Geotechnical investigation of low-plasticity organic soil treated with nano-calcium carbonate

Soil stabilization using nanomaterials is an emerging research area although,to date,its investigation has mostly been laboratory-based and therefore requires extensive study for transfer to practical field ap-plications.The present study advocates nano-calcium carbonate(NCC)material,a relatively unexplored nanomaterial additive,for stabilization of low-plasticity fine-grained soil having moderate organic content.The plasticity index,compaction,unconfined compressive strength(UCS),compressibility and permeability characteristics of the 0.2%,0.4%,0.6%and 0.8%NCC-treated soil,and untreated soil(as control),were determined,including investigations of the effect of up to 90-d curing on the UCS and permeability properties.In terms of UCS improvement,0.4%NCC addition was identified as the optimum dosage,mobilizing a UCS at 90-d curing of almost twice that for the untreated soil.For treated soil,particle aggregation arising from NCC addition initially produced an increase in the permeability coef-ficient,but its magnitude decreased for increased curing owing to calcium silicate hydrate(CSH)gel formation,although still remaining higher compared to the untreated soil for all dosages and curing periods investigated.Compression index decreased for all NCC-treated soil investigated.SEM micro-graphs indicated the presence of gel patches along with particle aggregation.X-ray diffraction(XRD)results showed the presence of hydration products,such as CSH.Significant increases in UCS are initially attributed to void filling and then because of CSH gel formation with increased curing.

Experiment and constitutive modelling of creep deformation in the frozen silt-concrete interface

To ensure the long-term safety and stability of bridge pile foundations in permafrost regions,it is necessary to investigate the rheological effects on the pile tip and pile side bearing capacities.The creep characteristics of the pile-frozen soil interface are critical for determining the long-term stability of permafrost pile foundations.This study utilized a self-developed large stress-controlled shear apparatus to investigate the shear creep characteristics of the frozen silt-concrete interface,and examined the influence of freezing temperatures(−1,−2,and−5°C),contact surface roughness(0,0.60,0.75,and 1.15 mm),normal stress(50,100,and 150 kPa),and shear stress on the creep characteristics of the contact surface.By incorporating the contact surface’s creep behavior and development trends,we established a creep constitutive model for the frozen silt-concrete interface based on the Nishihara model,introducing nonlinear elements and a damage factor.The results revealed significant creep effects on the frozen silt-concrete interface under constant load,with creep displacement at approximately 2-15 times the instantaneous displacement and a failure creep displacement ranging from 6 to 8 mm.Under different experimental conditions,the creep characteristics of the frozen silt-concrete interface varied.A larger roughness,lower freezing temperatures,and higher normal stresses resulted in a longer sample attenuation creep time,a lower steady-state creep rate,higher long-term creep strength,and stronger creep stability.Building upon the Nishihara model,we considered the influence of shear stress and time on the viscoelastic viscosity coefficient and introduced a damage factor to the viscoplasticity.The improved model effectively described the entire creep process of the frozen silt-concrete interface.The results provide theoretical support for the interaction between pile and soil in permafrost regions.

Microstructure Features and the Macroscopic Acoustic Behavior of Gassy Silt in the Yellow River Delta

The morphological changes in isolated bubbles in gassy silt play a critical role in the microscopic structures between soil particles and bubbles and macroscopic physical properties.Based on X-ray CT scanning experiments under various vertical loads(four levels),self-designed acoustic macro experiments,and a series of formula revisions to the macro-air-bearing silt sound-velocity prediction model,this paper discusses the macro-and micro-scale features of gassy silts from the Yellow River Delta.The samples consisted of different proportions of silt from the Yellow River Delta and porous media,and they were used to form two types of aerosol silts with initial gas contents of 4.23%and 7.67%.The results show that the air bubble content and external load considerably affect the microstructural parameters and acoustic behavior of gassy silt in the Yellow River Delta.The macroscopic sound velocity showed a linear positive correlation with vertical load and relation to microstructural parameters in varying manners and degrees.Based on the traditional Biot-Stoll acoustic model,the gas-phase medium coefficient was introduced for the proper calculation and prediction of the sound velocity of air-bearing silt.The errors of the overall prediction varied between 5.6%and 9.6%.

