Testing Studies on Rock Failure Modes of Statically Loads Under Dynamic Loading

By means of the improved split Hopkionson pressure bar(SHPB) with axial pre-pressure and confined pressure, two series of experiments on sandstone are carried out to research the failure mode of rock during the course of exploitation of resources in deep. One is under the conditions that the con-fining pressure is fixed and the axial pressure is changeable. The other is under the conditions that the confining pressure becomes and the axial pressure is fixed. It is found that samples break up evenly after impacting when axial static pressures are low, there is great disparity in size of fragments when axial static pressures are high, and the main bodies of samples after the tests under the combination of dy-namic and static loads frequently show the type of V or X. The samples are more close-grained at the elastic stage and impacts make many cracks be generated and developed, as makes samples more crackable. At the initial phase of damage stage, the static pressures make some cracks in the samples which are undeveloped and the impacts′ role is similar to that at the elastic stage. At the metaphase or anaphase of damage stage, these cracks in the samples develop adequately and the impacts mainly accelerate samples′ failure. The main bodies of samples show the type of V or X after impacting due to the confining pressures′ restraining samples′ lateral formation at the elastic stage or the initial phase of damage stage, the main bodies of samples have almost formed at the stage loading static pressures and the results after impacting usually are similar to those under the axial pressures tests.

NMR-based damage characterisation of backfill material in host rock under dynamic loading

It is not uncommon that backfill material used in underground mining being exposed to repetitive dynamic stresses induced by blasting operations or rockburst events. Understanding the strength and fracture evolution of backfilled stopes is critical to maintain the long-term stope stability and ensure safe mining activities. This paper aims to study the damage evolution of the backfill material and its host rock behaviour under three-dimensional(3D) dynamic loading. Using a true-triaxial testing machine, multiple samples of backfill material enclosed by country rock were fabricated and tested under various dynamic loadings with different true-triaxial confining stress conditions. In addition, the nuclear magnetic resonance(NMR) measurement was conducted on the samples before and after exerting static and dynamic loading to obtain their porosity distribution changes. The experiment results suggested that with the increase of the dynamic loading, the porosity of the backfill sample goes through a two-stage process,which shows a slightly linear decrease and then followed by an exponential increase. The research findings can help understand the damage mechanism and fracture development of backfilled stopes and its host rock in deep underground mines, which are constantly subject to the combination of 3D static confining stress and dynamic loading.

Mechanical properties of rock under coupled static-dynamic loads

Rock drilling machine,INSTRON testing system,and SHPB device are updated to investigate the characteristics of rocks at great depth,with high loads from overburden,tectonic stresses and dynamic impacts due to blasting and boring.It is verified that these testing systems can be used to study the mechanical properties of rock material under coupled static and dynamic loading condition and give useful guidance for the deep mining and underground cavern excavation.Various tests to determine the rock strength,fragmentation behavior,and energy absorption were conducted using the updated testing systems.It is shown that under coupled static-dynamic loads,if the axial prestress is lower than its elastic limit,the rock strength is higher than the individual static or dynamic strength.At the same axial prestress,rock strength under coupled loads rises with the increasing strain rates.Under coupled static and dynamic loads,rock is observed to fail with tensile mode.While shear failure may exist if axial prestress is high enough.In addition,it is shown that the percentage of small particles increases with the increasing axial prestress and impact load based on the analysis of the particle-size distribution of fragments.It is also suggested that the energy absorption ratio of a specimen varies with coupled loads,and the maximum energy absorption ratio for a rock can be obtained with an appropriate combination of static and dynamic loads.

