强风化岩路基湿化变形机理分析

在对强风化岩填料进行矿物成份、物理力学性质和水理性质实验数据分析的基础上,通过试验路堤修筑、现场浸水载荷试验研究强风化岩湿化、软化对强度和变形的影响;利用直径D=75cm的大尺寸平板载荷试验研究填石路基的回弹模量,为路面结构设计提供参数;结合试验数据分析了强风化岩的湿化变形机理,指出其可以作为路基填料使用;鉴于石料湿化变形以及膨胀变形这一特点,建议做好路基的放排水设计。     

考虑细观单粒强度的堆石料破碎特性研究

颗粒破碎是影响堆石料力学性质的主要因素之一,但由于测试手段的限制,荷载作用过程中堆石的颗粒破碎难以实时度量,因而影响堆石料力学特性的深入研究。通过单粒强度试验,发现同一粒组的堆石料单粒强度较好地服从Weibull分布,而破碎后颗粒的粒径级配曲线基本服从分形分布。在此基础上,推求了堆石料三轴试验过程中级配的演化过程,给出了颗粒破碎的实时预测方法,与三轴试验结果比较,验证了本文方法的有效性。     

人工模拟堆石料颗粒破碎应变的三轴试验研究

高应力作用下堆石料的颗粒破碎严重,其对堆石体变形的影响不可忽视。采用水泥净浆浇筑不同粒径和不同强度椭球颗粒的方法,探讨了一种人工模拟堆石料的制备方法。通过系列的三轴试验研究了不同破碎率情况下模拟堆石料应力变形和破碎体应变的特性。结果表明,试验中相对破碎率同颗粒强度和围压力的相对大小直接相关。颗粒破碎对堆石体的应力应变特性具有十分重要的影响。堆石体的破碎体应变均为正值,且随轴向应变的增加而增大,两者近似呈双曲线关系。破碎体应变和破碎率之间存在近似的幂函数关系。     

循环荷载作用下堆石料颗粒破碎特性试验研究

利用大型动三轴试验设备,针对3种堆石料进行了考虑周围压力、固结比以及动应力幅值影响的排水动三轴压缩试验,探讨了动力荷载作用下筑坝堆石料的颗粒破碎特性。研究表明:在循环荷载作用下,堆石料颗粒破碎率随母岩强度的提高而降低,随围压、固结比及动应力幅值的增加而增加;根据动三轴试验过程,在进行颗粒破碎分析时应将堆石料颗粒破碎的产生分为4个阶段予以分别考虑;堆石料在动荷载施加前的已有颗粒破碎状态及应力水平对其后续的颗粒破碎特性具有一定的影响,动力加载过程中试样的体积收缩能够在一定程度上反映这一过程中颗粒破碎率的变化。     

一个考虑颗粒破碎的堆石料弹塑性本构模型

基于广义塑性理论建立了一个考虑堆石料颗粒破碎的弹塑性本构模型。模型采用随平均应力增加而减小的峰值摩擦角和特征点摩擦角来反映堆石料因颗粒破碎而表现出的峰值应力比与剪胀应力比的非线性,在此基础上确定塑性流动和加载方向向量;运用指数型压缩函数建立依赖于体积应变和平均应力的压缩参数 λ ,并构造随平均应力与剪应力水平而变化的塑性模量表达式。模型共有 8 个参数,均可通过等向或单向压缩和三轴压缩试验确定。为验证本文模型的合理性,依据试验资料确定了 3 种不同堆石料的本构模型参数,并对典型三轴压缩试验进行了模拟。 3 种材料的模型预测结果与试验数据均吻合良好,表明本文模型可合理反映了颗粒破碎对堆石料强度与变形特性的影响。     

填石路基石料破碎特性研究

津蓟高速公路延长线工程经过山区，施工过程中的深挖路基和隧道施工将造成大量的碎石弃渣。为避免堆放碎石弃渣材料面大量占用土地、破坏沿线环境，考虑到充分利用当地资源，因此在工程中充分利用这些碎石材料作为路基填料使用。石料在碾压过程中经常伴有颗粒破碎现象，颗粒破碎会使岩块的力学性能发生变化，对岩块的颗粒级配及压密性产生很大的影响，本文通过对不同粒径石料的破碎规律进行了试验研究，并与有限元分析结果进行了比较，结果表明，理论分析与室内试验结果相吻合，对填石路基的施工有一定的指导意义。     

