Effects of freeze-thaw cycle and dry-wet alternation on slope stability

The typical loess on high slopes along the BaoLan High-speed Rail, China, was selected as the research object. The influence of the freeze-thaw cycle and dry-wet alternation on the shear-strength parameters of the unsaturated loess was investigated by laboratory experimental methods. Moreover, the temperature field, seepage field, and stability of slopes with different gradients were simulated under the effect of the freeze-thaw cycle and dry-wet alternation by using the geotechnical analysis software Geo-Studio. The research results showed(1) when the freeze-thaw cycle was repeated on the slope, with the frozen depth increasing, the melted depth did the same; besides, the closed loop of isotherms formed on the slope;(2) under the action of dry-wet circulation, the negative pore-water pressure and volumetric water content showed an upward tendency. However, owing to the different slope gradients, rainfall infiltration was not the same. As time went by, the differences of the negative pore-water pressure and volumetric water content between the slopes of different gradients continued to increase;(3) with the freeze-thaw cycle and dry-wet alternation increasing, the slope-safety factor decreased. Especially in the early period, the slope-safety factor changed remarkably. For slopes undergoing freeze-thaw action, the slope-safety factor was negatively correlated with the gradient. However, with regard to slopes undergoing dry-wet alternation, the result became more complex because the slope-safety factor was related to both seepage strength and slope grade. Accordingly, further research is needed to study the effect of seepage strength and slope grade on the stability of loess slopes.

Study on stability of permafrost slopes during thawing

A numerical simulation platform that analyzes the variation of the slope factor of safety with time instantaneously is proposed based on heat conduction theory to study the law of stability development of permafrost slopes during thawing.This platform considers ice-water phase change,elastoplastic constitutive behavior and strength reduction in thawing permafrost and can evaluate the factor of safety of permafrost slopes with different slope angles and water contents.Results indicate that under different slope angles and water contents,the evolution of the factor of safety with time displays two stages:nonlinearly decreasing at first and then essentially remaining constant.During the decreasing stage,the plastic slip line overlaps with the thawing front.In this stage,the selfweight of the post-thawed permafrost layer increases continuously while the shear strength of the frozen-thaw interface keeps unchanged.This is the main reason leading to the decrease in the factor of safety.In the second stage,the thawing depth increases continuously while the position of the plastic slip line remains unchanged,resulting in a constant safety factor stage.

Effect of the frozen layer on the stability of cut soil slopes during seasonal freezing and thawing

Research on the stability of soil slopes in seasonally frozen regions has mainly focused on slope failures during the thawing window.There are few studies on slope stability during the freezing window and its subsequent influence on slope failure in the next thawing window.In this paper,soil strength was tested during freezing and thawing to obtain temperature-dependent strength parameters for the simulation of slope stability.Then,the slope's temperature field over an entire year was accurately simulated so that characteristics of the frozen layer could be determined at any time.Based on the above results,the progressive failure modes of frozen soil slopes are discussed.The results show that:1)during the freezing window,depth of the frozen soil layer increases,as does the slope's safety factor,while a yield zone propagates towards the slope shoulder.(2)During the thawing window,the frozen soil layer shrinks in depth while the yield zone continuously expands,which decreases the safety factor.Comprehensive analysis of these results indicate that the frozen layer provides a“toe-locking effect”that increases the safety factor during the freezing window,while it also provides a“dragging effect”that propagates the yield zone towards the slope shoulder.During the thawing window,the“toe-locking effect”gradually diminishes;a continuous sliding surface is formed,which lead to a landslide.The frozen soil layer of the freezing window accelerates the slope sliding in the thawing window.

