Influences of different modifiers on the disintegration of improved granite residual soil under wet and dry cycles

The disintegration of granite residual soil is especially affected by variations in physical and chemical properties. Serious geologic hazards or engineering problems are closely related to the disintegration of granite residual soil in certain areas. Research on the mechanical properties and controlling mechanisms of disintegration has become a hot issue in practical engineering. In this paper, the disintegration characteristics of improved granite residual soil are studied by using a wet and dry cycle disintegration instrument, and the improvement mechanism is analyzed. The results show that the disintegration amounts and disintegration ratios of soil samples treated with different curing agents are obviously different. The disintegration process of improved granite residual soil can be roughly divided into 5 stages:the forcible water intrusion stage, microcrack and fissure development stage, curing and strengthening stage, stable stage, and sudden disintegration stage. The disintegration of granite residual soil is caused by the weakening of the cementation between soil particles under the action of water. When the disintegration force is greater than the anti-disintegration force of soil, the soil will disintegrate. Cement and lime mainly rely on ion exchange agglomeration, the inclusion effect of curing agents on soil particles, the hard coagulation reaction and carbonation to strengthen granite residual soil. Kaolinite mainly depends on the reversibility of its own cementation to improve and strengthen granite residual soil. The reversibility of kaolinite cementation is verified by investigating pure kaolinite with a tensile, soaking, drying and tensile test cycle. Research on the disintegration characteristics and disintegration mechanism of improved granite residual soil is of certain reference value for soil modification.

Effect of SAP on Properties of High Performance Concrete under Marine Wetting and Drying Cycles

The internal curing effect of superabsorbent polymer(SAP) on the properties of high performance concrete(HPC) under marine wetting and drying cycles(WD cycles) was investigated. Compressive strength, hydration and chloride migration were experimentally investigated and the results were evaluated by compasison with those under fresh water curing(FW). Water absorption and porosity were also evaluated only under WD cycles. The results showed the important influence of wetting and drying cycles on the properties of SAP modified HPC properties. Carefully designed, SAP minimized the long-term compressive strength of HPC under marine WD cycles. The hydration rate was faster in the initial curing, but became lower as compared with that cured in FW. In addition, SAP improved the long-term water absorption resistance and chloride migration resistance of HPC under marine WD cycles. The examination of the porosity showed a lower increase of the volume of capillary pores in SAP modified HPC under long term WD cycles compared with that without SAP. Therefore, internal curing by SAP could improve the durability properties of HPC under marine WD cycles.

Temporal Microbial Response to Wetting-Drying Cycles in Soils within and Outside the Influence of a Shrub in the Sahel

Piliostigma reticulatum is a native woody shrub found in cropped fields in the Sahel and has been shown to increase crop productivity and soil quality. Frequently occurring drying and rewetting cycles (DRW) may alter the soil quality beneath these shrubs. We investigated the effect of DRW cycles on microbial community in soil beneath and outside the P. reticulatum canopy and the roles of this shrub in the adaptation of the microbial community to abiotic stress. Soils were incubated in a climate controlled chamber for 45 days, after exposure to 10 consecutive days of DRW cycles at 75% of water holding capacity (WHC). Basal respiration, β-glucosidase activity, microbial biomass carbon (MBC), and available nitrogen (;) were measured at 2, 30, and 45 days after soil exposed to the DRW cycles. MBC increased significantly two days after the DRW cycles and was greater for soil beneath the shrub canopy compared with soil outside the shrub canopy. PCA analysis based on basal respiration, microbial biomass carbon, available nitrogen, and β-Glucosidase activity resulted in a tight clustering in the beneath shrub soil samples. Soils incubated for more than 30 days after DRW cycles had higher available nitrogen content than soils incubated for less than 30 days. Soil from beneath the shrub canopy significantly improved soil resilience based on β-glucosidase activity. Soil from beneath the shrub canopy also had higher nutrient levels and greater microbial activity even when subjected to DRW cycles, potentially improving the ability of crops to withstand in-season drought when they are adjacent to shrubs. The work should bring our scientific community into a more comprehensive assessment of potential effects of a crop-shrub intercropping that may allow for increased crop yields in semi-arid ecosystems under drought conditions.

