Stability analysis of loose accumulation slopes under rainfall:case study of a high‑speed railway in Southwest China

The high and steep slopes along a high-speed railway in the mountainous area of Southwest China are mostly composed of loose accumulations of debris with large internal pores and poor stability,which can easily induce adverse geological disasters under rainfall conditions.To ensure the smooth construction of the high-speed railway and the subsequent safe operation,it is necessary to master the stability evolution process of the loose accumulation slope under rainfall.This article simulates rainfall using the finite element analysis software’s hydromechanical coupling module.The slope stability under various rainfall situations is calculated and analysed based on the strength reduction method.To validate the simulation results,a field monitoring system is established to study the deformation characteristics of the slope under rainfall.The results show that rainfall duration is the key factor affecting slope stability.Given a constant amount of rainfall,the stability of the slope decreases with increasing duration of rainfall.Moreover,when the amount and duration of rainfall are constant,continuous rainfall has a greater impact on slope stability than intermittent rainfall.The setting of the field retaining structures has a significant role in improving slope stability.The field monitoring data show that the slope is in the initial deformation stage and has good stability,which verifies the rationality of the numerical simulation method.The research results can provide some references for understanding the influence of rainfall on the stability of loose accumulation slopes along high-speed railways and establishing a monitoring system.

Mechanical behaviors of warm and ice-rich frozen soil stabilized with sulphoaluminate cement

The warm and ice-rich frozen soil is characterized by high unfrozen water content, low shear strength and large compressibility, which is unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. In this study, a novel approach for stabilizing the warm and ice-rich frozen soil with sulphoaluminate cement was proposed based on chemical stabilization. The mechanical behaviors of the stabilized soil, such as strength and stress-strain relationship, were investigated through a series of triaxial compression tests conducted at -1.0℃, and the mechanism of strength variations of the stabilized soil was also explained based on scanning electron microscope test. The investigations indicated that the strength of stabilized soil to resist failure has been improved, and the linear Mohr-Coulomb criteria can accurately reflect the shear strength of stabilized soil under various applied confining pressure. The increase in both curing age and cement mixing ratio were favorable to the growth of cohesion and internal friction angle. More importantly, the strength improvement mechanism of the stabilized soil is attributed to the formation of structural skeleton and the generation of cementitious hydration products within itself. Therefore, the investigations conducted in this study provide valuable references for chemical stabilization of warm and ice-rich frozen ground, thereby providing a basis for in-situ ground improvement for reinforcing warm and ice-rich permafrost foundations by soil-cement column installation.

Impact of permafrost degradation on embankment deformation of Qinghai-Tibet Highway in permafrost regions

Based on long-term monitoring data, the relationships between permafrost degradation and embankment deformation are analyzed along the Qinghai-Tibet Highway(QTH). Due to heat absorbing effect of asphalt pavement and climate warming,permafrost beneath asphalt pavement experienced significant warming and degradation. During the monitoring period, warming amplitude of the soil at depth of 5 m under asphalt ranged from 0.21 °C at the XD1 site to 0.5 °C at the KL1 site. And at depth of 10 m, the increase amplitude of ground temperature ranged from 0.47 °C at the NA1 site to 0.07 °C at the XD1 site. Along with ground temperature increase, permafrost table beneath asphalt pavement decline considerably. Amplitude of permafrost table decline varied from 0.53 m at the KL1 site to 3.51 m at the NA1 site, with mean amplitude of 1.65 m for 8 monitoring sites during the monitoring period. Due to permafrost warming and degradation, the embankment deformation all performed as settlement at these sites. At present, those settlements still develop quickly and are expected to continue to increase in the future. The embankment deformations can be divided into homogeneous deformation and inhomogeneous deformation. Embankment longitudinal inhomogeneous deformation causes the wave deformations and has adverse effects on driving comfort and safety, while lateral inhomogeneous deformation causes longitudinal cracks and has an adverse effect on stability. Corresponding with permafrost degradation processes,embankment settlement can be divided into four stages. For QTH, embankment settlement is mainly comprised of thawing consolidation of ice-rich permafrost and creep of warming permafrost beneath permafrost table.