Rock burst mechanism analysis in an advanced segment of gob-side entry under different dip angles of the seam and prevention technology

In order to investigate the frequent occurrences of rock burst in gob-side entry during the mining process of the mining zone No. 7, the mechanical model of main roof of fully-mechanized caving mining before breaking was established by the Winkler foundation beam theory, and the stress evolution law of surrounding rock with different dip angles of the seam during the mining process was analyzed by using FLAC3 D. The results show that: with the dip angle changing from 45° to 0°, the solid-coal side of gobside entry begins to form an L-shaped stress concentration zone at a dip angle of 30°, and the stress concentration degree goes to higher and higher levels. However, the stress concentration degree of the coalpillar side goes to lower and lower levels; the influence range and peak stress of the abutment at the lateral strata of adjacent gob increase with dip angle decreasing and reach a maximum value at a dip angle of 0°, but the tailgate is not affected; the abutment pressure superposition of two adjacent gobs leads to stress concentration further enhancing in both sides of gob-side entry. With the influence of strong mining disturbance, rock burst is easily induced by dynamic and static combined load in the advanced segment of gob-side entry. To achieve stability control similar to that in the roadway, the key control strategy is to reinforce surrounding rock and unload both sides. Accordingly, the large-diameter drilling and high-pressure water injection combined unloading and reinforced support cooperative control technology was proposed and applied in field test. The results of Electromagnetic Emission(EME) and field observation showed that unloading and surrounding rock control effect was obvious.

Mechanism of rock burst caused by fracture of key strata during irregular working face mining and its prevention methods

To study the occurrence mechanism of rock burst during mining the irregular working face,the study took irregular panel 7447 near fault tectonic as an engineering background.The spatial fracture characteristic of overlying strata was analyzed by Winkler elastic foundation beam theory.Furthermore,the influence law of panel width to suspended width and limit breaking span of key strata were also analyzed by thin plate theory.Through micro-seismic monitoring,theoretical analysis,numerical simulation and working resistance of support of field measurement,this study investigated the fracture characteristic of overlying strata and mechanism of rock burst in irregular working face.The results show that the fracture characteristic of overlying strata shows a spatial trapezoid structure,with the main roof being as an undersurface.The fracture form changes from vertical‘‘O-X"type to transverse‘‘O-X"type with the increase of trapezoidal height.From the narrow mining face to the wide mining face,the suspended width of key strata is greater than its limit breaking width,and a strong dynamic load is produced by the fracture of key strata.The numerical simulation and micro-seismic monitoring results show that the initial fracture position of key strata is close to tailgate 7447.Also there is a high static load caused by fault tectonic.The dynamic and static combined load induce rock burst.Accordingly,a cooperative control technology was proposed,which can weaken dynamic load by hard roof directional hydraulic fracture and enhance surrounding rock by supporting system.

Application of high-pressure water jet technology and the theory of rock burst control in roadway

This paper puts forward using high-pressure water jet technology to control rock burst in roadway, and analyzes the theory of controlling rock burst in roadway by the weak structure zone model. The weak structure zone is formed by using high-pressure water jet to cut the coal wall in a continuous and rotational way. In order to study the influence law of weak structure zone in surrounding rock, this paper numerically analyzed the influence law of weak structure zone, and the disturbance law of coal wall and floor under dynamic and static combined load. The results show that when the distance between high-pressure water jet drillings is 3 m and the diameter of drilling is 300 mm, continuous stress superposition zone can be formed. The weak structure zone can transfer and reduce the concentrated static load in surrounding rock, and then form distressed zone. The longer the high-pressure water jet drilling is, the larger the distressed zone is. The stress change and displacement change of non-distressed zone in coal wall and floor are significantly greater than that of distressed zone under dynamic and static combined load. And it shows that the distressed zone can effectively control rock burst in roadway under dynamic and static combined load. High-pressure water jet technology was applied in the haulage gate of 250203 working face in Yanbei Coal Mine, and had gained good effect. The study conclusions provide theoretical foundation and a new guidance for controlling rock burst in roadway.

