Feasibility of using electrokinetics and nanomaterials to stabilize and improve collapsible soils

Loess as a subcategory of collapsible soils is a well-known aeolian deposit generally characterized as a highly-porous medium with relatively low natural density and water content and a high percentage of fine-grained particles.Such collapsible soil sustains large stresses under a dry condition with natural water content.However,it can experience high and relatively sudden decreases in its volume once it reaches a certain water content under a certain load and therefore,the natural condition of the soil might not be suitable for construction if the possibility of the exposure of the soil to excessive water exists during the lifetime of the project.This research presents the utilization of an innovative method for stabilization and improvement of Gorgan loessial soil.This method uses electrokinetics and nanomaterials to instigate additives to move through soil pores,as an in situ remedial measure.To assess the acceptability of this measure,the deformability and strength characteristics of the improved collapsible soil are measured and compared with those of the unimproved soil,implementing several unsaturated oedometer tests under constant vertical stress and varying matric suction.The result emphasizes the importance of the matric suction on the behavior of both improved and unimproved soils.The test results indicate that the resistance of the soil was highly dependent on the water content and matric suction of the soil.The oedometer tests on samples improved by 3% lime and 5% nanomaterials show considerable improvement of the collapse potential.Results also reveal that stabilized samples experience notably lower volume decrease under the same applied stresses.     

Geotechnical behaviour of guar gum-treated soil

Soil stabilization through biological methods is a sustainable, efficient and long-term alternative to conventional techniques. An elaborate study on the engineering behaviour of guar gum-treated soil, a gum-based biopolymer, is carried out through a concise experimental programme. The dry density of the treated soil shows a marginal increase and its optimum moisture content decreases with the increase in guar gum content. The marginal change in dry density over a range of water contents indicates that guar gum-treated soil can be compacted at low energies and that its sensitivity to changes in water content is not appreciable. The stress-strain behaviour of the treated soil indicates that guar gum stiffens the soil matrix, enabling it to resist loads at lower strains. The gain in strength of the soil-guar matrix is seen to depend on both the biopolymer content and the curing time. There is a substantial increase in the unconfined compressive strength of the treated soil – nearly 45% immediately and 131% after 90 days of curing at a 2% guar gum content. The compressibility of the soil is effectively reduced as the addition of guar gum results in the formation of hydrogels that not only clog the pore spaces, but also stiffen the soil matrix. Guar gum is susceptible to degradation; and hence, durability tests are conducted. The results show that there is no appreciable degradation of the treated soil samples within the investigated period of 90 days.     

Effect of wet-dry cycles on shear strength of residual soil

In order to investigate the relationship between the shear strength of residual soil and the number of repeated wet-dry cycles it underwent, the direct shear for different water content, different numbers of wet-dry cycles and different vertical stresses were examined. Based on the comprehensive structural potential theory, a comprehensive structural potential model considering the water content, the number of wet-dry cycles and the vertical stress was constructed. Then, the internal relationship between microstructure characteristics and structural strength attenuation of residual soil under alternate wet-dry conditions was emphatically discussed. As the number of wet-dry cycles and water content increased, the structural variability provided by the soil particle arrangement increased, while the structural stability provided by the soil particle cohesion decreased, causing the shear strength and structural potential of the soil to show a downward trend. As vertical stress increased, the variation range of structural stability was greater than that of structural variability. This asynchronous change caused decreased soil structural potential m_τ. Under the same levels of vertical stress and the same water content, the model we constructed well represented the exponentially decreasing trend between the structural potential and the increased number of wet-dry cycles. Scanning electron microscope (SEM) images of the sample after five wet-dry cycles showed that the surface layer had lifted and the overhead structure between aggregates was clear, suggesting that unit cell connections had changed from face-to-face contact to edge-to-surface contact. That is, the overall orientation of the unit cell was diminished. As the successive wet-dry progressed, the overhead structure provided a more open water migration channel. The nuclear magnetic resonance (NMR) test showed that the content of micropores in soil samples decreased, and the proportion of mesopores and macropores increased, resulting in a decrease in soil strength. With the further development of wet-dry cycles (>5), the peak and residual strength of the soil gradually decreased to be stable. This is related to the decrease in soil saturation after multiple wet-dry cycles, and the stronger the stabilizing effect provided by soil–water meniscus.     