Influence of the boundary effect on the mechanical response test of pavement cushion under the wetting effect of silt

Through a self-developed model test system,the mechanical properties of silt and the deformation characteristics of airport runways were investigated during the period of subgrade wetting.Based on the test results,the reliability of the numerical simulation results was verified.Numerical models with different sizes were established.Under the same cushion parameter and loading width ranges,the effects of the cushion parameters and loading conditions on the mechanical responses of the cushion before and after subgrade wetting were analyzed.The results show that the internal friction angles of silt with different wetting degrees are approximately 34°.The cohesion is from 8 to 44 kPa,and the elastic modulus is from 15 to 34 MPa.Before and after subgrade wetting,the variation rates of the cushion horizontal tensile stresses with the same cushion parameters and loading width ranges are different under the influence of boundary effects.After subgrade wetting,the difference in the variation rates of the cushion horizontal tensile stresses under the same cushion parameter range decreases compared with that before subgrade wetting;however,this difference increases under the same loading width range.Before and after subgrade wetting,the influence of the boundary effect on the mechanical response evaluation of the cushion is not beneficial for optimizing the pavement design parameters.When the cushion thickness is more than 0.25 m,the influence of the boundary effect can be disregarded.

Experimental Study on Clogging Characteristics of Silt Soft Soil in Nansha District of Guangzhou

The silt soft soil in Nansha District of Guangzhou was the softest soft soil in China. It had the characteristics of high natural water content, high compressibility, long consolidation time, and complex layered distribution of soil layers. These characteristics formed the clogging characteristics of silt soft soil, which greatly increased the construction difficulty and hindered the construction progress. Therefore, based on the basic physical and mechanical properties of silt soft soil in Nansha District of Guangzhou, this paper evaluated the clogging characteristics of three silt soft soil areas in Nansha District of Guangzhou through long-term permeability test, and carried out scanning electron microscope test to explore the influence of different parameters and microstructure on the clogging difficulty of silt soft soil. The results showed that the silt soft soil Zone I and Zone II (shallow layer) in Nansha District of Guangzhou were divided into slight siltation levels, and the silt soft soil Zone III (deep layer) was mild siltation level. Large pores were widely distributed in shallow silt soft soil, while the continuity of large pores in deep silt soft soil was poor. The migration of fine particles that failed to establish contact with surrounding particles in the soil blocks the small pores of seepage and thus produces siltation.

Silting模的一个推广

基于Angeleri Hügel等人提出的silting模的概念,以及Breaz等人对silting模生成的torsion类的研究,给出了n-silting模的定义.称左R模T是n-silting模,如果存在正合列Pn+1→Pn→…→P2→P1→T→0,其中Pi(1≤i≤n+1)为投射模,且Presn(T)=Dσ.n-silting模是silting模的一个推广,1-silting模与silting模是一致的.利用环模理论和同调代数的方法,研究了n-silting模的若干性质和等价刻画,得出当T是n-silting模时,Presn(T)=Gen(T)=Dσ■T^⊥i≥n成立,其中Dσ={X∈R-Mod| HomR(σ,X)是满同态}.并讨论了n-silting模与n-tilting模之间的关系,结果表明,如果存在左R模正合列0→Pn+1^σ→Pn→…→P2→P1→T→0且Dσ■T^⊥i≥n,其中Pi(1≤i≤n+1)为投射模,那么以下说法等价:(1)T是n-silting模;(2)T是n-tilting模.

砂质辫状河储集层构型表征——以孤东油田七区西馆陶组为例

孤东油田七区西馆陶组N1g45小层—N1g16小层为辫状河沉积,砂体内部构型复杂,需精细解剖储集层结构,揭示其对油气开发的影响。采用Miall构型要素分析法,以现代辫状河规模作为约束,进行砂体储集层构型表征,采用动静结合手段检验研究成果,总结储集层构型对注水开发和剩余油分布的影响。结果表明:研究区为砂质辫状河沉积,主要发育辫状河道、心滩、溢岸以及泛滥平原4种构型单元;辫流带宽度为150~750 m,宽厚比为47~74;在辫流带内,有辫状河道-辫状河道、心滩-心滩、辫状河道-心滩-辫状河道和心滩-辫状河道-心滩4类构型模式;心滩平均长度为250~350 m,平均宽度为110~140 m,长宽比为2.20~2.50,心滩与河道平面面积比为0.36~0.51;心滩内一般发育2~4个落淤层,落淤层延伸长度为70~150 m,产状近水平,背水面夹层倾角为0.9°~2.3°;生产动态揭示由于构型单元边部物性变差,构型拼接部位油气流动受阻,成为局部剩余油富集区;在构型单元主体部位,油藏连通性好,开发效果好。

