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Mechanical performances and microstructural characteristics of reactive MgO-carbonated silt subjected to freezing-thawing cycles

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第4期13卷 875-884页

作者： Guanghua Cai Songyu Liu guangyin du Zhen Chen Xu Zheng Jiangshan Li College of Civil Engineering Nanjing Forestry UniversityNanjing210037China Institute of Geotechnical Engineering Southeast UniversityNanjing211189China State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China Department of Civil and Environmental Engineering Washington State UniversityPullmanWA99163USA

The characteristics of reactive magnesia(MgO)-carbonated silt in respect to long-term stability have not been well understood in severely cold climate despite the usage of reactive MgO in enhancing the engineering *** the binder content of 15%and initial water content of 25%,MgO-admixed silt specimens were carbonized for 3 h and 6 h and then subjected to different numbers of freezingthawing(F-T)*** different F-T cycles,the physico-mechanical properties of MgO-carbonated silt were analyzed in comparison with Portland cement(PC)-stabilized silt through physical and unconfined compression ***,a series of micro tests on MgO-carbonated specimens was performed including X-ray diffraction(XRD),scanning electron microscopy(SEM)and mercury intrusion porosimetry(MIP)*** results demonstrate that both mass change ratio and moisture content of carbonated/stabilized silt decrease,and these values of MgO-carbonated silt are significantly lower while the density is higher compared to PC-stabilized *** strengths and moduli of MgO-carbonated silt are still two times higher than those of PC-stabilized specimens and the strength change ratio of keeps above0.8 after F-T *** is no visible transformation between nesquehonite and dypingite/hydromagnesite,although the XRD peaks of nesquehonite decrease and the bonding and filling effects weaken *** 6 and 10 F-T cycles,the pore-size characteristics changed from a unimodal distribution to a three-peak and bimodal distribution,*** total,macro and large pore volumes increase obviously while the medium and small pore volumes decrease except for intra-aggregate *** findings show better F-T durability of MgO-carbonated silt,which would be helpful for facilitating the application of MgO carbonation in the soil treatment.

关键词： Reactive magnesia(MgO) Freezing-thawing(F-T)cycle Carbonated/stabilized silt Engineering performance Microstructural characteristics

Mechanical properties and energy evolution of Beishan shallow-layer granite under different unloading paths

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Journal of Mountain Science 2024年第5期21卷 1728-1744页

作者： WANG Chuanle LI Erbing ZHANG Dengke HAN Yang LU Hui HE Kang du guangyin School of Transportation Southeast UniversityNanjing 211189China College of Defense Engineering Army Engineering University of PLANanjing 210007China Nanjing Urban Construction Management Group Co. Ltd.Nanjing 210006China College of Field Engineering Army Engineering University of PLANanjing 210007China

Rock has mechanical characteristics and a fracture damage mechanism that are closely related to its loading history and loading path. The mechanical properties, fracture damage features, acoustic emission(AE) characteristics, and strain energy evolution of the Beishan shallow-layer granite used in triaxial unloading tests were investigated in this study. Three groups of triaxial tests, namely, conventional triaxial compression test(Group Ⅰ), maintaining deviatoric stress synchronously unloading confining pressure test(Group Ⅱ), and loading axial pressure synchronously unloading confining pressure test(Group Ⅲ), were carried out for the cylindrical granite specimens. AE monitoring device was utilized in these tests to determine the degree to which the AE waves and AE events reflected the degree of rock damage. In addition, the crack stress thresholds of the specimens were determined by volumetric strain method and AE parameter method, and strain energy evolution of the rock was explored in different damage stages. The results show that the shallow-layer granite experiences brittle failure during the triaxial loading test and unloading test, and the rock has a greater damage degree during the unloading test. The crack stress thresholds of these samples vary greatly between tests, but the threshold ratios of all samples are similar in the same crack damage stage. The Mogi-Coulomb strength criterion can better describe the unloading failure strength of the rock. The evolution of the AE parameter characteristics and strain energy differs between the specimens used in different stress path tests. The dissipative strain energy is the largest in Group Ⅱ and the smallest in Group Ⅰ.

关键词： Beishan granite Unloading test Mechanical properties Damage mechanism Acoustic emission Strain energy

Comparison between bearing characteristics of pervious concrete pile composite foundations with different replacement ratios

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Geohazard Mechanics 2023年第3期1卷 255-261页

作者： Han Xia guangyin du Jun Cai Changshen Sun School of Transportation Southeast UniversityNanjing211189China Jiangsu Key Laboratory of Urban Underground Engineering and Environmental Safety Southeast UniversityNanjing211189China Changjiang Institute of Geotechnique and Survey of Ministry of Water Resource Wuhan430011China

The replacement ratio is an essential factor in evaluating the bearing capacity characteristics of compositefoundations. This study focuses on the bearing capacity of a pervious concrete pile with different replacementratios. The axial force, skin friction, and settlement were evaluated using a model test to assess the performance ofthe pervious concrete pile composite foundation. When the replacement ratio was reduced from 9.26% to 2.32%,the characteristic bearing capacity value was only 14%. Therefore, it may be unreasonable to use the settlementratio method to evaluate this composite foundation's bearing capacity in a model test. Appropriate loading cansignificantly improve the bearing capacity of a pervious concrete pile composite foundation with a lowreplacement ratio. The pile–soil stress ratio exhibited different decreasing ranges in the later loading stage. As theload increased, the axial force of the pervious concrete piles was small and nonobvious, and the average sidefriction resistance of the piles in the foundation with a lower replacement ratio slowly increased.