Effect of cyclic drying and wetting on engineering properties of heavy metal contaminated soils solidified/stabilized with fly ash

Solidification/stabilization （S/S） is one of the most effective methods of dealing with heavy metal contaminated soils. The effects of cyclic wetting and drying on solidified/stabilized contaminated soils were investigated. A series of test program, unconfined compressive strength （UCS） test, TCLP leaching test and scanning electron microscopy （SEM） test, were performed on lead and zinc contaminated soils solidified/stabilized by fly ash. Test results show that UCS and the leaching characteristics of heavy metal ions of S/S contaminated soils are significantly improved with the increase of fly ash content. UCS of S/S soils firstly increases with the increase of the times of drying and wetting cycles, after reaching the peak, it decreases with it. When the pollutant content is lower （1 000 mg/kg）, the TCLP concentration first slightly decreases under cyclic drying and wetting, then increases, but the change is minor. The TCLP concentration is higher under a high pollutant content of 5 000 mg/kg, and increases with the increase of the times of drying and wetting cycles. The results of scanning electron microscopy （SEM） test are consistent with UCS tests and TCLP leaching tests, which reveals the micro-mechanism of the variations of engineering properties of stabilized contaminated soils after drying and wetting cycles.

The first power generation test of hot dry rock resources exploration and production demonstration project in the Gonghe Basin,Qinghai Province,China

Hot dry rock(HDR)is a kind of clean energy with significant potential.Since the 1970s,the United States,Japan,France,Australia,and other countries have attempted to conduct several HDR development research projects to extract thermal energy by breaking through key technologies.However,up to now,the development of HDR is still in the research,development,and demonstration stage.An HDR exploration borehole(with 236℃ at a depth of 3705 m)was drilled into Triassic granite in the Gonghe Basin in northwest China in 2017.Subsequently,China Geological Survey(CGS)launched the HDR resources exploration and production demonstration project in 2019.After three years of efforts,a sequence of significant technological breakthroughs have been made,including the genetic model of deep heat sources,directional drilling and well completion in high-temperature hard rock,large-scale reservoir stimulation,reservoir characterization,and productivity evaluation,reservoir connectivity and flow circulation,efficient thermoelectric conversion,monitoring,and geological risk assessment,etc.Then the whole-process technological system for HDR exploration and production has been preliminarily established accordingly.The first power generation test was completed in November 2021.The results of this project will provide scientific support for HDR development and utilization in the future.

Investigation on microstructure evolution of clayey soils: A review focusing on wetting/drying process

Variability in moisture content is a common condition in natural soils.It influences soil properties significantly.A comprehensive understanding of the evolution of soil microstructure in wetting/drying process is of great significance for interpretation of soil macro hydro-mechanical behavior.In this review paper,methods that are commonly used to study soil microstructure are summarized.Among them are scanning electron microscope(SEM),environmental SEM(ESEM),mercury intrusion porosimetry(MIP)and computed tomography(CT)technology.Moreover,progress in research on the soil microstructure evolution during drying,wetting and wetting/drying cycles is summarized based on reviews of a large body of research papers published in the past several decades.Soils compacted on the wet side of op-timum water content generally have a matrix-type structure with a monomodal pore size distribution(PSD),whereas soils compacted on the dry side of optimum water content display an aggregate structure that exhibits bimodal PSD.During drying,decrease in soil volume is mainly caused by the shrinkage of inter-aggregate pores.During wetting,both the intra-and inter-aggregate pores increase gradually in number and sizes.Changes in the characteristics of the soil pore structure significantly depend on stress state as the soil is subjected to wetting.During wetting/drying cycles,soil structural change is not completely reversible,and the generated cumulative swelling/shrinkage deformation mainly derives from macro-pores.Furthermore,based on this analysis and identified research needs,some important areas of research focus are proposed for future work.These areas include innovative methods of sample preparation,new observation techniques,fast quantitative analysis of soil structure,integration of microstructural parameters into macro-mechanical models,and soil microstructure evolution charac-teristics under multi-field coupled conditions.

