Analysis and evaluation on seepage stability of Hongxing reservoir dam,Heilongjiang

Hongxing reservoir was constructed on the floodplain of Hulan River in Heilongjiang. The geological problem of the reservoir is the seepage of the dam base and its related seepage stability. The leakage of the reservoir is caused by the water head differences between the upstream and downstream of the dam. Severe seepage could decrease the engineering benefits of the reservoir. Moreover,infiltration function of water will influence the safety of the dam. Through the analysis on the granule constitute and the formation of the dam base,the types of the seepage failure apt to happen were defined and the anti-infiltration and the permissible depression ratio were determined. Using the numerical simulation software GMS,the two-dimension numerical modeling has been carried out to analyze the seepage field of the reservoir. Through the two conditions modeling with concrete impervious wall and no concrete impervious wall,the largest flow rate,single-wide seepage discharge and the max infiltration gradient of the dam base were calculated. According to the permeable depression ratio of the dam base,the seepage stability of Hongxing reservoir dam base was analyzed.

Stability analysis of shallow tunnels subjected to seepage with strength reduction theory

Based on strength reduction theory,the stability numbers of shallow tunnels were investigated within the framework of upper and lower bound theorems of limit analysis. Stability solutions taking into account of water seepage were presented and compared with those without considering seepage. The comparisons indicate that the maximum difference does not exceed 3.7%,which proves the present method credible. The results show that stability numbers of shallow tunnels considering seepage are much less than those without considering seepage,and that the difference of stability numbers between considering seepage and without considering seepage increase with increasing the depth ratio. The stability numbers decrease with increasing permeability coefficient and groundwater depth. Seepage has significant effects on the stability numbers of shallow tunnels.

Kinematic analysis of shallow tunnel in layered strata considering joined effects of settlement and seepage

The purpose of this work is to predict the state of collapse in shallow tunnel in layered strata by using a new curved failure mechanism within the framework of upper bound theorem.Particular emphasis is first given to consider the effects of seepage forces and surface settlement.Furthermore,the Hoek-Brown nonlinear failure criterion is adopted to analyze the influence of different factors on the collapsing shape.Two different curve functions which describe two different rock layers are obtained by virtual work equations under the variational principle.According to the numerical results,the parameter B in Hoek-Brown failure criterion and the unit weights in different rock layers have a positive relationship with the size of collapsing block while pore pressure coefficient and the parameter A in Hoek-Brown failure criterion present a reverse tend.

Impact of the Rainfall Intensity and Seepage on Slope Stability in Loess Plateau

In recent years,with the increase of traffic construction in mountainous areas in China,road slope traffic accidents have become more and more common.In addition,natural disasters such as landslides,collapses and subgrade settlements caused by rainfall,driving load,seasonal variation and groundwater distribution are frequent.In particular,rainfall is one of the most common factors leading to slope instability(landslide).Therefore,this paper proposes the seep module based on the application software Geo-studio,and analyzes the slope soil parameters and slope stability under five types of rainfall conditions:light rain(10 mm/d),moderate rain(25 mm/d),heavy rain(50 mm/d),rainstorm(100 mm/d),and torrential rain(250 mm/d).The critical safety factor under rainfall intensity is fitted with nonlinear curve by sine function.The results show that the fitting curve of rainfall intensity and safety factor on the upper slope is excellent.The residual points are evenly distributed in the belt area of±0.1,and the data basically conform to the nonlinear sine model,indicating that the curve plays an essential role in slope health diagnosis.

Influence of underground water seepage flow on surrounding rock deformation of multi-arch tunnel

Based on a typical multi-arch tunnel in a freeway, the fast Lagrangian analysis of continua in 3 dimensions(FLAC3D) was used to calculate the surrounding rock deformation of the tunnel under which the effect of underground water seepage flow was taken into account or not. The distribution of displacement field around the multi-arch tunnel, which is influenced by the seepage field, was gained. The result indicates that the settlement values of the vault derived from coupling analysis are bigger when considering the seepage flow effect than that not considering. Through the contrast of arch subsidence quantities calculated by two kinds of computation situations, and the comparison between the calculated and measured value of tunnel vault settlement, it is found that the calculated value(5.7-6.0 mm) derived from considering the seepage effect is more close to the measured value(5.8-6.8 mm). Therefore, it is quite necessary to consider the seepage flow effect of the underground water in aquiferous stratum for multi-arch tunnel design.