Freeze-thaw performance of chemically stabilized natural and recycled highway materials

This article provides an overview of several previous studies that investigated the stiffness and strength performance of chemically stabilized roadway materials under winter conditions （freeze-thaw cycling）. The objective of this research was to understand the behavior of different materials stabilized with different type of binders when they were subjected to freeze-thaw cycling. Nine different materials including natural soils （organic soil, clay, silt, sand, and road surface gravel）, reclaimed pavement material, and recycled asphalt pavement stabilized with nine different binders （five different fly ashes, lime, cement, lime kiln dust, cement kiln dust） were discussed. This article investigated how the volume, resilient modulus and unconfined compressive strength of soils/materials stabilized with different binders change in response to freeze-thaw cycling. Overall, the review results indicate that the stiffness and strength of all stabilized materials decrease somewhat with freeze-thaw cycling. However, the reduced strength and stiffness of stabilized materials after freeze-thaw cycling was still higher than that of unstabilized-unfrozen original soils and materials. In addition, materials stabilized with cement kiln dust provided the best performance against freeze-thaw cycling.

Effect of freeze-thaw cycles on uniaxial mechanical properties of cohesive coarse-grained soils

Freeze-thaw cycles are closely related to the slope instability in high-altitude mountain regions. In this study, cohesive coarse-grained soils were collected from a high-altitude slope in the Qinghai–Tibet Plateau to study the effect of cyclic freeze-thaw on their uniaxial mechanical properties. The soil specimens were remolded with three dry densities and three moisture contents. Then, after performing a series of freeze-thaw tests in a closed system without water supply, the soil specimens were subjected to a uniaxial compression test. The results showed that the stress-strain curves of the tested soils mainly performed as strain-softening. The softening feature intensified with the increasing dry density but weakened with an increase in freeze-thaw cycles and moisture content. The uniaxial compressive strength, resilient modulus, residual strength and softening modulus decreased considerably with the increase of freeze-thaw cycles. After more than nine freeze-thaw cycles, these four parameters tended to be stable. These parameters increased with the increase of dry density and decreased with the increasing moisture content, except for the residual strength which did not exhibit any clear variation with an increase in moisture content. The residual strength, however, generally increased with an increase in dry density. The soil structural damage caused by frozen water expansion during the freeze-thaw is the major cause for the changes in mechanical behaviors of cohesive coarse-grained soils. With results in this study, the deterioration effect of freeze-thaw cycles on the mechanical properties of soils should be considered during the slope stability analysis in high-altitude mountain regions.

Compressive strength and frost heave resistance of different types of semi-rigid base materials after freeze-thaw cycles

Freeze-thaw damage is the most common disease of semi-rigid bases in cold regions, which may greatly affect the dura- bility of roadways. In this study, the compressive strength and frost resistance of four different types of semi-rigid bases （lime-fly ash-stabilized sand, cement-stabilized sand, lime-fly ash-stabilized gravel, and cement-stabilized gravel） are assessed by varying the materials content. Based on freeze-thaw and compressive strength tests, this paper presents the performance of the different materials, each having different physical properties, and the optimal amounts of materials contents are proposed.

玄武岩纤维对聚氨酯改性沥青混合料水稳定性提升研究

为解决聚氨酯改性沥青混合料水稳定性不良的缺陷,通过浸水马歇尔试验、冻融循环条件下的劈裂试验、低温弯曲试验,研究不同玄武岩纤维掺量下聚氨酯改性沥青混合料的抗水损害能力。结果表明:在冻融循环作用下,玄武岩纤维降低了沥青混合料水损作用造成的空隙率变化,增强了沥青间的粘附性,当纤维掺量为0.3%时,其提升作用最强,残留稳定度和劈裂强度比分别提升了10.9%、32.3%,有效降低了冻融循环引起的弯拉强度与弯拉应变的下降速率,增强沥青混合料之间的粘结力,聚氨酯沥青混合料的水稳定性能得到提高。

