挤密桩应力的弹塑性理论及有限元分析

本文基于统一强度理论分析挤密桩桩周土体应力,得出挤压力与塑性挤密半径关系式,并推导出挤密桩桩周土体达到极限状态时的挤压力极限值表达式,分析了极限值随各参数的变化规律。然后,基于大型有限元分析软件ANSYS8.0对挤密桩挤密成孔过程进行三维有限元模拟,通过非线性计算得出各种情况下的极限荷载与理论分析结果进行对照分析。经比较,证明基于统一强度理论的分析结果更符合土体实际受力状态,与三维有限元分析结果更接近。结果对于全面研究挤密桩的综合作用效用有一定的参考价值。     

强夯法和强夯置换法在深厚人工填土层中的应用

采用强夯法和强夯置换法对某工程深厚人工填土层进行地基处理。分析了场地的地质条件及建设要求，介绍了强夯法和强夯置换法的应用及效果。     

SORTAN: An Analytical Method to Determine Fault Slip as Induced by Stress

We propose an analytical method, namely the SORTAN method, to determine the sense of slip on faults as induced by stresses. This method is useful to infer the sense of motion along faults whose surface cannot be directly accessed, such as faults imaged in the subsurface. Because the SORTAN method is based on the Wallace–Bott hypothesis, we assume that the shear stress vector applied to a given fault is parallel to the slip vector on this fault. The assumptions allow for simplification of the method that in turn implies very short calculation times. A concise formalism is adopted. We introduce the stress ratio ' that accounts for (1) the type of stress regime (i.e., strike-slip, reverse or normal) and (2) the degree of anisotropy of the stress state. The formalism of the SORTAN method permits an easy exploration and imaging of the complete collection of slip motions that may theoretically occur on fault planes. The input parameters are the fault plane orientation, the type and anisotropy of the stress regime, and the azimuth of the horizontal stress axes.     

Dynamic Modelling of Fault Slip Induced by Stress Waves due to Stope Production Blasts

Seismic events can take place due to the interaction of stress waves induced by stope production blasts with faults located in close proximity to stopes. The occurrence of such seismic events needs to be controlled to ensure the safety of the mine operators and the underground mine workings. This paper presents the results of a dynamic numerical modelling study of fault slip induced by stress waves resulting from stope production blasts. First, the calibration of a numerical model having a single blast hole is performed using a charge weight scaling law to determine blast pressure and damping coefficient of the rockmass. Subsequently, a numerical model of a typical Canadian metal mine encompassing a fault parallel to a tabular ore deposit is constructed, and the simulation of stope extraction sequence is carried out with static analyses until the fault exhibits slip burst conditions. At that point, the dynamic analysis begins by applying the calibrated blast pressure to the stope wall in the form of velocities generated by the blast holes. It is shown from the results obtained from the dynamic analysis that the stress waves reflected on the fault create a drop of normal stresses acting on the fault, which produces a reduction in shear stresses while resulting in fault slip. The influence of blast sequences on the behaviour of the fault is also examined assuming several types of blast sequences. Comparison of the blast sequence simulation results indicates that performing simultaneous blasts symmetrically induces the same level of seismic events as separate blasts, although seismic energy is more rapidly released when blasts are performed symmetrically. On the other hand when nine blast holes are blasted simultaneously, a large seismic event is induced, compared to the other two blasts. It is concluded that the separate blasts might be employed under the adopted geological conditions. The developed methodology and procedure to arrive at an ideal blast sequence can be applied to other mines where faults are found in the vicinity of stopes.     