堆石料的颗粒破碎规律研究

粗颗粒土剪切过程中的颗粒破碎现象已被广泛认识,并且在试验和理论方面进行了大量研究。利用大型三轴仪开展了一系列不同级配、不同密度、不同围压条件下堆石料的排水剪切试验,并对试验前后的试样分别进行了颗粒分析,以探讨堆石料的颗粒破碎规律及其影响因素。试验结果表明:密度对颗粒破碎影响较小,而级配和围压的影响较大,围压越高则颗粒破碎越严重。对比试验前后的粒径分布曲线发现,颗粒破碎主要集中在粒径20 mm以上的颗粒范围内,粒径变化幅度随粒径的减小呈减小趋势。基于分形理论,建立了颗粒破碎分形维数与围压和颗粒级配之间的关系表达式,为进一步研究堆石料的强度、变形及剪胀特性提供依据。     

堆石料的应力-应变特性及其三维破碎本构模型

综合已有的研究成果,从压缩、剪胀和强度三方面分析颗粒破碎对堆石料应力-应变特性的影响。基于堆石料的变形和强度特性,引入新的硬化参数H,并推导出相应的屈服函数表达式,进而提出一个能够考虑堆石料颗粒破碎影响的弹-塑性本构模型。利用基于空间滑动面准则（SMP准则）的变换应力方法将模型进行三维化,并参照某堆石料大三轴试验结果对...     

堆石料颗粒破碎对剪胀性及抗剪强度的影响

堆石料的一个比较明显的特点是在力的作用下常发生颗粒破碎，本文通过三峡花岗岩风化石碴的三轴试验和平面应变试验，结合日本森吉山安山岩和玄武岩的三轴试验成果，综合分析了颗粒破碎规律及有关力学特性，分析了破碎与剪胀性及破碎强度分量的关系。     

循环荷载作用下堆石料的颗粒破碎特性

通过大型动力三轴试验,研究了循环荷载作用下堆石料的颗粒破碎特性及其影响因素,首次根据堆石颗粒在混合料中所发挥的作用以及堆石料发生颗粒破碎后不同粒径范围颗粒含量的变化量,将堆石料的颗粒破碎形式划分为棱角破碎和骨架破碎。进而,基于堆石料发生颗粒破碎前后级配的分形维数定义了堆石料的颗粒破碎率,建立了循环荷载作用下堆石料颗粒破碎率与其动剪应变及体积应变关系表达式。     

Geosynthetic-encased stone columns: Numerical evaluation

Stone columns (or granular piles) are increasingly being used for ground improvement, particularly for flexible structures such as road embankments, oil storage tanks, etc. When the stone columns are installed in extremely soft soils, the lateral confinement offered by the surrounding soil may not be adequate to form the stone column. Consequently, the stone columns installed in such soils will not be able to develop the required load-bearing capacity. In such soils, the required lateral confinement can be induced by encasing the stone columns with a suitable geosynthetic. The encasement, besides increasing the strength and stiffness of the stone column, prevents the lateral squeezing of stones when the column is installed even in extremely soft soils, thus enabling quicker and more economical installation. This paper investigates the qualitative and quantitative improvement in load capacity of the stone column by encasement through a comprehensive parametric study using the finite element analysis. It is found from the analyses that the encased stone columns have much higher load carrying capacities and undergo lesser compressions and lesser lateral bulging as compared to conventional stone columns. The results have shown that the lateral confining stresses developed in the stone columns are higher with encasement. The encasement at the top portion of the stone column up to twice the diameter of the column is found to be adequate in improving its load carrying capacity. As the stiffness of the encasement increases, the lateral stresses transferred to the surrounding soil are found to decrease. This phenomenon makes the load capacity of encased columns less dependent on the strength of the surrounding soil as compared to the ordinary stone columns.     