酸性花岗岩沥青混合料水稳性试验

为提高高湿热地区花岗岩沥青混合料的长期水稳性能,分别进行单掺3%水泥、4%水泥及30%消石灰水浸泡处治,通过冻融、冻融烘循环的劈裂试验来评价酸性花岗岩沥青混合料的长期适用性与水稳性能,并与未处治酸性花岗岩沥青混合料进行对比分析。结果表明:随着冻融、冻融烘次数的增加,处治后酸性花岗岩沥青混合料在3种试验条件下的劈裂强度与残留强度比呈整体下降趋势;冻融循环条件下,4%水泥>3%水泥>30%消石灰水>未处治集料;冻融烘循环条件下,4%水泥>3%水泥>30%消石灰水>未处治集料。

冻融作用对露天矿山边坡稳定性的影响分析研究

为研究冻融作用对不同倾角层状岩质边坡稳定性的影响,以西藏墨竹工卡县高寒地区某露天矿山为研究对象,利用极限平衡法,通过岩土工程仿真分析软件GEO-Studio计算获得边坡的稳定安全系数,对冻融前后不同倾角层状岩质边坡的安全系数进行对比分析,研究了冻融和倾角对层状岩质边坡稳定性的影响。结果表明:(1)随着设计边坡角度逐步增加,冻融前后的边坡安全系数逐渐降低,冻融前下降幅度16.2%~32.6%,冻融后下降幅度15.2%~28.2%;(2)冻融作用后,边坡岩体黏聚力及内摩擦角有所下降,冻融后边坡整体安全系数较冻融前下降0.86%~3.32%,冻融对边坡整体稳定性有一定的影响。本研究成果对冻土地区边坡的损坏及防控具有一定的指导及参考价值。

冻融损伤过程中纤维加筋土的抗压性能与裂隙演化

冻融损伤土的微观结构,土中产生微裂隙,宏观上表现为土的力学性能下降。文章完成了石灰固化土和纤维与石灰加筋固化土的冻融试验、无侧限抗压强度试验、CT扫描试验,分析冻融损伤过程中石灰固化土和纤维与石灰加筋固化土的抗压性能与裂隙演化特征,评价纤维对提高土的抗冻融性能的积极作用。结果表明:石灰固化土、纤维与石灰加筋固化土的抗压强度与破坏应变均随冻融次数的增加呈阶段性下降,即降幅较大阶段、降幅较小阶段和强度基本稳定阶段,纤维加筋显著提高了土的抗变形性能;土的压实度越大,纤维加筋提高土的力学性能就越明显;冻融过程中,裂隙主要分布在试样的表面、上部和下部,面裂隙率随扫描层数的增加呈先减小后增大的变化规律;纤维与石灰加筋固化土的体裂隙率、裂隙长度均值、裂隙宽度均值均小于石灰固化土,纤维加筋延缓了裂隙的形成、发展与连通。纤维与石灰加筋固化土的抗压性能与抗冻融性能显著优于石灰固化土,纤维加筋减弱了冻融土的微观结构损伤程度。

水泥-石灰和水泥-稻壳灰稳定土的力学性能和冻融耐久性研究

为研究水泥-石灰和水泥-稻壳灰对土体进行加固良的效果及掺量,利用水泥、石灰和稻壳灰分别以水泥∶石灰=1∶1和水泥∶稻壳灰=1∶1制备两种稳定掺料。按照掺入比分别0%、2.5%、5%、7.5%和10%制备稳定土试样,并通过力学试验以及冻融试验对两种稳定土的三轴力学特性以及抗冻融循环的性能进行研究。结果表明:随着围压、稳定掺料和龄期的增加,稳定土的强度逐渐增加;脆性也明显增强;稳定土在3~7 d的强度增长率明显大于7~28 d的强度增长率,且在相同条件下,水泥-石灰稳定土的强度大于水泥-稻壳灰稳定土的强度。冻融循环后质量损失率和超声波变化规律表明土样的冻融耐久性顺序为:水泥-稻壳灰稳定土>水泥-石灰稳定土>纯土。

