Strength and deformation behavior of the Yellow River silt under triaxial drained condition considering characteristic states

Currently,the application of the Yellow River silt in subgrade,especially in expressway subgrade,has not been widely promoted.The main reason is that the research on the mechanical characteristics of the Yellow River silt used for subgrade filling is extremely limited.In this study,the static shear test of the Yellow River silt under drained condition was carried out using Global Digital Systems(GDS)triaxial apparatus,and the effects of confining pressure,relative density and shear rate on the strength and deformation behavior of the Yellow River silt were investigated.The cohesive force of the Yellow River silt is low,and the friction angle is the main factor determining the shear strength.Friction angle at phase transformation stateφpt,friction angle at peak stateφps,friction angle at critical stateφcs,were obtained via the observation on the evolution law of mobilized friction angle during the whole shearing process.The friction angles corresponding to three different characteristic states have the following magnitude relationship,namelyφps>φcs>φpt.The strength parameters for low-grade subgrade and highgrade subgrade were chosen to be 29.33°and 33.75°.The critical state line(CSL),envelop of phase transformation(EOP),and envelop of dilatancy(EOD)for three different characteristic states were determined.The critical stress ratio M,the phase transformation stress ratio Mptand the dilatancy stress ratio Mdof the Yellow River silt are 1.199,1.235,1.152,respectively.These results provide a basis for the mechanical analysis of the Yellow River silt subgrades and the subsequent establishment of dynamic constitutive model of the Yellow River silt.

Effect of Penetration Rates on the Piezocone Penetration Test in the Yellow River Delta Silt

Partial drainage often occurs during piezocone penetration testing on Yellow River Delta silt because of its intermediate physical and mechanical properties between those of sand and clay.Yet,there is no accurate understanding for the range of penetra-tion rates to trigger the partial drainage of silt soils.In order to fully investigate cone penetration rate effects under partial drainage condi-tions,indoor 1 g penetration model tests and numerical simulations of cavity expansion at variable penetration rates were carried out on the Yellow River Delta silt.The boundary effect of the model tests and the variation of key parameters at the different cavity ex-pansion rates were analyzed.The 1 g penetration model test results and numerical simulations results consistently indicated that the penetration rate to trigger the partially drainage of typical silt varied at least three orders of magnitude.The numerical simulations also provide the reference values for the penetration resistance corresponding to zero dilation and zero viscosity at any given normalized penetration rate for silt in Yellow River Delta.These geotechnical properties can be used for the design of offshore platforms in Yel-low River Delta,and the understanding of cone penetration rate effects under the partially drained conditions would provide some technical support for geohazard evaluation of offshore platforms.

In Situ Observation of Silt Seabed Pore Pressure Response to Waves in the Subaqueous Yellow River Delta

The in situ pore pressure response of silt under wave action is a complex process.However,this process has not been well studied because of limited field observation techniques.The dynamic response process is closely related to engineering geological hazards;thus,this process must be urgently explored.A long-term in situ observational study of the silt sediment pore water pressure response process under wave action was conducted in the subaqueous Yellow River Delta.The response characteristics of pore water pressure are affected by tidal level and wave height.Tidal level affects the overall trend of the pore water pressure response,while wave height influences the amplitude of the pore water pressure response.This study revealed a significant lag effect in the pore pressure response.The transient pore pressure in the seabed did not respond immediately to the wave-induced pressure stress on the seabed surface.This phenomenon may be attributed to the change in soil permeability.The maximum response depth was approximately 0.5 m with a 2 m wave height.A concept model of silt soil pore pressure response under different types of wave action was developed.The accumulation rate of the pore pressure is less than the dissipation rate;thus,the developed model highlights the oscillation pore pres-sure response mechanism.The highlighted response process is of considerable importance to transient liquefaction and the startup process of pore pressure response.