灰土再次利用力学性能初探

我国人口众多,住宅建设量大,能源消耗严重.建造节能环保可持续发展的建筑是我们努力的目标,符合我国的国情.夯土建筑是中华民族的历史文明的佐证和瑰宝,是祖先给我们留下的丰富遗产的重要内容,它具有就地取材、技术简单、循环利用、保温隔热性能优越的优点.本文对徐州地区夯土房的土料进行研究,主要是灰土被重新利用的强度,对其进行力学试验研究,研究夯土材料的循环利用效果,为夯土建筑的推广提供一定依据.     

Shaft capacity of prestressed high strength concrete (PHC) pile-cemented soil column embedded in clayey soil

This paper presents a series of laboratory tests on cemented soil with high water content, and the water content of cemented soil samples were all larger than the liquid limit. A group of model PHC pile-cemented soil interface shear tests were then conducted to investigate the interface frictional capacity. Finally, a group of full-scale tests on PHC pile-cemented soil columns were conducted to study the frictional capacity of cemented soil-soil interface. The test results show that: the cohesion of cemented soil with high water content had a linear relationship with the unconfined compressive strength; the cemented soil strength had a large effect on the frictional capacity of PHC pile-cemented soil interface, and the peak skin friction of PHC pile-cemented soil interface increased linearly with the increasing cemented soil strength; the frictional capacity of cemented soil-soil interface was better than the frictional capacity of conventional pile-soil interface.     

水泥土力学性质影响因素的理论与实证分析

根据多年水泥土室内试验统计结果,结合有关资料对影响水泥土力学性质的因素分别进行了分析总结,对岩土工程设计及施工提供相关依据。     

水泥改良土力学检测指标的对比分析

通过对几种力学检测指标试验方法的比较,提出了静态变形模量的检测结果较K30和Evd具有明显优点。对试验段几种力学检测指标的试验结果进行了对比分析,提出了合适的检测时间,并提出了降低无侧限抗压强度检测频率的建议,对水泥改良土的现场施工具有指导意义。     

Verification of unified effective stress theory based on the effect of moisture on mechanical properties of fiber reinforced unsaturated soil

The unified effective stress theory based on suction stress (SSCC theory) enables the characterization of soils under both saturated and unsaturated conditions with one closed-form relationship. This study provides experimental verification of this theory through the unconfined compressive strength test (UCS) and indirect tensile test strength (ITS) on silty clay soil stabilized with fiber. A series of matric suction, ITS, and UCS tests were conducted to validate the SSCC theory through the representation of the results of ITS and UCS tests in terms of mean total stress (p) versus deviatoric stress (q) and mean effective stress (p`) versus deviatoric stress (q). The results of the validation procedures showed that the SSCC theory is applicable and valid at a range of 6%–16% of water content on the silty clay and the silty clay fiber-reinforced soils. There is a small fluctuation in the increase of ITS and UCS values with increasing fiber content due to randomly oriented distribution of the fiber. The addition of glass fiber does not significantly affect the capacity of water retention of the soil. It improves the condition of the mechanical soil properties at the end of construction more than of the effective stress condition.     

路堤下水泥土桩复合地基性状的有限元分析

结合工程实例，对水泥土搅拌桩复合地基的变形、强度、承载特性、荷载传递、桩土间相互作用等力学性状进行了研究；探讨了桩土模量比、桩长、荷载对桩顶应力的影响，及桩土模量比对桩土中荷载传递规律的影响，得到了具有一定工程价值的结论。     