剪切与冻融对Pickering乳液稳定性的影响

Pickering乳液是用固体颗粒代替传统表面活性剂的新型乳液。与传统乳液相比,具有稳定性高,环境友好,安全性高等优势。目前,Pickering乳液被广泛应用于食品领域,例如应用于通过冷冻延长保质期的酱汁、奶油或将冷冻作为必备工艺的冰淇淋等产品中。剪切与冻融对Pickering乳液稳定性的应用有重要意义,剪切是乳液制备过程中的关键工艺,在产品运输储存中会发生冻融,二者均会影响Pickering乳液的稳定性,从而影响产品品质。本文综述剪切方式与冻融对Pickering乳液稳定性的影响因素及改善其冻融稳定性的方法,旨在提高冷冻食品的品质,拓展Pickering乳液冻融稳定性的应用。

奥扎格雷氨丁三醇注射用浓溶液使用中及低温冻融稳定性研究

目的 考察奥扎格雷氨丁三醇注射用浓溶液使用中及低温、冻融稳定性,为其临床使用、贮藏和运输提供参考。方法 奥扎格雷氨丁三醇注射用浓溶液分别采用0.9%氯化钠注射液和5%葡萄糖注射液稀释,于0,2,4,6,8和24 h检测配伍后溶液的性状、pH、有关物质、不溶性微粒、可见异物及含量;奥扎格雷氨丁三醇注射用浓溶液分别经低温(2~8℃)和冻融(-10~-20℃)各3个循环,考察性状、pH、有关物质、不溶性微粒、可见异物及含量的变化。结果 奥扎格雷氨丁三醇注射用浓溶液分别用0.9%氯化钠注射液与5%葡萄糖注射液稀释后,24 h内各项检测指标均符合规定,且与0时相比无明显变化;奥扎格雷氨丁三醇注射用浓溶液经历低温、冻融各3个循环,各检测指标也均符合规定,且与0时相比无明显变化。结论 奥扎格雷氨丁三醇注射用浓溶液与0.9%氯化钠注射液、5%葡萄糖注射液在24 h内配伍稳定性良好;短期内经历低温或冷冻条件,不影响奥扎格雷氨丁三醇注射用浓溶液的质量。

木薯淀粉和改性淀粉结构特性及其与粉圆品质的关系

【目的】粉圆市场需求量日益增加,探究不同淀粉对粉圆品质的影响,明确淀粉结构特性与粉圆品质的关系,为高品质粉圆的产品开发提供理论依据。【方法】以市售的3种木薯淀粉和2种木薯改性淀粉(羟丙基二淀粉磷酸酯淀粉、醋酸酯淀粉)为原料制作粉圆,分析淀粉的粒径、直链淀粉含量、膨胀度、溶解度、热力学特性和冻融稳定性差异,以及粉圆的质构特性,并对淀粉结构特性与粉圆的质构特性进行相关性分析。【结果】不同木薯淀粉和改性淀粉的粒径、膨胀度和溶解度存在显著差异(P<0.05),改性淀粉的粒径离散度(1.17~1.27)、膨胀度(30.48%~30.91%)显著高于木薯淀粉(粒径离散度0.89~1.08、膨胀度24.60%~26.38%)。淀粉的离散度、膨胀度与粉圆的硬度、咀嚼性具有显著负相关性(P<0.05),淀粉的溶解度与粉圆的粘性具有显著正相关性(P<0.05)。5种淀粉的热力学特性与冻融稳定性同样存在显著差异(P<0.05),改性淀粉的初始凝胶温度(55.45~59.90℃)和析水率显著低于木薯淀粉的初始凝胶温度(63.80~65.00℃)和析水率。淀粉的凝胶温度、焓变和析水率与粉圆的硬度、咀嚼性具有显著正相关性(P<0.05)。【结论】不同品牌木薯淀粉的粒度分布离散度、膨胀度和冻融稳定性与粉圆的硬度和咀嚼性具有显著相关性。3种木薯淀粉中,以TPK木薯淀粉制作的粉圆品质最好;改性淀粉具有较高的膨胀度和冻融稳定性,能降低粉圆的硬度和咀嚼性,具有抗老化效果,适合用于速冻粉圆和免煮速冻粉圆加工。