Strength weakening and its micromechanism in water–rock interaction,a short review in laboratory tests

Water–rock interaction(WRI)is a topic of interest in geology and geotechnical engineering.Many geological hazards and engineering safety problems are severe under the WRI.This study focuses on the water weakening of rock strength and its infuencing factors(water content,immersion time,and wetting–drying cycles).The strength of the rock mass decreases to varying degrees with water content,immersion time,and wetting–drying cycles depending on the rock mass type and mineral composition.The corresponding acoustic emission count and intensity and infrared radiation intensity also weaken accordingly.WRI enhances the plasticity of rock mass and reduces its brittleness.Various microscopic methods for studying the pore characterization and weakening mechanism of the WRI were compared and analyzed.Various methods should be adopted to study the pore evolution of WRI comprehensively.Microscopic methods are used to study the weakening mechanism of WRI.In future work,the mechanical parameters of rocks weakened under long-term water immersion(over years)should be considered,and more attention should be paid to how the laboratory scale is applied to the engineering scale.

干湿循环与加载先后顺序对砂泥岩混合料压缩特性的影响

为研究干湿循环与加载先后顺序对砂泥岩混合料压缩特性的影响,针对不同干湿循环次数、浸水时间和水温处置下的砂泥岩混合料,开展先干湿循环后加载、先加载后干湿循环的单向压缩试验。结果表明,两种试验方法所得砂泥岩混合料压缩量均随干湿循环次数增加、浸水时间增长、水温增高而增大;压缩量与干湿循环次数呈对数关系、与浸水时间呈幂函数关系、与水温呈线性关系,并推导出相应的压缩量计算公式;试验结果及理论分析均得出先干湿循环后加载的压缩量大于先加载后干湿循环的压缩量。

氯盐干湿循环作用下表面开槽CFRP-混凝土界面抗剪性能试验

为探究氯盐干湿循环作用下表面开槽CFRP-混凝土界面抗剪性能,开展干湿循环(0 d、60 d和120 d)不同沟槽形状(矩形、正梯形和倒梯形)的单搭接拉伸剪切试验,研究失效模式和断裂能的变化及影响最大剪应力的因素,结合试验结果推导了考虑干湿循环的界面黏结滑移本构方程,并通过数值模拟验证其有效性。结果表明:随干湿循环进行,表面开槽法失效模式由CFRP断裂破坏转变为剥离破坏;120 d界面断裂能下降量较未开槽法减少60.04%~69.42%;正梯形组120 d最大剪应力相比其他表面开槽形状提升7.18%~9.48%。表面开槽法在氯盐干湿循环作用下具有较好的抗剪性能,建立的界面本构劣化方程适用于氯盐干湿循环作用下表面开槽CFRP-混凝土界面黏结性能的分析和模拟。

浮选颗粒条栅结构表面润湿行为特性研究

矿物颗粒间表面润湿性差异是浮选成功的关键,受表面化学性质与物理形貌结构的双重影响。为进一步明确表面物理形貌结构对液滴在矿物颗粒表面上润湿行为的影响,采用光刻显影技术制备了5种具有不同粗糙度系数和表面面积分数的条栅结构聚二甲基硅氧烷(PDMS)表面,并利用自制的动/静态接触角测量系统及润湿三相接触线行为测试系统对液滴在PDMS表面上的润湿行为进行了测试。动/静态接触角测试结果表明:当表面粗糙度系数相同时,固体表面面积分数增加,条栅结构表面不同润湿方向上的接触角均呈减小趋势,而当表面面积分数相同时,条栅结构表面不同润湿方向上的接触角则与固体表面粗糙度系数呈正相关;此外,各样品表面垂直于条栅结构方向的动/静态接触角均大于平行方向(即θ_(⊥)>θ_(∥)),且不同润湿方向上接触角的差异随样品表面润湿性的增强而减小。动态接触角测试结果还表明:表面接触角滞后(Δθ=θ_(a)-θ_(r))与表面面积分数呈正相关,而与表面粗糙度系数呈负相关,且前进与后退接触角的预测值与试验值基本吻合,说明动态接触角能够真实地反映固体表面润湿性;此外,在液滴滚动时,其运动行为总是周期性地发生后端接触线先从固体表面分离,而后液滴重新与固体表面发生黏附形成新的前端接触线的过程,这种运动特性在不同条栅结构表面上完全相同。润湿三相接触线行为测试结果表明:液滴在条栅结构表面优先沿着条栅结构方向润湿或去润湿,而跨越条栅结构润湿时,受表面微结构的“钉扎”作用,润湿半径远小于平行润湿方向,且三相接触线在不同条栅结构表面的移动均呈现“解钉—钉扎—再解钉—再钉扎”的一种断续周期性过程。研究结果深化了矿物颗粒表面物理形貌结构对其润湿行为特性的影响,可为后续通过表面形貌调控颗粒表面润湿性起到一定的理论支撑作用。

