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1.
Piled embankments, which offer many advantages, are increasingly popular in construction of high-speed railways in China. Although the performance of piled embankment under static loading is well-known, the behavior under the dynamic train load of a high-speed railway is not yet understood. In light of this, a heavily instrumented piled embankment model was set up, and a model test was carried out, in which a servo-hydraulic actuator outputting M-shaped waves was adopted to simulate the process of a running train. Earth pressure, settlement, strain in the geogrid and pile and excess pore water pressure were measured. The results show that the soil arching height under the dynamic train load of a high-speed railway is shorter than under static loading. The growth trend for accumulated settlement slowed down after long-term vibration although there was still a tendency for it to increase. Accumulated geogrid strain has an increasing tendency after long-term vibration. The closer the embankment edge, the greater the geogrid strain over the subsoil. Strains in the pile were smaller under dynamic train loads, and their distribution was different from that under static loading. At the same elevation, excess pore water pressure under the track slab was greater than that under the embankment shoulder. 相似文献
2.
土体动力特性主要与其受力状态、土体加载类型、试验控制方式以及荷载等参数有关。以往非饱和黄土累积变形试验研究通过单向动应力加载方式开展相关研究,并不能真实反映土体受力状态。现运用WF-12440型动三轴-空心圆柱扭剪试验系统,通过单向荷载和双向荷载两种不同的动应力加载方式,进行黄土的长期重复载荷试验,对比不同动应力加载方式对非饱和黄土累积变形发展特征的影响。试验结果发现：黄土在单向荷载或双向荷载作用下,其软化指数均随着循环次数的增加,呈非线性减小的趋势,在相同循环振次时,土体软化指数随着动应力幅值的增大而减小;黄土在不同加载方式作用下,软化指数减小速率在循环振次100次以内较快,后期随振次增加,土体软化速率逐渐趋于平稳;黄土在双向荷载作用下,当轴向动荷载较小时,径向荷载的施加,将加速黄土的软化程度,随着轴向动荷载的增大,径向荷载对黄土软化的影响逐渐减弱,其对于黄土变形的影响存在一临界轴向循环动应力。本研究的开展,可更准确地进行不同荷载耦合变化下,黄土场地震陷评估或路基土体变形计算,实现有效控制路基的整体稳定和工后沉降量,以期根据路基土参数预测后期沉降,极具重要的科研和工程意义。 相似文献
3.
Laboratory cyclic triaxial tests were performed to investigate the effect of fine content on the pore pressure generation in sand. Strain-controlled, consolidated undrained tests have been performed with a cyclic shear strain range of 0·015-1·5%. These tests were carried to 1000 cycles or to initial liquefaction, which ever occurred first. Triaxial tests were performed on pure sand silt specimens and specimens with silt additions of 10, 20, 30, and 60% by weight. Two types of silt, a non-plastic silt and a low plasticity silt (PI 10) were used as control materials. The main parameters varied in this study were the amount of silt, the plasticity index of silt, and the void ratio where the observed parameter was the pore pressure generation. For all silt contents, silt plasticity and the number of loading cycles have no significant effect at strain levels below 0·01%. Therefore, threshold strain for silty sands have approximately the same value as sands. For both non-plastic and low plasticity silts, there is a significant increase in the generated pore pressure at high strain levels. 相似文献
4.
Vehicle load is among the main factors affecting the deformation of subgrade soil.In this research study,the concept of impact type traffic load is introduced to investigate the effects of vehicle load based on the dynamic stress and displacement time histories acquired from seasonal frozen subgrade soils.Using freezing-thawing and dynamic triaxial tests and considering the amplitude and loading sequence of impact type traffic load,the residual deformation characteristics of subgrade soil under impact type traffic loads and freezing-thawing cycles is studied.It was found that under impact type traffic load,the residual deformation of soils increased sharply as the amplitude of impact type traffic load increased.It was also found that the increase in the amplitude of impact type traffic load led to the increase of residual deformation in a scale of power and exponential function.The amplitudes of impact type traffic load affect the development stress-strain path of the residual strain.After the soil experienced the proper amount of pre-vibration of the light load,residual deformation decreased by 15%.After freezing-thawing,the residual strain of soil increased as the amplitude of the impact type traffic loads increased.Also,when the amplification effect of freezing-thawing on the residual strain was basically stable,the residual deformation increased by about 10%.The peak impact type traffic load had a large effect on soil deformation after the freezing-thawing process,leading to the observation that of the earlier the peaks,the stronger the effect of freezing-thawing.After the soil was subjected to preloading with a small load,the influence of the freezing-thawing cycles gradually stabilized.The results may be useful in preventing and controlling the risk of subgrade soil failure when construction takes place spring thaw periods. 相似文献
5.
