Characteristics, mechanism and development tendency of deformation of Maoping landslide after commission of Geheyan reservoir on the Qingjiang River, Hubei Province, China

Based on field investigation of the constituent structure and geological formation of the Maoping landslide, the authors made an in-depth study of the deformation characteristics and triggering mechanism of the reservoir-induced slide through comprehensive analysis of the about 13 years observation data. The Maoping landslide, the largest ancient landslide in Geheyan reservoir, with a volume of 23.5 million m³, is located on the left bank of the Qingjiang River, 66 km upstream of Geheyan dam. In April 1993 reservoir inundation reactivated the landslide, which resulted in relocation of a village of 290 people. Since then the landslide body has been experiencing persistent deformation with an observed maximum displacement of 2841.4 mm up to October 2005. Therefore, further development of deformation of the landslide becomes a great concern for the safety of the reservoir and dam. The analysis results show that the Maoping landslide is an ancient landslide that is an accumulation of several consequent slides along the bank slope and experienced several secondary slumps in its front in later stages. The ongoing deformation of the reactivated landslide is controlled by mechanical properties of materials and hydraulic effects induced by reservoir. The slip process is of creep deformation as a whole, and appears to be attenuating in later stage, which indicates very low possibility of the high-speed slip and integral failure of the slide.     

融雪诱发型黄土滑坡活动特征与应急响应模式——以新疆伊犁则克台滑坡为例

2019年4月30日,在新疆的伊犁地区一个高位黄土滑坡复活启动,并远距离掩埋公路和阻塞河道。大约5.04×105 m3黄土体高位滑移剪出冲击铲刮沟道及两侧岸坡。滑坡不定时复活启动机理难以琢磨。本文基于实地详细调查、遥感影像判识、气象数据分析和黄土特征试验等方法,以试图确定黄土滑坡的演变历史、运动过程和复活机理。研究表明,该滑坡曾发生两次大规模滑动破坏,且伴随着坡体地裂缝发展,每年黄土坡体发生不同程度的累积变形破坏。春季温度升高导致积雪快速消融入渗是黄土滑坡变形演化的最重要影响因素,春季融水和暴雨的耦合是控制黄土滑坡发生的根本原因。基于本次灾害发生后成功灾害应急响应过程,提出一种基于早期预警多部门联动的公路灾害应急响应模式。随着区域放牧活动增加和气候变暖加剧,该黄土滑坡将具有极大潜在复活滑动风险。研究可为寒冻区滑坡形成演化和破坏机理提供了新的视野,为服务新疆一带一路区域交通建设具有重要意义。     

Deformation and mechanism of landslide influenced by the effects of reservoir water and rainfall, Three Gorges, China

Since the impoundment of the Three Gorges Reservoir in June 2003, numerous preexisting landslides have been reactivated. This paper seeks to find the factors influencing landslide deformation and the relationship between displacement and fluctuation of the reservoir water level, while the displacement and the intensity of rainfall based on monitoring data; 6 years of monitoring were carried out on the Shiliushubao landslide, a old landslide, consisting of a deep-seated main block and two shallow blocks, with a volume of 1,180 × 10⁴ m³ and located on the left bank of the Yangtze River, 66 km upstream of the Three Gorges dam. This landslide was reactivated by the impoundment and since then the landslide body has been experiencing persistent deformation with an observed maximum cumulative displacement of 8,598.5 mm up to December 2009. Based on the monitoring data, we analyzed the relationship between the fluctuation of the reservoir water level and displacement, rainfall and displacement, and found that the rainfall is the major factor influencing deformation for two shallow blocks and the displacement has a positive correlation with the variation of rainfall intensity. The fluctuation of the reservoir water level is the primary factor for main block, and the deformation rate has a negative correlation with the variation of reservoir water level, declined with the rise of the water level and increased with the drawdown of the water level.     