Compaction bands induced by borehole drilling

Drilling experiments in rock blocks subjected to pre-existing true triaxial far-field stresses simulating real in situ conditions often result in localized failure around the created borehole, which brings about the formation of borehole breakouts. In weakly bonded quartz-rich porous sandstones breakouts take the form of narrow tabular (slot-like) openings extending along a plane perpendicular to the maximum applied-stress direction. Scanning electron microscopes images of failed boreholes strongly suggest that these breakouts are compaction bands that have been emptied to different extents. The bands form as a result of the stress concentration accompanying the creation of the borehole. The evacuation of the compaction bands is brought about by the circulating drilling fluid flushing out debonded and often fragmented grains from within these bands (Haimson and co-workers, 2003–2007). The objective of this paper is to predict the conditions under which compaction bands are formed around boreholes. To this end, a new analytical model is formulated that enables prediction of the stress field around emptied and filled compaction bands, the various factors affecting the breakouts lengths, and their final length. Good agreement of the developed analytical model with experimental results obtained by Haimson and co-workers (Haimson and Klaetsch in Rock physics and geomechanics in the study of reservoirs and repositories, vol 284, pp 89–105, 2007; Haimson and Kovachich in Eng Geol 69:219–231, 2003; Klaetsch and Haimson in Mining and tunneling innovation and opportunity, University of Toronto press, pp 1365–1371, 2002; Sheets and Haimson in Proceedings, paper ARMA/NARMS 04-484, 2004) is demonstrated. The presented study is of practical relevance: boreholes are often drilled deep into weak porous sandstone formations for the purpose of extracting oil and gas, and the question of borehole stability is crucial. In addition, borehole breakouts are often used to estimate the state of stress in the Earth’s crust, and our new formulation will help improve these estimates.     

石油污染土的击实特性

为了解石油污染对土的压实特性的影响,利用室内击实试验,以原油、柴油和水为介质,得到了单一液体介质和油水混合介质时土的击实曲线。结果表明:石油代替水作为壤粘土孔隙流体,其击实曲线无明显峰值,干密度随含油率增加略有增大但远小于无污染土的最大干密度。油水混合作为孔隙流体,随含油率的增加,原油污染土壤的击实曲线由钟型、双峰型转向无明显峰值曲线,出现类似高液限粘土压实特性;柴油污染土的击实曲线由尖锐型转变为无峰值型;最优含水率均减小,最大干密度随含油率变化规律与油品性质有关。提出了"油膜润滑"的新观点,可较好地解释石油污染壤粘土击实曲线的变化规律。     

Deformation Field around the Stress Induced Crack Area in Sandstone by the Digital Speckle Correlation Method

Abstract: The deformation field around sub-cracks was calculated using the digital speckle correlation method. First, the uni-axial compression tests on sandstone samples containing a pre-fabricated fracture were made. Photomicrographs showing the characteristics of the sub-crack development were taken using a scanning electron microscope (SEM). From these photomicrographs, the real-time images showing the initiation, growth and coalescence of sub-cracks and micro-cracks in the sandstone specimens were obtained and the effects of loading level as well as grain boundaries on the development of cracks were analyzed. Second, the intensity images of the sandstone specimen surface were captured from the observations of the SEM corresponding to different loading levels. Then correlation computation was carried out for the sequential pairs of intensity images to evaluate the displacement components, as well as the strain field. The results show that the deformation varies in different areas separated by sub-cracks during rock damage processes.     

Microseism Induced by Transient Release of In Situ Stress During Deep Rock Mass Excavation by Blasting

During deep rock mass excavation with the method of drill and blast, accompanying the secession of rock fragments and the formation of a new free surface, in situ stress on this boundary is suddenly released within several milliseconds, which is termed the transient release of in situ stress. In this process, enormous strain energy around the excavation face is instantly released in the form of kinetic energy and it inevitably induces microseismic events in surrounding rock masses. Thus, blasting excavation-induced microseismic vibrations in high-stress rock masses are attributed to the combined action of explosion and the transient release of in situ stress. The intensity of stress release-induced microseisms, which depends mainly on the magnitude of the in situ stress and the dimension of the excavation face, is comparable to that of explosion-induced vibrations. With the methods of time–energy density analysis, amplitude spectrum analysis, and finite impulse response (FIR) digital filter, microseismic vibrations induced by the transient release of in situ stress were identified and separated from recorded microseismic signals during a blast of deep rock masses in the Pubugou Hydropower Station. The results show that the low-frequency component in the microseismic records results mainly from the transient release of in situ stress, while the high-frequency component originates primarily from explosion. In addition, a numerical simulation was conducted to demonstrate the occurrence of microseismic events by the transient release of in situ stress, and the results seem to have confirmed fairly well the separated vibrations from microseismic records.     