Experimental study on DX pile performance in frozen soils under lateral loading

Experiments about working mechanism and mechanical characteristics of the DX model pile foundation under lateral dynamic and static loading were conducted by using a model system of the dynamic frozen soil-pile interaction. The horizontal displacement-force relationship of the pile head and bending moment distribution along the body in frozen soils of different temperatures were discussed. According to test results, both the horizontal disp!acement-force relationship of the DX pile head and bending moment distribution of the DX pile body are smaller than that of equal-diameter piles under same lateral loads. The piles with different plate positions show different displacements and bending moments. This phenomenon is mainly related to the soil temperature and bearing plates locations. Thus, dynamic response analysis of the pile foundation should be taken into account.

Process Monitoring and Terminal Verification of Cable-Stayed Bridges with Corrugated Steel Webs under Contruction

In this paper,the construction process of a cable-stayed bridge with corrugated steel webs was monitored.Moreover,the end performance of the bridge was verified by load test.Owing to the consideration of the bridge structure safety,it is necessary to monitor the main girder deflection,stress,construction error and safety state during construction.Furthermore,to verify whether the bridge can meet the design requirements,the static and dynamic load tests are carried out after the completion of the bridge.The results of construction monitoring show that the stress state of the structure during construction is basically consistent with the theoretical calculation and design requirements,and both meet the design and specification requirements.The final measured stress state of the structure is within the allowable range of the cable-stayed bridge,and the stress state of the structure is normal and meets the specification requirements.The results of load tests show that the measured deflection values of the mid-span section of the main girder are less than the theoretical calculation values.The maximum deflection of the girder is−20.90 mm,which is less than−22.00 mm of the theoretical value,indicating that the girder has sufficient structural stiffness.The maximum impact coefficient under dynamic load test is 1.08,which is greater than 1.05 of theoretical value,indicating that the impact effect of heavy-duty truck on this type of bridge is larger.This study can provide important reference value for construction and maintenance of similar corrugated steel web cable-stayed bridges.

新型预应力路基的静动载试验系统及应用分析

为深入研究静力加载与列车循环动荷载作用下新型预应力路基的工作性状,研制缩尺预应力路基模型试验系统(包括相似设计、模型箱构建、路基模型填筑、轨道结构设计、预应力施加方法、静力加载系统和列车动荷载模拟),开展不同预应力和列车轴重下的静动力模型试验,通过监测路基各测点处的竖向和侧向变形、加速度和动位移,量化分析施加水平预应力对路基性能的改善规律,深入分析预应力构件与路基结构的协同工作机理。研究结果表明,施加的预应力经扩散后可引起路基面产生隆起变形,当单排侧压力板施加100 kPa预压应力后,路基面最大隆起量为0.062 mm;荷载板试验中,相较于无预应力工况,预应力100 kPa下各测点处的沉降量下降了9.93%~15.77%。此外,预应力可限制荷载作用下路基坡面的外挤变形;列车动荷载试验下,各测点处的加速度和动位移均随预应力的增加而减小;预应力100 kPa下测点处的动位移幅值为无预应力工况下的82.97%~91.63%,说明施加预应力对路基的动力变形存在切实的抑制效应。研制的预应力路基静动载模型试验系统,为揭示水平预应力对路基静动力性能的强化机制提供了切实可行的物理和试验技术平台,获得的分析结果对明晰预应力加固对铁路路基服役性能的影响规律具有指导意义。

黔西南金矿砂岩动静组合加载岩石力学特性研究

为探究巷道开挖后围岩不同深度切向应力不同程度的增加对围岩动力学性能的影响,采用改进的分离式霍普金森压杆(split Hopkinson pressure bar,SHPB)试验系统,对黔西南金矿砂岩试件在0,10,20,30,40MPa的轴压下进行动静组合加载试验,旨在分析砂岩在不同轴压下的力学行为、变形特征与能量演化规律。研究发现:动静组合加载试样应力-应变曲线分为压密阶段、弹性阶段、塑性破坏和峰后阶段;轴压使得峰值应变逐渐增加,极限应变逐渐降低;动态弹性模量、动态抗压强度、应变率及各能量的演化规律均呈现以10MPa为转折点的变化规律。

