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.

Study of Mutual Improvement of Completed Weathered Phyllite and Red Clay Based on Neutralization Effects of Swelling and Shrinkage Deformation

Completely weathered phyllite(CWP)soil is a kind of special soil with high swell potential,while red clay is a special soil with high shrinkage.This means that these two kinds of special soils are usually not suitable for direct use as subgrade fill.To reduce the swell index of the CWP soil and the shrinkage of red clay at the same time,it was proposed to blend the CWP soil with red clay to improve their basic characteristics.A series of swell index tests and dry-wet cycle tests of the blended soils have been carried out at varying blending ratios,compaction coefficients and moisture contents.The test results show that the free swell index of the blended soil decreases with the increase of red clay,moisture content and compaction coefficient,respectively.The fissure density of the blended soil first decreases and then increases with the blending ratio,with the lowest being zero when the blending ratio is ranging from 20%to 40%.Through particle microscopic analysis and elemental composition analysis,it is found that the neutralization effect,the dilution effect of swell minerals,and the partition effect of coarse particles play an important role in restraining expansion and shrinkage deformation of the blended soil.Based on the liquid limit requirement of Chinese Railway Design Code(TB 10001-2016),the optimal blending ratio of red clay has been proposed to be 50%.Compared with the CWP soil,the free load swell index of the blended soil is reduced by 45.0%and the fissure density is reduced by 99.3%compared with that of red clay.Therefore,it is feasible to improve the CWP soil by blending it with red clay at an optimal ratio of 50%by using the neutralization effect of the expansion of CWP and shrinkage of red clay.

Experimental Study on Improvement Effects of Completely Weathered Phyllite Using Red Clay and Cement for High-Speed Railway Embankments

Completely weathered phyllite(CWP)has the characteristics of difficult compaction,low shear strength after compaction and large settlement after construction.The traditional improvement method using a single agent of red clay or cement for CWP satisfies the subgrade requirements for ordinary railway,but cannot meet the requirements of immediate strength and long-term post-construction settlement of high-speed railway at the same time.A series of experimental investigations were undertaken for the blended CWP soils,with three additives used.The first additive was red clay,the second was cement and the third was a combination of both red clay and cement at various portions.Results of consolidation test and shear strength test carried out for the treated CWP soils show that:1)The effect of cement on improving the compression modulus of CWP is much better than that of red clay;2)The settlement of an embankment of 10 m high formed by blended soil of CWP with 3%cement can be controlled within 15 mm,while the settlement will be 25.15 mm for the same embankment of blended soil of CWP with 40%red clay;3)The shear strength and ultimate bearing capacity of CWP improved by red clay are much better than those of 5%cement;4)The ultimate bearing capacity of CWP improved by 40%red clay is 3.42 times of that by 3%cement and 2.95 times by 5%cement.Furthermore,the bearing capacity of CWP when improved by red clay can meet railway subgrade requirements immediately after compaction,while cement improved CWP needs a curing time of 1 day or longer.This is an impediment to rapid construction process.The improvement mechanism of red clay is mainly filling effect and grading improvement effect,while the improvement mechanism of cement is mainly hardening reaction,which produces high strength material to cement.It is found that 40%red clay and 3%cement treated CWP,which is considered to be optimum,can meet the subgrade requirements of both immediate bearing capacity and long-term post-construction settlement for the high-speed railway.

Deformation and Failure Mechanism of Phyllite under the Effects of THM Coupling and Unloading

Although the study of TM(Thermo Mechanics),HM(Hydraulic-Mechanics) and THM(Thermo-Hydraulic-Mechanics) coupling under a loading test have been under development,rock failure analysis under THM coupling and unloading is an emerging topic.Based on a high temperature triaxial unloading seep test for phyllite,this paper discusses the deformation and failure mechanism of phyllites under the "H M,T→H,T→M" incomplete coupling model with unloading conditions.The results indicate that the elastic modulus and initial permeability decrease and the Poisson's ratio increases with increasing temperature;the elastic modulus decreases and the Poisson's ratio and initial permeability increase with increasing water pressure.During the unloading process,rock penetrability is small at the initial elastic deformation phase,but the penetrability increases near the end of the elastic deformation phase;mechanisms involving temperature and water pressure affect penetrability differently.Phyllite failure occurs from the initial thermal damage of the rock materials,splitting and softening(which is caused by pore water pressure),and the pressure difference which is formed from the loading axial pressure and unloading confining pressure.The phyllite failure mechanism is a transtensional(tension-shearing) failure.