碎屑岩成岩压实作用模拟实验研究

实验采用自行设计和组装的压实成岩模拟装置,以中砂级纯净石英碎屑为实验介质,开展压实模拟实验,通过对实验过程中所出现的物理和化学变化进行分析和研究,得到了一些认识:在压实过程中,砂体孔隙度和渗透率的变化具有明显的二分性,即压实初期的陡变带和随后出现的缓变带;缓变带实验数据分析表明,孔隙度和承载压力之间存在良好的线性关系,孔隙度和渗透率之间存在良好的半对数关系,渗透率和承载压力之间存在良好的指数关系。系统流体的实时取样测试表明,压实作用不仅仅是一个物理过程,同时也会发生化学变化,即使在较浅的埋藏条件下,石英砂体也发生了压溶现象。     

论强夯地基的双层构造问题

作者认为强夯使地基具有AB层即双层构造。根据实际资料说明。强夯地基的上部(即A层)和下部(B层)各具特点,自成独立系统。夯击过程动应力水平为临界值的那个深度位置即是AB两层的交界。A层属强夯实区,土层变形大且大部分位置经历过“破坏”夯实过程;B层属弱夯实区,变形小且不论击次增加到多大亦不会进入破坏阶段。A层是良好持力层,只要设计合理,施工得当,此层夯后承载力的增加值同夯前土层原有承载力相比,占明显比例;B层承载力大体维持土层原有水平,有时有提高或降低。从实用观点看,主要应查清A层情况及其底界深度;对B层的了解一般情况下达到一定深度即可。     

建筑废渣-黏土混合料压实特性试验研究

将建筑废渣按一定比例与黏土掺合形成的渣土混合料用作填筑材料,具有显著的社会经济与环保效益。为了揭示渣土混合料的压实特性,利用击实试验研究渣料含量和初始级配对渣土混合料压实性能及颗粒破碎特性的影响。研究结果显示,与黏土相比,渣土混合料的最优含水率较低而最大干密度较高,尽管渣料的初始级配有所不同,渣土混合料的最优含水率随掺渣量的增加而减小,最大干密度随掺渣量的增加而先增后减,并存在着一个约为30%的最优掺渣量;击实作用下渣料颗粒的相对破碎率随掺渣量的增加而增加,与初始级配均匀的渣料相比,相同掺渣量下初始级配不均匀渣料的相对破碎率较小,但受渣料初始颗粒大小的影响不大;与初始较小颗粒渣料的混合料相比,初始较大颗粒渣料的混合料的最大干密度较大,表明宽级配的渣土混合料压实性能较好。渣土混合料的压实特性通过结合掺渣量、颗粒破碎特性与渣土混合料结构响应分析得到合理解释。     

压密注浆在砂土液化处理中的应用

介绍了压密注浆法应用于安庆电厂地基液化处理的实践。通过现场检测资料的分析得出了压密注浆在处理液化地基的工程中可以达到设计要求，消除液化，提高地基土的承载力，而且在不便于大型施工机具进入的狭窄场所具有优越性的结论。     

强夯法在液化场地的应用探讨

对岩土勘察中饱和砂土和粉土的液化机理进行了阐述,主要对强夯法消除液化的影响因素进行了对比分析,对于在类似发生液化场地的岩土勘察中起到一定工程实践意义.     

