Centrifuge and numerical modeling of h-type anti-slide pile reinforced soil-rock mixture slope

Due to the loose structure,high porosity and high permeability of soil-rock mixture slope,the slope is unstable and may cause huge economic losses and casualties.The h-type anti-slide pile is regarded as an effective means to prevent the instability of soilrock mixture slope.In this paper,a centrifuge model test was conducted to investigate the stress distribution of the h-type anti-slide pile and the evolution process of soil arching during the loading.A numerical simulation model was built based on the similar relationship between the centrifuge model and the prototype to investigate the influence factors of the pile spacing,anchored depth,and crossbeam stiffness,and some recommendations were proposed for its application.The results show that the bending moment distribution of the rear pile exhibits Wshaped,while for the front pile,its distribution resembles V-shaped.The soil arching evolution process during loading is gradually dissipated from bottom to top and from far to near.During the loading,the change of bending moment can be divided into three stages,namely,the stabilization stage,the slow growth stage,and the rapid growth stage.In engineering projects,the recommended values of the pile spacing,anchored depth,and crossbeam stiffness are 4.0d,2.0d,and 2.0EI,where d and EI are the diameter and bending stiffness of the h-type anti-slide pile respectively.

Freeze-thaw damage mechanism of elastic modulus of soil-rock mixtures at different confining pressures

As a frequently-used roadbed filler,soil-rock mixture is often in the environment of freeze-thaw cycles and different confining pressures.In order to study the freeze-thaw damage mechanism of elastic modulus of soil-rock mixtures at different confining pressures,the concept of meso-interfacial freeze-thaw damage coefficient is put forward and the meso-interfacial damage phenomenon of soil-rock mixtures caused by the freeze-thaw cycle environment is concerned;a double-inclusion embedded model for elastic modulus of soil-rock mixtures in freezing-thawing cycle is proposed.A large triaxial test was performed and the influences of confining pressure and experimental factors on elastic modulus of soil-rock mixtures were obtained,and then the accuracy of the double-inclusion embedded model to predict the elastic modulus of soil-rock mixtures in freezing-thawing cycle is verified.Experiment results showed that as to soil-rock mixtures,with the increase of confining pressure,the elastic modulus increases approximately linearly.The most crucial factors to affect the elastic modulus are rock content and compaction degree at the same confining pressure;the elastic modulus increases with the increase of rock content and compactness;as the number of freeze-thaw cycles increases,the freeze-thaw damage coefficient of meso-structural interface and the elastic modulus decrease.

Numerical analysis of the failure process of soil-rock mixtures through computed tomography and PFC3D models

Soil-rock mixture （SRM） is a unique type of geomaterial characterized by a heterogeneous composition and a complicated structure. It is intractable for the continuum-based soil and rock mechanics theories to accurately characterize and predict the SRM＇s mechanical properties. This study reports a novel numerical method incorporating microfocus computed tomography and PFC3D codes to probe the deformation and failure processes of SRM. The three-dimensional （3D） PFC models that represent the SRM＇s complex structures were built. By simulating the entire failure process in PFC3D, the SRM＇s strength, elastic modulus and crack growth were obtained. The influence of rock ratios on the SRM＇s strength, deformation and failure processes, as well as its internal mesoscale mechanism, were analyzed. By comparing simulation results with experimental data, it was verified that the 3D PFC models were in good agreement with SRM＇s real structure and the SRM＇s compression process, deformation and failure patterns; its intrinsic mesomechanism can be effectively analyzed based on such 3D PFC models.

Soil-water characteristic surface model of soil-rock mixture

The relationship between the water content or saturation of unsaturated soils and its matrix suction is commonly described by the soilwater characteristic curve(SWCC).Currently,study on the SWCC model is focused on fine-grained soils like clay and silty soils,but the SWCC model for grinding soil-rock mixture(SRM)is less studied.Considering that the SRM is in a certain compaction state in the actual project,this study established a surface model with three variables of coupling compaction degree-substrate suction-moisture content based on the Cavalcante-Zornberg soil-water characteristic curve model.Then,the influence of each fitting parameter on the curve was analyzed.For the common SRM,the soil-water characteristic test was conducted.Moreover,the experimental measurements exhibit remarkable consistency with the mode surface.The analysis shows that the surface model intuitively describes the soil-water characteristics of grinding SRM,which can provide the SWCC of soils with bimodal pore characteristics under specific compaction degrees.Furthermore,it can reflect the influence of compaction degrees on the SWCC of rock-soil mass and has a certain prediction effect.The SWCC of SRM with various soil-rock ratios have a double-step shape.With the increase in compaction degree,the curves as a whole tend toward decreasing mass moisture content.The curve changes are mainly concentrated in the large pore section.