干湿循环与侵蚀耦合作用下碱渣固化淤泥的强度与损伤

为揭示干湿循环与侵蚀耦合作用对固化淤泥性质的影响,以碱渣、矿渣、电石渣为固化剂对疏浚淤泥固化处理,开展了毛细浸润干湿循环与蒸馏水、海水、硫酸镁等侵蚀耦合作用下固化淤泥外观、无侧限抗压强度及损伤研究,探究了耦合作用规律、机理和最优固化剂掺量。结果表明:硫酸镁侵蚀与干湿循环耦合作用下试样外观破损最严重、强度降低最明显;增加矿渣掺量可提高固化淤泥耐久性,当矿渣掺量分别为20%和15%时,碱渣掺量不宜超过25%和35%;多次干湿循环与海水和硫酸镁侵蚀耦合作用导致试样随应变迅速达到损伤破坏状态;干湿循环与海水侵蚀耦合作用导致试样中生成较多钙矾石和氯化钠结晶,并随循环次数的增加氯化钠结晶增多、试样不均匀性增强、中孔和大孔数量增多;干湿循环与硫酸镁侵蚀耦合作用导致水化硅酸钙等水化产物减少,碱渣掺量过高时还形成膨胀性的二水硫酸钙析出,导致固化淤泥耐久性下降;毛细浸润干湿循环与侵蚀耦合作用对固化淤泥产生严重的宏观和微观损伤。

淤泥固化填筑路基施工技术在滨海地区的应用

该文以滨海地区某市政道路为例,探究淤泥固化填筑路基施工技术的应用。该工程中选用由水泥、石灰和V粉按照5∶2∶2质量比组合成的固化剂,掺量为淤泥质量的14%。在排水降水和场地平整的基础上,摊铺淤泥并撒上固化剂,使用拌合机将2种材料充分拌匀后,再次摊平并分别使用双钢轮压路机、胶轮压路机进行多次碾压。然后进行压实度、平整度等指标的检测,结果表明各项指标均达到相关标准。最后使用石灰土进行路基顶面封层,防止路基结构层与淤泥固化填筑路基中间形成“软弱层”,进一步提高淤泥固化填筑路基的承载力。

河道淤泥疏浚及处置技术在圩区农村水系整治中的应用与思考

为了有效改善圩区河道淤积严重导致的水动力不足、河道功能减弱这一现状,本文以高淳区水系连通及农村水系综合整治试点县项目为例,提出了适用于南方圩区河道的清淤方式、淤泥就近处置方案等方面的做法和经验,成果可为圩区河道生态清淤或综合治理工程提供有效借鉴。

某海底管道沉积物类型及冲淤变化分析

海底输气管道须承受海底环境的变化,如发生管道安全事故,将带来巨大的损失。通过方案设计、资料收集、现场调查、样品采集、实验室测试、资料分析整理等工作,分析海底管道路由走廊区域范围内的海底沉积物类型及其分布情况,同时通过图件比对、数据分析,研究路由区海岸岸线和海床的变化特征,判断项目区海底底质的稳定状态,为管道工程设计、保护方案选择提供基础资料,以保证管道在海底长期运行中的稳定性。

Holocene Yellow Silt Layers and the Paleoclimate Event of 8200 a B.P.in Lop Nur,Xinjiang,NW China

Many yellow silt layers have been identified in the Holocene sediments in the last lake of Lop Nur (playa), Xinjiang, northwestern China. Statistics of drill-hole cores have revealed more than one hundred layers, which exhibit regularity in time sequence. Study has further verified that these yellow silt layers were deposited through eolian processes. The time-frequency distribution diagram shows an obvious peak occurring at about 8200 a B.P., which is consistent with the dry, windy and cold climate event occurring at 8200 a in other places around the world. Therefore, this event is regarded as a response to the global climate change.

黏粉土互层软土环境下深基坑降水技术研究与风险管控

长三角地区复杂的土层结构和地下水环境对基坑工程降水提出了严峻挑战。以上海市漕宝路快速路新建工程为例,针对该工程中黏土与粉土互层、疏干难度大等问题,制定了科学合理的疏干降水和防突涌减压方案。该方案采取了靠近支撑布置降水井、开挖期间不间断降水以及分阶段控制降水等优化措施。通过建立三维数值模型,模拟了基坑开挖和降水过程中的地下水流场,结果表明该方案能够有效降低各区域地下水位,满足工程降水要求,可为类似工程提供科学依据与实用参考。

Analysis of Wave-Induced Liquefaction in Seabed Deposits of Silt

The dynamic stress introduced in half elastic space by wave loading is characterized by the equation between the magnitude of half cyclic axial stress and cyclic torsion shear stress and the principal stress, whose direction rotates continuously and compression stress on seabed can be calculated by the use of small amplitude wave theory. With relationship curves of saturated silt of liquefaction cycles and cyclic stress ratios obtained by cyclic triaxial-torsional coupling shear tests and curve fitting method to different data points of relative density, it is suggested that the cyclic stress ratio corresponding to constant liquefaction impedance be taken as the critical cyclic stress ratio which implies liquefaction. There exists a linear relationship between critical cyclic stress ratio and relative density under different relative densities. Empirical formula for critical cyclic stress ratios of seabed liquefaction induced by wave loading under different relative densities is established. The possibility of seabed silt liquefaction and its influence factors are analyzed based on the small-amplitude wave theory and the data acquired in laboratory tests.

