Experimental study on dispersive soil in western Jilin

In order to research engineering geological properties of the soil in Zhenlai of western Jilin,especially the dispersivity of soil,the authors carried out the basic physicochemical test and dispersivity identification test.The results show that the dispersivity of the soil increases with the increase of depth within 0-30 cm (surface soil);it decreases as the depth increases within in 30-100 cm.Furthermore,the statistical analysis of the dispersivity indexes and physicochemical propertity indexes show that t...     

Experimental study on dispersive soil in western Jilin

In order to research engineering geological properties of the soil in Zhenlai of western Jilin, especially the dispersivity of soil, the authors carried out the basic physicochemical test and dispersivity identification test. The results show that the dispersivity of the soil increases with the increase of depth within 0-30 cm ( surface soil) ; it decreases as the depth increases within in 30-100 cm. Furthermore, the statistical analysis of the dispersivity indexes and physicochemical propertity indexes show that the DP is positively linear correlated with total soluble salt content, sodium ion content, ESP, pH and organic matter content. Meanwhile, it is negatively linear correlated with clay content, and the linear relationship is better. Through the study of the dispersion mechanism of soil samples, it can be concluded that sodium montmorillonite, higher percentage of exchangeable sodium and high pH are the main reasons for the dispersion of soils in western Jilin.     

Influence of different soil properties on the failure behavior of deposit slope under earthquake after rainfall

In this study, the influence of soil properties on the failure behavior and mechanism of slope under earthquake after rainfall was studied with shaking table test in the laboratory, in which the failure process of slope and instant responses of water content and pore water pressure were tested. Based on the principle of similarity, a model test was designed. The experimental results showed that soil properties exhibit significant influence on failure mode and failure mechanism of slope. Local fl...     

Effects of shrub on runoff and soil loss at loess slopes under simulated rainfall

Improved understanding of the effect of shrub cover on soil erosion process will provide valuable information for soil and water conservation programs.Laboratory rainfall simulations were conducted to determine the effects of shrubs on runoff and soil erosion and to ascertain the relationship between the rate of soil loss and the runoff hydrodynamic characteristics.In these simulations a 20° slope was subjected to rainfall intensities of 45,87,and 127 mm/h.The average runoff rates ranged from 0.51 to 1.26 mm/min for bare soil plots and 0.15 to 0.96 mm/min for shrub plots.Average soil loss rates varied from 44.19 to 114.61 g/(min·m~2) for bare soil plots and from 5.61 to 84.58 g/(min·m~2) for shrub plots.There was a positive correlation between runoff and soil loss for the bare soil plots,and soil loss increased with increased runoff for shrub plots only when rainfall intensity is 127 mm/h.Runoff and soil erosion processes were strongly influenced by soil surface conditions because of the formation of erosion pits and rills.The unit stream power was the optimal hydrodynamic parameter to characterize the soil erosion mechanisms.The soil loss rate increased linearly with the unit stream power on both shrub and bare soil plots.Critical unit stream power values were 0.004 m/s for bare soil plots and 0.017 m/s for shrub plots.     

Stress response characteristics of BFRP anchors on loess mudstone slope under rainfall conditions

To investigate the stress response characteristics and shear stress transfer mechanism of BFRP(basalt fiber reinforced plastics) anchors under rainfall conditions and to explore the reinforcement effect of BFRP anchors, a comparative indoor physical model test was conducted in this study using loess mudstone slope as a typical case, and multi-attribute response data, such as slope displacement, BFRP anchor strain and axial force, were obtained. Based on the variation law of slope displacement, i...     