Pore evolution and shear characteristics of a soil-rock mixture upon freeze-thaw cycling

The changes in pore structure within soil-rock mixtures under freeze-thaw cycles in cold regions result in strength deterioration,leading to instability and slope failure.However,the existing studies mainly provided qualitative analysis of the changes in pore or strength of soil-rock mixture under freeze-thaw cycles.In contrast,few studies focused on the quantitative evaluation of pore change and the relationship between the freeze-thaw strength deterioration and pore change of soil-rock mixture.This study aims to explore the correlation between the micro-pore evolution characteristics and macro-mechanics of a soil-rock mixture after frequent freeze-thaw cycles during the construction and subsequent operation in a permafrost region.The pore characteristics of remolded soil samples with different rock contents(i.e.,25%,35%,45%,and 55%)subjected to various freeze-thaw cycles(i.e.,0,1,3,6,and 10)were quantitatively analyzed using nuclear magnetic resonance(NMR).Shear tests of soil-rock samples under different normal pressures were carried out simultaneously to explore the correlation between the soil strength changes and pore characteristics.The results indicate that with an increase in the number of freeze-thaw cycles,the cohesion of the soil-rock mixture generally decreases first,then increases,and finally decreases;however,the internal friction angle shows no apparent change.With the increase in rock content,the peak shear strength of the soil-rock mixture rises first and then decreases and peaks when the rock content is at 45%.When the rock content remains constant,as the number of freeze-thaw cycles rises,the shear strength of the sample reaches its peak after three freeze-thaw cycles.Studies have shown that with an increase in freeze-thaw cycles,the medium and large pores develop rapidly,especially for pores with a size of 0.2–20μm.Freeze-thaw cycling affects the internal pores of the soil-rock mixture by altering its skeleton and,therefore,impacts its macro-mechanical characteristics.

Damage mechanism of soil-rock mixture after freeze-thaw cycles

As a widely distributed geological and engineering material,the soil-rock mixture always undergoes frequentative and short-term freeze-thaw cycles in some regions.Its internal structure is destroyed seriously,but the damage mechanism is not clear.Based on the damage factor,the damage research of properties of soil-rock mixture after different times of freeze-thaw cycles is investigated.Firstly,the size-distributed subgrade gravelly soil samples are prepared and undergo different times of freeze-thaw cycles periodically(0,3,6,10),and indoor large-scale triaxial tests are completed.Secondly,the degradation degree of elastic modulus is considered as a damage factor,and applied to macro damage analysis of soil-rock mixture.Finally,the mesoscopic simulation of the experiments is achieved by PFC3D,and the influence on strength between soil-rock particles caused by freeze-thaw cycles is analyzed.The results show that freeze-thaw cycles cause internal damage of samples by weakening the strength between mesoscopic soil-rock particles,and ultimately affect the macro properties.After freeze-thaw cycles,on the macro-scale,elastic modulus and shear strength of soil-rock mixture both decrease,and the decreasing degree is related to the times of cycles with the mathmatical quadratic form;on the meso-scale,freeze-thaw cycles mainly cause the degradation of the strength between soil-rock particles whose properties are different significantly.

Physical simulation test of soil-rock mixture from synthetic transparent soil

The waste dump of open-pit coal mine is remade of soil-rock mixture under the action of gravity,dynamic load of transportation equipment and earthquake,etc.By using artificial synthetic transparent soil,the developing process and migration law for soil-rock mixture are observed in the remade process.The mixture of fused quartz sand,liquid paraffin and n-tridecane is chosen as the material for synthetic transparent soil which is mixed with liquid paraffin and n-tridecane at a mass ratio of4.4at room temperature of17℃.Physical and mechanical properties of transparent soil are determined by physical test and compared with those in natural sandy soil.The results show that transparent soil and sandy soil have high similarity,in other words,transparent soil can be used for similar simulation experiments of soil-rock mixture.