Development of Cementitious Materials Utilizing Alkali-activated Yellow River Silt

The possibility of preparing cementitious materials by the alkali-activated method using Yellow River sediment(The second largest river in China)as raw material and the modification effect on different slag addition were investigated.Sodium silicate and calcium hydroxide were used as the activator,and the specimens were prepared by the press molding method.The hydration process,hydration products,pore characteristics,and mechanical properties were investigated using SEM/EDS,FTIR,TG/DTG,XRD,MIP,and uniaxial compressive strength experiments,respectively.The results showed that the compressive strength of the modified yellow river silt-based cementitious material was significantly increased when the water glass dosage was 12 wt%(Ms=1.8)and the slag dosage was 40%,and its 90-day maximum compressive strength could reach 53 MPa.

Evaluation of dynamic characteristics of silt in Yellow River Flood Field after freeze-thaw cycles

Frothing is a main disease of highways in Yellow River Flood Field, due to the loss of dynamic strength of roadbed soils under the couple effects of temperature, salt, and vehicle traffic load. This is strongly linked to the dynamic characteristics of silt in this region. To analyze these couple effects on the dynamic characteristics of silt, a series of tests(i.e., freeze-thaw cycling tests, vibration triaxial tests and ultrasonic wave velocity tests) were conducted and two kinds of silt(i.e., salt-free and 3%-salt silt) were designed. The results indicate that the dynamic shear strength and dynamic modulus decrease with increasing freeze-thaw cycles, while the damping ratio simultaneously increases. Furthermore, compared to salt-free silt, the decrement of dynamic shear strength and dynamic modulus of silt with 3% salt is more significant, but the damping ratio of 3%-salt silt is larger. In ultrasonic wave velocity tests, ultrasonic wave velocity of frozen soil specimens decreases as the number of freeze-thaw cycles increases. Based on the results of ultrasonic wave velocity tests, a preliminary model is proposed to evaluate damage of silt through field measurement ultrasonic data. The study could provide a theoretical basis for the treatment of silty soil highway.

Factors Influencing the Thermal Conductivity of Silt in the Yellow River Delta

The thermal conductivity of marine sediments is an important thermophysical parameter in the study of seafloor heat flow and marine engineering construction.Understanding the effect of thermal conductivity of marine sediments in the environment has a major engineering value and theoretical significance.In this work,a modified test method was used to measure the thermal conductivity of silt in the Yellow River Delta under different void ratios,moisture contents,temperatures,and salinities.Results showed that the thermal conductivity of silt in the Yellow River Delta decreased with the increase in the void ratio and increased with the water content.Compared with sand and clay,silt in the Yellow River Delta was the least affected by the void ratio and moisture content.Under low temperatures,the heat transfer of soil was controlled by the average velocity of the phonons;therefore,the thermal conductivity of silt in the Yellow River Estuary increased with temperature.The thermal conductivity of pore water decreased with increasing salinity.Moreover,certain salinity levels resulted in a phenomenon known as the‘compressing twin electrical layer’,which led to an increase in the contact area between soil particles.With the increase in salinity,the thermal conductivity of silt in the Yellow River Delta experiences an initial decline and a subsequent increase.The proposed thermal conductivity test method is more accurate than the existing technique,and the findings provide a basis for further study on the thermal characteristics of submarine sediments.

隧道施工引发粉土地面沉降模拟与分析

为研究黄泛区粉土地层内开挖双线地铁隧道对地上及其周边地面沉降的影响,以某双线地铁隧道开挖工程为例,考虑地下水、隧道间距对地面沉降的影响,采用流固耦合数值方法和理论分析方法对隧道施工引起的地面沉降规律进行分析。将数值模拟数据与Peck公式进行反演计算,并考虑隧道间隔和埋深的影响提出修正Peck公式,再结合叠加原理建立适用于双线隧道开挖引起地面沉降的修正叠加公式。结果表明:隧道开挖扰动地层将引起超静孔隙水压力现象;数值模拟与理论计算得到隧道间隔为4 m时,地面沉降曲线呈现“V”型,隧道间隔为8 m、12 m时,则沉降曲线呈现“U”形;粉土内开挖双线地铁隧道,地面容易受到扰动且沉降量大,随着隧道间距的增加,隧道上方土体沉降量逐渐减小;基于修正Peck公式计算结果与数值模拟结果基本一致,相对误差在3%左右,表明该公式具有很好的实用性。研究可为粉土地区隧道及地下工程建设提供理论依据和技术支撑。