A full-scale field experiment to study the thermal-deformation process of widening highway embankments in permafrost regions

As one of the widely used upgrading way in road engineering, the widening embankment(WE) has suffered evident differential deformation, which is even severer for highway in permafrost regions due to the temperature sensitivity of frozen soil and the heat absorption effect of the asphalt pavement. Given this issue, a full-scale experimental highway of WE was performed along the Qinghai-Tibet Highway(QTH) to investigate the differential deformation features and its developing law. The continuous three years' monitoring data taken from the experimental site, including the ground temperature and the layered deformation of WE and original embankment(OE), were used to analyze the thermal-deformation process. The results indicate that the widening part presented the remarkable thermal disturbance to the existing embankment(EE). The underlying permafrost was in a noteworthy degradation state, embodying the apparent decrease of the permafrost table and the increase of the ground temperature. Correspondingly, the heat disruption induced by widening led to a much higher deformation at the widening side compared to the original embankment, showing a periodic stepwise curve. Specifically, the deformation mainly occurred in the junction of the EE and the widening part, most of which was caused by the thawing consolidation near the original permafrost table. In contrast, the deformation of EE mainly attributed to the compression of the active layer. Furthermore, it was the deformation origination differences that resulted in the differential deformation of WE developed gradually during the monitoring period, the maximum of which reached up to 64 mm.

Long-term and short-term stability characteristics of receiver inter system bias for BDS3/BDS2

The study of inter-system bias(ISB)is important for multi-system fusion and the performance of different signal compatibility.In this paper,the stability of ISB at the BDS3/BDS2 receiver end is calculated and analyzed for different time spans(DOY 060~090 in 2021)from a total of 31 MGEX and iGMAS stations.We adopted two estimation strategies,random walk and constant approach,using the precision products of orbit and clock bias provided by WUM,the influence of which on ISB was also analyzed.Our results showed that the ISB value varied little within a day,and the mean of daily ISB standard deviation was only 0.037 m when the observation condition was good.The signal reception was continuous,indicating a high ISB stability for one day.If extending the time series to one month,however,the ISB standard deviation calculated by constant approach,in which a constant ISB is estimated on a daily basis was about 0.1 m,and the results of adjacent days were not continuous,with no apparent pattern.Concerning the random walk approach,the obtained ISB time series also had a jump,and the conclusion was the same as that of the constant strategy.Besides,receiver types showed a strong regularity in ISB numerical situation,and the distribution of ISB values corresponding to the same receiver type was relatively close.Therefore,we conclude that the ISB parameters remain stable in the short term(one day)and less stable in the long-term period.It is recommended that the ISB term should be set as a constant estimate every day in BDS3/BDS2 solutions,regardless of receiver type consistency.

Prediction-Based Thunderstorm Path Recovery Method Using CNN-BiLSTM

The loss of three-dimensional atmospheric electric field(3DAEF)data has a negative impact on thunderstorm detection.This paper proposes a method for thunderstorm point charge path recovery.Based on the relation-ship between a point charge and 3DAEF,we derive corresponding localization formulae by establishing a point charge localization model.Generally,point charge movement paths are obtained after fitting time series localization results.However,AEF data losses make it difficult to fit and visualize paths.Therefore,using available AEF data without loss as input,we design a hybrid model combining the convolutional neural network(CNN)and bi-directional long short-term memory(BiLSTM)to predict and recover the lost AEF.As paths are not present during sunny weather,we propose an extreme gradient boosting(XGBoost)model combined with a stacked autoencoder(SAE)to further determine the weather conditions of the recovered AEF.Specifically,historical AEF data of known weathers are input into SAE-XGBoost to obtain the distribution of predicted values(PVs).With threshold adjustments to reduce the negative effects of invalid PVs on SAE-XGBoost,PV intervals corresponding to different weathers are acquired.The recovered AEF is then input into the fixed SAE-XGBoost model.Whether paths need to be fitted is determined by the interval to which the output PV belongs.The results confirm that the proposed method can effectively recover point charge paths,with a maximum path deviation of approximately 0.018 km and a determination coefficient of 94.17%.This method provides a valid reference for visual thunderstorm monitoring.