Study on mechanical properties of soil-rock mixture of various compactness subjected to freeze-thaw cycles

The soil-rock mixture,a collection of soil particles and rock blocks,is inherently heterogeneous and anisotropic due to significant particle size and material strength differences.This study conducts triaxial tests on soil-rock mixture samples of various compactness subjected to varying freeze-thaw cycles.A mesoscopic simulation is carried out by particle flow code(PFC)to analyze the effects of freeze-thaw cycles on the mechanical properties of soil and rock particles.The results show that the mechanical properties of the soil-rock mixture under freeze-thaw cycles are greatly affected by the initial compaction.In general,when the degree of compaction is higher,the influence of freeze-thaw cycles on the soil-rock mixture is greater.The stress-strain curves of the samples with different compactness demonstrate strain-softening behavior.The freeze-thaw cycles greatly influence the failure strength of the samples with a higher degree of compaction but have little impact on the samples with a lower degree of compaction.On the microscopic level,during freeze-thaw cycles,the pore volume in the highly compacted sample is too small to accommodate the volume expansion from ice crystal formation,causing significant strength loss among the soil and rock particles and deterioration of the macroscopic properties of the soil-rock mixture.

Generation of 3D random meso-structure of soil-rock mixture and its meso-structural mechanics based on numerical tests

The mesoscopic failure mechanism and the macro-mechanical characteristics of soil-rock mixture(S-RM) under external load are largely controlled by S-RM's meso-structural features. The objective of this work is to improve the three-dimensional technology for the generation of the random meso-structural models of S-RM, for randomly generating irregular rock blocks in S-RM with different shapes, sizes, and distributions according to the characteristics of the rock blocks' size distribution. Based on the new improved technology, a software system named as R-SRM3 D for generation and visualization of S-RM is developed. Using R-SRM3 D, a three-dimensional meso-structural model of S-RM is generated and used to study the meso-mechanical behavior through a series of true-triaxial numerical tests. From the numerical tests, the following conclusions are obtained. The meso-stress field of S-RM is influenced by the distribution of the internal rock blocks, and the macro-mechanical characteristics of S-RM are anisotropic in 3D; the intermediate principal stress and the soil-rock interface properties have significant influence on the macro strength of S-RM.

Experimental Study on Seepage Characteristics of a Soil-Rock Mixture in a Fault Zone

A mixture of fault gouge and rubble taken out from a fault zone is used to prepare a S-RM(Soil-Rock Mixture)sample with rock block proportions of 20%,30%,40%,50%,60%and 70%,respectively.A GDS triaxial test system is used accordingly to measure the seepage characteristics of such samples under different loading and unloading confining pressures in order to determine the variation law of the permeability coefficient.The test results show that:(1)The permeability coefficient of the S-RM samples decreases as the pressure increases,and the decrease rate of this coefficient in the initial stage of confining pressure loading is obviously higher than in the semi-late period;(2)The permeability coefficient at different confining pressure levels presents a common trend as the rock block proportion is increased,i.e.,it decreases first then it increases(the permeability coefficient of the sample with rock block proportion 40%being the smallest,70%the largest);(3)In the stage of confining pressure unloading,the recovery degree of the permeability coefficient grows with the increase of rock block proportion(the recovery rate of S-RM sample with rock block proportion 70%reaches 50.2%);(4)In the stage of confining pressure loading and unloading,the sensitivity of the permeability coefficient to the rock block proportion displays the inverse“Z”variation rule(when rock block proportion reaches 60%,the sensitivity is highest);(5)In the stage of confining pressure loading,the relationship between the permeability coefficient and confining pressure can be described by an exponential relationship.

