Surrounding rock pressure in the tunnel portal section through moraine under freeze-thaw action

Moraines,characterized by the accumulation of rock and soil debris transported by glacial activity,present unique challenges for tunnel construction,particularly in portal sections,due to prevailing geographical and climatic conditions that facilitate freeze-thaw action.Despite these challenges,there is a dearth of studies investigating the influence of freeze-thaw action and water content on the mechanical properties of moraines,and no research on calculating surrounding rock pressure in moraine tunnels subjected to freeze-thaw conditions.In this study,direct shear tests under freeze-thaw cycles were conducted to examine the effects of freeze-thaw cycles and water content on the mechanical properties of frozen moraine.A comprehensive parameter K,integrating the number of freeze-thaws and water content,was introduced to model cohesion c.Drawing on Terzaghi Theory,we propose an improved algorithm for calculating surrounding rock pressure at the portal section of moraine tunnels.Using a tunnel as a case study,surrounding rock pressure was calculated under various conditions to validate the Improved Algorithm's efficacy.The results show that:(1)Strength loss exhibits a linear trend with the number of freeze-thaw cycles at water content levels of 4%and 8%,while at 12%water content,previous freeze-thaw cycles induce more significant damage to the soil.(2)Moraine saturation peaks between 8%and 12%water content.Following repeated freeze-thaw cycles,moraine shear strength initially increases before decreasing with varying water content.(3)The internal friction angle of moraine experiences slight reductions with prolonged freeze-thaw cycles,but both freeze-thaw cycles and water content significantly influence cohesion.(4)Vertical surrounding rock pressure increases after the initial freeze-thaw cycle,particularly with higher water content,although freeze-thaw cycles have minimal effect on it.(5)Freeze-thaw cycles lead to a substantial increase in lateral surrounding rock pressure,necessitating reinforced support structures at the arch wall,arch waist,and arch foot in engineering projects to mitigate freeze-thaw effects.This study provides a foundation for designing and selecting tunnel support structures in similar geological conditions.

CRITICAL HYDROLOGIC CONDITIONS FOR OVERFLOW BURST OF MORAINE LAKE

Floodwater and debris flow caused by glacial lake burst is an important land process and a serious mountain disaster in glacial area of Xizang (Tibet) Autonomous Region, and the overflow burst is mainly caused by glacial landslide falling into moraine lake. On the premise that moraine lake is full, instantaneous burst in part of the lake bank happens, as flow velocity at burst mouth caused by overflow head is higher than threshold flow velocity of glacial till. Under some supposes, d(90) and d(10) of the glacial till in the hank were used as the threshold sizes of coarse and fine grains respectively. Thus, the formula of calculating threshold flow velocity of uniform sand was simplified, and threshold flow velocity of glacial till was calculated with the formula. Then, with synthesis formula calculating flow velocity of instantaneous part burst, flow velocity at overflow burst mouth was calculated, and calculation formula of critical height (H(0)) of overflow head was derived. Overflow head was caused by volume and surge of glacial landslide falling into moraine lake, calculation formulas of ascendant height (H(1)) of lake water surface and surge height (H(2)) on burst mouth caused by glacial landslide falling into moraine lake were derived. To sum up, critical hydrologic conditions of moraine lake burst with overflow form are: the burst is inevitable as H(1) > H(0); the burst is possible as H(1) < H(0) and (H(1)+H(2)) > H(0); the burst is impossible as (H(1)+H(2)) < H(0). In the factors influencing the burst critical conditions, it is advantageous for the burst that scale of the lake is 10(5)m(2) range; terminal glacial till is more fine and is even more uniform; the width of overflow mouth is even smaller than the length of the bank; the landslide has large scale and steep slip surface; and glacial end is close to the lake. With burst of Guangxiecuo Lake in Midui Valley of the Polongzangbu River in Xizang as an example, the burst critical conditions were tested.