Huang Runhua 《地球表面变化过程与地形》1986,11(2):117-122
Data collected since 1973 show high levels of arsenic in the Yellow River, very largely from natural sources. Average and peak concentrations, and the downstream distribution of the arsenic suggest the most likely source as the loess which provides 90 per cent of the river's suspended load. Arsenic is strongly absorbed by the silt and clay in the river: some of it is deposited in reservoirs and delta sediments but most is carried out to sea. 相似文献
6.
This paper investigates the cyclic and post-cyclic shear behavior of low-plasticity silt and the impact of additional clay content. Bentonite clay was added to the low-plasticity Mississippi River Valley (MRV) silt (PI=6) to increase the clay content of the soil. A series of triaxial tests were conducted in the laboratory to examine the shear and pore pressure behavior during and after cyclic loading. As the bentonite content in the reconstituted specimens increased, the excess pore pressure developed at a slower rate and the total excess pore pressure decreased at the end of cyclic loading. In contrast to the MRV silt, the specimens modified with bentonite experienced cyclic softening rather than initial flow liquefaction. The cyclic shear strength increased with an increase in bentonite content. The post-cyclic reconsolidation behavior was a similar to a virgin compression process, and not recompression. Adding bentonite to the MRV silt results in changes in permeability, compressibility, undrained shear strength, and initial stiffness. Additionally, the cyclic loading had a marked effect on the shear behavior of low-plasticity soil with a PI<6, but not noticeable with a PI>6. This study suggests that the behavior of the Mississippi River Valley silt changes from contractive sand-like material to clay-like behavior at a PI≈6 due to the addition of clay. 相似文献
7.
To identify the effect of non-plastic silt on the cyclic behavior of sand–silt mixtures, total sixty undrained cyclic triaxial stress-control tests were carried out on sand–silt mixtures. These tests were conducted on specimens of size 71 mm diameter and 142 mm height with a frequency of 1 Hz. Specimens were prepared at a constant relative density and constant density approach. The effect of relative density, confining pressure as well as magnitude of cyclic loading was also studied. For a constant relative density (Dr=60%) the effect of limiting silt content, pore pressure response and cyclic strength was observed. The rate of generation of excess pore water pressure with respect to cycles of loading was found to initially increase with increase in silt content till the limiting silt content and thereafter it reverses its trend when the specimens were tested at a constant relative density. The cyclic resistance behavior was observed to be just opposite to the pore pressure response. Permeability, CRR and secant shear modulus decreased till limiting silt content; after that they became constant with increasing silt content. 相似文献
8.
During earthquake events, low-plasticity silt undergoes a reduction in shear strength and stiffness due to development of excess pore pressure induced by cyclic loading. With reconsolidation, during which process excess pore pressure is dissipated, the shear strength and stiffness can be regained. However, due to the low permeability of silts (compared to sands), the dissipation of excess pore pressure and the reconsolidation of low-plasticity silt takes much more time. This paper investigates the postliquefaction shear behavior of Mississippi River Valley (MRV) silt at various degrees of reconsolidation using triaxial tests. Test results indicate that there was a steady increase, in shear strength and stiffness, at both large and small deformations, with increase in the degree of reconsolidation. The postliquefaction silt showed the effect of the apparent OCR, which had a close effect on postcyclic shear behavior as did the OCR on the static behavior. The critical state lines of MRV silt were different for pre- and post-liquefaction conditions. 相似文献
9.