风化岩填筑路基沉降特性研究

以江西彭湖高速公路路基工程为例,对风化岩填料的沉降特性进行了深入研究,通过现场沉降监测,分析了软岩路基沉降规律,并对风化岩填料沉降机理进行了探讨,得出了一些有益的结论,以期指导实践。     

Performance enhancement of encased stone column with conductive natural geotextile under k0 stress condition

In this study, the performance of the stone column encased with conductive jute geotextile in improving the characteristics of soft clay under k₀ stress condition was evaluated using a custom-designed large-scale consolidation test setup. The electrokinetic-encased stone column (e-ESC) was designed as a cathode, while mild steel rods were chosen as anodes, and by applying a voltage gradient of 0.1 V/mm between the electrodes, electrokinetic processes were initiated. The efficacy of using the e-ESC in improving the performance of soft clay was assessed by comparing the results with an ordinary stone column (OSC) and encased stone column (ESC) reinforced soft clay. The results from the study reveal that the inclusion of stiffer material like OSC and ESC in soft clay has significantly increased undrained shear strength and modulus of subgrade reaction of the composite ground with a reduction in settlement and compression index. Due to the application of the voltage gradient between the electrodes, the rate of consolidation settlement of composite ground has significantly increased when compared to the OSC/ESC case. Further, it was confirmed from the chemical and mineralogical analysis that the pH, chemical composition, mineral phases, and microfabric of soft clay were altered with the voltage gradient.     

台华高速公路路堤失稳原因分析与对策

台华高速公路采用干振碎石桩进行软土地基处理,在路堤填筑过程中发生了地基失稳滑移.通过数值方法对路堤填筑过程中地基沉降、超静孔隙水压力及地基塑性区的发展变化进行了模拟计算,并结合现场补勘数据,分析了引起路堤失稳滑移的原因.在此基础上,提出刚性桩地基处理加固方案.数值计算及现场勘查结果表明,在强度较低的软土中采用干振碎石桩进行地基处理是不成功的,施工不仅没有形成完整的碎石桩体,还因扰动降低了原状地基土强度,路堤填筑速度过快则直接导致了地基滑移破坏;当采用刚性桩加固软基时,桩间土仅承担小部分路堤荷载,而大部分路堤荷载由桩承担并传递给深层承载力较高的土层,因此路堤的稳定性高、沉降小,可实现快速填筑.数值分析及现场刚性桩试验段测试结果均表明：刚性桩方案可以满足路堤填筑要求.     

Uniaxial compression behavior of geotextile encased stone columns

The bearing capacity and failure mechanism of encased stone columns are affected by many factors such as encasement length, relative density, strength and stiffness of the encasement material. In soft soils where surrounding soil pressure is low, especially in the top section, the stone columns may be close to a uniaxial compression state, where the uniaxial compression strength controls the bearing capacity of the stone columns. A series of large-scale triaxial tests on ordinary stone columns and uniaxial tests on geotextile encased stone columns have been performed. The stone columns were 300?mm in diameter and 600?mm in height. Samples of four different relative densities, and five types of geotextiles were used in the tests to study the effect of initial void ratio and encasing materials on the uniaxial compression behavior of the stone columns. The results show the uniaxial compressive strength of the encased stone columns is not affected by the initial void ratio but mainly by the tensile strength of the encasing geotextiles. The stress strain curves of the encased stone columns under uniaxial loading condition are nearly liner before failure, which is similar to the tensile behavior of the geotextiles.     

某山区高速公路路基试验研究

为了保证路基的填筑质量,增强路基的整体稳定性,通过详细调查并结合土工试验,提出采用强风化岩进行路基填筑方案,并进行填筑工艺试验,取得了圆满成功,积累了山区高速公路路基施工经验。     

Variation on physico-mechanical properties of Kota stone under different watery environments

The physico-mechanical properties of rocks play an important role in planning and designing of civil constructional works. These properties are adversely affected by acidic and alkaline environments, where they are exposed for a longer time. The natural forces and agents of weathering have degrading effect on the appearance and structural soundness of Kota stone. These agents include rain, temperature, wind and atmospheric pollutants. Weathering agents almost never work individually or in isolation, they always act in combination with one another or with other agents of deterioration.