Mapping of moraine dammed glacial lakes and assessment of their areal changes in the central and eastern Himalayas using satellite data

The relatively rapid recession of glaciers in the Himalayas and formation of moraine dammed glacial lakes(MDGLs) in the recent past have increased the risk of glacier lake outburst floods(GLOF) in the countries of Nepal and Bhutan and in the mountainous territory of Sikkim in India. As a product of climate change and global warming, such a risk has not only raised the level of threats to the habitation and infrastructure of the region, but has also contributed to the worsening of the balance of the unique ecosystem that exists in this domain that sustains several of the highest mountain peaks of the world. This study attempts to present an up to date mapping of the MDGLs in the central and eastern Himalayan regions using remote sensing data, with an objective to analyse their surface area variations with time from 1990 through 2015, disaggregated over six episodes. The study also includes the evaluation for susceptibility of MDGLs to GLOF with the least criteria decision analysis(LCDA). Forty two major MDGLs, each having a lake surface area greater than 0.2 km2, that were identified in the Himalayan ranges of Nepal, Bhutan, and Sikkim, have been categorized according to their surface area expansion rates in space and time. The lakes have been identified as located within the elevation range of 3800 m and6800 m above mean sea level(a msl). With a total surface area of 37.9 km2, these MDGLs as a whole were observed to have expanded by an astonishing 43.6% in area over the 25 year period of this study. A factor is introduced to numerically sort the lakes in terms of their relative yearly expansion rates, based on their interpretation of their surface area extents from satellite imageries. Verification of predicted GLOF events in the past using this factor with the limited field data as reported in literature indicates that the present analysis may be considered a sufficiently reliable and rapid technique for assessing the potential bursting susceptibility of the MDGLs. The analysis also indicates that, as of now, there are eight MDGLs in the region which appear to be in highly vulnerable states and have high chances in causing potential GLOF events anytime in the recent future.

A New Method to Identify Quaternary Moraine:Acoustic Emission Stress Measurement

How to effectively identify glacial sediments, especially Quaternary moraine, has been in dispute for decades. The traditional methods, e.g., sedimentary and geomorphologic ones, are facing challenge in eastern China where controversial moraine deposits are dominatingly distributed. Here, for the first time, we introduce the acoustic emission （AE） stress measurement, a kind of historical stress measurement, to identify Quaternary moraine. The results demonstrate that it can be employed to reconstruct stress information of glaciation remaining in gravels, and may shed light on the identification of Quaternary moraine in eastern China. First, we measured the AE stress of gravels of glacial origin that are underlying the Xidatan Glacier, eastern Kunlun Mountains in western China. Second, we calculated the stress according to the actual thickness of the glacier. The almost identical stress values suggest that the glacial gravels can memorize and preserve the overlying glacier-derived aplomb stress. And then we introduce this new approach to the controversial moraine in Mount Lushan, eastern China. The results indicate that the stress is attributed to the Quaternary glacier, and the muddy gravels in the controversial moraine in Mount Lushan are moraine deposits but not others.

New progress and problems of Quaternary moraine dating in the Tibetan Plateau

Since the 20th century, numerous Quaternary moraine dating methods have emerged, including lichenometric, moraine 14C, quartz sand thermoluminescence （TL）, electron spin resonance （ESR）, optically stimulated luminescence （OSL） and 10Be, 26A1, 36C1, 3H, 21Ne nuclide dating methods. These dating methods are widely applied to determine moraine ages and have provided a large dataset. Unfortunately each method has its defects. In this paper, we will review these various dating methods and provide some comments.

Post-sedimentary Transformation of Lateral Moraines——the Tributary Tongue Basins of the Kvíárjkull(Iceland)

The Kvíárjokull,a southern outlet glacier of the Vatnajokull,is confined in the mountain foreland by lateral moraines measuring a height of up to 150 m. Each of the lateral moraines shows considerable breaches with deviations of the main moraine ridges. The paper discusses the possible origins of these modifications of the lateral moraines as result of： 1） ice overlappings during glacier advances and subsequent breaches of the lateral moraine,2） bifurcations of the Kvíárjokull glacier tongue triggered by the preglacial relief conditions and the prehistorical moraine landscape leading to afflux conditions,3） drainage of ice-marginal glacier lakes and 4. volcanic activities,such as lava flows and volcanic-induced jokulhlaups. A historic-genetic model of the formation of the lateral moraines is presented considering the breaches in the lateral moraines as result from glacier bifurcations and therefore as former tributary tongue basins. Such breaches in the lateral moraines are also common landscape features at glaciers outside of Iceland and are from wider importance for the paleoreconstruction of former glacier stages. The knowledge of their development is essential for an adequate relative age classification of individual moraine ridges. In regard to the origin of the debris supply areas of the large-sized Kvíárjokull moraines,the resedimentation of prehistoric till deposits by younger glacier advances plays a role in the formation of the lateral moraines apart from englacial and supraglacial sediment transfer processes.

