预测岩石单轴抗压强度的神经网络方法

本文提出一种根据岩石点荷载强度、密度、岩石类型、孔隙率和粒度预测单轴抗压强度(Rc)的神经网络方法.以反向传播算法和包含96个样本的训练集训练网络模型,以包含71个样本的试验集检验网络.最后,以本模型预测黑沟铁矿钙质千枚岩的30个试件的抗压强度.结果表明,对于预测的单轴抗压强度,神经网络模型能给出比回归模型高得多的精度,比试验方法节省成本和时间.     

岩石点荷载强度与单轴抗压强度线性关系试验

针对目前岩石点荷载试验大部分采用规则试件进行,试件加工制作及试验的过程繁琐、成本高的问题,通过自制点荷载试验仪以及RMT-150B岩石力学伺服试验机,对煤矿顶底板常见岩性进行不规则岩石试件点荷载试验和规则岩石试件单轴抗压试验。试验结果表明：不规则岩石点荷载强度基本上满足正态分布规律,同时,点荷载破坏载荷与破坏面积之间呈线性关系,不同载荷破坏面积对点荷载试验中的尺寸、形状效应基本上没有太大的影响。通过分析点荷载强度与单轴抗压强度两者间的关系,得出通过点荷载强度确定单轴抗压强度的经验公式。     

根据测井数据评价煤层构造岩顶板抗压强度

河南登封煤田郜城井田二1煤层顶板为滑动构造形成的构造岩。通过对构造岩顶板测井曲线与其抗压强度指标关系的研究,明确指出,利用测井技术可以探测软弱岩体的力学性质     

基于P波模量的岩石单轴抗压强度预测

传统获取岩石单轴抗压强度参数需要钻进取样、加工制作等严格的试验步骤,需要建立一种参数易于获取且准确的岩石单轴抗压强度预测公式。基于岩石物理力学参数的内在联系,建立了岩石单轴抗压强度与岩石P波模量的关系式。根据英安斑岩和页岩两种岩石的干密度、P波速度及单轴抗压强度的测试数据,采用线性拟合的方法建立了岩石基于P波模量的单轴抗压强度预测公式,并采用统计检验的方法对上述预测公式与传统基于P波速度的预测公式进行了对比分析。结果表明,所建立的强度预测通式简单、精度高,模量容易获取,具有很强的实用性。     

软岩三轴加-卸载试验的破坏特征及抗压强度取值方法研究

软岩三轴加、卸载试验中的抗压强度参数取值是一个非常关键的问题,目前还没有比较确定的方法,通常根据经验或工程要求确定。基于此,结合一组砂质泥岩的三轴加、卸载试验进行了详细研究,试验结果表明:(1)当围压大于10 MPa时,不论是三轴加载试验还是卸载试验,砂质泥岩均表现出明显的应变硬化特性;(2)砂质泥岩在三轴压缩和三轴卸荷两种应力路径的力学响应差别明显,在卸荷条件下通常只存在一条完整的剪切破坏面,而压缩条件下岩样没有明显的控制破裂面,并且剪胀效应明显;(3)将半对数法引入到软岩三轴加、卸载试验数据分析中,可以比较方便地确定软岩三轴加、卸载试验的抗压强度;(4)基于三轴加、卸载试验过程中的应力、应变增量分析,将软岩变形破坏过程分为3个阶段:平滑阶段、规则跳跃阶段和急剧跳跃阶段,各阶段划分的意义明确,可以作为抗压强度确定时的重要参考,因此,在软岩三轴试验数据分析时,可以综合采用这两种方法。研究提出的抗压强度确定方法可操作性强,在其他软岩三轴试验数据分析中值得参考借鉴。     

Variability of unconfined compressive strength in relation to number of test samples

Unconfined compressive strength is one of the most commonly used properties in rock engineering. Estimation or selection of an appropriate value of unconfined compressive strength for a given rock can be difficult as it can vary greatly within the same rock unit. Considering this large variability, unconfined compressive strength obtained by testing just a few samples is questionable. The purpose of this study was to investigate the variability of unconfined compressive strength for a given rock and, based on this information, determine the minimum number of samples required for obtaining a reliable value. Unconfined compressive strength values for approximately 50 NX-size (2.125 in./5.4 cm) core samples were determined for five different rock types. Statistical analyses were performed on subsets of cores to determine the minimum number of samples required to render a reliable estimate of the average strength of the entire set of cores. The results indicate that the minimum number of samples needed for strength determination depends on the statistical method used, the chosen confidence interval, and the acceptable deviation from the mean. For a 95% confidence interval and a 20% acceptable strength deviation from the mean, either 9 or 10 samples are needed to test for strength, depending on the statistical analysis used.     