Effect of Pyrophyllite Particle Size on Properties of AI_2O_3-SiC-C Bricks for Iron Ladles

The Al2O3 -SiC-C bricks for iron ladles were pre-pared asing bauxite, fused corundum,pyrophyllite, SiC powder and flake graphite as main starting materials, and phenolic resin as binder. The effect of pyroph,yllite particle size on permanent change in dimensions, cold crushing strength, oxidation resistance, and corrosion resistance of Al2O3 - SiC - C bricks was investigated. The results show that with the decrease of the pyrophyllite particle size, the permanent change in dimensions of Al2O3 - SiC - C bricks decreases, cold crushing strength increases, the oxidation resistance at 1400 ℃ increases, and the corrosion resistance at 1500℃ decreases.

Multivariate Statistical Analysis of Phyllite Samples Based on Chemical(XRF)and Mineralogical Data by XRD

It is presented the results obtained of a multivariate statistical analysis concerning the chemical and phase composition, as a characterization purpose, carried out with 52 rock phyllite samples selected from the provinces of Almería and Granada (SE Spain). Chemical analysis was performed by X-ray fluorescence (XRF). Crystalline phase analysis was performed by X-ray powder diffraction (XRD) and the mineralogical composition was then deduced. Quantification of weight loss (100? and 1000?C) was carried out by thermal analysis. The aims of this investigation were to analyze and compare the chemical and mineralogical composition of all these samples and to find similarities and differences between them to allow a classification. Several correlations between results of the characterization techniques have been also investigated. All the data have been processed using the multivariate statistical analysis method. The XRF macro-elements (10) and microelements (39) data generate one macrogroup with two new subgroups (1 and 2), and an isolated sample. In subgroup 1 of macroelements, a positive correlation was found between XRF results and geographic location characterized by lower MgO content, which is associated to its geological origins. When multivariate statistical analysis is applied to results obtained by XRD, two groups appear: the first one with a sample with zero percentage of iron oxide and the second one with the rest of the samples, which is classified in two groups. A correlation is observed between the alkaline content (XRF) and illite (XRD), CaO and MgO with dolomite and indirectly between the weight loss after heating at 1000?C and the contents of phase minerals that lose structural water (illite + chlorite) or carbon dioxide (dolomite). The present investigation has interest and implications for geochemistry and analytical chemistry concerning earth rocks and silicate raw materials.

静动态压缩下千枚岩长径比效应影响研究

为了研究长径比效应对层状千枚岩力学特性、能量耗散及破坏模式的影响,文中选用4种倾角(α=0°、30°、60°、90°)下不同长径比(L/D=0.5、0.6、0.8、1.0、1.2、1.6、2.0)的千枚岩分别进行了静载单轴压缩和分离式霍普金森杆(SHPB)试验。结果发现,静载压缩试验条件下,不同倾角下千枚岩随长径比的增大,峰值强度和峰值应变均减小。通过单轴动态压缩试验,发现4种层理倾角千枚岩动态抗压强度与试样长径比呈二次函数关系,随着长径比的增加,动态抗压强度出现一个峰值后逐渐降低;千枚岩峰值应变与试样长径比呈指数函数关系下降;对动态冲击压缩试验进行能量分析,发现不同工况的千枚岩在同一冲击气压下,入射能、反射能、透射能均呈现出先缓慢上升再快速上升最后趋于稳定的三段式变化;随着试样长径比增大,千枚岩反射能比先增大后减小,透射能比先减小后增大;采用能量比值法进行对比分析,发现在长径比L/D=1.2时,千枚岩的反射能比达到最大,透射能比达到最小;对千枚岩的宏观破坏模式进行分析,发现动态冲击压缩下千枚岩的宏观破坏模式受长径比影响较大,长径比越小破坏越完全;长径比越大,破坏越不充分。

