Mechanical properties and rockburst proneness of phyllite under uniaxial compression

To investigate the influence of the bedding angle,β,on the mechanical properties and rockburst proneness,uniaxial compression tests were conducted using cylindrical phyllite specimens with different bedding angles.According to the results,the peak stress,peak strain,cumulative acoustic emission counts,and potential energy of the elastic strain exhibited a U-shaped change trend.With an increase in β from 0°to 90°,the failure mode transformed from tensile splitting failure along the bedding plane to shear slip failure along the weak bedding plane.Finally,the failure mode evolved into a tensile splitting failure across the bedding plane.When β=15°,30°,and 45°,the phyllite specimens exhibited strong,slight,and moderate rockburst proneness,with strong,slight,and moderate shear slip rockbursts,respectively.When β=0°,60°,75°,and 90°,the phyllite specimens had extremely strong rockburst proneness,and an extremely strong strain rockburst occurred.

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.

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.

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.

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.

Gement improved highly weathered phyllite for highway subgrades:A case study in Shaanxi province

In a cost-saving move, the soft rocks composed of highly-weathered phyllites available on- site were used to fill the subgrade in the eastern Ankang section of the expressway of Shiyan to Tianshui, China. Cement admixture was used to improve the performance of the weathered phyllites. In order to determine the best mix ratio, values corresponding to compaction performance, unconfined compressive strength, and the California bearing ratio （CBR） were analyzed for variable cement content weight percentages （3%, 4%, 5%, and 6%） using test subgrade plots in the field. Field measurements of resilience modulus and deflection confirmed that the strength of the subgrade increased as the cement ratio increased. In order to further evaluate the cement/phyllite mixture, the performance of the 3% cement ratio sample was evaluated under saturated conditions （with various levels of moisture addition and soaking time） using both the wetting deformation and resilient modulus values. Results suggest that moisture added and soaking time are key factors that affect the seepage depth, water content, and resilient modulus. The recommend values for the cement addition and for the water content are given out. This study can aid in pre- vention of highway damage by improving the foundation capacity and lengthening the lifecycle of the highway in phyllite distributed region at home and abroad.

Landslide susceptibility mapping using the infinite slope,SHALSTAB,SINMAP,and TRIGRS models in Serra do Mar,Brazil

Slope failure triggered by heavy rainfall is very common in tropical and subtropical regions and a cause of major social and economic damage.Landslide susceptibility maps can be generated using geographical information systems(GIS)and limit equilibrium slope stability models coupled or not to hydrological equations.This study investigated the efficacy of four models used for slope stability analysis in predicting landslide-susceptible areas in a GIS environment.The selected models are the infinite slope,the shallow slope stability model(SHALSTAB),the stability index mapping(SINMAP),and the transient rainfall infiltration and grid-based regional slope-stability(TRIGRS).For comparisons,the authors(a)included the infinite slope equation in all models,(b)clearly defined input parameters and failure triggering mechanisms for each simulation(soil depth,water table height,rainfall intensity),(c)determined appropriate values for each model to obtain stability levels that represented similar hydrogeotechnical conditions,and(d)considered upper-third areas of landslide scars to estimate the reliability of susceptibility maps using validation indices.An intense rainfall event occurred in Serra do Mar,Brazil in January 2014 triggered hundreds of landslides and was used for back analysis and evaluation of the slope stability analysis models.When rainfall intensity is not considered,the four models produced very similar results.The most reliable landslide susceptibility map was generated using TRIGRS and considering the granite residual granite soils geological-geotechnical unit,subjected to a rainfall intensity of 210 mm for 2 h under unsaturated conditions.

Behaviors of Rare Earths during Fluid-Rock Interaction and Its Significance of Geochemistry

Rare earths in ores, altered and unaltered sericite phyllite, altered and unaltered dacite porphyry were determined in order to examine behaviors of rare earths in hydrothermal alteration associating with ore-forming processes of Yinshan deposit. It is not sufficient to show the mobility only by the absolute abundance of trace elements changes before and after alteration. This can simply result from dilution or concentration if other elements are added to or removed from the rock. As shown by that in Yinshan deposit, less than 20% of the increment of RE was caused by the 'condensed' of leaching some of major elements (e.g. Si, Na) from the rock. The principal factor which should be responsible for the higher contents of RE in altered rock is the addition of RE into the rock by hydrothermal fluids. Eu is selectively leached from the altered sericite phyllite by a mild acidity and reducing fluid which is characterized by much lower LRE/HRE ratio and a large positive Eu anomaly. A major effect on the RE patterns is the tendency to develop relatively flatter chondrite-normalized patterns. The RE characteristics may be used to distinguish between small and large ore bodies at a later stage of exploration.

Petrochemistry and Petrogenetic Features of Metasedimentary Rocks of Igangan Area, Southwestern Nigeria

The study was carried out to delineate the geochemistry of unstudied meta-sedimentary rocks in the Igangan sheet 240 NW. Geological field mapping was undertaken to delineate the different metasedimentary rocks;three different metasedimentary rocks were observed and 17 samples were analyzed using ICP-AES/MS to obtain elemental concentrations. Geochemical analytical results revealed average concentration (%) of 74.5, 12.66, 1.99, 4.23, and 3.59 for SiO2, Al2O3, Fe2O3, Na2O and K2O respectively. Trace elemental average concentrations (ppm) for selected trace elements in the metasediments are as: U (0.4 - 4.8 ppm, 2.39), Th (0.9 - 25.60 ppm, 10.38), Ni (0.1 - 17.70 ppm, 7.40), Sr (37 - 124 ppm, 81.75), Ba (55 - 1228 ppm, 620.31), Sn (1.4 - 4.8), Be (1 - 11 ppm, 3.31), Li (2.6 - 48.50 ppm, 23.28), Rb (32 - 376.3 ppm, 140.16), Ta (0.5 - 65.20 ppm, 12.48), Nb (7.76 - 47.5 ppm, 23.82) and Cs (0.8 - 33.30 ppm, 8.33). REE patterns of all samples are parallel to sub-parallel, LREE-enriched, with weak to distinct negative Eu anomalies and weakly fractionated HREE segments. Source rocks of the metsediments underwent low to moderate chemical weathering and metasediments are derivatives of felsic igneous sources.