节理岩体关键块体稳定的概率分析

基于地下岩体受节理面的控制,节理面的几何和力学参数随机分布,从而导致岩体系统具有高度不确定性,提出以关键块体理论为基础,考虑节理几何和力学参数随机性的岩体开挖可靠度分析方法,并给出了块体稳定的总失效概率评价模型。以澳大利亚阿德莱德地区一铜矿地质条件为例,以节理面倾角、倾向、摩擦系数和黏聚力为随机变量,通过Monte Carlo模拟和概率图方法,进行了岩体可靠度和失效概率的计算。最后,采用条件概率的分析方法,计算了单面滑动块体的总失效概率。计算结果表明,块体沿单面滑动并且出现的概率为11.0%,总的失效概率为3.85%,超过一般岩体工程可允许的风险水平,认为该方法可以作为评价块体可靠性的依据。     

基于脆剪分析的岩体非线性强度特性在统一强度理论中的实现

针对统一强度理论（UST）拟合非线性强度的局限和岩土材料强度特点,提出拟合岩土非线性强度特征的脆性剪切分析方法,建立了过渡式双线性强度分解公式。以脆断、剪切双重破坏机制,解释Hoek-Brown准则的非线性特征机制,并推导出体现岩石、岩体类材料非线性强度特征的脆剪强度公式。Mine-by隧道和北山花岗岩强度数据分析显示,在岩体折减强度、试验数据直接拟合实例分析中,脆剪强度与Hoek-Brown强度相关性系数均在0.98以上,在该基础上建立岩体非线性强度脆剪分析的双线性过渡式,并提出对应的统一强度理论形式,实现统一强度理论在拟合岩土非线性强度准则中的扩展。     

重庆沙溪庙组地层岩石单轴抗压强度研究

岩石单轴抗压强度是工程勘察中最基本的岩体力学参数之一,已广泛应用于岩石地基设计、隧洞围岩分类、岩体质量分级、土石开挖分级和岩石地基验收中。重庆市区约70%面积坐落于侏罗系中统沙溪庙组地层之上,研究沙溪庙组地层岩石单轴抗压强度具有十分重要的意义。从工程勘察的实践出发,通过对重庆市沙溪庙组岩石抗压强度的统计和对软化系数的研究,建立了饱和抗压强度与天然抗压强度之间的经验公式。通过对计算值和试验值的大量对比,结果显示,计算值的可靠性高,可替代试验值,应用前景广阔。     

针贯入仪在软岩强度测试中的应用

软岩强度较低,结构松散,难以加工成标准试件测其单轴抗压强度,为解决这一工程实践难题,引入了日本的一种通过测试软岩针贯入指标间接推算其抗压强度的试验仪器——针贯入仪。首先简要地介绍了针贯入试验的仪器装置、操作过程、注意事项以及数据处理方法,然后运用该仪器在现场和室内分别对不同软岩进行强度测试。统计分析测试结果表明,测试数据离散性大小与岩性均一程度、结构面分布情况密切相关。最后,选取了一组软岩岩样进行针贯入和点荷载对比试验,计算得出两种试验结果相差不大。因此,采用针贯入仪测试软岩强度是合理可行的,可在软岩工程中推广使用。     