多因素耦合效应对层状千枚岩动力特性的影响

为了研究不同长径比和倾角下应变率对层状千枚岩动力特性的影响,选用4种倾角(α=0°,30°,60°,90°)两种长度(L=25,50 mm)的层状千枚岩为研究对象,采用分离式霍普金森压杆(SHPB)装置进行不同冲击气压(p=0.150,0.175,0.200,0.225和0.250 MPa)的动态压缩试验.研究了两种长径比层状千枚岩不同应变率下动力特性的影响,分析了层状千枚岩层理倾角、长径比和应变率之间的耦合效应对层状千枚岩强度特征的影响关系.结果表明:动态压缩下两种不同长径比层状千枚岩动态抗压强度随层理倾角增加呈现先减小后增大趋势,动态峰值强度和峰值应变均随应变率增大而增大,层状千枚岩动态抗压强度与应变率呈幂函数关系;动态峰值强度关于倾角α和长径比L/D呈二元函数关系,在α=60°时,层状千枚岩动态抗压强度的长径比效应最为显著,在L/D=1时,倾角效应最为显著;不同倾角下,峰值应变在0°倾角下长径比效应最为显著,在90°倾角下长径比效应最弱;动态冲击下层状千枚岩动态抗压强度和峰值应变的应变率效应均强于长径比效应.

甘肃阳山金矿区碳质千枚岩地层井故分析及预防

甘肃阳山金矿区主要赋矿地层为碳质千枚岩、钙质千枚岩、硅质灰岩等,其中以碳质千枚岩施工难度最大。碳质千枚岩结构为沉积层理,主要矿物为伊利石和高岭石,强度低、节理裂隙发育、遇水软化,其间有石英颗粒夹层,易破碎,在钻探施工过程中极易引发井故,且处理成功率极低。总结了矿区近年来在碳质千枚岩地层中钻进所遇井故的特征,从地层、人员、设备等3方面分析了井故诱因及处理困难的原因,提出了预防措施及处理要点:通过调节泥浆性能,增强泵的排砂能力改善孔内环境,保持钻机、钻杆、接手状态维持设备性能良好,可有效减少井故发生频率;针对孔壁垮塌、断钻、卡钻、埋钻,以快速处理为原则,采用灌水泥、导斜的方法绕过事故头,可大幅减少经济损失,缩短井故时间。

基于离散元方法的千枚岩隧道掌子面稳定性研究

千枚岩隧道在施工过程中由于围岩软弱破碎,易在掌子面附近发生失稳塌方。文章采用颗粒流软件PFC模拟炭质千枚岩三轴试验,标定围岩材料的细观参数,以此构建隧址区三维离散元数值计算模型,模拟隧道在不同开挖进尺和开挖方法下开挖支护全过程,分析隧道开挖后掌子面位移发展规律和开挖扰动区分布范围特征,揭示千枚岩隧道掌子面失稳机理。数值计算结果表明:随开挖进尺的增大,隧道开挖扰动区范围增大;在不同开挖方法中,台阶法的开挖扰动区范围最小。相关研究可为类似软弱破碎围岩隧道的设计和施工提供参考。

陕南千枚岩地区护坡基材优化及抗侵蚀性能

为了进一步探究适宜于陕南千枚岩地区的边坡生态防护基材,以陕南当地废弃的千枚岩碎石为主要基材,添加秸秆、硅酸盐水泥、有机肥、草炭土和保水剂,组成护坡基材。设计正交试验,选取陕南地区的乡土草本植物高羊茅作为试验草种进行盆栽种植。运用综合评分法和极差分析法分析护坡基材的最佳配比和各因素对高羊茅生长影响的重要性程度,最后用室内模拟降雨侵蚀试验来验证基材的强度。结果表明,在陕南地区,适合高羊茅生长的最优基材配比为秸秆含量4%、水泥含量4%、有机肥含量5%、草炭土含量8%、保水剂含量0.25%。根据极差结果分析可知,各因素对高羊茅生长因素的影响从大到小依次为水泥、秸秆、草炭土、保水剂、有机肥。室内模拟降雨侵蚀试验表明,本研究的护坡基材具有较好的抗侵蚀能力,实用性较强。

千枚岩地层隧道支护滞后破坏特征与防治措施探讨

针对隧道穿越高地应力炭质千枚岩地层时支护滞后性破坏现象,综合采用现场调研、数值计算和理论分析的方法,分析支护受力特征和破坏机理,探讨支护滞后破坏的防治措施。结果表明:支护拱部的压应力随千枚岩遇水软化而逐步增加导致破坏的产生,地下水的先无后有时支护滞后破坏的最关键影响因素,千枚岩地层隧道施工中应充分探明水文地质环境,通过加强支护和提高施工质量来预防滞后破坏的发生。