The durability of building stones is primarily judged by its reactivity with acidic and basic water of different pH values. The conditions are very obvious in any of the large scale construction and use of building stone like sandstones and Kota stones. During the mining of carbonate hosted mineral deposits, the interaction of ground water with ore minerals affect the surrounding environment and rock types. This may cause problem in exploitation of minerals and may cause failure of slope or pillars. To avoid such problems, the prior study of effect of ground water charged with ions released from ore minerals on carbonate rock is important.

In this paper, an attempt has been made to see the variation in the physico-mechanical properties of Kota stone under different watery environment. In the present study, the NX size cylindrical cores were prepared with the help of diamond core drilling machine as per ISRM standard. For each mechanical property, eight samples were prepared and tested. The prepared samples were put into the oven for 24 h at 104 °C to eliminate the moisture present and later submerged in to the water having different pH values ranging from nearly 0.89–12 for 24 h under stirring mode till it gets full saturation at room temperature. The study reveals that there is prominent change in strength properties under acidic and alkaline environments. Rock is considered as a neutral substance so at pH 7, Kota stone shows maximum strength due to non-reactive nature of the solution. Majority of rock mass is not neutral but some of the rock mass shows very minor changes in its strength. The chemical composition of the rock mass dominates the reaction process when it is submerged in varying pH solution.     

杭州市西湖区两处题刻防风化保护研究

根据户外石质文物保护特点及项目要求,对杭州市的朱熹昙山题刻和风水洞摩崖题记的风化机理进行了研究,并对其工程性能和影响因素进行评价。在现场调查中,通过回弹、超声波和表面吸水率测试等步骤,初步了解了题刻表面强度、风化程度和孔隙发育状况。在室内试验中,通过对岩样化学成分、微观结构、物理性能和风化产物分析,更详细地研究了岩石性能。最后依据上述结果,并结合实际情况制定了由防渗措施、表层加固和表面清洗三部分组成的题刻防风化保护内容。     

Effects of initial particle gradation and rock content on crushing behaviors of weathered phyllite fills——A case of eastern Ankang section of Shiyan—Tianshui highway,China

The objective of this paper is to investigate the effects of initial particle gradation and rock content on the crushing behavior(i.e.grain size before and after crushing) of weathered phyllite fills.Compaction tests were conducted on weathered phyllite fills with rock contents of 35%,45%,55%,65% and 75%(by weight).First,the particle size distributions(PSDs) were observed before and after compaction,and then the particle breakage of weathered phyllite fills was analyzed by fractal dimension.Relative fractal dimension was proposed to evaluate the effects of initial rock content and initial gradation on the particle breakage.It was found that the fractal dimension method can well characterize the crushing behaviors of the weathered phyllite fills.The finer the fills were,the more they were compacted.That is,after the first compaction,the relative fractal dimension of the weathered phyllite fills increased as the rock content increased,reaching the values of 0.013,0.016,0.024,0.037 and 0.08,respectively.After the second compaction,these relative fractal dimension values,dominated by the initial particle gradation,became 0.059,0.072,0.052,0.095 and 0.118,respectively.In conclusion,the weathered phyllite fills with 55% rock content exhibited the least breakage and were most suitable for filling the subgrade.Findings in this paper will provide significant guidance for the construction of weathered phyllite filling subgrade in future projects.     

Critical length of encased stone columns

Encased stone columns are vertical inclusions in soft soils formed by gravel wrapped usually with a geotextile. Their critical length is the one where further lengthening of the column provides a negligible improvement and it is therefore not effective to build columns longer than it. This paper aims to obtain common values of the critical length using simplified two-dimensional axisymmetric and full three-dimensional finite element analyses. A uniform soft soil layer with a linear elastic perfectly plastic behaviour is considered for the sake of simplicity. For the studied cases, the critical column length is around 1.3–2.5 times the footing diameter for encased stone columns, and slightly lower for ordinary stone columns, namely around 1.1–1.9. The critical length of the encasement is found to be slightly lower than the critical column length. The value of the critical column length is related to the extent of plastic deformation and that may be used to decide the column length in the design phase without the need of parametric analyses. As a first approximation, a general value of the critical column length of 2 and 2.5 times the footing diameter may be considered for ordinary and encased stone columns, respectively.