Effectiveness of predicting tunneling-induced ground settlements using machine learning methods with small datasets

Prediction of tunneling-induced ground settlements is an essential task,particularly for tunneling in urban settings.Ground settlements should be limited within a tolerable threshold to avoid damages to aboveground structures.Machine learning(ML)methods are becoming popular in many fields,including tunneling and underground excavations,as a powerful learning and predicting technique.However,the available datasets collected from a tunneling project are usually small from the perspective of applying ML methods.Can ML algorithms effectively predict tunneling-induced ground settlements when the available datasets are small?In this study,seven ML methods are utilized to predict tunneling-induced ground settlement using 14 contributing factors measured before or during tunnel excavation.These methods include multiple linear regression(MLR),decision tree(DT),random forest(RF),gradient boosting(GB),support vector regression(SVR),back-propagation neural network(BPNN),and permutation importancebased BPNN(PI-BPNN)models.All methods except BPNN and PI-BPNN are shallow-structure ML methods.The effectiveness of these seven ML approaches on small datasets is evaluated using model accuracy and stability.The model accuracy is measured by the coefficient of determination(R2)of training and testing datasets,and the stability of a learning algorithm indicates robust predictive performance.Also,the quantile error(QE)criterion is introduced to assess model predictive performance considering underpredictions and overpredictions.Our study reveals that the RF algorithm outperforms all the other models with the highest model prediction accuracy(0.9)and stability(3.0210^(-27)).Deep-structure ML models do not perform well for small datasets with relatively low model accuracy(0.59)and stability(5.76).The PI-BPNN architecture is proposed and designed for small datasets,showing better performance than typical BPNN.Six important contributing factors of ground settlements are identified,including tunnel depth,the distance between tunnel face and surface monitoring points(DTM),weighted average soil compressibility modulus(ACM),grouting pressure,penetrating rate and thrust force.

The Influence of Localized Slumping on Groundwater Seepage and Slope Stability

Transverse cracks and localized slumps frequently occur within loose deposits slopes when the slope base is removed either from natural or manmade processes. Although the contribution of rainfall to the slope failures was intensely discussed, the influence of localized slumps on hydrogeological conditions has received less attention. Usually, loose deposits slopes are composed of soil layers with different permeability; localized slumps may cause flow paths partly blocked in the permeable layer that is adversely confined between impermeable layers. In this study, a case history of such failure, Xiaodan （/J~ ~__） landslide, is introduced in detail. The localized slump caused the pressure head in the permeable layer to increase substantially, which reduced the stability of the slope. To quantify the influence, Ber- noulli equations are used to analytically study the increase of the pressure head with a hydrogeologicai model simplified from the slope. The factor of safety assessed by limit equilibrium methods may decrease up to 20% when the 80% of flow path is blocked. Thus, we should pay attention not only to changes of stress filed due to localized slumps but also to the influence of seepage variation on the slope stability.

Seismic stability of loess tunnels under the effects of rain seepage and a train load

Loess tunnels are widely used in transportation engineering and are irreplaceable parts of transportation infrastructure. In this paper, a dynamic finite element method is used to analyze the coupled effects of a train vibration load and rainfall seepage. By calculating the variation in the safety factor of a loess tunnel because of the effects of various factors, such as different rainfall intensities and soil thicknesses, the dynamic stability of the loess tunnel is studied under the condition of a near-field pulse-like earthquake. The results show that the security and stability of the tunnel decrease gradually with decreasing burial depth. In addition, the plastic strain of the tunnel is mainly distributed on both sides of the vault and the feet, and the maximum value of the critical strain occurs on both sides of the arch feet. Because of the effects of the train vibration load and rainfall seepage, the safety factor of the loess tunnel structure decreases to a certain degree. Moreover, the range and maximum value of the plastic strain increase to various degrees.