高地应力千枚岩竖井结构受力研究分析

高地应力千枚岩竖井工程案例在国内较为少见,且目前竖井受力机理研究较少,也没有相应的设计规范,因此对其进行相应的结构受力研究分析来指导设计和施工是非常必要的。依托九绵高速某高地应力千枚岩竖井工程,借助大型有限差分数值软件FLAC3D构建工程区三维数值计算模型还原施工现场,模拟竖井施工全过程,通过分析围岩和竖井结构的位移和应力分布规律揭示高地应力软岩环境竖井受力机理。研究结果表明,与隧道相似,当竖井支护采用复合衬砌时,初期支护是主要的受力结构,二衬则作为安全储备,现有支护结构设计满足相应的强度和刚度要求。同时,受水平方向应力和竖直方向应力变化以及围岩的自承能力影响,不同深度衬砌结构受力呈现交替性变化,尽管地压随着埋深增加,但深层岩体环境下竖井结构受力不会随埋深的增加而无限增大。

富水炭质千枚岩隧道集束水平袖阀管注浆加固施工技术

针对富水炭质千枚岩隧道在开挖过程中,炭质千枚岩遇水软化呈流塑状,导致掌子面失稳发生溜塌无法掘进的问题,本文采用一种新的注浆工艺进行止水与围岩固结。超前注浆采用前进式分段注浆、钻杆后退式分段注浆、集束水平袖阀管分段注浆相结合的注浆施工工艺。结果表明:所采用的超前注浆加固方案合理、施工安全高效,能够对该段富水炭质千枚岩地层实现有效加固,研究成果可为同类工程借鉴。

层状千枚岩各向异性力学特性与脆性评价研究

为了研究层状千枚岩的力学特性与各向异性特征,开展了不同层理倾角与不同围压下的千枚岩力学试验。对比分析了千枚岩试样强度、变形、脆性与破坏模式等各向异性特征。结果表明:(1)随着层理倾角β增加,岩样的强度、变形特征曲线形状呈U型;随围压增加,岩样强度及塑性增强,各向异性度逐渐减弱稳定。(2)采用多种强度准则描述岩样强度各向异性,其中Saeidi准则和改进Ramamurthy准则能很好地预测岩样在不同层理倾角下的抗压强度。(3)基于岩样峰前应力-应变曲线与能量特征提出了综合脆性评价指标,在层理倾角β=45°左右时,岩样脆性指标较低,更易发生剪切滑移破坏,得出脆性下降顺序为:沿层理面拉伸劈裂>穿层理面拉伸劈裂>沿层理面剪切>穿层理面剪切。(4)千枚岩的破坏模式与层理倾角和围压有关,单轴条件下,岩样劈裂破坏后易形成复杂裂纹网络;高围压下,岩样破裂后多形成单一的沿层理面或贯穿多层理面的剪切破坏。

红黏土、石灰复合改良千枚岩土胀缩特性研究

为降低千枚岩土的膨胀率和红黏土的收缩率,笔者提出了一种物理-化学联合改良千枚岩土的方法,设计红黏土质量掺和比为0、20%、40%、60%、80%和100%,石灰质量掺量为0、3%、5%和8%共计24种不同组合改良方案。通过全风化千枚岩复合改良土胀缩性试验,分析了复合改良土的胀缩特性,并从微观角度解释了红黏土、石灰复合改良千枚岩土胀缩特性的机理。试验发现自由膨胀率演化规律与无荷膨胀率相似,膨胀率随红黏土掺和比的增加而降低,随石灰掺量增加,膨胀率先快速下降后趋于稳定,得出石灰优化掺量为3%。掺入石灰后的膨胀力随红黏土掺和比先降低后增大,红黏土掺和比60%时达到最低。当石灰掺量>3%时,改良效果较石灰掺量3%时提升不显著。土样线缩率随红黏土掺和比的降低、石灰掺量的增加而减小,且石灰掺量>3%时降幅较小。综合收缩试验结果可知:千枚岩土降低红黏土收缩变形效果优于石灰;各石灰掺量下,缩限皆随红黏土掺和比的增加先降低后升高,在红黏土掺和比约40%时达到最低;综合胀缩试验结果,建议优化掺量为红黏土掺和比40%~60%、石灰掺量3%,此时自由膨胀率降低24%~26%,无荷膨胀率降低25.9%~27.0%,膨胀力降低639~593 kPa,线缩率降低0.7%~0.8%。