低掺量水泥土物理力学特性试验研究

通过界限含水量试验研究了不同掺量水泥对水泥土液、塑限的影响,利用无侧限抗压强度实验研究了水泥土在饱水养生条件下的强度特性,并得出了一些对工程有益的结论。     

咸池沟弃渣场渣体大型三轴试验研究

结合咸池沟弃渣场地质条件与现场工况,通过饱和试样大型三轴试验,分析了渣体材料在不同围压下应力—应变关系特性、变形特性以及抗剪强度特性。试验结果表明：该渣体材料不同于一般堆石料,其在轴向压力作用下无明显应变软化特性;随围压增大,渣体由剪胀逐渐过渡到剪缩,且在低围压下,渣体剪胀性在不同应力水平时表现不同;围压较低时,经典线性摩尔—库伦模型仍然适用于该渣体强度分析,但设计数据偏于保守;在高围压下应建立非线性强度模型。在试验分析和理论研究的基础上,认为有必要开展应力路径与应力历史对渣体材料力学特性影响的研究,为依托工程的设计及后期防护奠定理论基础。     

麦秸秆加筋盐渍土的尺寸效应与制样问题处置

制备均匀且整体性较好的试样是保证室内实验结果可靠的前提条件。提出了两端压实的静力制样法,围绕制样中出现的几个问题,制定了适宜的应对措施。同时完成了不同直径的盐渍土和麦秸秆加筋土试样的抗压强度实验,分析了试样抗压强度的尺寸效应,以及试样直径与加筋条件间的比例关系。结果显示:采用两端压实的静力制样方法制备加筋土试样是可行的;两种试样均存在明显的尺寸效应;由于麦秸秆的加筋作用,使得麦秸秆加筋土不同尺寸试样的抗压强度尺寸效应大于盐渍土的,且其抗压强度的尺寸效应随试样尺寸的增大而越来越明显;适宜加筋长度为0.316倍试样直径,适宜加筋率0.25%。研究结果可为制备合格的加筋土试样提供参考,也有益于在未来的研究中选择更合理的麦秸秆加筋条件。     

土壤固化用特种砂浆的物理力学性能研究

针对土壤固化处理要求,利用不同激发剂制备土壤固化专用特种砂浆,研究了特种砂浆的物理力学性能及其土壤固化效果。结果表明,固定激发剂掺量情况下,几种土壤固化专用特种砂浆均具有良好的物理力学性能和土壤固化作用;其中以硫酸钠为激发剂的特种砂浆综合性能较佳,具体表现为流动度较大、凝结时间略长、抗折和抗压强度最高,土壤固化效果最好,固化土强度发展快,且28 d无侧限抗压强度最高。     

冻融循环对闭孔珍珠岩水泥土力学性能的影响

由于水泥土抗冻性能较差,在多年冻土和季节性冻土地区,水泥土的应用和推广受到了一定的限制,如何提高反复冻融条件下水泥土的强度和耐久性,保证工程的使用寿命,是水泥土材料在寒冷地区进一步推广应用的关键.通过在水泥土中加入闭孔珍珠岩,得出水泥土在不同闭孔珍珠岩掺量下冻融循环后的强度值,分析了冻融循环次数对闭孔珍珠岩水泥土性能的影响及冻融循环前后闭孔珍珠岩水泥土强度变化,对掺入闭孔珍珠岩的水泥土做了初步的机理分析.     

加筋复合土工作机理初探

对加筋土进行了介绍,研究了加筋复合土的工作机理,分析得出了准粘聚力计算模型及公式,以促进加筋复合土技术的研究,推广加筋土技术的应用。     

Mechanical properties of stabilized artificial organic soil

In order to study the influence of organic matter on the mechanical properties of stabilized soil and the effect of XGL2005 on stabilizing organic soil, unconfined compressive strength tests were carried out. Test results indicated that the strength of stabilized soil decreased in the form of a logarithmic function as the organic matter content increased. In contrast, the strength increased in the form of a power function as the content of the stabilization agent increased. The strength of cement stabilized organic soil was reinforced greatly by adding the stabilizer XGL2005. Based on the law obtained from the test, a strength prediction model was established by regression analysis. The model included the influence of the curing time, the content of the cement, the organic matter content and the stabilization agent on the strength of stabilized soil. __________ Translated from Journal of Zhejiang University (Engineering Science), 2007, 41(1): 109–113 [译自: 浙江 大学学报(工学版)]     

