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Giant landslides and dammed lakes occurred frequently during the prehistoric period; however, their mechanisms often remain an open issue because they are complex. This study used field investigations to observe four old landslides and three landslide dams in Daning County, Shanxi Province, China. Remote sensing images captured during different periods were used to compare the landforms of landslides, landslide dams, and their surrounding environments in detail. Subsequently, their shapes, scales, spatial distributions, and positional relationships were determined. The ages of 14C obtained from the paleolandslide dam lake (PDL) deposits were 3742 ± 95, 4115 ± 121, 6544 ± 91, 7814 ± 109 cal a BP. The 14C ages of the deposits under the sliding surfaces of the old landslides were 2748 ± 27, 4470 ± 54, and 8245 ± 79 cal a BP. Based on the actual physical geographical conditions and geomorphological characteristics of the region, combined with the above age data, that the following conclusions were made: (i) During the Holocene, from 2700 to 8200 years ago, heavy rainfall was the main reason for the occurrence of landslides and landslide dams in the region. (ii) Under the condition of heavy rainfall, the slopes with angles >60° in the Loess Plateau are prone to form landslide masses, and the size of the landslide is related to rainfall intensity. A landslide dam was easily formed when the sliding direction was perpendicular to the direction of the valley. It is difficult to form landslide dams when the sliding direction is almost consistent with the downward direction of the valley. (iii) The formation mechanism of old landslides shows that collapse or sliding may occur suddenly in loess geological masses under an external rainfall scenario. Moreover, the process of landslide dams is related to the geomorphic forms of the original valley.

The platforms of old landslides triggered by historical earthquakes have often been important residential and agricultural places in active tectonic regions. In recent years, many old landslides have been reactivated due to various causes. Previous studies have shown that the hydrodynamic effect is an important triggering factor for landslide reactivation. However, as an old landslide has undergone a long consolidation period, the permeability of deposits is generally very low, and surface water can hardly infiltrate into deep zones of landslide deposits. Through field investigation, it is found that many old landslides are reactivated due to the coupled action of water infiltration and cracks in the east Tibetan Plateau. The cracks are controlled by fault creep in the initial formation process. In this paper, taking the Chashushan old landslide in the upstream of Jinsha River as a case study, field investigation, experimental study, numerical simulation, and PS-InSAR technique are performed to investigate the reactivation mechanism of the old landslide. The influences of cracks, rainfall, and canal leakage on old landslide reactivation are discussed. The cracks controlled by fault creep provide channels or media for the rapid infiltration of surface water, which is the triggering factor of landslide reactivation. The results in this paper can provide an important reference for research on the reactivation mechanism and risk control of old landslides in the east Tibetan Plateau and even in active tectonic areas around the world. [ABSTRACT FROM AUTHOR]

Engineering construction disturbs old landslides and becomes an important factor for the revival of old landslides.The revival of the old landslide affects the construction and safe operation of the project.The Meigu Ramajue landslide in Sichuan is a typical giant old landslide, the leading edge of the old landslide is reactivated, through field monitoring and numerical simulation, the characteristics and influencing factors of landslide revival deformation were studied, the results show that: (1) Rainfall and human engineering activities are the main factors that induce the resurrection of the old landslide.The resurrected landslide is located at the front of the old landslide, and the creep deformation volume of the landslide is about 2.556 million cubic meters. (2)The landslide body slides rigidly, showing the characteristics of single sliding surface and rocky landslide, and the sliding surface is generally located at the base-covering interface. (3) After two stages of treatment, the anti-sliding piles have obvious effect of blocking the sliding body, and the stability of the sliding body has been significantly improved. At present, the deformation of the sliding body tends to be stable, which can meet the deformation and stability requirements of the normal operation of power facilities.The research of this paper is carried out based on engineering examples, and its research results provide a certain theoretical basis for landslide stability evaluation, prevention and control engineering design, and engineering effect evaluation after treatment.