大豆脲酶诱导碳酸钙固化黄河泥沙水稳定性试验研究

随着国家“交通强国”战略的提出,沿黄工程建设发展迅速,填筑用土需求剧增。黄河泥沙作为填筑材料的可行性已被证实,但其在多雨地区的服役性能需要改善,探索一种生态、高效的泥沙加固方法提高其水稳定性十分关键。本文基于酶诱导碳酸钙沉淀(EICP)技术固化黄河泥沙的方法,分别开展了常规浸水条件和干湿循环条件下固化黄河泥沙的水稳定性试验,研究了浸水后试样的质量损失及强度折损情况,分析了干湿循环对固化后黄河泥沙试样强度软化系数的影响规律。结果表明:采用EICP技术固化的黄河泥沙试样浸水崩解过程相比原状试样更加缓慢;胶结液浓度1.5 mol/L的黄河泥沙试样长期(56 d)浸水后,几乎保持完整,质量损失率仅为6.36%,强度折损率仅为6.21%;10次干湿循环后,不同胶结液浓度处理后的黄河泥沙试样均出现了不同程度的颗粒松散和脱落现象,胶结液浓度1.5 mol/L、灌浆10次的黄河泥沙试样的抗压强度损失仅为9.96%,抗干湿循环能力最强。利用EICP技术可以有效的固化黄河泥沙并提升其水稳定性,这对推进黄河泥沙的资源化利用进程十分重要。

长期循环荷载下黄泛区黄河泥沙的变形特性及安定性分析

随着国家“黄河高质量发展”战略的提出,沿黄工程建设飞速发展,填筑土体材料需求量剧增,建筑资源短缺的问题突显。黄河泥沙作为一种新型工程填料,其资源利用前景被相关部门和研究人员重视。为研究长期循环荷载作用下的黄河泥沙的动力服役特性,选取黄河泥沙典型试样,基于GDS三轴试验系统进行了排水条件下的大周次(10000次)循环三轴试验,结合安定理论系统分析围压、循环应力比、加载频率和密实度对黄河泥沙变形特性的影响,并对黄河泥沙的长期动力稳定性进行研究。研究结果表明:累积应变和回弹应变随着围压的增大而增大,随着频率的升高和密实度的增大而减小,循环应力比较小时,应变累积在加载初期几百次循环内就迅速稳定;随着循环应力比增大,应变的发展逐渐具有蠕变的性质,在5000次循环后仍不断累积;随着循环应力比继续增大,轴向应变将在加载初期迅速增大,泥沙试样在很少的周次内达到破坏状态。通过与代表性的相似土体进行对比,发现黄河泥沙的蠕变性介于粉土和砂砾土之间。基于黄河泥沙的安定性分析,提出了黄河泥沙容许循环应力比的表达式,用以初步判断排水状态下黄河泥沙的长期动力稳定状态。研究结果为泥沙土在实际工程中的进一步应用和推广提供了参数支撑。