Numerical simulation of geosynthetic-reinforced soil walls under seismic shaking

This paper presents the results of numerical simulation of three full-scale geosynthetic-reinforced soil walls that were seismically loaded by a shaking table. Material model parameters were determined from the available laboratory data. In particular, the backfill was simulated with a cap model with parameters dependent of stress level. Hardening parameters of cap model were determined from hyperbolic relation derived from the relevant hydrostatic compression tests. A discussion on the calibration of modeling parameters is presented. Responses compared include (a) maximum wall displacement, (b) maximum backfill settlement, (c) maximum lateral earth pressure, (d) maximum bearing pressure, (e) maximum reinforcement tensile load, (f) absolute maximum acceleration in reinforced soil zone, and (g) absolute maximum acceleration in retained soil zone. Qualities of simulations were evaluated and are discussed. It was found that not all the calculated results agree well with the measured data. However, strong inference or high confidence is anticipated for the closely matched responses such as lateral earth pressure and horizontal displacement utilizing the calibrated model described herein. As indicated by the calculated results, seismic wall displacement decreases with decreasing reinforcement spacing. Factors responsible for comparison discrepancy are discussed. Variability within the measured data is thought to have contributed to some of the comparison discrepancies.     

麦秸秆的物理力学性能及加筋盐渍土的抗压强度

为研究滨海盐渍土的工程处理新方法,开展了防腐前后的麦秸秆吸水率、抗拉性能和加筋土的无侧限抗压强度试验。在SH胶中浸泡后的麦秸秆吸水率较天然麦秸秆明显降低,SH胶增强了麦秸秆的防腐能力;浸胶干燥后麦秸秆与天然麦秸秆相比、浸胶干燥后再浸水麦秸秆与天然浸水麦秸秆相比,前者的极限拉力和极限延伸率都高于后者,浸胶使麦秸秆的抗拉性能提高。考虑掺加不同加筋长度、不同加筋率、浸胶后呈干燥和湿润状态、不同形状的麦秸秆,测试了加筋滨海盐渍土的无侧限抗压强度。试验证实,石灰+麦秸秆加筋滨海盐渍土的抗压强度较石灰土有较大提高;加筋率0.25%和加筋长度10mm时的麦秸秆加筋土(试样直径50mm)的抗压强度最大;浸胶后呈湿润状态麦秸秆加筋土的抗压强度均高于浸胶后呈干燥状态麦秸秆加筋土的;掺加四等分的片状麦秸秆能更有效地增强加筋土的抗压强度。麦秸秆加筋不仅提高了土体的整体性和抗压强度,还限制了土体的横向变形。     

简化增量法计算土钉轴力的模型准确性分析

基于朗肯主动土压力原理的土钉轴力简化增量计算方法虽己广泛应用于工程实践,其模型预测精度尚缺乏系统性评估.鉴于此,本文首先从在中国建造和监测的土钉墙中收集了178根土钉共466个实测土钉轴力数据,建立数据库并进行全面分析,排查异常数据.利用剩下的143根土钉的正常数据,对上述朗肯简化增量法的模型准确性进行评估,并考察3种...     

硬化土体模型分析基坑挡土壁与地盘变形的评估

基坑开挖引致挡土壁体和地盘变形预测的准确度,会显着影响基坑四周结构物损害潜能评估的正确性。运用有限元数值程序分析基坑变形问题时,土壤本构模型描述土壤行为的优劣居关键角色。采用工程界和学术界常用的数值软件PLAXIS中两个高级土壤模型(硬化土壤模型及硬化土壤小应变模型),分析一个著名的基坑开挖案例之壁体变形、地表沈陷和地盘水平变位,藉以评估两个土壤模型预测基坑开挖引致挡土壁体和地盘变形预测的准确度。分析结果显示:若土壤模型可以考虑小应变高初始刚度模量和刚度劲度随应变衰减的行为,可以更合理地预测开挖引致之壁体变形与地盘变形量。