冻融循环作用下木质素磺酸钙改良黄土的力学特性研究     

黄雨灵  张吾渝  季港澳  解邦龙  董超凡 《冰川冻土》2022,44(6):1863-1874

木质素磺酸钙作为一种绿色环保的改良材料,近年来被应用于土体加固领域。为探究木质素磺酸钙对黄土的固化效果,通过开展侧限浸水压缩试验、冻融循环试验、不固结不排水三轴剪切试验、扫描电镜试验和X射线衍射试验,分析冻融循环次数、掺量和围压对木质素磺酸钙改良黄土力学性质和微观机理的影响规律。研究结果表明：掺入木质素磺酸钙,可有效消除黄土的湿陷性。此外,改良黄土的应力-应变曲线随木质素磺酸钙掺量的增加向一般硬化型转变,而随着冻融循环次数的增加,应力-应变曲线向弱硬化型转变。改良黄土的破坏强度随木质素磺酸钙掺量的增加呈先增大后减小的趋势,木质素磺酸钙掺量为1%时破坏强度最高,各掺量改良黄土随冻融循环次数的增加先减小后趋于稳定,同时抗剪强度指标呈现下降的趋势。通过扫描电镜试验和X射线衍射试验,发现改良黄土内部有胶结物生成并填充了土颗粒间的孔隙,使土体密实度提高,进而提高土体强度;而冻融作用导致土颗粒的接触方式由面-面接触向点-点、点-面接触过渡。此外,木质素磺酸钙改良黄土中未发现有新的矿物成分生成,且冻融作用未造成土体矿物成分的消解。  相似文献   

干湿循环效应下玄武岩纤维加筋黄土三轴剪切力学行为研究     

许健  武智鹏  陈辉 《岩土力学》2022,(1):28-36

通过干湿循环效应下的数字图像三轴剪切试验、CT扫描试验及扫描电镜SEM(scanning electron microscopy)试验,研究了玄武岩纤维加筋黄土干湿循环过程的三轴剪切力学行为及微细观结构演化机制。结果表明:随干湿循环次数增加,纤维含量较高试样的三轴剪切鼓胀破坏形态转变为剪切带破坏;干湿循环早期阶段,剪切破坏形态随纤维含量增加,由剪切带破坏转变为鼓胀破坏。干湿循环作用和纤维含量对应力-应变曲线的类型及特征无明显影响,均表现为应变硬化型。破坏偏应力随干湿循环次数增加而逐渐减小,但衰减速率逐渐减小;破坏偏应力随纤维含量增大先增加而后减小,呈抛物线变化特征,存在一个最佳纤维含量为0.6%。CT数均值ME值呈现与破坏偏应力相似的变化规律。干湿循环作用下筋-土界面产生一定的开裂和松弛现象,弱化了纤维的加筋效应,但与素黄土相比,纤维加筋黄土的微观结构表现出显著的整体稳定性。构建了干湿循环效应下玄武岩纤维加筋黄土的宏细观损伤变量,其表现出一致的变化规律。  相似文献   

考虑含水率影响的结构性黄土临界状态模型     

侯乐乐  翁效林  李林  周容名 《岩土力学》2022,43(3):737-748

根据不同初始含水率原状黄土结构性演化规律,基于临界状态土力学理论,以应力、初始含水率和应变为基本变量,提出了一个可以反映原状黄土结构性演化规律及软化特性的临界状态本构模型。模型通过对比不同初始含水率下重塑与原状黄土等向压缩曲线,建立了不同含水率下原状黄土的结构性参数及其演化方程。此外,模型采用非相关联流动法则,以剪胀方程的形式来求解塑性偏应变。模型共计9个材料参数,均可由压缩试验和常规三轴剪切试验求得。通过与已有试验数据的对比发现,本模型不仅可以较好地体现初始含水率对原状黄土结构强度、变形特性以及结构破坏规律的影响,而且能较为合理地预测原状黄土的硬化及软化特性。所建立的结构性黄土临界状态模型为深化黄土力学特性研究提供了可能,同时为有效计算黄土地基湿陷变形提供了一定的理论依据。  相似文献   

桩间黄土卸荷湿陷过程中卸荷量计算方法初探     

金鑫  王铁行  郝延周  赵再昆  张亮  张猛 《岩土力学》2022,43(9):2399-2409

为确定桩间黄土卸荷湿陷过程中卸荷量的合理取值,开展桩−土界面大型剪切试验,研究桩间黄土卸荷湿陷状态下桩−土界面剪切强度、剪切位移及桩−土界面法向力之间的相关关系。结果表明：在桩间土中性点深度范围内,不同竖向应力和含水率状态下的桩−土界面剪切强度可代表桩侧负摩阻力。利用卸荷量与桩侧负摩阻力互为作用力与反作用力的力学原理,并在分析卸荷量随湿陷深度和湿陷进程变化规律的基础上,提出黄土卸荷湿陷过程中卸荷量计算方法,通过对比卸荷量计算值与不同黄土地区桩侧负摩阻力现场实测值,以验证其合理性。该方法不仅为科学评价黄土卸荷湿陷特性提供卸荷作用量化手段,还为相关黄土工程的优化设计提供理论参考依据。  相似文献   