挤压体系中可得然胶对小麦淀粉回生特性和冻融稳定性的影响

小麦淀粉的回生现象和较差的冻融稳定性是限制面制品加工的重要原因。为探索一种有效抑制小麦淀粉回生及改善其冻融稳定性的方法,该文研究了挤压体系中不同质量分数的可得然胶对小麦淀粉回生特性和冻融稳定性的影响,利用差示扫描量热仪、X-射线衍射和傅里叶红外光谱等技术表征了可得然胶-小麦淀粉复合物的分子结构,并结合化学试剂处理、质构仪和扫描电镜探讨了可得然胶与小麦淀粉的结合机制。结果表明:随着可得然胶浓度的增加,可得然胶-小麦淀粉复合物的回生值和析水率先降低后增加;与挤压小麦淀粉相比,添加质量分数0.6%的可得然胶能够显著提高小麦淀粉的糊化温度(P<0.05),并降低小麦淀粉的相对结晶度、短程有序性和碘结合力,抑制直链淀粉的重结晶;挤压体系中可得然胶与小麦淀粉主要通过氢键和弱的静电相互作用结合,使小麦淀粉的结构更加致密,从而抑制小麦淀粉的回生并改善其冻融稳定性,该研究可为开发抗回生和低析水率的挤压小麦淀粉基食品提供参考。

基于稀土氧化物示踪法探究冻融循环对黑土团聚体周转的影响

为区分土壤团聚体形成和破碎过程,阐明冻融循环对黑土土壤结构的影响,本文利用稀土氧化物(REOs)示踪技术,通过室内模拟试验,探究不同初始含水量(50%田间持水量(T50)vs.100%田间持水量(T100))和冻融循环次数(0次、3次、6次、12次和20次)对团聚体粒径分布、平均质量直径(MWD)以及团聚体周转过程的影响。结果表明:同一初始含水量下,随着冻融循环次数的增加,MWD、>0.25mm和<0.053mm团聚体含量显著降低,0.25~0.053mm团聚体含量显著增加(P<0.05)。6次冻融循环后,T50处理下的MWD显著高于T100处理(P<0.05),5~2mm和<0.25mm团聚体含量无显著差异。除5~2mm团聚体外,冻融循环处理下,相邻粒级团聚体之间周转更为激烈。在同一冻融循环次数下,5~2 mm团聚体向0.25~0.053 mm团聚体的破碎量在T100处理下显著高于T50处理(P<0.05)。冻融循环促进了>0.25 mm团聚体的破碎和<0.053mm团聚体的团聚,表现为0.25~0.053mm团聚体的累积。冻融循环过程中,MWD与各粒径团聚体相对形成量呈显著正相关,与其相对破碎量呈显著负相关(P<0.05)。随着冻融循环次数的增加,各粒径团聚体周转时间显著增加(P<0.05)。同一冻融循环次数下,>0.25mm团聚体的周转时间高于<0.25mm团聚体,T100处理下的团聚体周转时间显著高于T50处理(P<0.05)。综上所述,冻融循环次数和土壤初始含水量通过影响团聚体形成和破碎过程改变土壤结构的稳定性。本研究结果可为进一步探究冻融循环下黑土土壤结构变化提供理论依据。