基于正交试验的不同胶结强度Bimrock岩体力学特性试验研究

Bimrock在不同胶结强度下的力学特性鲜有研究,而胶结强度对Bimrock力学特性和变形破坏特征有着重要影响。为探究不同胶结强度对Bimrock力学特性的影响规律,通过正交试验设计法,开展Bimrock基质配比试验,对不同配比基质试样的强度力学参数进行参数敏感性分析,基于正交试验结果,制作不同胶结强度的Bimrock试样,通过单轴压缩试验,分析不同胶结强度对Bimrock力学特性的影响。结果表明：Bimrock试样的单轴抗压强度和弹性模量与其胶结强度呈正相关,从弱胶结到强胶结,单轴抗压强度从11.02 MPa增加到34.21 MPa,弹性模量从2.11 GPa增加到5.57 GPa;随着胶结强度的增加,试样在变形至破坏的各阶段表面裂纹数量均减少;强胶结试样的压缩破坏模式表现为单条主裂纹的贯通破坏,破坏时间较短,脆性破坏明显;中等胶结试样发生整体与局部剪切破坏,表现为一条明显贯穿整个试样和一条仅贯穿试样下半部分的剪切破坏面;弱胶结试样发生横向拉张破坏,可见多条沿竖直方向的张拉裂纹,局部出现张剪破坏并存的破坏特征,从变形到破坏产生的裂纹较多且较为破碎,破坏时间相对较长。Bimrock岩体工程问题复杂而且较难处理,针对Bimrock力学特性与变形破坏特征的研究对工程建设以及地质灾害防治有重要意义。     

A FORM-based approach for probabilistic analysis in geotechnics: Application to a reinforced concrete drainage culvert

As numerical models are increasingly used as a design tool in geotechnical engineering, it is highly desirable if geotechnical reliability analysis can be conducted based on numeral models. Currently, the practical use of geotechnical reliability analysis-based numerical models is still quite limited. In this study, an easy to access method is derived to conduct geotechnical reliability analysis based on numerical models. To facilitate its application, a procedure is outlined to implement the suggested method such that geotechnical reliability analysis can be automated using existing geotechnical numerical packages. The procedure is illustrated in detail with an example, and the source codes provided can be easily adapted to analyze other similar problems. The method described in this paper is used to study the reliability of a deteriorating reinforced concrete drainage culvert in Shanghai, China. The suggested method provides a convenient means for reliability analysis of complex geotechnical problems.     

Numerical study of the biaxial compressive strength of high strength concrete based on a yield design micromechanical approach

This paper presents a numerical study of high strength concrete microstructure effects on its uniaxial and biaxial compressive strengths. Concrete is first represented as a set of angular aggregates interacting within a cement paste matrix. Then, a yield design kinematic approach is conducted at the mesoscopic scale in order to determine the concrete compressive strength for a given loading path. The proposed model, having a low computational cost, is able to capture the main microstructure effects already observed in literature on concrete uniaxial compressive strength, in particular, the aggregates volume fraction and maximal size effects. Finally, the proposed model also predicts the biaxial failure envelope of high strength concrete and confirms some experimental trends observed in literature.     

注浆材料和预制裂纹缺陷角度对类岩石试件单轴抗压强度及破坏模式的影响

选用环氧树脂和纯水泥浆作为注浆材料,对含不同角度和不同注浆材料裂隙试样进行单轴压缩试验。试验结果表明,注浆材料和裂纹缺陷角度对类岩石试件单轴抗压强度及破坏模式具有重要影响;环氧树脂加固效果优于纯水泥浆,环氧树脂可以有效地消除预制裂纹尖端的应力集中;在裂纹缺陷角度很小( <30°)和角度很大( =90°)的情况下无论裂隙是注环氧树脂还是纯水泥浆,注浆效果都不明显,当 =60°时两种注浆材料的加固效果都很好。提出滑动裂纹模型,对注浆裂隙进行力学分析发现,含注浆裂隙试样的抗压强度随着注浆材料和完整材料胶结面摩擦系数和黏聚力的增大而增大,不同注浆材料和完整材料胶结面的摩擦系数和黏聚力不同,解释了为什么不同的注浆材料对注浆试样强度提升作用不同。研究成果为分析工程中注浆材料和裂纹缺陷角度对岩体强度的影响提供了一定的理论基础。     

基于量纲分析的岩石相似材料抗压强度计算模型

物理相似模型试验是复杂、难采矿技术研究的有效手段,而岩石相似材料物理力学特性的研究是试验有效进行的前提。根据相似原理和岩石的力学特性,论证了岩石相似材料单轴抗压强度的力学代表性。统计并分析了影响岩石相似材料单轴抗压强度的一系列因素,基于量纲分析的方法构建了岩石相似材料单轴抗压强度与砂粒径、配比材料总量、充填材料（砂）用量、水用量、养护方式等重要因素间的无量纲计算模型,结合岩石相似材料配比试验得到了定量关系式。选取3组具有代表性的岩石相似材料配比试验对所建立的单轴抗压强度计算关系式进行验证,其计算结果与实验室实测结果相吻合,平均误差为4.20%,定量关系式在岩石相似材料参数的研究上具有一定的合理性。研究结果可以为相似材料物理力学参数的预测及岩土工程物理模型试验相似材料的高效选取提供参考。     