从法国通用技术条款看中国标准走出去

Despite the booming of China’s infrastructure construction and relevant standards in recent decades,the application of Chinese standards in foreign construction projects is rare.In former French colonial countries and regions,French standards are widely used.The paper introduces the French General Technical Clauses,including the countries that adopt them,their composition and status quo.Based on a project in Senegal,the application of the clauses is demonstrated,and their pros and cons are analyzed.The difficulties to promote Chinese standards worldwide are discussed,and suggestions are given.

Pore evolution and shear characteristics of a soil-rock mixture upon freeze-thaw cycling

The changes in pore structure within soil-rock mixtures under freeze-thaw cycles in cold regions result in strength deterioration,leading to instability and slope failure.However,the existing studies mainly provided qualitative analysis of the changes in pore or strength of soil-rock mixture under freeze-thaw cycles.In contrast,few studies focused on the quantitative evaluation of pore change and the relationship between the freeze-thaw strength deterioration and pore change of soil-rock mixture.This study aims to explore the correlation between the micro-pore evolution characteristics and macro-mechanics of a soil-rock mixture after frequent freeze-thaw cycles during the construction and subsequent operation in a permafrost region.The pore characteristics of remolded soil samples with different rock contents(i.e.,25%,35%,45%,and 55%)subjected to various freeze-thaw cycles(i.e.,0,1,3,6,and 10)were quantitatively analyzed using nuclear magnetic resonance(NMR).Shear tests of soil-rock samples under different normal pressures were carried out simultaneously to explore the correlation between the soil strength changes and pore characteristics.The results indicate that with an increase in the number of freeze-thaw cycles,the cohesion of the soil-rock mixture generally decreases first,then increases,and finally decreases;however,the internal friction angle shows no apparent change.With the increase in rock content,the peak shear strength of the soil-rock mixture rises first and then decreases and peaks when the rock content is at 45%.When the rock content remains constant,as the number of freeze-thaw cycles rises,the shear strength of the sample reaches its peak after three freeze-thaw cycles.Studies have shown that with an increase in freeze-thaw cycles,the medium and large pores develop rapidly,especially for pores with a size of 0.2–20μm.Freeze-thaw cycling affects the internal pores of the soil-rock mixture by altering its skeleton and,therefore,impacts its macro-mechanical characteristics.

Seismic response analysis of road vehicle-bridge system for continuous rigid frame bridges with high piers

The objective of this study is to investigate the effects of earthquakes on road vehicle-bridge coupling vibration systems. A two-axle highway freight vehicle is treated as a 13 degree-of-freedom system composed of several rigid bodies, which are connected by a series of springs and dampers. The framework of the earthquake-vehicle-bridge dynamic analysis system is then established using an earthquake as the extemal excitation. The equivalent lateral contact force serves as the judgment criteria for sideslip accidents according to reliability theory. The entire process of the vehicle crossing the bridge is considered for a very high pier continuous rigid frame bridge. The response characteristics of the vehicle and the bridge are discussed in terms of various parameters such as earthquake ground motion, PGA value of the earthquake, incident angle, pier height, vehicle speed and mass. It is found that seismic excitation is the most influential factor in the responses of the vehicle-bridge system and that the safety of vehicles crossing the bridge is seriously impacted by the dual excitations of earthquake and bridge vibration.