冻融循环作用对东北农田黑土团聚体及有机碳的影响

为研究冻融循环作用对东北农田黑土土壤团聚体及结合碳的影响,本研究以黑龙江省海伦市农田黑土为研究对象,利用室内培养试验研究了-9、-18、-26℃3个温度下冻融频次对农田黑土团聚体及有机碳含量的影响。结果表明:随着冻融循环次数的增加,1~0.5 mm和0.25~0.053 mm团聚体含量在3种冻融温度下均发生了显著变化(P<0.05)。与冻融循环1次相比,在相同温度下冻融循环17次后1~0.5 mm团聚体含量在-9、-18、-26℃下分别降低了68.53%、10.91%和40.96%,0.25~0.053 mm团聚体含量分别升高了10.93%、40.89%和99.72%。在-9℃下土壤团聚体分形维数显著升高(P<0.05),由2.09增加到2.74,在-18、-26℃下则变化幅度较小,分别变化了0.1和0.05。土壤团聚体结合碳随着冻融频次的增加没有出现显著的变化(P>0.05),在-18℃和-26℃下,<0.053 mm团聚体有逐渐降低的趋势,在冻融循环17次后分别降低了10.31%和13.73%。冻融作用会显著降低东北农田黑土土壤团聚体的稳定性,冻融作用会显著降低1~0.5 mm团聚体含量并提高0.25~0.053 mm团聚体含量(P<0.05);冻融次数和冻融温度均是影响土壤团聚体稳定性的重要因素。

高寒地区某高陡露天矿山边坡冻融循环条件下稳定性分析

为分析西部高寒高海拔地区某露天矿山设计边坡在冻融影响下的稳定性及变形破坏特征,本文参考设计情况选定了典型计算剖面,并基于岩石的冻融强度试验结果及常规力学计算结果,确定了岩体的计算力学参数;针对冻融对岩体边坡的影响,推断冻融层的分布规律,在此基础上结合地层信息确定数值计算的力学参数赋值;此后采用有限差分程序,定量分析了在自重、岩体开挖、爆破及地震荷载作用下边坡的力学响应特性,并结合强度折减算法,求解得到了对应的潜在滑动面形态及安全系数,结果显示研究边坡安全系数分别为:自重+地下水—1.465,自重+地下水+爆破振动—1.402,自重+地下水+地震—1.363,均满足现行规范要求。本研究成果为高寒地区冻融岩层的力学特性以及受冻融影响露天煤矿的边坡稳定性研究提供了参考。

丙烯酸酯接枝木质素磺酸钠共聚物乳液土壤固化剂的合成及性能

为了研究出稳定性强、经济环保、抗水性良好的有机高分子类土壤固化剂,选取丙烯酸(AA)、丙烯酸丁酯(BA)、苯乙烯(St)为功能单体,以木质素磺酸钠(SLS)进行接枝共聚,利用反应型乳化剂ANPEO10和DNS-86提升乳化效率及稳定性,采取预乳化半连续加料方式和种子乳液法进行接枝反应,制得一种新型高分子乳液土壤固化剂PAAB与PAAS,对其进行结构表征和性能测试。结果表明高分子乳液性能稳定,TSI均小于0.2;加入固化土中,其交联网状结构包覆土颗粒,乳液中的功能基团与土壤中阳离子键合,形成凝胶物质,固化土/水表面接触角可达到91.68,99.21,PAAS固化土养护7 d后抗压强度可达到368.4 kPa,减小了试样土膨胀率及降低了冻融循环作用对固化土的影响。

寒区露天矿板岩冻融力学特性及边坡稳定性研究

为了探究寒区板岩边坡在冻融条件下的力学参数劣化规律及其失稳机理,通过室内冻融循环力学试验,并基于广义Hoek-Brown强度准则计算岩体内聚力和内摩擦角随冻融循环次数的衰减规律,以此修正未考虑冻融损伤的白云鄂博南帮内聚力和内摩擦角块体模型,实现南帮岩体力学参数的时空演化表征,最后通过数值模拟分析白云鄂博铁矿主矿区南帮边坡在冻融效应下的循序破坏机理。结果表明:经20次冻融循环后,矽质板岩、云母化板岩、碳化板岩、断层岩内聚力降低率分别为21.64%、22.66%、28.09%、28.53%,内摩擦角降低率分别为12.76%、14.72%、19.37%、21.35%;在冻融效应下,南帮边坡稳定系数由1.19逐渐降至0.92,1650~1570 m区域剪应变逐渐增大,最终滑体于1570 m平台滑移剪出。