Calculation of Hydro-Dynamic Stability of the Soil Inside Bucket in the Process of Bucket Foundation Penetration

The offshore platform with bucket foundations is a;new type of offshore platform that distinguishes from traditional template platforms by replacing driven piles with bucket foundations. The suction penentration of bucket foundation is a complicated hydro-dynamic process. The key of this process is the seepage field caused by the difference of pressure applied on purpose inside and outside the bucket. The appearance and developement of seepage field has a decisive influence on the suction penetration process. In this study, the finite element analysis method is applied to the dynamic simulation of the seepage field of suction penetration of bucket foundation. A criterion is suggested to distinguish the hydro-dynamic stability of the soil inside the bucket according to the critical hydraulic gradient method. The reliability of the model and its applicability to engineering practice have been proved through comparison between the results of model test and finite element calculation.

Structural Types of Sea Embankment and Their Stability Analysis

In this paper based on investigation on the structural types of sea embankments in the southeast coastal area of China, as well as the related tidal stages, waves and strength of marine soils, the finite element method (FEM) calculations for seepage flow stability, including the overall stability against sliding and local stability of sloping surface under the action of tidal stage and waves are carried out. A comparison of the computational results of FEM for single circular slip, composite circular slip and geogrid reinforcement against sliding shows that for calculation of stability against sliding of marine soft soil foundation it is even more reasonable to use the composite circular slip. The stability of sloping type sea embankment against sliding is slightly better than that of the vertical face type; for the combination of three defences (wave, scour and seepage defences) the sea embankment structural type of a composite cross section with a platform should be a good one, but it still should be suitable to local conditions. For the local stability of riprap slope blocks and wall face loose masonry blocks, according to the analyses of wave-induced seepage flow fields, calculating formulas are given and they are verified by model test on block stability of breakwaters.

Effects of freeze-thaw cycle and dry-wet alternation on slope stability

The typical loess on high slopes along the BaoLan High-speed Rail, China, was selected as the research object. The influence of the freeze-thaw cycle and dry-wet alternation on the shear-strength parameters of the unsaturated loess was investigated by laboratory experimental methods. Moreover, the temperature field, seepage field, and stability of slopes with different gradients were simulated under the effect of the freeze-thaw cycle and dry-wet alternation by using the geotechnical analysis software Geo-Studio. The research results showed(1) when the freeze-thaw cycle was repeated on the slope, with the frozen depth increasing, the melted depth did the same; besides, the closed loop of isotherms formed on the slope;(2) under the action of dry-wet circulation, the negative pore-water pressure and volumetric water content showed an upward tendency. However, owing to the different slope gradients, rainfall infiltration was not the same. As time went by, the differences of the negative pore-water pressure and volumetric water content between the slopes of different gradients continued to increase;(3) with the freeze-thaw cycle and dry-wet alternation increasing, the slope-safety factor decreased. Especially in the early period, the slope-safety factor changed remarkably. For slopes undergoing freeze-thaw action, the slope-safety factor was negatively correlated with the gradient. However, with regard to slopes undergoing dry-wet alternation, the result became more complex because the slope-safety factor was related to both seepage strength and slope grade. Accordingly, further research is needed to study the effect of seepage strength and slope grade on the stability of loess slopes.

The Influence of Water Level Change in Slope Stability of Earth Dam

The analysis of seepage flow and slope stability to earth dam in water level change is performed. FEM is used to analyzing the influence of percolation and the results including the pore water head of any point, seepage discharge and so on are obtained. The method of slices is introduced to calculating the slope stability of the earth dam. Through an example it is separately discussed the influence of seepage flow when water level is changed in earth dam slope and the effects of percolation in the stability of the earth dam slope. Some helpful conclusions are gained.This can be making the best of the tow methods and the results can be used in engineering for reference.