This paper describes a laboratory model test carried out on high-density polyethylene (HDPE), small diameter pipes buried in trenches, which subjected to repeated loadings to simulate the vehicle loads. Deformation of the pipe was recorded at eight points on the circumference of the tested pipes to measure the radial deformations and detect cross-sectional pipe profiles. Also settlement of the soil surface during the test up to 1000 cycles of loadings was recorded, until its value become stable or the excessive settlement was happened. The parameters varied in the testing program include height of buried depth, relative density of the sand and intensity of stress on the soil surface. The influence of various repeated loads (with magnitude of 250, 400 and 550 kPa) at relative densities of 42%, 57% and 72% in different embedded depth of 1.5–3 times of pipe diameter were investigated. Based on the results, in medium and dense sand relative density, the pipe embedded in depth of 3.0D and 2.0D, respectively, mostly remained undamaged (the maximum value of VDS is less than 5%) and increased the safety of buried pipes under different magnitude of repeated loads. The records of the pipe deformation and settlement of the soil surface due to the repeated loads have been compared in different conditions. These values increase rapidly during the initial loading cycles by a rate decreasing significantly as the number of cycles increase. The influence of the first cycle was also found to be one of the main behavioral characteristics of buried pipes under repeated loads. The ratio of deformation of pipe at first cycle to last cycle changes from 0.60 to 0.85 in different of tests. Finally for the obtained results, a non-linear power model has been developed to estimate the vertical diametral strain of buried pipe and settlement of the soil surface based on the model test data. It should be noted that only one type of pipe and one type of sand are used in laboratory tests. 相似文献
10.
Consolidation of sediments discharged from the Yellow River: implications for sediment erodibility 总被引：1，自引：0，他引：1
Consolidation processes acting on an intertidal mudflat in the Yellow River delta, China, were investigated using field and laboratory experiments. The dissipation of excess pore pressure was examined in an excavated experimental plot to characterise the short-term consolidation of sediments discharged from the Yellow River. Changes in sediment strength were monitored over a 5-year period, together with measurements of physical and mechanical properties using laboratory experiments. In addition, the erodibility of silty sediments under wave loading conditions was also tested in the field. Results showed that sediments discharged from the Yellow River experienced a high rate of consolidation after initial deposition. Excess pore pressure dissipated completely after approximately 45 to 51 h. Sediments were then in a state of quasi-overconsolidation and showed heterogeneity in strength. Hydrodynamic action appears to be crucial to sediment consolidation in the primary period and plays a decisive role in the development of a stiff stratum. Changes in sediment strength due to wave-induced secondary modifications over varying temporal and spatial scales are consistent with variations in sediment erodibility. This factor should be considered in the development of erosion models for intertidal mudflat sediments. 相似文献
11.
为探究黄土路基在冻融循环和交通荷载耦合作用下的累积塑性应变变化规律,选取西宁地区重塑黄土为研究对象,采用GDS双向动三轴测试系统对其进行一系列动三轴试验,研究不同冻融循环次数、围压、动应力幅值以及频率对累积塑性应变的影响规律,并通过引入拟合参数建立考虑多因素的累积塑性应变预测模型。结果表明：累积塑性应变随冻融循环次数的增大而增大,在6次冻融循环后增长速率减缓且趋于稳定;减小动应力幅值和增大围压能显著抑制累积塑性应变的发展;加载初期累积塑性应变随频率变化不明显,随着振次的增加,频率作用凸显,累积塑性应变随着频率的增大而减小;基于试样的累积塑性应变演变规律,分别采用幂指数模型和对数模型进行拟合,发现后者拟合效果好;综合考虑4种因素对累积塑性应变的影响,建立累积塑性应变预测模型,并对试验的实测值与预测值进行对比,验证模型的可行性。研究成果可为季冻区黄土路基永久变形的计算提供理论参考依据。 相似文献
12.
地铁循环荷载作用下饱和软黏土的动力特性研究对于揭示软黏土在地铁荷载下的孔压、强度以及变形模式具有重要意义,可以为控制地铁长期沉降、降低运营风险提供理论依据。试验加载形式的不同会带来不同的动力特性表征,需选取最能反映地铁列车真实性质的荷载形式。本文在列车荷载作用下研究土动力特性,采用室内动三轴试验的方法,对比分析不同形式下动力荷载作用效果。试验研究表明:偏压正弦波可以作为简化波形研究列车荷载,它不仅可以确保加载过程中地基土只有压应力,而且能较好地模拟列车循环荷载。 相似文献
13.
Sediment discharge of the Yellow River (China) and its effect on the sedimentation of the Bohai and the Yellow Sea 总被引：6，自引：0，他引：6
The Yellow River is noted for its small water discharge and huge sediment load, which amounts to about11 × 108 tons every year, contributing 17% of the world's fluvial sediment discharge to the ocean. This has a profound effect on the sedimentation of the Bohai and the Yellow Sea. Changes of the outlet in the modern delta every 10 y result in frequent changes in the recession and progradation of the deltaic coastline both in space and time, and is the main reason why the Yellow River has not succeeded in building a bird-foot delta like the Mississippi. Owing to the huge sediment input from the Yellow River, the sedimentation rate of the Bohai is very high, about 0.6 m ka−1, but it is unlikely that the Bohai will be filled up in a few thousand years. In the late Quaternary period, the Yellow River extended its course across the Yellow Sea at least 4 times and probably discharged its heavy load into the Okinawa Trough during the last glacial maximum (15,000 B.P.). 相似文献
14.