The Hong Kong–Zhuhai–Macao Bridge

The Hong Kong–Zhuhai–Macao Bridge (HZMB) is located at the Pearl River Estuary on the southeast coast of China;it is the longest as-build marine crossings made of island, tunnel, and bridge. It links Hong Kong in the east with Zhuhai–Macao in the west with a total length of 55 km. The link was built according to the highway standard of six lanes with three lanes going each way;it has a design speed of 100 km·h^-1 and a design life of 120 years. The HZMB has improved traffic conditions on the east and west sides of the coast of the Pearl River Estuary and strengthened the communication, transportation, and economic integration of the three regions, thus accelerating the formation of the Guangdong–Hong Kong–Macao Greater Bay Area. This paper introduces the design and construction of the HZMB, with a focus on the new technologies involved in building the artificial islands and immersed tunnel.

Numerical study on the fracturing mechanism of shock wave interactions between two adjacent blast holes in deep rock blasting

With the application of electronic detonators, millisecond blasting is regarded as a signifi cant promising approach to improve the rock fragmentation in deep rock blasting. Thus, it is necessary to investigate the fracturing mechanisms of short-delay blasting. In this work, a rectangle model with two circle boreholes is modeled as a particles assembly based on the discrete element method to simulate the shock wave interactions induced by millisecond blasting. The rectangle model has a size of 12 × 6 m (L × W) and two blast holes have the same diameter of 12 cm. The shock waves are simplifi ed as time-varying forces applied at the particles of walls of the two boreholes. Among a series of numerical tests in this study, the spacing between two adjacent boreholes and delay time of millisecond blasting are considered as two primary variables, and the decoupling charge with a coeffi cient of 1.5 is taken into account in each case. The results show that stress superposition is not a key factor for improving rock fragmentation (tensile stress interactions rather than compressive stress superposition could aff ect the generation of cracks), whereas collision actions from isolated particles or particles with weakened constraints play a crucial role in creating the fracture network. The delay time has an infl uence on causing cracks in rock blasting, however, whether it works heavily depends on the distance between the two holes.

Structural damage assessment using improved Dempster-Shafer data fusion algorithm

As an efficient tool in handling uncertain issues, Dempster-Shafer evidence theory has been increasingly used in structural health monitoring and damage detection. In applications, however, Dempster-Shafer evidence theory sometimes leads to counter-intuitive results. In this study, a new fusion algorithm of evidence theory is put forward to address various counter-intuitive problems and manage the reliability difference of the evidence. The proposed algorithm comprises the following aspects:(1) Dempster's combination rule is generalized by introducing the concept of evidence ullage. The new rule allows classical Dempster's rule and can resolve counter-intuitive problems cause by evidence conflict and evidence compatibility;(2) a reliability assessing method based on a priori and posterior knowledge is proposed. Compared with conventional reliability assessment, the proposed method can reflect the actual evidence reliabilities and can efficiently reduce decision risk. Numerical examples confirm the validity and utility of the proposed algorithm. In addition, an experimental investigation on a spatial truss structure is carried out to illustrate the identified ability of the proposed approach. The results indicate that the fusion algorithm has no strict request on the accuracy and consistency of evidence sources and can efficiently enhance diagnostic accuracy.

Geomechanical model test for analysis of surrounding rock behaviours in composite strata

Due to the large differences in physico-mechanical pro perties of composite strata,jamming,head sinking and other serious consequences occur frequently during tunnel boring machine(TBM)excavation.To analyse the stability of surrounding rocks in composite strata under the disturbance of TBM excavation,a geomechanical model test was carried out based on the Lanzhou water supply project.The evolution patterns and distribution characteristics of the strain,stress,and tunnel deformation and fracturing were analysed.The results showed that during TBM excavation in the horizontal composite formations(with upper soft and lower hard layers and with upper hard and lower soft layers),a significant difference in response to the surrounding rocks can be observed.As the strength ratio of the surrounding rocks decreases,the ratio of the maximum strain of the hard rock mass to that of the relatively soft rock mass gradually decreases.The radial stress of the relatively soft rock mass is smaller than that of the hard rock mass in both types of composite strata,indicating that the weak rock mass in the composite formation results in the difference in the mechanical behaviours of the surrounding rocks.The displacement field of the surrounding rocks obtained by the digital speckle correlation method(DSCM)and the macro-fracture morphology after tunnel excavation visually reflected the deformation difference of the composite rock mass.Finally,some suggestions and measures were provided for TBM excavation in composite strata,such as advance geological forecasting and effective monitoring of weak rock masses.