Stability of loess high-fill slope based on monitored soil moisture changes

This paper aims to assess the influence of moisture content changes during rainfall on the stability of loess high-fill slopes by taking a loess high-fill slope in Lanzhou City as an example.First,according to the moisture content monitoring data collected from a slope online monitoring system,direct shear tests were performed on soil samples of different moisture content to determine the relationship between the shear strength parameters and moisture content.Next,a coupled hydro-mechanical model with soil shear strength related to moisture content was established and used to analyze 16 working conditions with various rainfall intensities and durations for two cases:shear strength parameters from the site exploration report and those from this study.Finally,the results from the two cases were compared regarding the changes in stresses and displacements after rainfall infiltration to analyze the influence of moisture content on the stability of loess high-fill slopes.The conclusions are as follows:(1)Segmental relationship equations of cohesion and angle of internal friction were established for loess with various moisture content.(2)Under the conditions of different rainfall intensities,significant differences were observed in the trends of slope stress and displacement changes.(3)The slope displacement occurred in the shallow soil layer within about 12.5 m from the slope top,and the plastic strain concentrated in the soil layer within about 6 m from the slope top.(4)The results of slope stability analyses based on moisture content monitoring data are more in line with the observed.

矿山采空区边坡动态稳定性评价方法

矿山边坡因采空区沉降引发的斜面岩土体崩塌破坏,是一种破坏力极强的地质灾害.由于传统的稳定性评价方法未考虑采空区沉降造成的应力场变异,难以实现矿山边坡的动态稳定性评价,因而在矿山地质灾害预警预防方面存在诸多限制.基于此,本研究针对矿山采空区滑坡的成因机制,建立了一套适用于矿山边坡的动态稳定性评价方法.首先通过构建采空区沉降分析模型,计算采空区上方岩体的沉降范围及其产生的冲击作用力,分析沉降对坡体应力场的影响,并在此基础上对传统不平衡推力法进行修正.案例分析结果显示,传统方法未考虑采空区沉降作用和锁固段的破坏情况,导致稳定性系数计算偏大,为1.355.而改进方法通过考虑采空区沉降信息,计算得出锁固段稳定性系数为0.667,整体稳定性系数为0.979,与矿山采空区边坡实际破坏情况一致.当沉降位移比(SHDR)大于0.73时,采空区边坡稳定性会发生明显变异,因而会在相对安全的工况下发生失稳破坏.改进方法通过考虑采空区沉降作用和锁固段的破坏情况,可以更好地实现矿山边坡稳定性的评价,为矿区更好地应对类似地质灾害提供有效参考.

公路压覆石膏矿采空区勘探与稳定性评价——以江苏省邳州X301县道某段为例

石膏采空区具有隐蔽性和复杂性,造成的塌陷严重威胁人民生命和财产安全。为查明江苏省邳州X301县道某段压覆石膏采空区分布及其稳定性,通过In SAR监测对面积1.64 km^(2)的研究区在2017~2021年间的地面沉降特征进行分析并圈定了沉降异常,投入高密度电阻率法测线6.24 km和验证钻探261.10 m实施地下采空区勘探,综合多源信息建立三维地质模型,推断解释了采空区7处;确定6项采空区稳定性影响因素,采用综合评价法进行了采空区稳定性评价。评价结果表明,研究区共有2处不稳定采空区和5处基本稳定采空区。实践证明,在InSAR监测和高密度电阻率法联合勘探隐伏采空区的基础上,采用多因素综合评价法进行采空区稳定性评价,具有可靠的效果和良好的推广意义。