Optimal Interpolation and Kriging Mapping of Soil Characters in Glacial Moraine Landscapes

The objective of this research is to analyze optimal interpolation and Kriging mapping of soil characters in Glacial Moraine Landscapes. The research site is located in sloping landscapes, Kuehren, North Germany. The survey method was detailed using maps with scales of 1：5,000. Soil sampling was performed by soil pits and borings and completely analyzed in laboratory. Collected data were evaluated by Geostatistics program for spatial soil variability analyses. All maps （produced by Kriging interpolation） picture redistribution of soil nutrients and soil fractions and all map isolines run in similar directions according to landscape nets. The position in the landscape is responsible for increased soil variability. Soil variability becomes higher with decreasing elevation; this means it increases from hilltops to lower slopes. All observed soil characters show relationships to the soil variability. This variability system is caused by convex depressions and hedgerows （Knicks） function as barriers for the redistribution of transported material and offsite sedimentation. Therefore fluxes can be assessed by soil gain and loss balances.

Variogram Analyses of Soil Characters in Glacial Moraine Landscapes

The objective of this research is to analyze variogram analyses of soil characters in Glacial Moraine Landscapes. The research site is located in sloping landscapes, Kuehren, North Germany. The survey method was detailed using maps with scales of 1：5,000. Soil sampling was performed by soil pits and borings and completely analyzed in laboratory. Collected data were evaluated by geostatistics program for spatial soil variability analyses. The variogram models show that spatial soil variability ranges between 70-120 m （mean： 85 m）. Effective distances of sampling are calculated at around 50 m. The range values of soil characters are proportional with the range of elevation （range： 70 m, effective distance： 40 m）. The relief determines mainly the spatial variability of soil characters.

Compression Characteristic and Creep Behavior of Moraine Soil at Xingkang Bridge,West Sichuan,China

The compression and creep characteristics of moraine soil are important mechanical properties of geomaterials to be analyzed during the construction process of engineering projects.However,related references about these characteristics through large-size in-situ tests have rarely been reported.In this study,in-situ tests of particle size distribution,compression deformation,and compression creep were conducted at the Xingkang Bridge,West Sichuan,China.The results show that the uniformity coefficient of moraine soil ranges from 12.1 to 183.3,and gradation coefficient ranges from 0.4 to 2.8.The total compression deformations of moraine samples during the conventional compression deformation test are 4.70,4.07,and 0.47 mm,and their residual deformations are 2.81,2.45,and 0.22 mm,respectively.The deformation modulus ranges from 127.3 to 676.4 MPa,and elastic modulus ranges from 316.3 to 765.7 MPa.During compression creep tests,moraine soil enters the steady creep stage after 3.8 h of loading pressure at 445 k Pa,and it keeps steady after 14 h of loading pressure at 900 k Pa.The Burgers model and generalized Kelvin model predict the deformation well in transient,deceleration and steady creep stages.Results provide a valuable reference for the analysis of the compression deformation and creep behavior of moraine soil during engineering construction and management.

Characteristics of mountain glacier surge hazard: learning from a surge event in NE Pamir, China

Abnormal glacier movement is likely to result in canyon-type hazards chain,such as the barrier lake of Yarlung Zangbo Grand Canyon formed by glacier debris flow in October 2018 in China.Glacier hazard usually evolves from the glacier surge and may occur in a regular cycle.Understanding the characteristics and process of glacier surge is important for early hazard recognition and hazard assessment.Based on field investigations,remote sensing interpretations and SAR offset-tracking surveys,this study confirms a typical glacier surge in the northeast Pamir,and presents its characteristics and processes."Black ice"mixed moraines choking uplift and overflowing lateral marine are the most important scenic characteristics,which were formed under the conditions of stagnant glacier downstream and abundant super-glacial moraine.Glacier movement event can be divided into a five-period cycle including quiescent,inoculation,initiation,fracture and decline.This surge event lasted for about 300 days,initiated in February 2015 developed extensive fracturing zone in spring and early summer at maximum velocity of 10±0.95 m/day,declined after August 2015 and recovered to quiescent status in October 2015 for the next inoculation.The average height of glacier"receiving"area increased by 20-40 m with 2.7-3.6×10^8 m^3 ice transferred from glacier"reservoir",and this volume accumulation again require 50-100 years for glacier mass balance which gives approximately 100 years frequency of the glacier surge.Nevertheless,long-period increase of precipitation and temperature were favorable for the occurrence,hydrological instability is the direct triggering mechanism,and while the Glacier Lake Outburst Flood(GLOF)hazards are unlikely to occur with this surge.

