Sichuan-Tibet Highway Research Articles

Geohazard cascade and mechanism of large debris flows in Tianmo gully, SE Tibetan Plateau and implications to hazard monitoring

Alpine glaciers and permafrost are sensitive to climate change, and their degradation due to annual temperature increasing has already induced many mass movements such as debris flows. On September 4 of 2007, July 25–31 and September 5–8 of 2010, three large debris flows took place in Tianmo gully, a left-bank tributary of Parlung River, southeast Tibetan Plateau. The debris flows blocked the river, and a section of highway 450m long including a bridge 76m long were destroyed by the subsequent outburst flood. This paper, based on post-event investigations, witness accounts, news reports and satellite image interpretation, systematically analyses the geo-environments, climate conditions and sources of these debris flow events. Their differences in flow process, surge numbers and velocity suggest that they resulted from different geohazard processes, cascades and initiation mechanisms. The 2007 debris flow originated from a bare rock/moraine collapse next to the cirque due to strong alternation of wet and dry conditions. The mass moved down the gully with velocity of 30–40m/s estimated by back-calculation using superelevation and run-up. It entrained moraine, avalanched snow-ice and water from the channel, and transformed into high-speed debris flow, crossing the Parlung River and finally depositing onto the highway. The other two events in July and September of 2010 initiated from two channel-bank landslides triggered by melt-water and concentrated rainfall, which dammed the channel. The subsequent landslide dam failure generated debris flows over several days, with velocities of 12–14m/s, that temporally blocked Parlung River. The initiation mechanisms of most large debris flows recorded in Parlung region are similar to the events in Tianmo gully, originating either from rock/moraine avalanches or from the collapse of a landslide dam. This implies that the periglacial degradation of bedrock and moraine is the key process to be monitored and assessed under climate warming. The paper applies the geohazard mechanisms and cascade to hazard monitoring in order to protect the existing Sichuan-Tibet highway and the forthcoming railway.

The 102 Landslide: human–slope interaction in SE Tibet over a 20-year period

The evolution of large-scale landslides should be studied because, over long periods of time, primary remediation measures may suffer reduced efficiency or have to be adjusted many times. The 102 Landslide in southeast Tibet, which originally formed in 1991 with a volume of 5.1 million m3 and still exhibits post-failure activity, provides a distinctive case study. The landslide evolved from earthquake destruction and unloading, rainfall-triggered sliding, and debris flow to sands sliding slopes. The NE ringed scarp receded by 38.96 m during a five-year period (2003–2008). The total recession was 160 m with a total area of 2500 m2 during a 17-year period (1991–2008). Although several types of remediation measures were applied and were temporarily effective, the normal function of the Sichuan–Tibet Highway was affected by landslide reactivation from time to time. Actual effects of the engineering measures such as retaining walls, prestressed anchor cables, and drainage ditches confirm that hasty governance of this type of large-scale landslide is generally unfeasible over long time periods. Finally, an approach involving a tunnel running backward from the front face has been adopted as a permanent solution to large-scale moraine slope failures: This engineering practice has been in progress since April 2012. This paper describes the evolution of the 102 Landslide, the engineering interventions to mitigate the effects of the landslide on the Sichuan–Tibet Highway, and the choice of tunneling as a final mitigation measure. The present study concludes that approaches that allow escape from developing geo-hazards should always be the initial choice.

Integrated Application of Micro Steel Pipe Piles and Soil Nailing Frame Beam for Loose Deposit Slopes

Loose deposit is widely distributed along the south route of Sichuan-Tibet highway (in Tibet). Slope disasters often occur because of the broken loose deposit and the low grade highway without complete safeguards for the slope. The paper proposed the integrated treatment technology with micro steel pipe piles and soil nailing frame beam and its work theory and structure design. The slope stability was simulated numerically with Midas-GTS on typical sections to verify the effectiveness of the technology. During simulation, the stable coefficient of slope with or without the integrated treatment technology was calculated. Results showed that the technology with micro steel pipe piles and soil nailing frame beam can improve the stability of loose deposit cutting slopes greatly.