Effect of hysteresis on the stability of residual soil slope

Soil-water characteristic curve (SWCC) is an essential parameter in unsaturated soil mechanics.Matric suction in unsaturated residual soils changes with varying climatic conditions associated with cyclic drying-wetting conditions that result in hysteresis in the SWCC.The soil mechanical behaviour under wetting is crucial since numerous rainfall-induced slope failures occur during the wetting process.However,many slope stability analyses were carried out using drying SWCC.Consequently,the factor of safety (FoS) calculation may not represent the actual field condition.This paper presents the effect of hysteresis in SWCC on the stability of unsaturated residual soil slopes from Bukit Timah Granite in Singapore.The study focused on the analyses considering the differences in pore-water pressure and water content variations under drying and wetting conditions by performing numerical seepage and stability analyses.Each analysis was carried out on a slope subjected to dry and rainy periods under three different conditions:i) using only drying SWCC;ii) using only wetting SWCC;iii) using combined drying and wetting SWCCs.The results indicated that the FoS variations obtained from the numerical analyses incorporating combined SWCC matched more closely those obtained by incorporating only wetting SWCC than those obtained by incorporating only drying SWCC,regardless of the wetting or drying processes that the soil experienced.Moreover,the numerical analyses under high rainfall intensity by incorporating only wetting SWCC gave a more conservative FoS as compared to those obtained by incorporating combined SWCC.Numerical analyses incorporating only drying SWCC gave the most conservative FoS regardless of rainfall intensity.

Study on coupled 3D seepage and stress fields of the complex channel project

Seepage is a vital reason that may bring many adverse consequences such as subsidence,inclination and fracture to the channel,and is harmful to the safety and stability of the channel.Thus,a 3D visualization model is established for the engineering geological information of the research channel section by using NURBS-TIN-BRep hybrid data structure.Coupled with the VOF(volume of fluid)method,the N-S(Navier-Stokes)equations are applied to seepage simulation of the research channel section.Then the stability of the channel is studied coupled with the seepage simulation results,to comprehensively analyze the stress and displacement conditions of the channel under the impact of different factors such as seepage and underground goafs.The results of this study illustrate that the channel seepage has great influence on its stability,especially on the displacement field:it will lead to a significant sedimentation to the foundation.Therefore,during the practical construction,it is suggested that the certain part of the channel should be reinforced and effective seepage control measures should be taken.

Settlement Prediction for Buildings Surrounding Foundation Pits Based on a Stationary Auto-regression Model

To ensure the safety of buildings surrounding foundation pits, a study was made on a settlement monitoring and trend prediction method. A statistical testing method for analyzing the stability of a settlement monitoring datum has been discussed. According to a comprehensive survey, data of 16 stages at operating control point, were verified by a standard t test to determine the stability of the operating control point. A stationary auto-regression model, AR(p), used for the observation point settlement prediction has been investigated. Given the 16 stages of the settlement data at an observation point, the applicability of this model was analyzed. Settlement of last four stages was predicted using the stationary auto-regression model AR (1); the maximum difference between predicted and measured values was 0.6 mm, indicating good prediction results of the model. Hence, this model can be applied to settlement predictions for buildings surrounding foundation pits.

Effect of variations in rainfall intensity on slope stability in Singapore

Numerous scientific evidence has given credence to the true existence and deleterious impacts of climate change.One aspect of climate change is the variations in rainfall patterns,which affect the flux boundary condition across ground surface.A possible disastrous consequence of this change is the occurrence of rainfall-induced slope failures.This paper aims to investigate the variations in rainfall patterns in Singapore and its effect on slope stability.Singapore's historical rainfall data from Seletar and Paya Lebar weather stations for the period of 1985–2009 were obtained and analysed by duration using linear regression.A general increasing trend was observed in both weather stations,with a possible shift to longer duration rainfall events,despite being statistically insignificant according to the Mann-Kendall test.Using the derived trends,projected rainfall intensities in 2050 and 2100 were used in the seepage and slope stability analyses performed on a typical residual soil slope in Singapore.A significant reduction in factor of safety was observed in the next 50 years,with only a marginal decrease in factor of safety in the subsequent 50 years.This indicates a possible detrimental effect of variations in rainfall patterns on slope stability in Singapore,especially in the next 50 years.The statistical analyses on rainfall data from Seletar and Paya Lebar weather stations for the period of 1985–2009 indicated that rainfall intensity tend to increase over the years,with a possible shift to longer duration rainfall events in the future.The stability analyses showed a significant decrease in factor of safety from 2003 to 2050 due to increase in rainfall intensity,suggesting that a climate change might have existed beyond 2009 with possibly detrimental effects to slope stability.