The reactivation mechanism of old landslides has been extensively studied from building load, erosion of the slope toe, heavy rainfall, and slope cutting for existing research. However, previous research on the reactivation of old landslides pays little attention to the combined action of engineering disturbance and heavy rainfall is rarely studied. This paper describes an old landslide in Wushan County, Chongqing, China, that was reactivated in August 2019 due to engineering disturbance and heavy rainfall. The deformation of the old landslide was first observed in 2007 and 2008, resulting from excavation and rainfall, respectively, and remained stable for about 11 years after treatment. In August 2019, the landslide was reactivated by slope cutting and damaged anti-sliding piles at the toe, and entered a state of imminent sliding due to the concentrated heavy rainfall events that occurred from October 4 to 22, 2019. In order to reveal the deformation features and reactivation mechanism of the landslide, field investigations, drilling activities and monitoring were performed. The results showed that tectonic effects and the stratigraphic lithology were the main reasons for the formation of the old Dashuitian landslide. The cut slope and damaged anti-sliding piles at the toe of the landslide provided the sliding space and reduced the anti-sliding force, and therefore resulted in the reactivation of the landslide. Continuous intense rainfall increased the weight of the landslide, decreased the mechanical properties and increased the pore water pressure of the weak interlayer, which accelerated the deformation rate. Therefore, 1.5 million m3 of rock and soil masses slid along the weak interlayer under the action of gravity, threatening the safety of Wuliu Road, Ring Road, National Road G42 and the Wu-Da Expressway. Our research provides a theoretical basis for reducing the hazard of similar engineering projects involving slopes.

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The southern slope of the Cetățuia-Hoia Hill, located in the urban setting of Cluj-Napoca (Romania), consists of clayey deposits interbedded with sands and sandstones. The slope deposits belong to the Moigrad Formation and are representative of “red bed” continental deposits found across the world. Although documented as a landslide-prone area, the hillslope receives increased attention due to urban development and real estate pressure. The slope was affected by an old, deep-seated landslide; mudflows; and anthropogenic interventions. The stability of the old landslide is close to equilibrium (1.35) and its reactivation may be triggered by rainwater infiltration. The Moigrad Formation deposits are mostly active, expansive, and display medium to high plasticity. Their shearing resistance is described by effective friction angles of 6.7–33.7° and effective cohesive strengths of 7–122 kPa. With regard to mineralogy, the deposits are made up of quartz, feldspar, calcite, dolomite, and phyllosilicates (micas, chlorite, kaolinite, and minerals belonging to the smectite group), while their clay-sized fraction (< 2 µm) is made up of illite–smectite interstratifications, illite, chlorite, kaolinite, and quartz. The physical and mechanical properties of the deposits are closely related to the type and amount of clay-sized minerals, especially to the illite–smectite interstratifications and illite, which are the main components in the clay-sized fraction. Interactions between these components and water infiltrated within the hillslope are proposed as driving mechanisms for landslide reactivation and as active phenomena undermining the stability of the area. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Using advanced Differential Interferometric Synthetic Aperture Radar (InSAR) with small baseline subsets (SBAS) and Permanent Scatter Interferometry (PSI) techniques and C-band Sentinel-1A data, this research monitored the surface displacement of a large old landslide at Xuecheng town, Lixian County, Sichuan Province, China. Based on the MassMov2D model, the effect of the dynamic process and deposit thickness of the potentially unstable rock mass (deformation rate < −70 mm/year) on this landslide body were numerically simulated. Combined with terrain data and images generated by an Unmanned Aerial Vehicle (UAV), the driving factors of this old landslide were analyzed. The InSAR results show that the motion rate in the middle part of the landslide body is the largest, with a range of −55 to −80 mm/year on average, whereas those of the upper part and toe area were small, with a range of −5 to −20 mm/year. Our research suggests that there is a correlation between the LOS (line of sight) deformation rate and rainfall. In rainy seasons, particularly from May to July, the deformation rate is relatively high. In addition, the analysis suggests that SBAS can provide smoother displacement time series, even in areas with vegetation and the steepest sectors of the landslide. The simulation results show that the unstable rock mass may collapse and form a barrier dam with a maximum thickness of about 16 m at the Zagunao river in the future. This study demonstrates that combining temporal UAV measurements and InSAR techniques from Sentinel-1A SAR data allows early recognition and deformation monitoring of old landslide reactivation in complex mountainous areas. In addition, the information provided by InSAR can increase understanding of the deformation process of old landslides in this area, which would enhance urban safety and assist in disaster mitigation.