干湿循环作用下片岩片理面抗剪性能劣化实验设计

为揭示片岩片理面在干湿循环作用下抗剪性能劣化规律,选取云母石英片岩设计相应的直剪实验方案进行研究,并将该方案应用于实验教学。实验结果表明:干湿循环作用下,片理面抗剪性能劣化明显,干湿循环20次后,粘聚力和内摩擦角分别下降49.05%、15.34%,粘聚力下降幅度约为内摩擦角的3.2倍;片理面不断渗出黄褐色物质浸染岩样,使片理面逐渐显化,且逐渐沿片理面产生裂隙并不断向岩石内部扩展发育;片理面是水进出片岩内部的良好通道,水可将片理面间的泥质胶结物和可溶性矿物溶解并带出,使得片理面间胶结物及胶结面积逐渐减少,抗剪性能逐渐劣化。该实验教学对培养学生科研创新思维及理论联系实际能力具有重要意义。

砂浆胶-水泥改良膨胀土试验研究

为改良宿迁至连云港段航道膨胀土,选取地表以下0.5~2 m的中等膨胀土,在土中掺入不同比例高分子化合物砂浆胶和水泥混合物,通过直剪试验、膨胀率试验、干湿循环试验和裂隙分析,研究改良后膨胀土的物理力学性质。试验结果表明,随着砂浆胶和水泥的掺入和养护天数增加,膨胀土黏聚力和内摩擦角明显增加,膨胀率减小。改良后的膨胀土裂隙明显减小,且不会随干湿循环次数增加而产生更多裂隙,因此改良后膨胀土强度明显提高、胀缩性明显降低。砂浆胶和水泥改良膨胀土效果显著,成本低,优于其他改良方法,可满足工程需求。

干湿循环下炭质泥岩软弱夹层剪切强度及渗透性演化规律研究

针对云南某露天矿边坡中的炭质泥岩软弱夹层,开展了室内干湿循环加速模拟试验、直接剪切试验和变水头渗透试验,研究了干湿循环作用下炭质泥岩软弱夹层抗剪强度和渗透性的演化规律,分析了循环次数对抗剪强度和渗透系数的影响,结果表明:干湿循环对炭质泥岩软弱夹层的抗剪强度影响显著,不同竖向荷载下,抗剪强度劣化趋势基本相同;随着干湿循环次数的增加,其内摩擦角基本不变,但黏聚力显著减小,且在干湿循环1次时黏聚力减幅最大,2~7次时黏聚力劣化速率较快,在干湿循环超过7次时,炭质泥岩软弱夹层的黏聚力变化速率趋于平缓,最终拟合得出黏聚力与干湿循环次数之间的指数函数关系模型;炭质泥岩软弱夹层的渗透系数和干湿循环次数呈正相关,循环次数在0~4次时渗透系数变化较为平缓,4次之后渗透系数显著增大,在7次循环时达到最大值,之后渗透系数基本不变。研究结果可为类似矿山边坡软弱夹层的强度和渗透系数预测提供参考。