Accumulative deformation in railway track induced by high-speed traffic loading of the trains 总被引：1，自引：0，他引：1
Prediction and control of the permanent settlement of a track caused by traffic loading from trains is crucial to high-speed
railway design and maintenance. In this study, a unified prediction model of accumulative deformation of geomaterials used
in railway construction subjected to cyclic loadings is introduced and calibrated using physical model testing. Based on this
versatile model, a calculation approach to determine the track structure settlement under repeated loadings caused by the
movement of the wheel axle of the train is proposed. Regression analysis on the physical model testing is adopted to determine
the parameters involved in the computational approach. Comparison of model test data and computed results shows that the parameters
obtained from the back-analysis are consistent throughout the various testing conditions, and the proposed calculation approach
is capable of satisfactorily predicting the accumulative settlement of the railway roadbed and subgrade soil for various axle
loads and loading cycles. A case study of a high-speed railway is performed to demonstrate the feasibility of the proposed
approach in realistic engineering applications. The computation results from the settlement development of a roadbed and subgrade
soil are presented and discussed. 相似文献
15.
IINTRODUCTIONTheYellowRiverisfamousforitsttemendousamountofsedimenttransport.Basedonastatisticaldataanalysis,along-timeaverageannualof1.6billiontonsofsedimententerstheLowerYellowRiver,inwhich400milliontonsaredepositedintherivercharmel.Thesedimentdepositioncausesavapidriseofthebedelevation.Withahistoricalevollltionoftheriverchanges,aso-called"suspendedriver"graduallyformed.UPtonow,thegroundleveloftheareaolltsidetheriverleveesismuchlowerthanthewaterlevelintheriver.Thissituationbringsanex… 相似文献
16.
波浪荷载能引起海床土体的主应力轴连续旋转。不同于地震、交通等循环荷载,在周期性波浪荷载作用的土体应力路径方式下,软黏土的软化效用更为明显。本文分别对天然和扰动的海床土体在波浪荷载作用下的应力响应进行模拟,并分析应力路径的特点;为描述软化后的应力-应变关系,将软化效用和累积塑性应变的参数引入到能够反应土体动力非线性的Hardin-Drnevich模型中,建立修正模型,使之能够反应软黏土体软化与塑性应变累计特性;通过与模拟波浪荷载下土体应力特征的循环耦合试验结果进行对比分析,验证该修正模型的可靠性。 相似文献
17.
不同地域的软黏土表现出不同的动力学特性,针对舟山地区海相软黏土,采用Wille动三轴仪开展了一系列不排水三轴试验,研究了不同加载频率及循环应力比对软黏土的动应力-应变-孔压及软化指数等的影响规律。结果表明：低频荷载的应力-应变滞回曲线对应的面积较大且曲线趋势更倾向于应变轴,随着循环次数的增加土体的软化程度明显增加(软化指数减少),且在高循环应力比下产生较大的累积塑性应变和残余动孔压;在低频较大循环振次和高频荷载作用下,不仅需要关注循环应力比CSR的影响,也需要进一步分别关注围压和轴向偏应力各自数值不同所导致的土体累积塑性应变、残余动孔压的变化;降低循环应力比可以显著减少不同频率荷载对软黏土地基动力特性的影响。此外,实验所测的累积塑性应变和残余动孔压分别采用相关修正模型拟合,取得了一致的拟合结果。该研究将为舟山海相软黏土的工程应用提供参考依据。 相似文献
18.