Progressive evolution and failure behavior of a Holocene river-damming landslide in the SE Tibetan Plateau,China

This paper presents a study on an ancient river-damming landslide in the SE Tibet Plateau, China, with a focus on time-dependent gravitational creep leading to slope failure associated with progressive fragmentation during motion. Field investigation shows that the landslide, with an estimated volume of 4.9?×?10⁷ m³, is a translational toe buckling slide. Outcrops of landslide deposits, buckling, toe shear, residual landslide dam, and lacustrine sediments are distributed at the slope base. The landslide deposits formed a landslide dam over 60 m high and at one time blocked the Jinsha River. Optically stimulated luminescence dating for the lacustrine sediments indicates that the landslide occurred at least 2,600 years ago. To investigate the progressive evolution and failure behavior of the landslide, numerical simulations using the distinct element method are conducted. The results show that the evolution of the landslide could be divided into three stages: a time-dependent gravitational creep process, rapid failure, and granular flow deposition. It probably began as a long-term gravitationally induced buckling of amphibolite rock slabs along a weak interlayer composed of mica schist which was followed by progressive fragmentation during flow-like motion, evolving into a flow-like movement, which deposited sediments in the river valley. According to numerical modeling results, the rapid failure stage lasted 35 s from the onset of sudden failure to final deposition, with an estimated maximum movement rate of 26.8 m/s. The simulated topography is close to the post-landslide topography. Based on field investigation and numerical simulation, it can be found that the mica schist interlayer and bedding planes are responsible for the slope instability, while strong toe erosion caused by the Jinsha River caused the layered rock mass to buckle intensively. Rainfall or an earthquake cannot be ruled out as a potential trigger of the landslide, considering the climate condition and the seismic activity on centennial to millennial timescales in the study area.

     

Characteristics and mechanism of a landslide at Anqian iron mine,China

Owing to the heavy rainfall, a landslide occurred at the Anqian Iron mine, at 18:00(UTC + 8) on November 24, 2019, in China. The landslide was about 3.0?×?10⁴ m³ and caused damage to the road of transporting waste materials. Failure characteristics and the mechanism of this landslide were analyzed in this study. The landslide area was divided into three parts: the rear tension cracking area, the middle sliding deformation area, and the front colluvium area. A contact-free measuring technique using the new ShapeMetrix3D system was applied and 204 joints were analyzed based on equal-angle stereographic projection. Thus, a conceptual model of the mechanism of the landslide was constructed and the formation process of the landslide was divided into three stages: the first shearing and dislocation stage; the second sliding, front bulging, and rear tractive cracking stage; and the third local rock mass collapse and colluvium depositing stage. Numerical modeling was performed to discover the landslide mechanism by progressively reducing the shear strength of rock mass. The results showed that the original slope was stable, whereas heavy rainfall triggered the landslide, and the predicted failure surface matched closely the field investigations. The factor of safety obtained by real three-dimensional analyses was slightly higher than that obtained by plane problem analyses, and the difference was attributed to the three-dimensional effect of the landslide. This paper also presents the results obtained from the parametric analysis in order to understand the impact of shear strength parameters on the overall stability of the slope.

     

Risk management study on impulse waves generated by Hongyanzi landslide in Three Gorges Reservoir of China on June 24, 2015

On June 24, 2015, Hongyanzi slope located in Wushan County of the Three Gorges Reservoir collapsed, generating 5–6-m-high impulse waves, which overturned 13 boats, killed 2 persons, and injured 4 persons. It is the second incident of landslide-generated impulse waves since the 175-m experimental impoundment in 2008. The emergency investigation shows that Hongyanzi landslide is a bedding soil landslide with a volume of 23?×?10⁴ m³ induced by a series of triggering factors such as rainfall, flooding upstream, and reservoir drawdown. The nonlinear Boussinesq water wave model is used to reproduce the impulse waves generated by the landslide of June 24th. The numerical simulation results suggest that the wave propagation process was influenced by the T-shaped geomorphic conditions of river valley, and the coastal areas in the county seat were the major wave-affected areas, which is opposite to the landslide. The numerical wave process accord well with the observed incident, and the investigation values were in good agreement with the calculated values. Moreover, the worst-case scenario of the 7?×?10⁴ m³ deformation mass beside Hongyanzi landslide is potential to generate impulse waves, which was predicted with the same numerical model. This adjacent deformation mass will probably generate impulse waves with maximum height and run-up of 2.2 and 2.0 m, respectively, and only a very few areas in the water course had waves rising to a height of 1 m or above. The research results provide a technical basis for emergency disposal to Hongyanzi landslide and navigation restriction in Wushan waterway. More importantly, it pushes the risk management of the navigation based on the impulse wave generated by landslide. It is advised that the Three Gorges Reservoir and other reservoirs around the world should put more efforts in performing special surveys and studies on the potential hazards associated with landslide-generated impulse waves.     