考虑岩块定向性的汶马高速公路千枚岩堆积体渗透特性试验研究

汶马高速沿线千枚岩堆积体广泛发育,考虑到千枚岩具有明显的扁平状几何特征,其在堆积体中的空间分布大多具备一定程度的定向性,导致千枚岩堆积体的渗透特性与均质堆积体存在差异。将扁平状岩块的最大面积岩面与水平面的夹角定义为岩块定向角,将堆积体中具有定向性岩块的质量占岩块总质量的比率定义为岩块定向率,采用自制的大尺度渗透仪分别研究了定向角和定向率对千枚岩堆积体渗透特性的影响。试验结果表明:随着定向角的增大,其渗透系数增大,临界水力梯度减小,而破坏水力梯度呈现“减小—增大—缓慢减小”的阶段性演化趋势;随着定向率的增大,其渗透系数增大,临界、破坏水力梯度均减小。研究成果可为千枚岩堆积体的渗透变形研究及水力特性评价提供参考。

水温循环条件下千枚岩动态力学特性研究

对0°层理倾角千枚岩分别在温度循环自然降温、温度循环冷水降温、干湿循环3种水温劣化条件下开展1、3、5、8、11次劣化处理,而后采用分离式霍普金森杆(SHPB)试验系统开展水温循环条件下千枚岩动力学特性研究。结果表明:温度循环作用将有效缩短千枚岩应力-应变曲线的屈服阶段,干湿循环条件下千枚岩屈服阶段则较为明显,水温耦合作用后延性增强;千枚岩动态峰值抗压强度随着水温循环次数的增加不断减小,服从负指数分布规律;温度循环冷水降温、干湿循环水温耦合作用下千枚岩峰值抗压强度降幅大于温度循环自然降温作用下的抗压强度;千枚岩耗散能比随着水温循环次数的增加均呈动态增长的规律,因此水温循环对千枚岩耗散能比增幅具有放大效应;水温循环次数较少时,千枚岩发生贯穿层理面的压致张裂破坏;随着水温循环次数的增加,千枚岩破坏碎块数逐渐增多,碎块尺寸逐渐减小,分形维数不断增加,破坏模式也逐渐转为张剪破坏的复合破坏模式;水温耦合作用下,千枚岩更易产生多碎块破裂,碎块平均尺寸总体上更低。

库水浸泡下全-强风化千枚岩桥基岸坡稳定性分析

全—强风化千枚岩具有极强的水敏感性,在库水浸泡后岩体物理力学特性不可避免地存在劣化的趋势,对岸坡的稳定性极其不利。鉴于此,以某全—强风化千枚岩桥基岸坡为研究对象,通过野外详细调查、室内物理力学试验以及Geo-Slope软件分析,考虑水库蓄水对岸坡千枚岩抗剪强度的劣化效应,计算得到该桥基岸坡稳定性的变化规律。结果表明:在水库蓄水后短时间内全—强风化千枚岩抗剪强度参数及岸坡安全系数降低幅度较大,后逐渐减缓;水库蓄水后,黏聚力的劣化幅度比内摩擦角大,黏聚力的水敏感性更强;计算得到在浸水95 d后,安全系数为1.189,小于1.200,处于欠稳定状态,提出岸坡加固建议措施。

祁门县地质灾害及其相似试件力学试验分析

千枚岩的矿物含量对岩石的强度和断裂破坏形式有较大的影响。石英含量高的岩石强度较高,断裂形式多为脆性断裂,易发生崩塌地质灾害;绢云母含量高的岩石强度相对较低,多产生剪切断裂,易发生滑坡地质灾害。通过水泥、砂和绢云母的相似试件力学试验,发现片理对千枚岩的破坏起着决定性的作用,片理倾角为45°时,千枚岩的抗压强度最小,最容易发生地质灾害。通过加入玄武岩纤维能起到改良千枚岩力学性质的作用,实验表明加入玄武岩纤维可将千枚岩的抗压强度提高19.1%。