The changes of Lop Nur Lake and the disappearance of Loulan

The causes of the disappearance of the ancient town of Loulan in Xinjiang, China have been generally agreed to derive from two factors: human activities and natural factors (environmental variations). In this paper, the Muzart Glacier was selected as an example, and found that the length of the glacier has been gradually decreasing and the snow line has been retreating to a higher altitude, both results contributing to a decrease in river flow below the Muzart Glacier. From the distribution of moraines in the Tianshan Mountains and adjacent areas in different periods, the paper speculates that there have been four minor glacial periods since the Quaternary. Although the durations and scales of the four minor glacial periods were different, they all indirectly influenced the formation and disappearance of the Lop Nur Lake. The events of the fourth minor glacial period are the important impact factors in the existence and disappearance of Loulan. Whether the disappearance of Loulan can be related to the events of the three previous minor glacial periods needs further investigation.

Grain Size Distribution of Soils within the Cordillera Blanca, Peru: An Indicator of Basic Mechanical Properties for Slope Stability Evaluation

This paper presents results of a study on the mechanical properties of sandy and gravely soils within the Cordillera Blanca, Peru. The soils were divided into groups according to their origin(glacial, fluvial, or debris flow). The grain size distribution of forty three soil samples was used to classify the soils according to the scheme of the Unified Soil Classification System(USCS). These distributions have then been used to estimate shear strength and hydraulic properties of the soils. There are clear differences between the soils which reflect their divergent origins. The glacial soils normally fit within one of two distinctive groups according to the proportion of fines(Group A, 7%-21.5%; Group B, 21%-65%). The estimation of shear strength at constant volume friction angle and peak shear strength of the glacial sediments with low content of fines was made using published data relating to the measured shear strength characteristics of soils with similar origins and grain size distributions. The estimated values were supported by measurements of the angle of repose taken from fourteen samples from two moraines and by shear tests on samples from one locality. The results of the grain size distribution werealso used to estimate the average hydraulic conductivity using the empirical Hazen formula which results were verified by field infiltration tests at two localities.

Marine Oxygen Isotope Stage(MIS)-6 Glacial Advances on the Tibetan Plateau More Extensive than during MIS-2 due to More Abundant Precipitation

Numerous studies dated glacial deposits within the Himalayan-Tibetan orogen.While most focus on young deposits,i.e.,younger than the Last Glacial Maximum(LGM or Marine oxygen Isotope Stage(MIS)-2,~20 ka),older moraines such as those from MIS-6(~130–191 ka)are much harder to date and interpret due to the less well-preserved nature of their surfaces and boulders,as well as their scattered and continuous age distribution due to long-lived erosion since deposition.Here,we dated with~(10)Be,two imbricated moraines near Yadong in southern Tibet,as MIS-2 and 6,showing that the most extensive,smooth surfaces were abandoned during MIS-6.Compiling published data from 54 MIS-6 moraines on the Tibetan Plateau reveals that they exist in most regions,dry or humid.They are particularly well-preserved(sharp crests)in eastern and northern Tibet,while in southern and central Tibet,their crests are rounded to sub-rounded.Because both MIS-2 and 6 were equally cold,and because MIS-6 moraines are much more extensive than those from the LGM,we conclude that MIS-6 glacial advances were controlled by more abundant precipitation than during MIS-2.This would be consistent with the peak in Asian monsoon during MIS-6,revealed by sediments from the South China Sea.