黄河淤背区高等级公路路基沉降及其对大堤安全的影响分析

为评价淤背区新建道路沉降对黄河大堤安全的影响,基于黄河淤背区路用粉土试验结果,提出黄河淤背区粉土累积应变预测模型和路基沉降计算方法。结合路基内部应力计算结果,采用分层总和法对循环荷载作用下淤背区路基沉降与路堤填筑引发的施工期沉降进行计算分析。结果表明:车辆通行初期沉降发展较快,对大堤影响显著,沉降主要集中在路基上部50 cm内。沉降和大堤安全受汽车轴重和超载影响显著,车流量影响次之,路堤高度和地下水埋深影响较小,沉降与超重倍数成幂函数关系。路堤高度每增加1 m,施工期沉降增加约50 mm。路基总沉降量随车重、路堤高度、车流量、超载倍数的增大而增大,随地下水埋深的增大而减小;工后沉降比随轴重、超载倍数、车流量的增大而增大,随路堤高度增加而减小,且近似成反比例关系。为保证大堤安全,淤背区路段应控制车辆轴重、超载及车流量。

开封市黄河大堤植物资源现状与选择应用建议

通过实地调查开封市黄河大堤的植物种类、长势和植物配置情况,根据黄河大堤场地现状的防洪固堤需求与沙尘暴频发问题,查阅相关文献资料,从抗旱性、耐湿性、滞尘性、抗风性和乡土植物的生态视角进行分析,提出适合黄河大堤的植物物种的选择及具体种植位置的应用建议,以期改善黄河大堤下游现阶段生态问题,为营建生态景观线提供借鉴与参考。

黄河冲积粉土的渗透特性研究

黄河冲积粉土分布范围广,工程性质差,作为填料时容易出现渗透破坏现象。为研究粉土的渗透特性,以郑州地区黄河冲积粉土为研究对象,在分析黄河冲积粉土基本物理性质和颗粒级配的基础上,实验研究不同压实度粉土的渗透系数,并验证了常用渗透系数经验公式对黄河冲积粉土渗透系数预测的适用性。研究结果表明:郑州地区黄河冲积粉土颗粒以粉粒组为主,其渗透系数随压实度的增大而减小,大致与压实度呈负指数关系;此外,修正kozeny-carman公式更适于预测压实黄河冲积粉土的渗透系数。

黄泛区非饱和粉土动模量和阻尼比特性研究

黄泛区粉土水敏感性强,力学性质独特,易受振动荷载的影响。本文通过循环三轴试验,研究固结围压和饱和度对黄泛区粉土动模量、阻尼比特性的影响。研究结果表明,黄泛区粉土骨干曲线符合双曲线关系;随动应变的增大,黄泛区粉土动弹性模量先急剧减小而后逐渐趋于稳定;随固结围压的增大和饱和度的减小,粉土动弹性模量逐渐增大,阻尼比则逐渐减小;二元线性方程可用于估算最大动弹性模量随固结围压和饱和度的变化规律,修正Hardin-Drnevich模型可较为准确预测黄泛区非饱和粉土的动弹性模量和阻尼比。本研究可为黄河流域工程建设提供理论支撑。

小浪底水库调控后黄河下游冲淤规律与水沙调控指标

为科学指导黄河调水调沙调度实践,根据小浪底水库调控后黄河下游冲淤规律对水沙调控指标进行优化。选取2011—2022年黄河下游实测121场不同含沙量级水沙过程,分析黄河下游水沙特点及其冲淤效率与水沙条件的响应关系,以黄河下游不淤积以及主槽过流能力不降低为总体目标提出水沙调控指标。结果表明:①小浪底水库对黄河下游水沙过程具有两极分化的调控作用,高含沙量水流(平均含沙量S av>10 kg/m^(3))的沙量全年占比为94%,清水水流(S av<1 kg/m^(3))的水量全年占比为85%。②高含沙量水流的淤积效率与平均含沙量呈正相关线性关系。③清水水流的冲刷效率与平均流量呈正相关对数关系。④对于高含沙量水流,丰水年调控水量为80亿m^(3),平均流量为2000~4600 m^(3)/s,平均含沙量为50 kg/m^(3);平水年调控水量为10亿m^(3),平均流量为2000~4600 m^(3)/s,平均含沙量为150 kg/m^(3);枯水年水库不排沙。对于清水水流,需要避免下泄平均流量在800~1800 m^(3)/s范围内的水流过程。