渗流-应力耦合下侏罗系红砂岩力学及渗透特性试验研究

三峡库区广泛分布侏罗系红砂岩,在水库运行期间红砂岩的渗流-应力耦合特性关乎库区内多数滑坡和岩质边坡的稳定性。借助岩石多场耦合三轴试验系统,对三峡库区侏罗系红砂岩开展了不同围压、不同渗透压下的三轴压缩试验,系统研究了红砂岩的三轴压缩力学特性和渗透率演化特征。研究结果表明：(1)红砂岩的峰前应力-应变曲线可分为孔隙压密阶段、弹性变形阶段、微裂隙稳定发展阶段和非稳定发展阶段。红砂岩的力学参数与渗透压的关系呈负相关,与围压呈正相关。(2)随着围压升高,红砂岩的破坏模式由张拉破坏过渡到剪切破坏。(3)不同渗透压下,渗透率曲线呈平稳发展→缓慢上升→快速上升3阶段演化规律;不同围压下,渗透率曲线先降低后升高。(4)从能量角度分析了渗透压和围压对岩石的作用,验证了渗流对岩石的劣化效应以及围压对裂纹发展的抑制作用。本试验对鲜有报道的侏罗系红砂岩的强度、变形和渗透特性做了系统的研究,对渗流-应力耦合课题有补充意义。其工况根据三峡库区边坡岩体的应力水平来确定,试验结果对分析库区边坡稳定性具有指导意义。     

Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions

Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare land area. However, the effect of slope on runoff generation remains unclear in many different soils including Chinese purple soil. The aim of this study was to investigate the relationship between different slope gradients and surface runoff for bare-fallow purple soil, using 5 m × 1.5 m experimental plots under natural rainfall conditions. Four experimental plots(10°, 16°, 20° and 26°) were established in theYanting Agro-ecological Experimental Station of Chinese Academy of Science in central Sichuan Basin. The plot was equipped with water storage tank to monitor water level change. Field monitoring from July 1 to October 31, 2012 observed 42 rainfall events which produced surface runoff from the experimental plots. These water level changes were converted to runoff. The representative eight rainfall events were selected for further analysis, the relationship between slope and runoff coefficient were determined using ANOVA, F-test, and z-score analysis. The results indicated a strong correlation between rainfall and runoff in cumulative amount basis. The mean value of the measured runoff coefficient for four experimental plots was around 0.1. However, no statistically significant relationship was found between slope and runoff coefficient. We reviewed the relationship between slope and runoff in many previous studiesand calculated z-score to compare with our experimental results. The results of z-score analysis indicated that both positive and negative effects of slope on runoff coefficient were obtained, however a moderate gradient(16°-20° in this study) could be a threshold of runoff generation for many different soils including the Chinese purple soil.     

Effectiveness of Fiber Bragg Grating monitoring in the centrifugal model test of soil slope under rainfall conditions

Centrifugal model tests are playing an increasingly important role in investigating slope characteristics under rainfall conditions. However, conventional electronic transducers usually fail during centrifugal model tests because of the impacts of limited test space, high centrifugal force, and presence of water, with the result that limited valid data is obtained. In this study, Fiber Bragg Grating (FBG) sensing technology is employed in the design and development of displacement gauge, an anchor force gauge and an anti-slide pile moment gauge for use on centrifugal model slopes with and without a retaining structure. The two model slopes were installed and monitored at a centrifugal acceleration of 100 g. The test results show that the sensors developed succeed in capturing the deformation and retaining structure mechanical response of the model slopes during and after rainfall. The deformation curve for the slope without retaining structure shows a steep response that turns gradual for the slope with retaining structure. Importantly, for the slope with the retaining structure, results suggest that more attention be paid to increase of anchor force and anti-slide pile moment during rainfall. This study verifies the effectiveness of FBG sensing technology in centrifuge research and presents a new and innovative method for slope model testing under rainfall conditions.     

Experimental study on the effectiveness of TLDs under wave loading

The objective of this study is to experimentally investigate the effectiveness of Tuned Liquid Dampers (TLDs) for suppressing the dynamic response of a platform structure subjected to wave loading and to explore the applicability of TLDs for suppressing the structural vibration of fixed offshore platforms. The experimental model is scaled according to a full size platform by matching its dynamic properties. Rectangular and circular TLDs of various sizes and water depths are examined.The experiments were performed in a 2-D wave flume. The effectiveness of TLDs is evaluated based on their response reduction. By observing the performance and the behavior of TLDs through laboratory experiments, the effects of a number of parameters including container shape, container size, number of dampers, frequency ratio, mass ratio, and incident wave characteristics are investigated.     