Experimental study on the applicability of Westergaard＇s formula for calculating earthquake-induced hydrodynamic pressure in small lake

Moraine-dammed lake outbursts usually threaten highways, railways, and key facilities in alpine regions. The varying amplitudes and distribution of hydrodynamic pressures significantly affect the stability of the dam. We utilize a shaking table to investigate the development of hydrodynamic pressure caused by different sinusoidal waves and seismic Wolong wave. A series of shaking table tests indicate that the hydrodynamic pressure varia- tion significantly follows seismic acceleration wave motion. The maximum hydrodynamic pressures calculated by Westergaard＇s equation are compared with the experi- mental values under different waves. It is shown that the Westergaard＇s values are lower than the experimental ones under the sinusoidal waves. However, the Westergaard＇s method is able to predict the earthquake-induced hydro- dynamic pressure caused by Wolong wave in small lake with desirable accuracy.

Study of Holocene glacier degradation in central Asia by isotopic methods for long-term forecast of climate changes

This article presents a summary of our studies of Holocene moraines and glaciers of the Tien-Shan, Pamir, and Himalaya moun- mills with the purpose of providing pattern regularity of the Holocene glaciation decomposition. We developed a method for ob- taining reliable radiocarbon dating of moraines with the use of autochthonous organic matter dispersed in fine-grained morainic material, as well there were shown new possibilities of isotope-oxygen and isotope-uranium analysis for the Holocene glaciations dynamics. We found that Holocene glaciations disintegrate stadiaUy according to the decaying principle, and seven main stages may be distinguished. We achieved the absolute dating of the first three stages, identifying these periods as 8,000, 5,000, and 3,400 years ago. The application of the above-mentioned isotope methods of the Holocene glaciations and moraines study will allow re- searchers to improve the offered model of the Holocene glaciations disintegration; it will be great contribution to salvation of the problem of long-term climatic and glaciations forecast.

The morphological characteristics of glacial deposits during the Last Glaciation, taking the Parlung Zangbo River Basin as an example

Moraine morphology is a valuable indicator of climate change. The glacial deposits of ten valleys were selected in the Parlung Zangbo River Basin, southeastern Tibetan Plateau, to study the glacial characteristics of the Last Glaciation and the climate change processes as revealed by these moraines. Investigation revealed that a huge moraine ridge was formed by ancient glacier in the Marine Isotope Stage 2 （MIS2）, and this main moraine ridge indicates the longest sustained and stable climate. There are at least two smaller moraine ridges that are external extensions of or located at the bottom of the main moraine ridge, indicating that the climate of the glacial stage before MIS2 was severer but the duration was relatively shorter. This distribution may reflect the climate of MIS4 or MIS3b. The glacial valleys show multi-channel, small-scale moraine ridges between the contemporary glacial tongue and the main moraine ridge. Some of these multi-channel mo- raine ridges might be recessional moraine, indicating the significant glacial advance during the Younger Dryas or the Heinrich event. The moraine ridges of the Neoglaciation and the Little Ice Age are near the ends of the contemporary glaciers. Using high-precision system dating, we can fairly well reconstruct the pattern of climate change by studying the shape, extent, and scale characteristics of glacial deposits in southeastern Tibet. This is valuable research to understand the relationship between regional and global climate change.

Outburst mechanism of Yindapu Glacial Lake in Tibet

At present,the mechanism research on glacial lake outburst mainly focuses on the ice quake and ice landslide,etc. To some glacial lakes,the seepage deformation is the dominant factor in outburst process. Taking the Yindapu Glacial Lake in Tibet as an example,using SEEP/W module of FEM software (GEO-STUDIO),the authors analyzed seepage stability of terminal moraine ridge dam. The leading role of seepage deformation in some glacial lake outburst mechanism is proposed and proved.