Development of an empirical model for predicting peak breach flow of landslide dams considering material composition

The existing empirical models do not consider the influence of material composition of landslide deposits on the peak breach flow due to the uncertainty in the material composition and the randomness of its distribution. In this study, based on the statistical analyses and case comparison, the factors influencing the peak breach flow were comprehensively investigated. The highlight is the material composition-based classification of landslide deposits of 86 landslide cases with detailed grain-size distribution information. In order to consider the geometric morphology of landslide dams and the potential energy of dammed lakes, as well as the material composition of landslide deposits in an empirical model, a multiple regression method was applied on a database, which comprises of 44 documented landslide dam breach cases. A new empirical model for predicting the peak breach flow of landslide dams was developed. Furthermore, for the same 44 documented landslide dam failures, the predicted peak breach flow obtained by using the existing empirical models for embankment and landslide dams and that obtained by using the newly developed model were compared. The comparison of the root mean square error (E_rms) and the multiple coefficient of determination (R²) for each empirical model verifies the accuracy and rationality of the new empirical model. Furthermore, for fair validation, several landslide dam breach cases that occurred in recent years in China and have reliable measured data were also used in another comparison. The results show that the new empirical model can reasonably predict the peak breach flow, and exhibits the best performance among all the existing empirical models for embankment and landslide dam breaching.

     

Giant ancient landslide in the Alma water gap (Crimean Mountains,Ukraine): notes to the predisposition,structure, and chronology

Large-scale ancient landslides of the area of more than 5 km² and volume exceeding 200 × 10⁶ m³ are characteristic features of the valleys incised in the northern periphery of the Crimean Mountains (Ukraine). The largely affected area is located in the outermost cuesta range of the Crimean Mountains which consists of rigid Sarmatian limestones overlying weak Middle Miocene and Upper Palaeogene deposits. A giant landslide arose in the Alma water gap as a reflection of several coincident preparatory factors such as suitable bedrock stratification, smectite-rich bedrock exposed to swelling activity, presence of faults parallel to the valley trend, and river capture event which preceded the landslide event. The occurrence of such ancient megaslides is particularly interesting in the area which is characterized by low precipitation (<500 mm/year) and weak contemporary seismicity. It probably reflects a more dynamic environment in humid phases of the Holocene; however, seismic triggering along the Mesozoic suture zone cannot be rejected. Compressional features such as gravitational folds in the central and distal parts of the landslide, which probably correlate with the whole landslide genesis or its significant reactivation, arose, according to the radiocarbon dating, during the Holocene climatic optimum in the Atlantic period. The slope deformation has been relatively quiescent since that time, except minor historic reactivization which took place in the frontal part of the landslide. We suppose that the studied landslide could be classified as a transitional type of slope deformation with some signs of spreading and translational block slides.     

Topographical features of rainfall-triggered landslides in Mon State,Myanmar, August 2019: spatial distribution heterogeneity and uncommon large relative heights

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?<?27°) shows a relative high mobility and the relation between landslide mobility and the slope angle of the landslide source area is similar to the one of earthquake-triggered landslides, even though the triggering mechanism, landslide type, and landslide volume are dramatically different.

     

1,000-year record of landslide dams at Halden Creek, northeastern British Columbia

Large, rapid, low-gradient landslides are common in clay-rich glacial sediments in northeastern British Columbia. Many of the landslides create upstream impoundments that may persist for years in small watersheds in the region. We have documented such events in the Halden Creek watershed, 60 km southeast of Fort Nelson. The events are recorded geologically in two ways. First, trees are drowned in lakes dammed by the landslides and subsequently buried by deltaic sediments, where they are protected from decay. Bank erosion later exhumes the drowned trees. Second, landslide deposits with entrained wood are exposed along stream banks. We have reconstructed the recent history of landslide damming at Halden Creek by performing radiocarbon dating on exhumed trees and wood in and beneath landslide deposits at 13 sites in the watershed. Drowned trees range in age from 169±59 to 274±49 ¹⁴C year bp. Wood in and below landslide deposits yielded radiocarbon ages ranging from modern to 965±49 ¹⁴C year bp.     