Numerical analysis of soil-rock mixture's meso-mechanics based on biaxial test

Soil-rock mixture(S-RM)is a widely distributed geotechnical medium composed of "soil" and "rock block" different both in size and strength. Internal rock blocks form special and variable meso-structural characteristics of S-RM. The objective of this work was to study the control mechanism of meso-structural characteristics on mechanical properties of S-RM. For S-RM containing randomly generated polygonal rock blocks, a series of biaxial tests based on DEM were conducted. On the basis of research on the effects of rock blocks' breakability and sample lateral boundary type(rigid, flexible) on macroscopic mechanical behavior of S-RM, an expanded Mohr-Coulomb criterion in power function form was proposed to represent the strength envelop. At the mesoscopic level, the variations of meso-structure such as rotation of rock block, and the formation mechanism and evolution process of the shear band during tests were investigated. The results show that for S-RM with a high content of rock block, translation, rotating and breakage of rock blocks have crucial effects on mechanical behavior of S-RM. The formation and location of the shear band inside S-RM sample are also controlled by breakability and arrangement of rock blocks.

Mechanical Properties of Soil-Rock Mixture Filling in Fault Zone Based on Mesostructure

Soil-rock mixture(SRM)filling in fault zone is an inhomogeneous geomaterial,which is composed of soil and rock block.It controls the deformation and stability of the abutment and dam foundation,and threatens the long-term safety of high arch dams.To study the macroscopic and mesoscopic mechanical properties of SRM,the development of a viable mesoscopic numerical simulation method with a mesoscopic model generation technology,and a reasonable parametric model is crucially desired to overcome the limitations of experimental conditions,specimen dimensions,and experiment fund.To this end,this study presents a mesoscopic numerical method for simulating the mechanical behavior of SRM by proposing mesoscopic model generation technology based on its mesostructure features,and a rock parameter model considering size effect.The validity and rationality of the presented mesoscopic numerical method is experimentally verified by the triaxial compression tests with different rock block contents(RBC).The results indicate that the rock block can increase the strength of SRM,and it is proved that the random generation technique and the rock parameter model considering size effect are validated.Furthermore,there are multiple failure surfaces for inhomogeneous geomaterial of SRM,and the angle of the failure zone is no longer 45◦.The yielding zones of the specimen are more likely to occur in thin sections of soil matrix isolated by blocks with the failure path avoiding the rock block.The proposed numerical method is effective to investigate the meso-damage mechanism of SRM.

Cultivar Mixture Cooperation(CMC)of rice varieties(lines) with different blast resistant gene

We studied Cultivar Mixture Cooperation(CMC)of rice varieties(lines)by screening mixture ofrice varieties which possess different genes,1983-1996.

粒化高炉矿渣粉沥青混合料路用性能研究

为了拓宽废弃粒化高炉矿渣的利用途径,文中采用不同比例的粒化高炉矿渣粉代替矿粉后,进行AC-13C沥青混合料配合比设计,并对其高温稳定性、水稳定性和低温抗裂性等路用性能进行对比分析。结果表明,将粒化高炉矿渣粉作为填料应用于沥青混合料中,提高了沥青混合料的高温稳定性和高温水稳定性,但降低了其低温水稳定性。当粒化高炉矿渣粉替代率不超过50%时,沥青混合料的低温抗裂性可以得到提高,而当粒化高炉矿渣粉替代率超过75%时,沥青混合料的低温抗裂性降低。综合分析结论得出,AC-13C沥青混合料的粒化高炉矿渣粉替代率不超过50%。

MgO掺杂对高炉渣熔融调质钢渣物相组成及结构的影响

为了探明MgO掺杂对高炉渣熔融调质钢渣(混合渣)物相组成与结构的影响,采用X射线衍射仪和SEM-EDS扫描电镜对高温调质后混合渣物相组成及形貌进行了分析。结果表明,掺杂MgO能有效抑制MgFe_(2)O_(4)相和非胶凝性Ca_(2)Al_(2)SiO_(7)物相生成、促进MgFeAlO_(4)物相生成,提高混合渣熔点。MgO掺杂量2%的高温调质混合渣截面呈层状结构,内层MgFeAlO_(4)物相占比增加,孔洞均匀且细小;中间具有层状结构的MgFe_(2)O_(4)尖晶石包裹在MgFeAlO_(4)物相周围;外层Ca_(2)Al_(2)SiO_(7)物相孔洞均匀,致密度适中;此结构的混合渣是较好的重金属离子过滤材料。