The influence of freeze-thaw cycles on the granulometric composition of Moscow morainic clay

The freeze-thaw cycling process considerably changes the composition, structure, and properties of soils. Since the grain size is the most important factor in determining soil characteristics, our current research primarily aims to investigate dynamic changes of the soil fraction when exposed to freeze-thaw conditions. We observed two series of Moscow morainic clayey specimens （gQⅡm）： （Ⅰ） the original series, and （Ⅱ） the remolded series. We subjected each series of soil specimens to different frequencies of freeze-thaw cycles （3, 6, 20, and 40 cycles）, and we used granulometric tests to analyze both series before and after exposure to freeze-thaw conditions. As a result of our experiments, the granulometric compositions tended to be distributed evenly after 40 freeze-thaw processes （i.e., content of fraction for 0.1-0.05 mm was increased after 40 freeze-thaw cycles） because the division of coarse grains and the aggregation of fine grains were synchronized during the freeze-thaw process. The soil grains in both series changed bi-directionally. In the original series, changes of the sand grains were conjugated with the clay grains, and in the remolded series, changes of the sand grains were conjugated with the silt grains, because potential energy difference caused the division and aggregation processes to relate to the counteraction process. The even distribution of soil grain size indicated the state of equilibrium or balance. The granulometric compositions were altered the most during the sixth freeze-thaw cycle, because the coefficient of the intensity variation of the grain fineness （Kvar） had its maximum value at that time.

Dynamic Characteristics of the Long Runout Rock-ice Avalanche at High Altitude——A Case from the Zelongnong Basin,Eastern Himalayan Syntaxis,China

Rock-ice avalanches have frequently occurred in the Eastern Himalayan Syntaxis region due to climate change and active tectonic movements.These events commonly trigger catastrophic geohazard chains,including debris flows,river blockages,and floods.This study focuses on the Zelongnong Basin,analyzing the geomorphic and dynamic characteristics of high-altitude disasters.The basin exhibits typical vertical zonation,with disaster sources initiating at elevations exceeding 4000 m and runout distances reaching up to 10 km.The disaster chain movement involves complex dynamic effects,including impact disintegration,soil-rock mixture arching,dynamic erosion,and debris deposition,enhancing understanding of the flow behavior and dynamic characteristics of rock-ice avalanches.The presence of ice significantly increases mobility due to lubrication and frictional melting.In the disaster event of September 10,2020,the maximum flow velocity and thickness reached 40 m/s and 43 m,respectively.Furthermore,continuous deformation of the Zelongnong glacier moraine was observed,with maximum cumulative deformations of 44.68 m in the distance direction and 25.96 m in the azimuth direction from March 25,2022,to August 25,2022.In the future,the risk of rock-ice avalanches in the Eastern Himalayan Syntaxis region will remain extremely high,necessitating a focus on early warning and risk mitigation strategies for such basin disasters.

Quaternary glacial geomorphology and glaciations of Kongur Mountain,eastern Pamir,China

Kongur Mountain is the largest center of modern glaciation on the Pamir Plateau.During the glacial-interglacial cycles of the Quaternary,Kongur Mountain was extensively and repeatedly glaciated,and the glacial landforms from multiple glaciations are well-preserved in valleys,in basins,and on the piedmonts.Dating samples have been collected according to the distribution and weathering of the glacial tills,the relationship among the glacial deposits,and the loess or soil developed on the moraines. Electron spin resonance(ESR) dating of the samples was done using the germanium(Ge) centers in the glacial quartz grains,which are sensitive to both sunlight and grinding.The ages of the glacial deposits can be divided into four clusters,i.e.,13.1±0.8-27.0±2.2,36.4±3.3-48.7±5.7,65.6±6.8-86.6±8.9,and 105.6±9.4-178.3±17.8 ka.Six glacial advances in this region have been confirmed,which are equivalent in age to the Little Ice Age(LIA) ,Neoglaciation,marine oxygen isotope stages(MIS) 2,mid-MIS3,MIS4,and MIS6.The largest local last glacial maximum(LGML) occurred during MIS4 rather than the global Last Glacial Maximum(LGMG) of MIS2,and a glacial advance that occurred during mid-MIS3 was also larger than the LGMG.Furthermore,deeply weathered tills below 3500 m a.s.l.on the western slope of Kongur Mountain,when compared with the ages of the oldest glaciation of the Muztag Ata region,likely occurred prior to the penultimate glacial cycle.The glacial landforms prior to the penultimate glacial cycle on the northern slope are not well-preserved due to erosion after deposition. Several glacial deposits are only speculated to be distributed at higher elevations on the southwest side of the Gaizi Checkpoint. The extensive hummocky moraines on the western slope were formed by multiple glacial advances,and the latest glacial advance corresponded to mid-MIS3.