甘肃通渭“9·14”常河滑坡成因机理

2019年9月14日11时,受多日降雨影响,甘肃省定西市通渭县常家河镇小庄村发生大规模黄土滑坡,体积约800万m³。滑坡造成部分农田、公路及阳坡大桥损毁,直接经济损失约2 347.2万元。在对滑坡现场进行大量地面调查的基础上,通过无人机航拍、现场测绘、走访调查和数值模拟等手段对滑坡的变形破坏特征进行了分析,并在此基础上探讨了其成因机制。结果表明:斜坡体是在震裂、蠕变、软化、水动力等多种条件下按照一定的先后顺序由稳态逐步演化至失稳;该滑坡的失稳演化过程和灾变机制可以概括为原始斜坡(黄土、泥岩二元层状结构)-地震触发(滑坡堆积体、坡体震裂损伤)-蠕变弱化(层间剪切带、裂缝和落水洞扩展)-降雨激发(滑带软化、泥化,水压力作用)-失稳滑动(滑面贯通)5个阶段;由于长期的蠕变和雨水的渗透冲蚀,坡体上的落水洞和地下暗河十分发育,且是控制本次滑坡边界的关键因素;滑坡后缘和前缘变形剧烈,中部变形相对稍弱,推断该滑坡为受地形及地下水作用控制明显的牵引-推移式复合滑坡。     

甘肃舟曲垭豁口滑坡复活机理及成因探讨

2019年7月19日18时许,甘肃舟曲县垭豁口滑坡复活,约3.92×106 m3的滑体顺坡而下,迅速流入岷江,堵塞河道,造成河道水位上升,江边公路中断,滑坡变形持续至8月中旬。基于野外勘察、遥感解译、钻孔勘探等方法获取了滑坡变形的基本特征,并开展了滑坡监测工作,并结合气象资料,探讨了该滑坡复活原因及启动机制。初步研究认为,该滑坡为降雨诱发。通过对滑坡变形历史进行梳理,结合滑带证据,滑坡复活机理可概括为:首先上部块体缓慢蠕变,降雨后发生塑性流滑;其次,因上部滑体堆积在滑坡中部,造成中部平台堆载,引发中部滑体变形;最终一滑而下,刮产连带下部滑体坠入河道。滑坡的上中下三部分滑体逐步被激活,最初缓慢变形,随后加速启动。滑坡变形模式为蠕滑—拉裂—流滑。对滑坡变形过程和机理的初步判断为滑坡灾害应急处置提供了科学依据。     

Numerical simulation of Qiaotou Landslide deformation caused by drawdown of the Three Gorges Reservoir,China

Landslides located beside reservoirs tend to be unstable or are characterized by large deformation during the drawdown process. This has been accepted by many experts. In this paper, we use Qiaotou Landslide, which is located beside the Three Gorges Reservoir (TGR), as a typical case study to investigate and predict the deformation mechanism during the drawdown process of TGR in detail. According to field investigation, the landslide mass is mainly composed of thick, loose silt and clay mixed with fragments of rock. Bedrock is mainly composed of silty sandstone. Field and laboratory tests indicate that the landslide mass has a high permeability coefficient. If the water level declines fast, intense seepage force may result. Based on these data, we establish a three-dimensional geological model of Qiaotou Landslide by FLAC^3D and perform a numerical simulation using the saturated–unsaturated fluid–solid coupling theory. For the simulation, we assume that the drawdown from 175 to 145 m takes place with a speed of 25 cm/day, which is based on the extreme water level regulation program of TGR. The simulation shows that this causes a significant deformation in the landslide mass and that the maximum displacement within the landslide is 24.2 cm. During the drawdown process, the maximum displacement zone is shifting from the upper part of the landslide where bedrock surface is steeper and thickness of loose deposits is less to the middle part of the landslide where bedrock surface is less steep and thickness of loose deposits is higher. The deformation mechanism indicates that in the early stage of the drawdown the deformation of the landslide mass is mainly caused by seepage and in the later stage mainly by consolidation.     