水-温循环作用下千枚岩的动态拉伸特性

为研究水-温耦合作用下0°层理倾角千枚岩的动态拉伸特性变化规律,分别对3组试样进行0、1、3、5、7、8、11次温度循环自然降温、温度循环冷水降温、干湿循环后,采用霍普金森杆试验装置对0°层理倾角千枚岩试样开展动态巴西劈裂试验,从动态拉伸应变曲线、动态峰值抗拉强度、动态弹性模量、能量分析与宏观破坏5个角度研究水、温劣化条件下千枚岩的动态拉伸特性。结果表明:千枚岩应力应变曲线包括极速弹性变形阶段、屈服变形阶段、破坏变形阶段;随着水-温循环次数的增加,千枚岩应力-应变曲线极速弹性变形阶段逐渐缩短,屈服变形阶段的应变增长率不断增大;千枚岩动态峰值抗拉强度呈负指数函数关系变化,耗散能比不断减小;水-温耦合条件下,千枚岩峰值抗拉强度、耗散能比普遍小于温度循环自然降温时;动态冲击下,千枚岩发生贯穿层理的张拉破坏,主要破碎为2块;随着水-温循环次数的增加,千枚岩主碎块发生沿层理面的张拉与穿层理面的剪切复合破坏,千枚岩碎块的平均尺寸不断减小;温度循环冷水降温条件下,千枚岩碎块的平均尺寸更小,且降幅最为显著。

高填方粗粒土干湿循环及蠕变特性三轴试验研究

白鹤滩水电站库区蓄水后,其高填方场地将长期经历水位升降,对于场地的变形和稳定来说十分不利。依托于白鹤滩水电站库区移民安置区消落带高填方场地稳定性研究项目,通过大型常规三轴剪切试验和蠕变试验分析了粗粒土在干湿循环作用和饱水条件下的应力应变关系、剪切形态特征、长期强度、变形规律等,得到主要结论如下:①粗粒土的强度随着干湿循环次数的增加逐渐降低;②干湿循环次数n≤3时,粗粒土试样先剪缩后剪胀,n>3时,粗粒土只有剪缩变形;③粗粒土的峰值偏应力随着干湿循环次数的增加逐渐降低,围压越高干湿循环作用对粗粒土抗剪强度损伤劣化的影响越大;④粗粒土的长期强度较剪切破坏强度有所降低,在低围压下降幅较小,一般情况下可达到剪切破坏强度的80%甚至更高,在高围压下由于颗粒破碎严重粗粒土的长期强度损伤较大。

Effects of dry/wet ratio and pre-immersion on stress corrosion cracking of 7050-T7451 aluminum alloy under wet-dry cyclic conditions

The stress corrosion cracking(SCC) behavior and mechanism of 7050-T7451 aluminum alloy under wet-dry cyclic conditions were investigated. Slow strain rate tests(SSRTs) and electrochemical tests were used to study the effects of dry/wet ratio(DWR) and pre-immersion on SCC.Fracture and side surface characterizations were observed by scanning electron microscopy(SEM).The results demonstrate that SCC susceptibility decreases with an increase of the DWR. With an increase of the pre-immersion time, both continuous pre-immersion(CP) and wet-dry cyclic preimmersion(WDP) samples are more sensitive to SCC, and the cracking mode in the SCC fracture region is intergranular. Furthermore, the effect of WDP on SCC is greater than that of CP when the total time immersed in solution before an SSRT is the same with each other. In fact, each single wetdry cycle can be divided into three processes with respect to the change of solution on samples’ surface. Volatilization of water on the surface results in an increase in solute concentration, thus accelerating corrosion.

根直径及干湿循环对根土复合体抗剪强度影响的试验研究

探究植被根系对土体的加固效应及干湿循环对根土复合体强度的劣化机制,为边坡生态治理及灾害防治提供帮助。开展了不同根直径及干湿循环的根土复合体三轴试验,利用电子显微镜对根土复合体的微观结构进行分析。研究结果表明:新鲜根、饱和根和干燥根的抗拉强度随直径的增大呈幂律减小。干燥根的抗拉强度最大,其次是新鲜根和饱和根。根土复合体的应力—应变曲线表现为持续硬化。随着应变的增大,偏应力先迅速增大后缓慢增加,最终保持稳定。随着根直径的增大,根土复合体的抗剪强度先增大后减小。根直径过小或过大,根对土壤的加固效果减弱。根系显著改变土壤黏聚力,对内摩擦角影响较小。抗剪强度随围压的增加而增大,随干湿循环的增加而减小。随着干湿循环次数的增加,抗剪强度和黏聚力呈线性下降,土颗粒团聚体分解,土体裂缝和孔隙面积呈指数增长。根土复合体的破坏形式为剪胀破坏。考虑干湿循环,修正的根土复合体强度预测模型是有效的,预测结果与试验数据吻合较好。