Positioning performance analysis on combined GPS/BDS precise point positioning

Combining the observation data from five Multi-GNSS Experiment(MGEX)stations with the precise orbit and clock products from Global Positioning System(GPS)and BeiDou Navigation Satellite System(BDS),we studied the model of combined GPS/BDS precise point positioning,and then analyzed the convergence speed and short-time(6 h)positioning accuracy.The calculation results show that in static positioning,the average convergence time of GPS is about 50 min,and its horizontal accuracy is better than 2 cm while the vertical accuracy is better than 4 cm.The convergence speed of combined GPS/BDS is about 40 min,and its positioning accuracy is close to that of GPS.In kinematic positioning,the average convergence time of GPS is about 72 min,and its horizontal accuracy is better than 5 cm while the vertical accuracy is better than 12 cm.The average convergence time of GPS/BDS is about 57 min,and its horizontal accuracy is better than 3 cm while the vertical accuracy is better than 9 cm.Combined GPS/BDS has significantly improved the convergence speed,and its positioning accuracy is slightly than that of GPS.

Coupling vibration analysis of high-speed maglev train-viaduct systems with control loop failure

The risk of failure of the control loop can occur when a high-speed maglev train runs on viaduct.Meanwhile,the failure of the levitation magnets which balances the gravity of the maglev train could cause the train collision with track.To study the dynamic response of the train and the viaduct when the levitation magnet control loop failure occurs,a high-speed maglev train-viaduct coupling model,which includes a maglev controller fitted by measured force-gap data and considers the actual structure of train and viaduct,is established.Then the accuracy and effectiveness of the established approach are validated by comparing the computed dynamic responses and frequencies with the measurement results.After that,the dynamic responses of maglev train and viaduct are discussed under normal operation and control loop failures,and the most disadvantageous combination of control loop failures is obtained.The results show that when a single control loop fails,it only has a great influence on the failed electromagnet,and the maglev response of adjacent electromagnets has no obvious change and no collision occurs.But there is a risk of rail collisions when the dual control loop fails.

Undrained Bearing Capacity of Spudcan Under Combined Loading

The bearing capacities of spudcan foundation under pure vertical （/1）, horizontal （H）, moment （M） loading and the combined loading are studied based on a series of three-dimensional finite element analysis. The effects of embedment ratio and soil non-homogeneity on the bearing capacity are investigated in detail. The capacities of spudcan under different pure loading are expressed in non-dimensional bearing capacity factors, which are compared with published results. Ultimate limit states under combined loading are presented by failure envelopes, which are expressed in terms of dimensionless and normalized form in three-dimensional load space. The comparison between the presented failure envelopes and available published numerical results reveals that the size and shape of failure envelopes are dependent on the embedment ratio and the non-homogeneity of the soil.

General design of Sutong Bridge

The main span of Sutong Bridge is a double-pylon,double-plane cable-stayed bridge with steel box girder,which has the world's longest central span of 1 088 m within cable-stayed bridges.To overcome problems caused by severe meteorological conditions,perplexing hydrological conditions,deep buried bedrock and higher navigation level,many new technics and methods were created.Keys including structural system,steel box girder,stayed cable,tower,pier,tower foundation,collision avoidance system,wind-resistance,seismic-resistance,structural nonlinear response and structural static stability were presented individually in this paper.