三峡库区典型顺斜向岩质滑坡变形破坏特征及失稳机制分析

近年来,三峡库区城集镇开发区顺斜向岩质滑坡失稳破坏现象时有发生,研究顺斜向岩质滑坡的变形破坏特征及失稳机制对防治此类滑坡具有重要意义。本文以巫山县白杨湾滑坡为例,通过现场踏勘、钻探和多种监测手段,对这一典型顺斜向岩质滑坡的变形破坏特征及失稳机制进行了深入研究。此滑坡所处地层为巴东组第二段泥岩,岩体破碎,地下水较丰富。滑坡岩层向右边界倾斜,右边界受断层控制,断层面与岩层面相交切割形成楔形体顺斜向滑移。滑坡体积约320×104 m3,滑动方向与岩层倾向夹角60°。受坡脚开挖和坡体建筑荷载等人类工程活动的影响,滑坡于2019年7月开始出现显著变形,滑坡中部的位移速率达到2～5 mm/d。2019年9月中旬,滑坡前部设置应急抗滑桩后,滑坡变形开始减缓至0～0.5 mm/d。白杨湾滑坡对城集镇开发区金科城造成巨大威胁,建议采取“搬迁避让+工程治理+专业监测”的防治对策。本文的研究成果对指导三峡库区顺斜向岩质滑坡防治和人工开挖诱发滑坡的防治具有重要借鉴意义。     

兰溪洞源村滑坡治理工程的土体变形分析与处理措施

滑坡土体变形及其处理是滑坡治理施工中的重要问题。本文以浙江省金华市兰溪洞源村滑坡隐患治理工程为例,介绍了施工过程中出现局部不稳定问题后,施工单位与相关单位一道采取的一系列措施,包括对土体的新近变形特征与变形原因分析、应急抢险措施、应急排险效果监测、后续施工方案等内容。这些措施取得了良好的效果,为类似施工提供了借鉴。     

Glacial advances constrained by Be exposure dating of bedrock landslides, Kyrgyz Tien Shan

Numerous large landslide deposits occur in the Tien Shan, a tectonically active intraplate orogen in Central Asia. Yet their significance in Quaternary landscape evolution and natural hazard assessment remains unresolved due to the lack of "absolute" age constraints. Here we present the first ¹⁰Be exposure ages for three prominent (> 10⁷ m³) bedrock landslides that blocked major rivers and formed lakes, two of which subsequently breached, in the northern Kyrgyz Tien Shan. Three ¹⁰Be ages reveal that one landslide in the Alamyedin River occurred at 11–15 ka, which is consistent with two ¹⁴C ages of gastropod shells from reworked loess capping the landslide. One large landslide in Aksu River is among the oldest documented in semi-arid continental interiors, with a ¹⁰Be age of 63–67 ka. The Ukok River landslide deposit(s) yielded variable ¹⁰Be ages, which may result from multiple landslides, and inheritance of ¹⁰Be. Two ¹⁰Be ages of 8.2 and 5.9 ka suggest that one major landslide occurred in the early to mid-Holocene, followed by at least one other event between 1.5 and 0.4 ka. Judging from the regional glacial chronology, all three landslides have occurred between major regional glacial advances. Whereas Alamyedin and Ukok can be considered as postglacial in this context, Aksu is of interglacial age. None of the landslide deposits show traces of glacial erosion, hence their locations and ¹⁰Be ages mark maximum extents and minimum ages of glacial advances, respectively. Using toe-to-headwall altitude ratios of 0.4–0.5, we reconstruct minimum equilibrium-line altitudes that exceed previous estimates by as much as 400 m along the moister northern fringe of the Tien Shan. Our data show that deposits from large landslides can provide valuable spatio-temporal constraints for glacial advances in landscapes where moraines and glacial deposits have low preservation potential.     