Experimental study of motion characteristics of rock slopes with weak intercalation under seismic excitation

In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation. The dynamic response of the prototype slopes were studied in laboratory with the consideration of law of similitude. The initiation failure was observed in the rock slope model with a counter-tilt thin-weak intercalation firstly, not in the slope model with a horizontal thin-weak intercalation. Furthermore, it was interesting that the fracture site is shifted from crest top to the slope surface near the weak intercalation, which is different with the location of failure position in a normal layered slope. We also discussed the effect of the dip angle and the thickness of weak intercalation on the failure mechanism and instability mode of the layered rock slope. From the experimental result, it was noted that the stability of the slope with a counter-tilt weak intercalation could be worse than that of the other slopes under seismic excitation. The findings showed the difference of failure in slopes with a horizontal and counter weak intercalation, and implicated the further evaluation of failure of layered slopes caused by seismic loads.     

Experimental study on pore water pressure dissipation of mucky soil

Pore water pressure has an important influence on mechanical properties of soil. The authors studied the characteristics of pore water pressure dissipating of mucky soil under consolidated-drained condition by using refitted triaxial instrument and analyzed the variation of pore pressure coefficient with consolidation pressure. The results show that the dissipating of pore water pressure behaves in different ways depends on different styles of loading. What is more, the pore water pressure coefficient of mucky soil is less than 1. As the compactness of soil increases and moisture content reduces, the value of B reduces. There is a staggered dissipating in the process of consolidation, in which it is a mutate point when U/P is 80%. It is helpful to establish the pore water pressure model and study the strength-deformation of soil in process of consolidation.     

Experimental study on pore water pressure dissipation of mucky soil

Pore water pressure has an important influence on mechanical properties of soil. The authors studied the characteristics of pore water pressure dissipating of mucky soil under consolidated-drained condition by using refitted triaxial instrument and analyzed the variation of pore pressure coefficient with consolidation pressure. The results show that the dissipating of pore water pressure behaves in different ways depends on different styles of loading. What is more, the pore water pressure coefficient of mucky soil is less than 1. As the compactness of soil increases and moisture content reduces, the value of B reduces. There is a staggered dissipating in the process of consolidation, in which it is a mutate point when U/P is 80%. It is helpful to establish the pore water pressure model and study the strength-deformation of soil in process of consolidation.     

海上高-特高含水期稠油油藏提高采收率实验研究

为了探索高-特高含水期稠油油藏不同提液方式下提高剩余油采出程度的机理, 设计不同提液方式、不同原油黏度下的海相砂岩稠油油藏驱替实验, 采用在室内搭建长岩心物理模拟实验, 研究高含水期、特高含水期时不同提液方式、原油黏度等因素对提高采收率的影响, 结合核磁共振成像和T₂图谱研究不同注水方式下剩余油分布。研究表明, 提液相比于恒定低速驱, 可提高11%左右的采出程度; 以驱替至含水率大于99%作为驱替结束条件, 高含水期油藏通过多次控幅提液采出程度最高; 岩心低速水驱至特高含水期后, 岩心核磁共振图像饱和度明显降低, 随着驱替的进行, 孔隙度分量逐渐降低, 即剩余油逐渐减少; 高含水期多次提液对不同孔径动用程度比一次大幅提液效果好, 微孔、小孔和中孔均有不同程度波及, 整体采出程度提高17.01%, 其中, 中小孔导致采出程度提高13.31%, 占提高幅度的78.2%;特高含水期, 多次提液比一次大幅提液原油采出程度提高9.2%, 其中中孔采出程度的提高作出主要贡献, 占提高幅度的97.2%, 微小孔波及程度较小。研究成果可为高-特高含水期稠油油藏提高采收率提供技术支持。      

Numerical investigation on the initiation mechanism of debris-flow under rainfall

Rainfall is an important factor to trigger the debris flow.Numerical simulation on the responses of slopes and the initiation of debris flow under rainfall was processed by using the software FLAC2D based on the soil parameters in Weijia Gully,Beichuan County,Sichuan Province,China.The effects of the slope angle,rainfall intensity,soil parameters on the developments of the stress and pore pressure and deformation of the slope were studied.It indicates that large displacements of the slope are mainly located near the slope toe.With the increase of the rainfall intensity the stability of the slope decreases and so the debris-flow is easy to occur.     