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.

Salinity effect on the compaction behaviour,matric suction,stiffness and microstructure of a silty soil

To better understand the salinity effect on the compaction behaviour of soil,standard Proctor compaction test was conducted on soil samples with different salinities.Matric suction and small-strain shear modulus,G_(max),were determined and pore size distribution was also investigated on samples statically compacted at different water contents.Results showed that with the decrease of soil salinity from initial value of 2.1‰(g of salt/kg of dry soil)to zero,the maximum dry density increased and the optimum water content decreased,whereas there was no significant change with the increase of soil salinity from 2.1‰ to 6.76‰.Interestingly,it was observed that G_(max) also decreased when the soil salinity decreased from initial value of 2.1‰ to zero and kept almost constant when the soil salinity increased from 2.1‰ to 6.76‰,for dry samples with similar matric suction and also for samples compacted at optimum state and on wet side whose matric suctions were slightly different due to the difference in remoulded water content.Furthermore,the effect of salinity on compaction behaviour and G_(max) decreased for samples compacted from dry side to wet side.The pore size distribution exhibited bi-modal characteristics with two populations of micro-and macro-pores not only for samples compacted on dry side and at optimum state,but also for those compacted on wet side.Further examination showed that the modal size of micro-pores shifted to lower values and that of macro-pores shifted to higher values for saline soil compared to the soil without salt.

CALCULATION AND PREDICTION FOR MUDDY BEACH PROTECTION AND SILTATION ACCELERATION

This paper firstly deals with the two different siltation patterns with siltation accelerating project on sandy beach and muddy beach, and then puts forward the calculation method for siltation of the project on muddy beach based on the behavior of suspension and settlement of fine sediment particles. This method not only can qualitatively explain quite a number of natural phenomena, but also is examined by practical projects. Therefore, this method is of important practical significance in the practice of foreshore reclamation and beach protection as well as siltation acceleration.

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.

Effect of dry density on the liquefaction behaviour of Quaternary silt

Quaternary silt is widely distributed in China and easily liquefies during earthquakes. To identify the influence of the dry density on the liquefaction behaviour of Quaternary silt, 40 cyclic triaxial liquefaction tests were performed on loose silt(dry density rd=1.460 g/cm^3) and dense silt(rd=1.586 g/cm^3) under different cyclic stress ratios(CSRs) to obtain liquefaction assessment criteria, determine the liquefaction resistance, improve the excess pore water pressure(EPWP) growth model and clarify the relationship between the shear modulus and damping ratio. The results indicate that the initial liquefaction assessment criteria for the loose and dense silts are a double-amplitude axial strain of 5% and an EPWP ratio of 1. The increase in the anti-liquefaction ability for the dense silt is more significant under lower confining pressures. The CSR of loose silt falls well within the results of the sandy silt and Fraser River silt, and the dense silt exhibits a higher liquefaction resistance than the sand-silt mixture. The relationships between the CSR and loading cycles were obtained at a failure strain of 1%. The EPWP development in the dense and loose silts complies with the "fast-stable" and "fast-gentle-sharp" growth modes, respectively. The power function model can effectively describe the EPWP growth characteristics of the dense silt. Finally, based on the liquefaction behaviour of silt, a suggestion for reinforcing silt slopes or foundations is proposed.

Characteristics of Pore Water Pressure of Saturated Silt Under Wave Loading

The characteristics of dynamic stress in the seabed under wave loading are constant principal stress and continuous rotation of the principal stress direction. Cyclic triaxial-torsional coupling shear tests were pefformed on saturated silt by the hollow cylinder apparatus under different relative densities, deviator stress ratios and vibration frequencies to study the development of pore water pressure of the saturated silt under wave loading. It was found that the development of pore water pressure follows the trend of ＂fast - steady - drastic＂. The turning point from fast to steady stage is not affected by relative density and deviator stress ratio. However, the turning point from steady to drastic stage relies on relative density and deviator stress ratio. The vibration cycle for the liquefaction of saturated silt decreases with increasing deviator stress ratio and increases with relative density. The vibration cycle for the liquefaction of the saturated silt increases with vibration frequency and reaches a peak value, after which it decreases with increasing vibration frequency for the relative density of 70%. But the vibration cycle for the liquefaction of saturated silt increases with vibration frequency for the relative density of 30%. The development of pore water pressure of the saturated silt is influenced by relative density and vibration frequency.