干湿循环对压实红黏土动强度与动模量影响研究

采用自制一次成型模具制备压实度分别为90%、93%和96%的三轴试样,自制干湿循环试验装置对试样进行喷雾加湿和暖风干燥,定量模拟现场路基土含水率变化过程获得不同湿度和不同干湿循环次数的试样,通过常含水率动三轴试验测试其动强度与动模量变化规律。结果表明:累积应变随振次的变化分为塑性安定型、临界型和破坏型;临界动应力和最大动弹模随压实度的降低而减小,且减小幅度逐渐增大,随含水率的增大压实度的影响减弱;临界动应力和最大动弹模随含水率的增大而减小,临界动应力在含水率大于最优含水率时减小幅度相对较大;临界动应力和最大动弹模随循环次数的增多而降低,且降低幅度逐渐减小。

基于压实与干湿循环综合作用的粉土路堤稳定性演变规律研究

为研究压实和干湿循环综合作用下路堤边坡的长期稳定性,基于室内三轴试验与数值仿真分析,以某高速公路路堤段粉土为研究对象,开展了不同干湿循环次数、压实度下的室内三轴剪切试验,获取了不同干湿循环次数下的抗剪强度参数,并将参数导入至数值仿真模型中开展计算分析,获取了干湿循环对潜在滑移面的影响规律,探索了粉土路堤长期稳定性演变特征。研究表明,压实粉土的强度随干湿循环次数增加而减小,以K=0.93为例,经历干湿循环2、4、6、8次后,黏聚力分别下降24.1%、38.4%、44.1%、51.0%,内摩擦角分别下降11.4%、17.5%、21.9%、25.4%;在不同干湿循环次数下,粉土路堤边坡均存在明显的潜在滑移面,同时滑体上还出现了大量剪切裂隙;路堤边坡在填筑初期的安全系数可满足规范要求,但干湿循环会使路堤的稳定性会出现明显降低,K=0.96、0.93、0.90时,经历8次干湿循环后路堤的安全系数分别下降0.878、0.736、0.587,可见在路堤设计时留足安全储备十分必要,在极端气候偏多的环境下更是应该如此;为提升粉土路堤长期稳定性,提高抵抗病害的韧性,应当重视压实质量和排水。研究成果可为粉土路堤安全储备设计提供有益参考。

干湿冻融循环条件下重塑性黄土的强度劣化规律及非线性模型研究

新疆某地的输水明渠工程途经大面积湿陷性黄土区域,在间歇供水的运行工况及季节性温差变化的共同作用下,经常发生渠坡滑动破坏现象。为深入研究渠坡变形破坏机制,通过开展干湿冻融循环条件下黄土的三轴试验和扫描电镜试验,研究其变形规律及微观机制,最后基于黄土的变形规律对邓肯-张模型进行改进。三轴试验结果表明:随着干湿冻融循环次数的增加,黄土的应力-应变曲线下降,体变曲线上升,且变化幅度越来越小,当循环次数大于5次后,应力-应变曲线和体变曲线基本不变,黏聚力和内摩擦角均呈现出指数函数衰减的变化趋势,其中黏聚力受干湿冻融循环作用的影响较大。电镜扫描试验结果表明:通过扫描电镜进行微观分析,在干湿冻融循环作用下,大的颗粒和团聚体被分裂,颗粒间的胶结物质减少,面接触增加,大孔隙面积占比减少,小孔隙和中孔隙面积占比、三维孔隙率和孔隙圆形程度增加,分形维数下降;三维孔隙率和分形维数与黏聚力呈显著相关,大孔隙面积占比与内摩擦角呈显著相关。由于邓肯-张模型不能合理反映土体的软化现象,采用二次函数对邓肯-张模型进行修改,并通过修改公式对泊松比进行拟合,以此提出改进邓肯-张模型,改进后的模型对不同循环次数下黄土三轴试验结果拟合效果较好。随着循环次数的增加,应力-应变模型参数k和q呈指数函数下降的趋势,应力-应变模型参数o呈指数函数上升的趋势,体变模型参数j、l呈指数函数上升的趋势,体变模型参数t呈指数函数下降的趋势。