超大直径盾构隧道下穿黄河大堤沉降研究

济泺路隧道为第一条下穿黄河的市政道路与轨道交通合建盾构隧道。针对盾构隧道引发的黄河大堤沉降值预测,基础Peck公式的应用受到局限。在既有研究基础上,提出超大直径泥水平衡盾构隧道三维Peck公式,其横向沉降计算预测、纵向沉降计算预测与黄河大堤实测沉降数据拟合效果较好。通过相关参数分析可知:随着地表以下竖向深度的增大,沉降槽形态变深收窄,最大沉降值增加、横向影响范围减少;竖向深度超过临界值后,沉降曲线向上凸起,横向沉降不再满足高斯分布;沉降槽形态变化与隧道横向间距、沉降槽宽度、隧道相对埋深、地质条件有关;先行线盾构隧道穿越大堤后,大堤土层已产生扰动,后行线盾构隧道穿越大堤,大堤地层累积沉降值及地层损失率更大。

济南城区段黄河淤背区土地利用规划探讨

淤背区是黄河防洪工程重要的组成部分。本文系统介绍了济南城区段黄河淤背区开发利用现状,深入分析了淤背区开发中存在的主要问题,提出了以黄河生态景观线建设为主导,合理开发利用淤背区土地资源,因地制宜大力推进种植业,搞活防汛抢险物资仓储业,积极发展黄河水生态旅游业等土地利用规划建议,为科学开发利用淤背区土地提供借鉴。

黄河废弃三角洲海底冲淤演变规律研究

1976年黄河改道清水沟流路后 ,钓口流路三角洲叶瓣废弃 ,由于大量陆源沉积物供应的断绝 ,原来形成的快速堆积地形变得极不稳定 ,水下三角洲岸坡受到海洋动力快速冲蚀作用。根据长期水深资料的对比研究 ,波浪侵蚀使水下岸坡整体变缓以适应新的沉积动力环境 ,正逐渐形成新的冲淤平衡剖面。对整个研究区的水深资料进行叠加 ,总结其海底冲淤演变规律。采用 2 0 6 6 0、2 0 6 5 6、2 0 6 5 2和 2 0 6 4 8剖面上的散点 (整数水深点 )水深变化 ,结果表明废弃三角洲海底由浅水区向深水区冲淤组合呈带状分布 ,且越向深水区周期性越明显。

近、现代黄河三角洲发育演变研究进展

系统综述了1980年以来国内有关近、现代黄河三角洲发育演变的研究进展。总结了三角洲变迁对黄河下游近口河段的反馈影响和三角洲发育模式等研究成果。重点评述了黄河三角洲的形成影响因素和冲淤演变过程,肯定了数值计算方法和遥感与GIS技术已经成为定量计算与半定量分析黄河三角洲冲淤演变的重要研究手段。并指出今后研究的主要问题,包括突发性事件在潮滩冲淤变化中的作用、人类活动影响程度的定量表达、岸滩处于不冲不淤时的最佳剖面形态、现有冲淤数值模型的完善和GIS与数值模型系统的集成研究等。

考虑土性参数空间变异性的边坡可靠度分析

采用基于Morgenstern-Price法的Monte-Carlo模拟对黄河大堤开封段边坡进行了可靠度分析,并用抽样法进行了考虑土性参数空间变异性的可靠度分析,讨论了土性参数互相关性对可靠指标的影响,得到了一些有益的结论。对边坡工程安全度评价研究有一定的理论意义和实际应用价值。

黄河中游淤地坝拦沙机理及作用

本文分析了淤地坝形成后水文泥沙条件的变化，探讨了淤地坝的淤积形态和拦沙机理，从单坝拦沙定额、小流域对比分析、河流泥沙变化、典型暴雨洪水等方面讨论了淤地坝的拦沙作用．