Giant landslides and dammed lakes occurred frequently during the prehistoric period; however, their mechanisms often remain an open issue because they are complex. This study used field investigations to observe four old landslides and three landslide dams in Daning County, Shanxi Province, China. Remote sensing images captured during different periods were used to compare the landforms of landslides, landslide dams, and their surrounding environments in detail. Subsequently, their shapes, scales, spatial distributions, and positional relationships were determined. The ages of 14 C obtained from the paleolandslide dam lake (PDL) deposits were 3742 ± 95, 4115 ± 121, 6544 ± 91, 7814 ± 109 cal a BP. The 14 C ages of the deposits under the sliding surfaces of the old landslides were 2748 ± 27, 4470 ± 54, and 8245 ± 79 cal a BP. Based on the actual physical geographical conditions and geomorphological characteristics of the region, combined with the above age data, that the following conclusions were made: (i) During the Holocene, from 2700 to 8200 years ago, heavy rainfall was the main reason for the occurrence of landslides and landslide dams in the region. (ii) Under the condition of heavy rainfall, the slopes with angles >60° in the Loess Plateau are prone to form landslide masses, and the size of the landslide is related to rainfall intensity. A landslide dam was easily formed when the sliding direction was perpendicular to the direction of the valley. It is difficult to form landslide dams when the sliding direction is almost consistent with the downward direction of the valley. (iii) The formation mechanism of old landslides shows that collapse or sliding may occur suddenly in loess geological masses under an external rainfall scenario. Moreover, the process of landslide dams is related to the geomorphic forms of the original valley., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)

Unfavorable hydrodynamic evolution is considered as the major cause leading to reservoir slope instability and is often modeled by numerical method. However, this simulation is seldom checked by systematic field instrumentation. Taking the opportunity of filling the Three Gorges Reservoir, a system was established in Xietan landslide to monitor reservoir water level, subground water level, seepage pressure, rainfall and deformation, etc. The monitored data during reservoir filling shows that: (1) The water level rise in the bank lags behind the reservoir filling and the lag time depends on the bank permeability; (2) rainfall-induced subground water rise and its lag time is closely correlated to hourly rainfall, indicating that it is not feasible or sufficient to use daily rainfall for analysis; (3) the effect of inverse seepage during reservoir filling on stability is ephemeral and reservoir filling is the major cause leading to bank instability. [ABSTRACT FROM AUTHOR]

Using advanced Differential Interferometric Synthetic Aperture Radar (InSAR) with small baseline subsets (SBAS) and Permanent Scatter Interferometry (PSI) techniques and C-band Sentinel-1A data, this research monitored the surface displacement of a large old landslide at Xuecheng town, Lixian County, Sichuan Province, China. Based on the MassMov2D model, the effect of the dynamic process and deposit thickness of the potentially unstable rock mass (deformation rate < −70 mm/year) on this landslide body were numerically simulated. Combined with terrain data and images generated by an Unmanned Aerial Vehicle (UAV), the driving factors of this old landslide were analyzed. The InSAR results show that the motion rate in the middle part of the landslide body is the largest, with a range of −55 to −80 mm/year on average, whereas those of the upper part and toe area were small, with a range of −5 to −20 mm/year. Our research suggests that there is a correlation between the LOS (line of sight) deformation rate and rainfall. In rainy seasons, particularly from May to July, the deformation rate is relatively high. In addition, the analysis suggests that SBAS can provide smoother displacement time series, even in areas with vegetation and the steepest sectors of the landslide. The simulation results show that the unstable rock mass may collapse and form a barrier dam with a maximum thickness of about 16 m at the Zagunao river in the future. This study demonstrates that combining temporal UAV measurements and InSAR techniques from Sentinel-1A SAR data allows early recognition and deformation monitoring of old landslide reactivation in complex mountainous areas. In addition, the information provided by InSAR can increase understanding of the deformation process of old landslides in this area, which would enhance urban safety and assist in disaster mitigation. [ABSTRACT FROM AUTHOR]