基于原位双环、试坑浸水试验和数值模拟反演的Q3黄土饱和渗透系数对比研究     

蒋小虎  黄跃廷  胡海军  陈铄  陈锐  王崇华  汪慧  康顺祥 《岩土力学》2022,43(11):2941-2951

为准确获取原状Q3黄土的竖向和水平饱和渗透系数,进行了原位、室内试验测试以及数值模拟反演,并应用大型试坑浸水试验检验了所获饱和渗透系数的可靠性。进行了不同内径尺寸的原位双环入渗试验,获取了竖向饱和渗透系数,并应用室内试验测试了竖向和水平饱和渗透系数以及持水曲线;应用COMSOL软件对双环入渗试验进行数值模拟,检验了所测饱和渗透系数的可靠性,利用正交试验获得了最优的竖向和水平饱和渗透系数取值,并利用反演结果对试坑进行数值模拟,将其水分入渗情况与实测值对比。研究结果表明：在现场进行双环入渗试验时选取较大内径的双环获得的竖向饱和渗透系数更为合理。针对双环入渗试验,数值模拟反演所得最优饱和渗透系数在竖向上接近于原位试验所得竖向饱和渗透系数、水平向上接近室内所测水平向饱和渗透系数,竖向饱和渗透系数比水平向饱和渗透系数更加显著地影响水分入渗过程。通过对大型试坑水分入渗情况的验证,检验了反演所得最优饱和渗透系数的可靠性。  相似文献   

Variations in the sensitivity of the optically stimulated luminescence from quartz in the Xifeng section: A spatiotemporal comparison across the Chinese Loess Plateau since the last interglaciation     

《Quaternary Geochronology》2022

The sensitivity of the optically stimulated luminescence (OSL) from quartz is thought to be mainly influenced by source rock (crystallization temperature and quartz defect types) and depositional history (irradiation/bleaching cycles). In this study, the OSL sensitivity of quartz of different grain sizes from loess (L1) and paleosol (S1) layers at the Xifeng section of the Chinese Loess Plateau was analyzed. The OSL sensitivity of the samples from the Xifeng section shows a distinct difference between glacial and interglacial cycles, which is consistent with the patterns observed from magnetic susceptibility (MS) and grain sizes. The highest OSL sensitivity is observed in S1, which is twelve times the lowest sensitivity observed in L1. Moreover, the contribution of the fast component of quartz OSL from the paleosol accounts for more than 90% of the total OSL signal. In contrast, the middle and slow components contribute more in loess, and a significant variation among different aliquots was observed.Comparison of the data obtained from loess sections from different regions, including Xifeng, Luochuan, Jingyuan and Shimao, show significant differences in the magnitudes of OSL sensitivity but a similar pattern between glacial and interglacial periods. The results of this study suggest that, except for the wildfire model proposed to interpret the high OSL sensitivity in paleosol (Zhang, 2018), the shift of wind pattern of westerly wind (i.e., transporting “dim” source from North Tibetan Plateau and northwesterly wind (i.e., transporting “bright” source from Alxa Arid Lands and the subsequent mixture from the different sources may partially contribute to the different OSL sensitivities observed for Xifeng and Luochuan. In contrast, the OSL sensitivity of Shimao samples from L1 was affected by the input from the Mu Us Desert, and those of Jingyuan may affected by the contribution from the Yellow River.  相似文献   

A detailed luminescence chronology of the Lower Volga loess-palaeosol sequence at Leninsk     

《Quaternary Geochronology》2022

We present a detailed luminescence chronology of the loess-palaeosol sequences in the Lower Volga region of Russia at the Leninsk site – an important palaeogeographic archive describing the climate and environmental conditions of regressive stages of the Caspian Sea. The chronology of these sediments has received very little attention compared to the under- and overlying marine deposits. The degree of bleaching was addressed by making use of the differential resetting rates of quartz and feldspar. Our results show that the quartz OSL and feldspar pIRIR_50,290 signals were sufficiently bleached before deposition and uncertainties in bleaching have a negligible impact on the reliability of the luminescence ages. The combined quartz OSL and K-feldspar pIRIR_50,290 chronology constrains the main stages of the Northern Caspian Lowland evolution during the Late Quaternary. During early MIS 5 (130–120 ka), the northern part of the Lower Volga was covered by a shallow brackish water estuary of the warm Late Khazarian Caspian Sea transgression. After ∼122 ka, the Volga incised the Northern Caspian Lowland surface following sea-level decrease and the start of subaerial conditions at Leninsk. Loess accumulation rate increased towards the end of MIS 5 and two palaeosols of presumably MIS 5с and MIS 5a age formed, exhibiting features evidencing a dry, cold climate, influenced by long seasonal flooding by the Volga River. Cryogenesis affecting the MIS 5a soil is a regional phenomenon and is dated to between ∼70 and 90 ka. The overlying thick Atelian loess unit formed during the cold periods of MIS 4 and MIS 3. Clear erosional features at the top of the Atelian loess are constrained by luminescence to ∼35 to ∼24 ka, allowing reconstruction of erosion of 150–200 cm of loess.  相似文献   

