis for the dangerous parts of the road, we have used Bejerman’s Method. We have reviewed satellite images of the road and all those potential areas were checked in the field; accordingly, eleven stations were recognized. Landslide Possibility Index was determined at the studied stations following Bejerman’s field method. The road climbs the southern face (dip slope) of the mountain through very hard carbonate rocks of the Pila Spi Formation, where the bedding planes daylight in the slope face near the road cuts. This produced many large landslides. Along the northern face of the mountain, the road runs through soft clastic rocks where joint planes in the rock mass intersect and daylight in the slope face near the road cut. In order to prevent future wedge failures, a 30 m offset was created from the toe of the slope to the road. In almost all cases, the Landslide Possibility Index indicated a moderate to very high likelihood for failure along all road cuts.

Wave and storm signals in a lacustrine succession and their relationship to paleowind direction (Tanan Depression, Mongolia, early Cretaceous)

Existing fan-delta depositional models for lacustrine basins do not adequately address significant wave- and storm-related processes. However, in many lakes, such high-energy processes can be effectively driven by winds. As such, the prevailing wind direction determines the propagation direction of wind-induced waves. Observations from modern examples show that wave-dominated deposits commonly exist on one side of the lake, and their sedimentary processes are completely distinct from those on the opposite side. However, equivalent deposits have seldom been identified from subsurface data. We present an ancient example from the Upper Tongbomiao Formation in the Tanan Depression (Tamtsag Basin, Mongolia), which was previously interpreted as a fan-delta depositional system. Based on extensive core investigations, eighteen lithofacies, six lithofacies associations and two genetic deposition systems are identified, and a new sedimentological interpretation is proposed comprising a wave-dominated clastic littoral system in the western half-graben dip slope and a fluvial-dominated fan-delta system in the eastern half-graben. Sediments within the eastern half-graben unit include braidplain, fan-delta front and prodelta environments, while those within the western half-graben dip slope unit comprise dominantly alluvial fan, wave-reworked beach, storm-affected shoreface and offshore sediments. The strikes of the sediments in the western half-graben dip slope unit are parallel to the westward shoreline trend, while the progradation direction of sediments in the eastern half-graben unit is perpendicular to the eastern shoreline. This indicates approximately northwestward-propagating waves that were possibly driven by southeasterly winds, which has implications for understanding the prevailing wind direction in Northeast Asia during the depositional period. Other factors contributing to the preservation of these two distinct sedimentary systems are the paleotopography and subsequent climate shift towards more humid climatic conditions which intensified sediment supply and hydrodynamic conditions that were able to rework the sediments.

Regional geology, extreme weather events and natural disasters: Environmentally-forced, involuntary settlement migrations of the indigenous people of southern Taiwan

Active mountain belts in monsoonal climates are characterized by rapid denudation due to erosion and mass wasting processes. In such areas, unstable topography caused by local geological conditions combined with extreme rainfall or earthquakes impact on indigenous people, especially through involuntary settlement migration. Anthropological surveys in southern Taiwan show that the oral traditions of indigenous people preserve records of natural disasters that took place several hundred years ago. When combined with geological data, these stories allow us to assess the triggers and underlying causes that led to settlement migrations. These settlements are located in the Central Range of southern Taiwan, a high-relief terrain comprised of Miocene formations characterized by well-developed slaty cleavage (S1) that forms dip slopes that are prone to landslides. Here, we investigate how extreme events coupled with the geological setting caused two relocations of a settlement of the Paiwan group within approximately 350 years. We also draw attention to the point that the oral traditions of indigenous groups can provide important data sets for reconstructing landslides in the recent past (less than 500 years) which other, more traditional methods (e.g. digital data archives) do not record. We conclude that extreme weather provides the trigger, and local geological conditions the underlying factors, for natural disasters that have had a significant impact on the indigenous people in southern Taiwan.

Deformation of landslide revealed by long-term surficial monitoring: A case study of slow movement of a dip slope in northern Taiwan

A natural hillslope developing into a landslide shows ground cracks and topographic deformation. Geomorphological and subsurface investigations using appropriate methodology are essential to understand the failure mechanisms and stability of a hillslope. Huafan University campus located on a dip slope in northern Taiwan is facing a potential landslide hazard. Slope movement was detected through the development of ground cracks and persistent deformation of campus buildings and facilities. To monitor the sliding behavior of the dip slope, a nail network consisting of 144 ground monitoring points was set in 2001, and its coordinates were measured using conventional traverse surveying twice a year until 2017. The 17-year surficial surveying results were presented as a time series of displacements with constraints of geometry and distribution of ground cracks and underground observations. The long-term surveying results reveal multiple potential sliding blocks within the Huafan University campus. A model of landslide movement with a listric sliding surface is proposed. Additionally, from the velocity field derived from the monitoring points, the horizontal strain rates of the slope are estimated. The pattern of strain rates indicates that a plausible fault passing through the campus may have affected the movement of the dip slope. The long-term surface monitoring of a potential landslide slope in this study provides a reliable and economical way to understand the mechanism of movement behavior of the slope and evaluate slope stability.

Stability analysis of rock slope along selected road sections from Gutane Migiru town to Fincha sugar factory, Oromiya, Ethiopia

The slope instability was one of the common problems along the road that connects Gutane Migiru town to Fincha sugar factory, Western Ethiopia. The effect of the problem was intense mostly; during the rainy season, that triggers different modes of rock slope failure. As a result, the road was frequently damaged and blocked by the failed rock that in turn hinders the traffic activities. Thus, this study aimed at stability analyses of the critical slope sections using kinematic and limit equilibrium methods (LEM). The estimation of the most important input parameter in LEM analyses like cohesion and friction angle along the failure plane is often intricate and cumbersome. Hence, this paper used Rocscience software to effortlessly and instantly compute cohesion and friction angle along specific failure planes and then to carry out kinematic and LEM analyses. Besides, the strength of the intact rock was determined by the Schmidt hammer in the field and point load laboratory test. According to the kinematic analysis result, the wedge mode of rock slope failure occurred at slope sections D1S2 and D1S3 though the planar mode of failure occurred at slope sections D1S4 and D4S1. The factor of safety determined under all anticipated conditions became less than and greater than one at slope sections D1S2, D1S3, D1S4, and D4S1, and this depicts an unstable and stable slope, respectively. From the analysis result, the combined effect of rainfall, steepness of the slope dip, and joint set was the main factors that caused the slope insatiability.