Experimental study on the energy dissipation characteristics of debris flow deceleration baffles

Debris flow can cause serious damages to roads, bridges, buildings and other infrastructures.Arranging several rows of deceleration baffles in the significant influence on the mobility and deposition characteristic of debris flow. The deposit amount first increased then decreased when the flow density rises,flow path can reduce the flow velocity and ensure better protection of life and property. In debris flow prevention projects, deceleration baffles can effectively reduce the erosion of the debris flow and prolong the running time of the drainage channel.This study investigated the degree to which a 6 m long flume and three rows of deceleration baffles reduce the debris flow velocity and affect the energy dissipation characteristics. The influential variables include channel slope, debris flow density, and spacing between baffle rows. The experimental results demonstrated that the typical flow pattern was a sudden increase in flow depth and vertical proliferation when debris flow flows through the baffles. Strong turbulence between debris flow and baffles can contribute to energy dissipation and decrease the kinematic velocity considerably. The results showed that the reduction ratio of velocity increased with the increase in debris flow density,channel slope and spacing between rows. Tests phenomena also indicated that debris flow density hasand the deposit amount of debris flow density of 1500kg/m~3 reached the maximum when the experimental flume slope is 12°.     

不同冷却方式下高温花岗岩巴西劈裂及声发射特性试验研究

干热岩地热开发中的钻井、储层压裂及热交换等环节均涉及高温岩石冷却的问题,为揭示其中岩石损伤演化规律,基于巴西劈裂试验和声发射技术,研究了不同高温及冷却方式对花岗岩抗拉性质的影响。结果表明:①25~600℃下花岗岩抗拉强度随温度升高而下降,遇水冷却使抗拉强度进-步下降并使其开始大幅下降的温度阈值提前到200,500℃后抗拉强度对遇水冷却更敏感。②荷载达到峰值,声发射累计振铃计数突增,岩样内形成断裂区;受遇水冷却影响,岩样的振铃计数峰值和能量峰值有所下降,间接反映岩石内裂纹更发育,200~300℃时降幅均较大,300℃时和500℃后花岗岩对热处理方式较敏感。③花岗岩破裂面随温度升高由平整向粗糙曲折变化,由脆性向延性转变,遇水冷却促进岩石破裂并促使脆性向延性转变的温度区间提前。研究结果为地热开采中高温岩石的稳定性评价提供理论参考。      

The effects of rainfall regimes and rainfall characteristics on peak discharge in a small debris flow-prone catchment

Peak discharge plays an important role in triggering channelized debris flows. The rainfall regimes and rainfall characteristics have been demonstrated to have important influences on peak discharge. In order to explore the relationship between rainfall regimes and peak discharge, a measuring system was placed at the outlet of a small, debris flow-prone catchment. The facility consisted of an approximately rectangular stilling basin, ending with a sharp-crested weir. Six runoff events were recorded which provided a unique opportunity for characterizing the hydrological response of the debris flow-prone catchment. Then, a rainfall–runoff model was tested against the flow discharge measurements to have a deep understanding of hydrological response. Based on the calibrated rainfall-runoff model, twelve different artificially set rainfall patterns were regarded as the input parameters to investigate the effect of rainfall regimes on peak discharge. The results show that the rainfall patterns have a significant effect on peak discharge. The rainfall regimes which have higher peak rainfall intensity and peak rainfall point occur at the later part of rainfall process are easy to generate larger peak discharge in the condition of the same cumulative rainfall and duration. Then, in order to explore the relationship between rainfall characteristics and peak discharge under different cumulative precipitation and different duration, 167 measured rainfall events were also collected. On the basis of rainfall depth, rainfall duration, and maximum hourly intensity, all the rainfall events were classified into four categories by using K-mean clustering. Rainfall regime 1 was composed of rainfall events with a moderate mean P(precipitation), a moderate D(duration), and a moderate I_(60)(maximum hourly intensity). Rainfall regime 2 was the group of rainfall events with a high mean P, long D. Rainfall regime 3, however, had a low P and a long D. The characteristic of Rainfall regime 4 was high I_(60) and short duration with large P. The results show that the rainfall regime 2 and 4 are easier to generate peak discharge as the rainfall intensity plays an important role in generating peak discharge. The results in this study have implications for improving peak discharge prediction accuracy in debris flow gully.     