Characteristics and mechanisms of large deformation in the Zhegu mountain tunnel on the Sichuan–Tibet highway

The Zhegu mountain tunnel is a typical long, deep-buried highway tunnel at a high altitude, subjected to low temperatures and high geostress. The tunnel is excavated in carbon phyllite and slate at depths of up to 1000m below ground, which has resulted in extreme deformation, especially in a depth of 3m from the tunnel perimeter. The maximum deformation was monitored to be 60cm, with a maximum deformation speed of 39.3mm/day. In addition, it took 60–120days to complete 90% of the deformation. The deformation of the Zhegu mountain tunnel is characterized by serious subsidence of the arch, squeezing outwards of sidewalls, buckling failure of sidewalls and local collapse. The swelling of soft rock is found not to be a main factor of large deformation in the subject tunnel. Three mechanisms of large deformation are derived based on the characteristics and geological conditions, which are plastic flow of soft rock, shear sliding of wedges, and bending of thin-layered soft rock.

Study on Time-Space Motivation and Operation Mechanic of Landslide - A Case of Zhenzilin Landslide in Sichuan-Tibet Highway

The time-space movement feature of landslide was a geological process that landslide mass change from a state to another under the effect of internal and external factors. The ground surface and deep displacement feature of landslide with time and space was a reflection and externalization also a trace record of landslide time-space movement. Particularly, deep displacement of landslide provided direct and reliable evidence for studying space-time motion characteristics of slide. This paper studied on ZhenziLin landslide in Sichuan-Tibet highway, based on monitored deep displacement information of boreholes in landslide. It systematically analyzed time-space movement features and operation mechanic of integral revived area, disturbed deformation zone and foreland slump zone of landslide from the aspects of accumulated or relative displacement and displacement vector etc. of confirming or potential slide plane and hole top at different time. Results obtained provided data and dependence for studying landslide stability prediction.

Using fuzzy relations and GIS method to evaluate debris flow hazard

The study area, located in the southeast of Tibet along the Sichuan-Tibet highway, is a part of Palongzangbu River basin where mountain hazards take place frequently. On the ground of field surveying, historical data and previous research, a total of 31 debris flow gullies are identified in the study area and 5 factors are chosen as main parameters for evaluating the hazard of debris flows in this study. Spatial analyst functions of geographic information system (GIS) are utilized to produce debris flow inventory and parameter maps. All data are built into a spatial database for evaluating debris flow hazard. Integrated with GIS techniques, the fuzzy relation method is used to calculate the strength of relationship between debris flow inventory and parameters of the database. With this methodology a hazard map of debris flows is produced. According to this map, 6.6% of the study area is classified as very high hazard, 7.3% as high hazard, 8.4% as moderate hazard, 32.1% as low hazard and 45.6% as very low hazard or non-hazard areas. After validating the results, this methodology is ultimately confirmed to be available.

Engineering geological zonation using interaction matrix of geological factors: An example from one section of Sichuan-Tibet Highway

In linear engineering projects such as those of the highways and railways in the northern Yarlu-Tsangpu Grand Canyon of Tibet that cross various geological and geomorphological units, engineering geological zonation must be carried out in advance because of complicated and diverse engineering geological conditions. Previous zonations have been based on qualitative approaches together with an overview of regional physio-geographic and geological settings. Such an approach is suitable for a broad regional development plan. However, it is not adequate for remediation of highways. In this paper, an interaction matrix approach was adopted and applied as an Engineering Geological Zonation Index (EZI) for the semi-quantitative analysis of the data from the Basu—Linzhi section of the Sichuan-Tibet Highway in China. Eight zonations and 19 sub-zonations of the section were made and evaluated, in accordance with a qualitative evaluation procedure. The results of the research presented in this paper will provide useful information for future railway design and construction.