岩石力学试验中试样选择和抗压强度预测方法研究

岩石力学试验是岩石力学的基础,是研究岩石力学与工程的重要手段之一,但岩石力学试验的结果往往要受到很多因素的影响,试验结果的离散是普遍存在的,有时可能会得到完全相反的结论。以超声波传播速度、回弹值与岩石强度之间相互关系为基础,综合两种方法的优点,把超声-回弹综合法应用到岩石试样选择中,在正式试验之前,挑出那些可能会使试验结果很离散的试样,可以提高室内试验的测试准确程度。实践表明,这种综合选样方法具有较好的适用性,对有缺陷的试样有较好的识辨能力,而且方便、快速、对试样没有损伤,同时,超声-回弹综合法可以较好地预测岩石的抗压强度。因此,这种综合方法在岩石试样选择和强度预测中值得借鉴。     

An investigation of the relationship between uniaxial compressive strength and degradation for selected rock types

The relationship between uniaxial compressive strength and degradation was investigated for selected rock types, by using regression analyses to determine whether degradation was a useful predictor of compressive strength. In addition, the effects of aggregate particle size, number of hammer blows during the degradation test, engineering index properties, petrographic characteristics, and water saturation on the compressive strength-degradation relationship were evaluated. The results show that strong inverse relationships exist between compressive strength and degradation (measured on a 9.5-4.75-mm size aggregate) for sandstones and igneous/metamorphic rocks, but that no significant relationship exists for limestones/dolomites. The results also indicate a strong positive correlation between degradation and L.A. abrasion loss and can be used to establish a limit of allowable degradation for practical applications. Engineering index properties do not significantly affect the relationship between compressive strength and degradation but petrographic characteristics are important in explaining the strength and degradation behavior of the rocks studied. Water saturation decreases compressive strength and increases degradation to varying degrees.     

Random field characterization of uniaxial compressive strength and elastic modulus for intact rocks

Rock properties exhibit spatial variabilities due to complex geological processes such as sedimentation,metamorphism, weathering, and tectogenesis. Although recognized as an important factor controlling the safety of geotechnical structures in rock engineering, the spatial variability of rock properties is rarely quantified. Hence, this study characterizes the autocorrelation structures and scales of fluctuation of two important parameters of intact rocks, i.e. uniaxial compressive strength(UCS) and elastic modulus(EM).UCS and EM data for sedimentary and igneous rocks are collected. The autocorrelation structures are selected using a Bayesian model class selection approach and the scales of fluctuation for these two parameters are estimated using a Bayesian updating method. The results show that the autocorrelation structures for UCS and EM could be best described by a single exponential autocorrelation function. The scales of fluctuation for UCS and EM respectively range from 0.3 m to 8.0 m and from 0.3 m to 8.4 m.These results serve as guidelines for selecting proper autocorrelation functions and autocorrelation distances for rock properties in reliability analyses and could also be used as prior information for quantifying the spatial variability of rock properties in a Bayesian framework.     

基于岩体抗压强度折减的边坡稳定性分析方法

在岩体边坡稳定性分析方法中,基于非线性Hoek-Brown准则的强度折减法,存在折减方案不统一或计算太复杂等问题。针对这一问题,提出了一种基于岩体抗压强度的广义Hoek-Brown准则强度折减法,比直接折减材料参数,更能体现强度衰减的物理意义。方案以岩体单轴抗压强度作为折减依据,对岩石单轴抗压强度s_ci和反映岩体结构特征的参数组合s^a（s、a 均为模型参数）进行同比折减,分析该方案下抗剪切强度和抗拉强度的折减比例,并基于平均抗剪强度定义安全系数。应用该方案,对两个经典边坡算例进行稳定性分析,将所得安全系数、临界滑动面与局部线性化强度折减法、极限平衡法进行对比。结果表明,对于两算例,本方法所得安全系数与其他两种方法结果接近,相对误差低于2%;在算例1中,本方法得到的临界滑动面位置与其他两种方法结果一致性很高;在算例2中,本方案滑动面位置更接近于局部线性化法,且能同时反映剪切和拉伸破坏。以上结果验证了本强度折减方案和安全系数定义法的可靠性和合理性。