降雨模式对震后泥石流起动模式影响的试验研究: 以九寨天堂沟为例

降雨过程中降雨强度的变化会影响土体渗透率及饱和过程, 从而改变土体的力学性质, 影响泥石流起动模式及破坏规模。为探究不同降雨模式对震后泥石流起动机制的影响, 自制了小比例模型槽, 结合可控雨型的降雨模拟系统, 进行了人工降雨诱发泥石流的室内模型试验; 基于不同降雨模式下泥石流的起动过程分析, 对坡体内部含水率和孔隙水压力的变化规律进行了研究。研究结果表明: 递增型降雨模式下泥石流发生突然, 呈整体滑坡转化为泥石流起动模式, 坡体破坏规模最大; 递减型降雨模式下表现为后退式溃散失稳起动模式; 均匀型降雨模式下则表现为溯源侵蚀起动模式; 中峰型降雨模式下以局部滑坡转化为泥石流起动模式; Ⅴ型降雨模式下则由坡面侵蚀加剧转化为泥石流启动模式, 破坏规模最小。研究结果可以为九寨沟地区泥石流的预报预警提供参考。      

黑方台地区马兰黄土渗透特性及结构损伤试验研究

持续引水灌溉改变了马兰黄土的结构,降低了土体的抗剪强度,导致黑方台地区黄土滑坡频繁发生,严重影响着当地居民生命和财产安全。为了明析马兰黄土的渗透过程,取黑方台马兰黄土为研究对象,分别开展核磁共振(NMR)试验及扫描电镜(SEM)试验,以解释此类黄土在不同初始含水率及不同干密度下的渗透特性及结构损伤微观特征。研究结果表明：入渗速率与土体初始含水率呈负相关关系,土体初始含水率越高,其充水微小孔隙增加速率越慢,充水中大孔隙增加速率越快;入渗速率与土体干密度呈负相关关系,且会率先形成高含水率区域,土体干密度越大,其充水微小孔隙增加越慢,充水中大孔隙增加越快。入渗前后对比发现,试样初始含水率越高,微小孔隙增加比例越小,颗粒间接触方式变化越不明显;干密度越大的试样不同孔隙体积基本按等量变化,接触面积明显减少,形成更多的架空孔隙,连通性较好,具有较好的储水能力。入渗后试样原本的致密结构丧失,颗粒破碎严重,部分细长状颗粒向似椭圆状颗粒演化,颗粒间接触方式变为点边接触,粒间胶结作用遭受损伤破坏,甚至部分团粒中颗粒分离、脱落,使得土体强度丧失,最终导致滑坡发生。研究结果可为黄土滑坡的防治提供依据。     

Assessment of the performance of WEPP in purple soil area with simulated rainfall experiments

The water erosion prediction project(WEPP) model is a popular water erosion prediction tool developed on the basis of the physical processes of water erosion.Although WEPP has been widely used around the world,its application in China is still insufficient.In this study,the performance of WEPP used to estimate the runoff and soil loss on purple soil(Calcaric Regosols in FAO taxonomy) sloping cropland was assessed with the data from runoff plots under simulated rainfall conditions.Based on measured soil properties,runoff and erosion parameters,namely effective hydraulic conductivity,inter-rill erodibility,rill erodibility,and critical shear stress were determined to be 2.68 mm h-1,5.54 × 106 kg s-1 m 4,0.027 s m 1 and 3.5 Pa,respectively,by using the recommended equations in the WEPP user manual.The simulated results were not good due to the low Nash efficiency of 0.41 for runoff and negative Nash efficiency for soil loss.After the four parameters were calibrated,WEPP performed better for soil loss prediction with a Nash efficiency of 0.76.The different results indicated that the equations recommended by WEPP to calculate parameters such as erodiblity and critical shear stress are not suitable for the purple soil areas,Sichuan Province,China.Although the predicted results can be accepted by optimizing the runoff and erosion parameters,more research related to the determination of erodibility and critical sheer stress must be conducted to improve the application of WEPP in the purple soil areas.