安徽某地铜尾矿资源的综合利用研究

介绍了我国铜尾矿的排放和利用现状,并利用安徽某地铜尾矿分别制备45μm孔筛筛余小于30%的普通铜尾矿粉、中位粒径小于10μm的超细铜尾矿粉及超细铜尾矿粉-超细矿渣粉复合超细粉,研究其粒度分布、活性指数和流动度比以及作为水泥混合材在水泥中应用性能。结果表明:将铜尾矿粉超细粉磨后活性指数和在水泥中应用性能显著提升;超细铜尾矿粉与超细矿渣粉按照5:5复配后可接近S95级矿渣粉技术指标,用于替代矿渣粉作水泥混合材,可降低水泥生产成本。

Influence of water content and shear rate on the mechanical behavior of soil-rock mixtures

Soil-rock mixtures(S-RMs) are widely distributed in the nature. The mesoscopic deformation and failure mechanisms as well as the macro-mechanical behaviors of the S-RMs depend largely upon the rate of deformation, water content and particle sizes. In this research, a series of large-scale direct shear tests with different water contents and different grain-size distributions were conducted to study the influence of the aforementioned factors on the mechanical properties of the S-RMs. Due to the effect of the rock blocks' breakage in the S-RMs, the relationship between the shear strength and the vertical stress of S-RM follows a power law instead of a linear one. It is found that there exists a threshold value for the vertical stress during the shearing process,below which the soil strength is mainly determined by the inter-locking of particles and the re-arrangement of meso-structure,and otherwise large-sized rock blocks are gradually broken into smaller fragments, resulting in a decrease in the soil strength.The shear rate can also significantly influence the degree of particle breakage and the meso-structural rearrangement of the SRMs, namely, under low shear rate, the particles of the samples are fully broken resulting in enhanced macro-strength. As a result, the lower the shear rate, the higher the macroscopic strength. So under unsaturated conditions, the water content will affect the strength of the S-RMs by reducing the strength of rock blocks. As the water content increases, the soil strength decreases gradually, and assumes a moderate value when the water content reaches 8%. At the same water content, the soil strength increases with the sizes of large rock blocks. For the occlusion, breakage and structure re-arrangement of the oversized rock blocks inside S-RM, which have a huge influence on the mechanical characteristics of the samples.

水稻品种混植控制稻瘟病技术研究

2002—2003年分别在吉林省蛟河市新站镇和梅河口市海龙镇选择抗性不同的当地主栽品种按不同比例搭配种植,进行了控制稻瘟病试验。结果表明:水稻品种混合间栽可有效控制稻瘟病的发生,控病效果主要体现在感病品种上。对感病品种"吉优1号"的控制效果达95 94%,对"丰优301"的控病效果达57 14%和49 21%,对"超产2号"的控病效果达63 59%。选择抗谱不同的品种搭配种植可取得较好的效果。"松粳6号"与"吉优1号"组合,2个品种的致病菌谱完全不同,对感病品种"吉优1号"的控病效果高达95 94%。

四川不同生态条件下水稻杂糯间栽技术对稻瘟病的控制作用

为了明确杂糯间栽技术在不同生态条件下控制稻瘟病的效果,在四川省的叙永、资中、营山、蒲江、雅安5个不同的生态区进行试验。结果表明,杂糯间栽在不同生态区不同发病程度下对稻瘟病的控制作用不同。在发病较重的生态区（叙永,发病率86.46%,病指53.61）,间栽糯稻发病程度与净栽糯稻无显著差异。在发病较轻的生态区（营山,发病率6.90%,病指1.08）,部分间栽处理中糯稻发病程度极显著低于净栽。在叙永,杂糯间栽对感病糯稻叶瘟的控制效果在12%~26%,对颈瘟的效果为0;在发病较轻的雅安、营山,对叶瘟的控制效果最高达到46%~88%,对糯稻颈瘟控制效果的范围在11%~76%。总体来说,在发病较轻的生态区,杂糯间栽对感病糯稻稻瘟病的控制效果较好。

掺矿渣活性粉末混凝土配制技术的研究

活性粉末混凝土(RPC)是一种超高性能的水泥基材料。本文在传统RPC配制技术的基础上,掺入矿渣组分,配制出新型的混凝土材料,并对该混凝土的力学性能、配合比以及养护条件等进行系统的研究。实验显示,该种混凝土具有较高的力学性能;存在一个最优配合比;热养护有助于改善RPC的微观结构,提高其力学性能。材料的微观结构致密,其CH的含量因二次火山灰反应已经很低。