强夯地基处理振动效应的研究

强夯法是地基处理的重要方法之一,在进行强夯地基处理时要评价强夯振动效应,评价的基础正是强夯振动振幅和振动衰减规律。以昌平区沙岭新村工程场地为例,通过对回填场地进行强夯振动监测,分析了强夯振动最大振幅及其随距离的衰减规律,并用频率的四次多项式表示场地介质衰减指数。在场地介质作用谱和强夯激励谱的基础上,通过计算得到介质作用函数和强夯激励函数。通过不断积累强夯振动效应资料,建立起不同性质岩土体与场地介质作用函数之间的关系,进而明确工程岩土体的物理力学性质和动力学表现之间本构关系。     

The Generation and Compaction of Partially Molten Rock

The equations governing the movement of the melt and the matrixof a partially molten material are obtained from the conservationof mass, momentum, and energy using expressions from the theoryof mixtures. The equations define a length scale _c called thecompaction length, which depends only on the material propertiesof the melt and matrix. A number of simple solutions to theequations show that, if the porosity is initially constant,matrix compaction only occurs within a distance _c of an impermeableboundary. Elsewhere the gravitational forces are supported bythe viscous stresses resulting from the movement of melt, andno compaction occurs. The velocity necessary to prevent compactionis known as the minimum fluidization velocity. In all casesthe compaction rate is controlled by the properties of the matrix.These results can only be applied to geological problems ifthe values of the permeability, bulk and shear viscosity ofthe matrix can be estimated. All three depend on the microscopicgeometry of the melt, which is in turn controlled by the dihedralangle. The likely equilibrium network provides some guidancein estimating the order of magnitude of these constants, butis no substitute for good measurements, which are yet to becarried out. Partial melting by release of pressure at constantentropy is then examined as a means of produced melt withinthe earth. The principal results of geological interest are that a meanmantle temperature of 1350?C is capable of producing the oceaniccrustal thickness by partial melting. Local hot jets with temperaturesof 1550?C can produce aseismic ridges with crustal thicknessesof about 20 km on ridge axes, and can generate enough melt toproduce the Hawaiian Ridge. Higher mantle temperatures in theArchaean can produce komatiites if these are the result of modestamounts of melting at depths of greater than 100 km, and notshallow melting of most of the rock. The compaction rate ofthe partially molten rock is likely to be rapid, and melt-saturatedporosities in excess of perhaps 3 per cent are unlikely to persistanywhere over geological times. The movement of melt througha matrix does not transport major and trace elements with themean velocity of the melt, but with a slower velocity whosemagnitude depends on the distribution coefficient. This effectis particularly important when the melt fraction is small, andmay both explain some geochemical observations and provide ameans of investigating the compaction process within the earth.     

强夯法处理可液化地基施工实践

地基液化是高地震烈度区影响地基稳定性的重要因素之一，是引起构筑物破坏的主要形式。通过工程实例说明采用强夯法处理可液化地基，可有效消除液化，提高地基承载力。     

含砂低液限粉土的压实特性研究

通过级配分析、击实试验，分析了含砂低液限粉土的物理力学特性和压实特性。认为现行以压实度为指标的压实控制标准的不完备，是引起公路病害的主要原因之一。为了解决这一问题，引入空气体积率作为粉土压实的辅助控制标准，并建议提高现行路堤的压实度控制标准。     

废轮胎颗粒与黄土混合物压实性能研究

选择废轮胎颗粒以0～50%的掺量与黄土混合,研究了混合土的压实特性,并采用专门设计的环刀击实设备,对环刀击实和标准击实进行了对比分析。试验结果表明,掺量小于20%时混合土的压实特性类似黄土,掺量大于40%时的压实特性类似无黏性土;不同掺量的混合土最大干密度与最优含水率存在幂函数关系,击实能对10%～30%掺量的混合物有效最大干密度影响较小;不同击实能下掺量与最优含水率存在函数关系;混合土存在最佳压实掺量,轻、重型击实能下分别为30%和40%左右。根据室内试验结果,给出了不同掺量混合土击实指标建议值供设计参考。     

冲击压实技术在上海浦东机场跑道浅层地基处理中的试验应用

总结了上海浦东机场二期飞行区3种不同组合的冲击碾压试验——冲击碾压联合高真空排水、冲击碾压联合塑料排水板、冲击碾压，试验结果表明，冲击碾压联合高真守排水方法压实效果最为显著，并在二期飞行区浅层地基处理实践中得到应用。