关键词： Pervious concrete piles Model test Replacement ratios Bearing capacity

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基于CPTU土类指数的标贯值液化判别

东南大学学报（自然科学版） 2017年第4期47卷 812-817页

作者：杜广印罗涛程远潘皇宋东南大学岩土工程研究所南京210096 江苏省城市地下工程与环境安全重点实验室南京210096 苏州市轨道交通集团有限公司苏州215004

为提高可液化地基液化判别的准确性,依托宿新高速公路共振法加固可液化地基项目,对共振法处理后的液化地基进行CPTU试验和SPT试验.对CPTU试验得到的土类指数I_c和SPT试验得到的标贯值N_(63.5)进行处理分析.结果表明,饱和砂土和粉土的标... 详细信息

为提高可液化地基液化判别的准确性,依托宿新高速公路共振法加固可液化地基项目,对共振法处理后的液化地基进行CPTU试验和SPT试验.对CPTU试验得到的土类指数I_c和SPT试验得到的标贯值N_(63.5)进行处理分析.结果表明,饱和砂土和粉土的标贯值N_(63.5)是土类指数I_c的一次函数(N_(63.5)=-18.8I_c+52.0),即土类指数越大,土性越接近黏性,标贯值越小.基于N_(63.5)与I_c的拟合关系式提出一种新型液化判别方法,即根据标贯值参照《建筑抗震设计规范》进行饱和砂土和粉土地基的液化判别,其中标贯值根据I_c计算获得,I_c则通过CPTU试验获取.与规范中SPT判别法相比,该方法可以提供连续的标贯值参数,与基于CPT的周期阻力比法相比,该方法计算简单.

关键词：液化地基孔压静力触探标贯值土类指数

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钉形粉喷桩加固海相软土地基的现场试验研究

西南交通大学学报 2012年第2期47卷 204-209页

作者：谢胜华刘松玉杜广印东南大学交通学院江苏南京210096 安徽工业大学建筑工程学院安徽马鞍山243002

针对常规粉喷桩处理海相软土地基中存在的搅拌不均匀、桩身强度低等问题,提出了钉形双向搅拌粉喷桩的施工工艺.以连云港至临沂高速公路软基处理项目为例,进行了现场单桩施工扰动、单桩静载试验,并对试验过程中的孔隙水压力、土压力等参... 详细信息

针对常规粉喷桩处理海相软土地基中存在的搅拌不均匀、桩身强度低等问题,提出了钉形双向搅拌粉喷桩的施工工艺.以连云港至临沂高速公路软基处理项目为例,进行了现场单桩施工扰动、单桩静载试验,并对试验过程中的孔隙水压力、土压力等参数进行监测.结果表明:钉形粉喷桩由于上部桩径扩大且进行复搅,使变径深度处的超静孔隙水压力最大,且超过土体的上覆有效应力,单桩施工影响在5～10倍桩体半径范围内;由于增大了上部桩径,承载力比相同直径的双向搅拌粉喷桩和常规(单向)粉喷桩的单桩极限承载力分别提高了36%和76%.因此,钉形粉喷桩具有对施工扰动小、单桩承载力高等优越性.

关键词：钉形双向搅拌粉喷桩施工工艺超静孔隙水压力静载试验承载特性

基于孔压静力触探测试的刚性桩承载力非线性计算方法

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工业建筑 2018年第5期48卷 122-126页

作者：居俊杜广印常熟理工学院江苏常熟215500 东南大学交通学院南京210096

在＂欧洲法＂的基础上,引入基于孔压静力触探测试（CPTU）不排水计算方法的基桩承载力计算式。基于世界范围内不同土质的试验成果,通过反分析给出算式中相应参数的非线性确定方法;在此基础上,提出了基于CPTU的刚性桩承载力非线性计算方... 详细信息

在＂欧洲法＂的基础上,引入基于孔压静力触探测试（CPTU）不排水计算方法的基桩承载力计算式。基于世界范围内不同土质的试验成果,通过反分析给出算式中相应参数的非线性确定方法;在此基础上,提出了基于CPTU的刚性桩承载力非线性计算方法。结合工程实例,将文中方法与其他4种基于静力触探试验或孔压静力触探试验估算的单桩承载力与现场实测值进行对比分析。结果表明：文中提出的非线性计算方法不仅考虑了桩周土的应力历史和桩土响应的非线性,同时考虑了桩长效应;并且侧摩阻力修正系数并非一定值,而是根据修正锥尖阻力和水平应力确定,更加符合现场情况,该法计算的单桩极限承载力更加接近实测值。