Distribution of landslides adjacent to the northern side of the Yarlu Tsangpo Grand Canyon in Tibet, China

This paper presents results of recent studies on distribution and category of landslides in one section of the Sichuan–Tibet Highway, adjacent to the northern side of the Yarlu Tsangpo Grand Canyon, Tibet, Southwestern China. In the tectonic setting predominated by compression and strike-slipping, active faults are dominant and result in the genesis of the great alpine relief together with fluvial incision and unloading. In this section, with a distance of about 290 km between Ranwu and Lulang, 34 landslides occurred. Among them, the 12 large and super-large landslides comprise the most dangerous part of the highway system to road users over the past 50 years. The landslides usually occurred in slopes comprised of moraine with a large thickness, fluvio-pluvial and lacustrine deposits and fractured rocks. Based on the examination of the physical geography, structural geology, Quaternary geology, stratigraphy and petrography, this paper presents the temporal-spatial distribution of landslides along the section and classification of them into three types with respect to mechanism and composites of landslides. Type 1. Landslide initiated at high elevation and transformed into a distal debris flow damming the river with a long reoccurrence interval Type 2. Landslide at stream banks, in different ranks of mass movements in dissecting layers of moraines Type 3. Landslide of fractured rock mass with quick translation movements. Each of the three types is presented by distinctive case examples. Type 1 is Yigong Landslide; type 2 includes Dongjiu Landslide group, 102 Landslide group, Suotong Landslide group, Songzong Landslide; and the type 3 is Layue Landslide. A binary landslide, which is seldom seen in nature and which occurred in the outlet of one creek under the integrative function of fluvial incision and road cut, is also presented. These are distributed in different parts of the area with characterized structural geology, topography and composites (gneiss and Quaternary deposits) with accumulative quantity between Suotong and Dongjiu. The most occurred with frequent and rapid translation, shallow shearing planes, various influential factors and unique triggering factors, and a variable period of reoccurrence with a tendency of increasing magnitude. In this region, six influential factors greatly contribute to their occurrence: (a) intensive neotectonic movements, (b) ongoing alpine canyon relief, (c) earthquakes, (d) heavy precipitation, (e) stream erosion, and (f) human activities, to a certain extent. Mostly, the latter four factors play major roles in triggering landslide occurrence. The earthquake causes the rock and soil to fracture and deform, and tends to be unstable, or cause earth-induced landslides. The heavy rainfall in monsoon seasons which saturates the soil and lower the shearing strength is mostly responsible for the occurrence of landslides. The stream erosion disturbs slope toes causing progressive failure. Road construction and deforestation decrease the natural slope stability. Comments and suggestions on the physical measures for remediation of landslides and safety of highways are also made.

Research on evolution and prevention of the No.1 large-scale dangerous slope of Erlang Mountain on the Sichuan-Tibet Highway

Sichuan-Tibet Highway traverses the two principal geomorphic units and their transition belt in western China; it has some hazardous slopes characterized by high altitude and chilliness, high elevation, large scale and complexity. Various hazards usually concur in groups. The integrated hazards of these slopes cannot be reflected by any single hazardl they act on one another and develop at the same time, like many other things experiencing a recurrent evolving course from growth to demise. Based on the mechanisms of the typical dangerous No.1 slope of Erlang Mountain on the Sichuan-Tibet Highway, various simulations through geotechnical test, numerical calculation, and in-situ monitoring have been carried out to control and regularize the last phase of evolution of the slope. The text shows that such slopes have developed under geological and engineering conditions that might have enforced the potentiality of hazards; interactions between different hazards are of more menace than any single factor; structures in cooperation with the hazardous bodies may be effective for preventing such calamities.

Addressing severe slope failure hazards along Sichuan-Tibet Highway in Southwestern China

Addressing severe slope failure hazards along Sichuan-Tibet Highway in Southwestern China