The monitoring of slow-moving landslides and assessment of stabilisation measures using an optical–mechanical crack gauge

It is possible to monitor slow-moving landslides and assess landslide stabilisation measures over protracted periods using an optical–mechanical crack gauge called a TM-71. This technical note outlines the theoretical background to the gauge and illustrates its practical application through a number of case studies. These studies are drawn from a range of landslide types and stabilisation measures. In terms of monitoring slow-moving landslides, three studies of deep-seated deformations are presented. The Taukliman coastal landslide on the Black Sea Coast is characterised by vertical and horizontal displacements of up to 0.2?mm?year^?1 and sudden earthquake-induced dilations of up to 6?mm. The Parohy ridge spreading landslide in the Malá Fatra Mountains is characterised by gravitationally induced vertical displacements of 0.7?mm?year^?1. The slope deformation that formed Cyrilka Cave in the Beskydy Mountains is characterised by very slow sinistral strike–slip movements of 0.8?mm?year^?1. In terms of assessing landslide stabilisation measures, two studies are presented from Orava Castle in Slovakia and Tetín in the Czech Republic. The data recorded at these sites demonstrate that the constructed stabilisation measures have successfully alleviated the potential landslide hazard in both localities. These case studies clearly demonstrate that the gauge represents an important tool with which to monitor slow-moving landslides and assess landslide stabilisation measures. It is able to provide a precise three-dimensional record of deformation, withstand harsh environmental conditions, and record reliable data over protracted periods.     

An anthropogenic landslide dammed the Songmai River,a tributary of the Jinsha River in Southwestern China

On March 20, 2019, a landslide (named Yagu landslide) occurred in eastern Tibetan Plateau. It produced a 10-m-high dam, resulting in a lake on the Songmai River, a tributary of the Jinsha River. This paper describes this slope failure and analyzes the process and cause of the landsliding based on the combination of Google Earth images, PlanetScope satellite optical images, field photography and geologic data. It is speculated that this event was likely induced by local human activity, such as quarrying rather than natural factors. This example raises a challenging issue whether the ongoing projects along the Jinsha River can induce landslides. In addition, the emergency responses of the government and the effort for risk removal of the dammed lake are presented.

     

The February 2010 large landslide at Maierato, Vibo Valentia, Southern Italy

A large landslide formed at Maierato (Vibo Valencia District), Southern Italy, on 15 February 2010, at 1430?hours local time, when rapid failure occurred after several days of preliminary movements. The landslide has an area of 0.3?km², a runout distance of 1.2?km and an estimated volume of about 10?Mm³. The landslide caused nearly 2,300 inhabitants to be evacuated, with high economic losses. The most probable trigger of the landslide was the cumulative precipitation over the preceding 20?days (having a return period of more than 100?years), which followed a long period of 4?C5?months of heavy rainfall (of about 150% of the average rainfall of the period). This report presents a summary of our findings pertinent to the landslide??s activities based on our field investigations. In particular, this report covers (1) details of land deformation caused by the landslide, (2) geology pertinent to landslide development, (3) identification of the landslide mechanism and its triggering factors based on the analysis of the boring core specimens and landform features, as well as the available video of the event, and (4) preliminary evaluation of the stability of the original slope before the landslide using the finite element-based shear strength reduction method. The aim of the paper was to describe the landslide and explain its mechanism of occurrence.     

Temporal evolution of weathered cataclastic material in gravitational faults of the La Clapiere deep-seated landslide by mechanical approach

After a few years of research, the observation and the analysis of the deep-seated landslides suggest that these are mainly controlled by tectonic structures, which play a dominant role in the deformation of massif slopes. The La Clapière deep-seated landslide (Argentera Mercantour massif) is embedded in a deep-seated gravitational slope deformation affecting the entire slope, and characterized by specific landforms (trenches, scarps??). Onsite, the tangential displacement direction of the trenches and the scarps are controlled by the tectonic structures. The reactivation of the inherited fault in gravitational faults create a gouge material exposed to an additional mechanical and chemical weathering as well as an increased of leaching. The displacement of these reactivated faults gets increasingly important around the area of the La Clapière landslide and this since 3.6?ka BP. In this study, mechanical analysis and grain size distributions were performed and these data were analysed according to their proximity the La Clapiere landslide and times of initiation of the landslide by ¹⁰Be dating. Triaxial test results show that the effective cohesion decreases and the effective angle of internal friction increases from the unweathered area to the weathered area. The whole distribution of the grain size indicates that the further the shear zone is open or developed, the further the residual material loses its finest particles. This paper suggests that the mechanical evolution along the reactivated fault is influenced by the leaching processes. For the first time, we can extract from these data temporal behaviour of the two main mechanical parameters (cohesion and angle of internal friction) from the beginning of the La Clapiere landslide initiation (3.6 ka BP) to now.