舰载飞机着舰撞击载荷实测技术研究

针对国内飞机起落架载荷测量中普遍存在的静标动测问题,从理论和机理上分析了静标定的应变法实测动态载荷存在问题的原因。同时,考虑到舰载飞机因定点着舰方式遭受严重的动态载荷,重点研究了舰载飞机着舰撞击载荷的静标动测问题。通过动态落震试验模拟飞机着舰过程,根据测力平台的实测载荷分析,获取了应变法实测载荷精度受动态影响的程度,提出一种改进的惯性修正方法,即:通过落震试验数据辨识质量矩阵,通过辨识的质量矩阵和实测加速度修正应变法的实测载荷。试验结果表明,改进的惯性修正方法进一步提高了垂向载荷的测量精度,显著提高了航向和侧向载荷的实测精度。

动静组合加载下裂隙试样力学特性和破坏模式

目的为了深入了解裂隙岩石在同时受到地应力和动力扰动时的工程灾变机制。方法采用改进的分离式霍普金森压杆系统,对预制裂隙类岩石试样进行了动静组合加载试验。研究了应变率、裂隙倾角和预应力对试样动态力学特性和能耗特征的影响,并对试样的破坏模式进行了分析。结果当应变率从61.82s^(-1)增加到195.57s^(-1),裂隙试样的动态增长因子不断增大,具有显著的应变率效应;动态弹性模量变化规律不明显,应变率效应不显著。随着入射能的增加,裂隙试样的单位耗散能密度不断增加。当裂隙倾角由0°变化到90°,试样的动态增长因子增不断增加,动态弹性模量和单位耗散能密度不断降低。当施加预应力后,30°、45°和60°裂隙试样的动态增长因子增长均有所增加;45°裂隙试样动态弹性模量有所增加,30°和60°裂隙试样的变化规律不明显;45°和60°裂隙试样单位耗散能密度有所降低,30°裂隙试样的变化规律不明显。裂隙试样的破坏模式主要包括张拉破坏、剪切破坏和张拉-剪切复合破坏3种,施加预应力对试样破坏模式的影响不明显。结论0°裂隙对工程岩体的承载能力削弱程度最小,90°裂隙有利于提高破岩效率。预应力在一定程度上会提高工程岩体的承载能力。研究结果可以为预测和评估岩石工程中的风险,制定合理的加固措施提供参考。

粉煤灰改良粉砂土动静力学特性研究

为探究不同粉煤灰掺量粉砂土的动力特性和粉煤灰改良粉砂土的改性机理,以绥化—大庆高速公路路基填土为研究对象,开展无侧限压缩试验和动三轴试验,分析粉煤灰掺量对粉砂土静力学特征影响情况,以及围压、动荷载加载次数和粉煤灰掺量对改良粉砂土动强度的影响规律。结果表明:围压相同的情况下,土体的无侧限压缩强度和动强度,均随粉煤灰掺量增加先升高后降低;加载次数相同时,围压越大,土体动强度越大;选取加载次数为100次动强度进行拟合分析,得出粉煤灰掺入量与动剪切强度对应关系的经验公式。为改善路基强度,加快粉煤灰综合利用进程,结合试验结果与数据分析,建议在粉砂土路基掺加质量比15%粉煤灰进行路基施工。15%粉煤灰掺入量的改良粉砂土对比素土,存在颗粒紧凑,孔隙更小,结构相对致密,骨架更强等优点,可为东北地区粉砂土改良等工程建设提供参考。