In-situ testing study on convection and temperature characteristics of a new crushed-rock slope embankment design in a permafrost region

For the purpose of enhancing air convection and controlling solar radiation, a new crushed-rock slope embankment design combined with a sun-shade measure is proposed. A newly designed embankment was constructed in the Tuotuohe section of the Qinghai-Tibet Railway and a field-testing experiment was carried out to determine its convection and temperature characteristics. The results show that distinct air convection occurred in the crushed-rock layer of the new embankment, especially in cold seasons, which was enhanced when it flowed upwards along the slope. This preliminarily indicated that the new design of the embankment slope was good for reinforcing air convection in the crushed-rock layer. The frequent fluctuations of the convection speed and the environmental wind speed were in good agreement, suggesting that the convection in the crushed rock primarily came from the ambient wind. It was also preliminarily determined that the new embankment had a better cooling effect and sun-shade effect for decreasing the temperature of the embankment slope compared with a traditional crushed-rock slope embankment, and the mean temperature difference between them was up to 1.7 °C. The mean annual temperature at the bottom boundary of the crushed-rock layer was obviously lower than that at the top boundary, and heat flux calculation showed that the shallow soil beneath the embankment slope was weakly releasing heat, all of which indicated that the new embankment slope design was beneficial to the thermal stability of the embankment. This study is helpful in providing some references for improved engineering design and maintenance of roadbeds in permafrost regions.

Improved plane layout of stabilizing piles based on the piecewise function expression of the irregular driving force

The paper presents an improved plane layout for stabilizing piles based on a proposed piecewise function expression for the irregular driving force. Based on the specific morphological characteristics of a highway landslide, the piecewise function is used to calculate the irregular driving force by dividing the landslide into several sub-areas.Furthermore, the reasonable layout range and pile spacing can be obtained based on the piecewise function expression of the irregular driving force and on relevant research results of the plane layout for stabilizing piles. Therefore, an improved plane layout of stabilizing piles is presented in consideration of a piecewise function expression of the irregular driving force. A highway landslide located in eastern Guizhou Province, China, is analyzed as a case study using the proposed method. The results demonstrate that the theory presented in this paper provides improved economic benefits and can reduce the requirednumber of stabilizing piles by 28.6% compared with the conventional plane layout scheme.

Study on tensile damage characteristics of sandstone under freeze-thaw cycles

The meso-structure of sandstone has a significant effect on its mechanical properties under external loads.In this paper,by taking two types of sandstone with different grain sizes as the study objects,the effects of grain size and freeze-thaw cycles on tensile strength and damage mode of sandstone are analyzed using a combination of laboratory tests,theoretical analysis,and numerical calculation.The Brazilian splitting tests are carried out on sandstone samples subjected to freeze-thaw cycles.The results show that:(1)The Brazilian splitting mode of the fine-grained sandstone is dominated by the central fracture,whereas that of the coarse-grained sandstone is controlled by a noncentral fracture.(2)The freeze-thaw cycles aggravate the initial damage of sandstone,and the cumulative freeze-thaw damage has a greater impact on the Brazilian splitting damage mode of the coarse-grained sandstone than on the fine-grained sandstone.(3)The numerical analysis software RFPA2D system can simulate the Brazilian splitting failure process of the two types of sandstone with varying grain sizes under different freeze-thaw cycles.It is shown to be an effective method to reveal the tensile failure process and deterioration mechanism of sandstone under freeze-thaw cycling.(4)The formation mechanisms of the two splitting modes are analyzed according to the energy principle.The energy release of coarse-grained sandstone forms a noncentral splitting mode along the rock sample internal weak structural plane,whereas the fine-grained sandstone sample's energy accumulates in the rock sample center and releases it instantaneously at its center,showing the failure mode of central splitting.In addition,based on damage mechanics theory,the damage evolution equation of sandstone subjected to freeze-thaw cycles under tension is established,and the influence of energy release and dissipation on the sandstone's tensile properties is quantitatively analyzed.