Railway ballast forms a major component of a conventional rail track and is used to distribute the load to the subgrade, providing a smooth running surface for trains. It plays a significant role in providing support for the rail track base and distributing the load to the weaker layer underneath. Ballast also helps with drainage, which is an important factor for any type of transportation structure, including railroads. Over time, ballast progressively deforms and degrades under dynamic loading and loses its strength. In this study, extensive laboratory tests were conducted to investigate the effect of load amplitude, geogrid position, and number of geogrid layers, thickness of ballast layer and clay stiffness on the behavior of the reinforced ballast layer and induced strains in a geogrid. A half full-scale railway was constructed for carrying out the tests, which consisted of two rails 800 mm in length with three wooden sleepers(900 mm × 10 mm × 10 mm). Three ballast thicknesses of 200, 300 and 400 mm were used in the tests. The ballast was overlying 500 mm thickness clay in two states, soft and stiff. The tests were carried out with and without geogrid reinforcement; the tests were performed in a well-tied steel box of 1.5 m length ×1 m width ×1 m height. Laboratory tests were conducted to investigate the response of the ballast and the clay layers where the ballast was reinforced by a geogrid. Settlement in ballast and clay, soil pressure and pore water pressure induced in the clay were measured in reinforced and unreinforced ballast cases. It was concluded that the amount of settlement increased as the simulated train load amplitude increased, and there was a sharp increase in settlement up to cycle 500. After that, there was a gradual increase that leveled out between, 2500 to 4500 cycles depending on the frequency used. There was a slight increase in the induced settlement when the load amplitude increased from 0.5 to 1 ton but it was higher when the load amplitude increased to 2 tons. The increased amount in settlement depended on the existence of the geogrid and other parameters studied. The transmitted average vertical stress for ballast thicknesses of 30 cm and 40 cm increased as the load amplitude increased, regardless of the ballast reinforcement for both soft and stiff clay. The position of the geogrid had no significant effect on the transmitted stresses. The value of the soil pressure and pore water pressure on ballast thicknesses of 20 cm was higher than for 30 cm and 40 cm thicknesses. This meant that the ballast attenuated the induced waves. The soil pressure and pore water pressure for reinforced and unreinforced ballast was higher in stiff clay than in soft clay. 相似文献
19.
The impact of silt trapping in large reservoirs on downstream morphology: the Yangtze River 总被引：2，自引：0，他引：2
The sediment load of the Yangtze River (China) is decreasing because of construction of dams, of which the Three Gorges Dam (TGD) is the best known example. The rate of the decline in sediment load is well known, but changes in the sediment grain size distribution have not been given much attention. The TGD mostly traps sand and silt while clay is flushed through the reservoir. A large amount of sand is available in the Yangtze River downstream of the reservoir, and therefore the pre-dam sand concentration is not substantially reduced. The availability of silt on the Yangtze River bed is limited, and it is expected that most silt will be removed from the riverbed within one to two decades. In order to evaluate the impact of the change in grain size distribution on the tidal flats of the Yangtze Estuary, a highly schematized tidal flat model is setup. This model broadly reveals that the observed deposition rates are exceptionally large because of the high sediment concentration, the abundance of silt, the seasonal dominance of waves (shaping a concave profile), and the offshore tidal asymmetry. The model further suggests that deposition rates will be limitedly influenced by reductions in clay or fine silt but strongly impacted by reductions in median to coarse silt. The response of the downstream morphology to reservoir sedimentation therefore strongly depends on the type of trapped sediment. As a consequence, silt-dominated rivers, such as the Yangtze River and the Yellow River may be more strongly impacted than sand-dominated systems. 相似文献
20.
Evolution of the Yellow River delta,China: Impacts of channel avulsion and progradation 总被引：1，自引：0，他引：1
The evolution of the Yellow River delta is characterized by heavy sediment load,rapid seaward migration,frequent avulsions,and intense anthropogenic disturbances.Evolution of the delta channel following avulsions is very complex and has not yet been thoroughly understood.In the research presented by this paper,we conducted comprehensive analyses of the changes in the water stages,slopes,longitudinal profiles,and the erosion and deposition in the Yellow River delta channels during a time period of over five decades.Results showed that,following each avulsion,channels migrated seaward at decaying rates and the slopes at the downstream of the avulsion point decreased exponentially with time and completed its major adjustment within about four to five years.A generalized geometric model was proposed to describe the changes in the longitudinal profiles of the delta channels.A calculation method to determine the characteristic water stages at the delta was proposed based on the geometric model and the delayed response model for the morphological responses of fluvial rivers to perturbations.Water stages corresponding to a discharge of 3000 m3/s at Lijin and Xihekou during 1954 through 2012 were calculated by using the proposed method.The proposed method may be used to predict the evolution of the delta channels in response to artificial avulsions at the Yellow River delta in the future. 相似文献