First high-resolution luminescence dating of loess in Western Siberia     

《Quaternary Geochronology》2022

The south of Western Siberia is an important part of the Eurasian loess belt, containing an extensive record of Quaternary landscape and climate evolution in up to 100 m thick loess deposits with as many as 10 pedocomplexes. However, this important Quaternary archive lacks a reliable absolute chronology, and this has prevented the linking of the widely accepted regional chronostratigraphic correlations with those of other parts of the Eurasian loess belt. Here we present the first results of detailed luminescence dating of the Late Pleistocene loess-palaeosol sequence at the Western Siberian stratotype section of Lozhok. According to the classical regional chronostratigraphic scheme, this sequence records the main stages of the environmental evolution of the region, including three palaeosols correlated with the warming stages of MIS 5e, MIS 5c and MIS 3. Our absolute chronology is based on 38 new luminescence ages (OSL, IR₅₀, pIRIR₂₉₀). Good agreement between the OSL and pIRIR₂₉₀ ages suggests sufficient bleaching before deposition. The resulting chronology reveals that, rather than being only Upper Pleistocene in age, the loess-palaeosol sequence at Lozhok actually formed in the Middle and Upper Pleistocene. The ages of individual horizons do not correspond to the previously accepted stratigraphic units and morphological features of pedocomplexes. Our Bayesian chronological model reveals remarkable variation in dust accumulation and preservation at the site. The new results unambiguously identify the presence of an erosional boundary with a hiatus lasting ∼90 ka. The upper pedocomplex, immediately below this discontinuity, formed in sediment deposited between 131 ± 9 ka and 122 ± 11 ka and clearly corresponds to MIS 5. The lower pedocomplex is found in sediment deposited between 240 ± 12 and 199 ± 9 ka, and correlates closely with MIS 7. These new findings demonstrate the urgent need for a wider programme to date the main stratotypes of loess-palaeosol sections in Western Siberia. Only then can the global implications of the regional climate record in this important continental-scale archive be correctly interpreted.  相似文献   

Experimental study on the dynamic modulus of compacted loess under bidirectional dynamic load     

Liguo Yang  Shengjun Shao  Qilong Sun  Ping Wang 《地震研究进展（英文）》2022,2(3):100115

The dynamic characteristics of compacted loess are of great significance to the seismic construction of the Loess Plateau area in Northwest China, where earthquakes frequently occur. To study the change in the dynamic modulus of the foundation soil under the combined action of vertical and horizontal earthquakes, a hollow cylindrical torsion shear instrument capable of vibrating in four directions was used to perform two-way coupling of compression and torsion of Xi'an compacted loess under different dry density and deviator stress ratios. The results show that increasing the dry density can improve the initial dynamic compression modulus and initial dynamic shear modulus of compacted loess. With an increase in the deviator stress ratio, the initial dynamic compression modulus increases, to a certain extent, but the initial dynamic shear modulus decreases slightly. The dynamic modulus gradually decreases with the development of dynamic strain and tends to be stable, and the dynamic modulus that reaches the same strain increases with an increasing dry density. At the initial stage of dynamic loading, the attenuation of the dynamic shear modulus with the strain development is faster than that of the dynamic compression modulus. Compared with previous research results, it is determined that the dynamic modulus of loess under bidirectional dynamic loading is lower and the attenuation rate is faster than that under single-direction dynamic loading. The deviator stress ratio has a more obvious effect on the dynamic compression modulus. The increase in the deviator stress ratio can increase the dynamic compression modulus, to a certain extent. However, the deviator stress ratio has almost no effect on the dynamic shear modulus, and can therefore be ignored.  相似文献   

不同温控曲线对石灰改良黄土强度影响研究   总被引：1，自引：1，他引：0  

解邦龙  张吾渝  孙翔龙  刘乐青  刘成奎 《冰川冻土》2022,44(1):262-274

青海季节性冻土地区工程建设受冻融循环作用和黄土湿陷性的双重影响,工程上常采用石灰与黄土拌和作为垫层材料以满足工程要求,但冻融循环作用依旧对地基土体的性能有所影响。为探究青海季节性地区气候变化对地基土所带来的不利影响,采用3种温控曲线（1#、2#和3#温控曲线）模拟了青海季节性冻土地区气候变化规律,通过无侧限抗压强度试验和SEM等微观试验,分析不同温控曲线对2∶8、3∶7灰土强度和微观结构的变化规律。结果表明3∶7和2∶8灰土的应力-应变关系均呈现应变软化型,0~6次冻融过程中试样的无侧限抗压强度随着冻融循环次数的增加逐渐降低,继续增加冻融循环次数后其强度有所上升;冻融循环6次时灰土内部孔隙分布相较于冻融20次时多,且随着冻融循环次数的增加颗粒间接触方式由点-点、点-面接触向面-面接触转变;1#温控曲线的微观定量参数较2#、3#温控曲线变化明显,经历1#曲线时试样内部孔隙更为圆滑,结构排列疏松,1#温控曲线对试样结构和强度的影响程度相对较弱。  相似文献