关键词：孔压静力触探刚性桩承载力非线性方法

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透水混凝土桩复合地基的承载特性模型试验

东南大学学报（自然科学版） 2020年第5期50卷 814-821页

作者：杜广印蔡俊孙长申夏涵章定文东南大学岩土工程研究所南京211189 浙江省交通规划设计研究院有限公司杭州310006

为研究透水混凝土桩复合地基的承载特性,采用模型试验获得了分级加载过程中的沉降、桩土应力比、桩身侧摩阻力和孔压消散规律.结果表明,骨料粒径为3~5 mm、孔隙率为30%的透水混凝土模型桩可以兼顾强度和透水性.处理饱和粉土地基时,相比... 详细信息

为研究透水混凝土桩复合地基的承载特性,采用模型试验获得了分级加载过程中的沉降、桩土应力比、桩身侧摩阻力和孔压消散规律.结果表明,骨料粒径为3~5 mm、孔隙率为30%的透水混凝土模型桩可以兼顾强度和透水性.处理饱和粉土地基时,相比不透水混凝土桩复合地基,透水混凝土桩复合地基使固结时间缩短30.3%,侧摩阻力平均提升0.12 kPa,并降低了荷载引起的超孔压峰值.水平方向越靠近桩体,透水混凝土桩的排水减压作用越明显.对比不同深度的超孔压峰值,靠近桩体时,透水混凝土桩对上部地基的排水减压效果较好,而远离桩体时,透水混凝土桩对下部地基的排水减压效果较好.透水混凝土桩可以快速提高桩周土体的承载能力.

关键词：透水混凝土桩复合地基承载特性模型试验

基于孔压静力触探试验的土类指数共振法加固液化地基效果评价

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岩石力学与工程学报 2013年第S2期32卷 4105-4114页

作者：邹海峰蔡国军刘松玉杜广印东南大学岩土工程研究所江苏南京210096

采用自行研制的十字形振动杆结合共振理论,对液化地基进行了加固处理。基于孔压静力触探(CPTU)试验对共振前后的地基进行测试和分析,指出传统振动密实法适用性评价标准低估了共振法的可加固土类范围。土类指数Ic可用于反映加固处理前后... 详细信息

采用自行研制的十字形振动杆结合共振理论,对液化地基进行了加固处理。基于孔压静力触探(CPTU)试验对共振前后的地基进行测试和分析,指出传统振动密实法适用性评价标准低估了共振法的可加固土类范围。土类指数Ic可用于反映加固处理前后土层状态的改变,进而提出基于土类指数Ic的共振法适用性评价标准。根据标准贯入试验SPT钻孔取样的室内试验结果,建立土类指数Ic与黏粒含量之间的关系式,提出适合于共振法加固的土层中黏粒含量的界限值。分析不同共振方案的抗液化地基处理效果,进一步验证所提出基于土类指数评价标准的可靠性。结果表明,土类指数Ic<2.40或黏粒含量不高于15%时土层可适合于共振法加固处理。加固方案不同,抗液化处理效果存在差异,3桩中心处理效果最好,其次为2点中心和常规点位。共振法扩展了传统振动密实法的应用局限性,可在液化地基处理领域中推广应用。

关键词：土力学孔压静力触探试验共振法土类指数液化地基

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北山花岗岩断裂力学行为及其声发射特征研究

岩石力学与工程学报 2020年第S2期39卷 3237-3244页

作者：刘亮杜广印李二兵郭乾夏涵东南大学岩土工程研究所江苏南京210096 解放军陆军工程大学国防工程学院江苏南京210007

利用MTS815 Flex Test GT岩石力学试验系统及声发射(AE)三维定位实时监测系统,对北山花岗岩试样开展静态加载和循环加载两种加载方式的人字形切槽巴西圆盘(CCNBD)试验,旨在研究不同加载方式下北山花岗岩的断裂力学行为及声发射特征。测... 详细信息

利用MTS815 Flex Test GT岩石力学试验系统及声发射(AE)三维定位实时监测系统,对北山花岗岩试样开展静态加载和循环加载两种加载方式的人字形切槽巴西圆盘(CCNBD)试验,旨在研究不同加载方式下北山花岗岩的断裂力学行为及声发射特征。测试结果表明,北山花岗岩在静态加载下的平均断裂韧度值为1.180 MPa·m^(1/2),循环加载下的平均断裂韧度值为1.153MPa·m^(1/2),循环加载下岩石的断裂韧度降低了2.3%。通过循环加载试验证实了亚临界裂纹扩展的存在,并发现循环加卸载并不会改变CCNBD试样的破坏模式,试样仍保持脆性特征。结合力学特征曲线和声发射特征,对静态加载及循环加载下CCNBD试样的裂纹扩展过程进行分析,深化对不同加载方式下的CCNBD试样断裂特征的认识。

关键词：岩石力学人字形切槽巴西圆盘北山花岗岩断裂韧度声发射循环加载