动静组合加载下锚固裂隙岩体的止裂与吸能机理

为研究锚杆对深部含裂隙岩体的锚固止裂效应,进行了不同冲击气压下的动静组合加载试验.基于优化的锚杆界面力学模型,建立了新型有限差分法-离散元法(FDM-DEM)耦合数值分离式霍普金森杆系统及锚杆模型.对裂隙岩体和锚固裂隙岩体的力学特性、能量耗散及破坏特征进行了研究,并从细观能量耗散角度阐述了锚杆在动荷载下对裂隙岩体的锚固机理.结果表明:裂隙岩体和锚固裂隙岩体的动态抗压强度随冲击气压的增大而增加,锚杆对裂隙岩体的锚固效应可提高动态抗压强度,减小裂隙岩体的冲击后破坏程度,锚固裂隙岩体能量吸收率变化规律趋同于完整岩体;从细观角度分析,锚杆加固使得裂隙岩体的摩擦滑移耗散能和破坏后碎块携带动能降低,整体吸收能量减少.

铁路下承式连续钢桁梁桥静动力性能评估

成昆铁路复线完工后,部分老线区段将并入复线,并开行时速为160 km的动车组。为评估老线中典型桥梁在开行动车组后的服役性能,通过数值仿真及现场静动力荷载试验的方式,对某3×64 m连续钢桁梁桥的静力及动力性能进行检测与评估。研究表明,静力荷载作用下,主桁杆件最大轴向拉、压应力分别为143.1,175.4 MPa,均小于容许应力240 MPa,结构具有足够的强度安全储备。第34、35、36孔挠跨比分别为1/1 756、1/1 940、1/1 732,均小于规范规定的1/1 250,表明该桥具备通行动车组的刚度条件。各工况下活动支座纵向位移最大值为3.195 mm,小于支座纵向位移允许限值,表明各活动支座工作状态良好。动荷载作用下,主梁振型、自振频率与既有检定结果差异不大,且均小于理论计算值。主梁跨中竖向加速度、主梁跨中横向加速度、桥墩横向振幅及活动支座横向变形均满足规范要求,表明该钢桁梁桥主梁、桥墩及支座等主要组成部分的技术指标均满足行车要求。

钢螺杆锚桩压重联合静载试验钢梁设计与验证

为保证大吨位桩基静载试验安全实施,加载反力结构的合理设计至关重要。建立了加载反力平台钢梁的简化计算模型,分析不同受荷工况下钢梁的内力与变形发展规律,并对主、次钢梁截面尺寸进行优化设计。最后,针对实际静载试验项目对钢梁竖向位移、倾斜及锚桩抗拔力进行监测,验证钢梁计算模型的合理性。分析结果表明,钢梁在整个静载试验过程中的变形实测值均小于理论计算值;当施加的静载试验总反力超过堆载块和钢梁自重后,钢螺杆锚桩参与受荷,随着加载荷载的增大,其抗拔承载力的贡献逐渐增大;对于采用钢螺杆锚桩联合压重反力装置的静载试验,监测的各根钢梁竖向位移和倾斜总体一致,未出现明显偏心受力情况,表明该静载试验方法具有较高的安全性。

服役15年大跨跨海预应力混凝土梁桥荷载试验及结构性能评价

大跨预应力混凝土梁桥因其结构刚度大、行车平顺舒适、抗震性能好、施工技术成熟等优势得到广泛应用,该类桥梁在服役较长时间后,由于自然环境和超载的长期影响可能导致结构出现裂缝,并影响结构的安全承载能力,这一问题对于跨海桥梁显得尤为突出。因此,为准确评估在役跨海混凝土桥梁的实际工作状态与承载能力,通过对一座已服役15年的大跨跨海预应力混凝土梁桥进行现场静载、动载试验,并结合有限元对其振型等特性进行了分析。研究结果表明,桥梁结构的工作性能仍保持良好,但由于所处海域环境及长期服役导致的结构损伤和裂缝的影响,使其实际承载能力有所下降。研究成果可为在役同类桥梁的维修加固提供参考。

高墩大跨连续刚构桥的荷载试验研究

为探明某高墩大跨连续刚构桥在正常运营状态及最不利受力状态下的动静态荷载特性,基于成桥荷载试验方法,开展不同车辆位置、车速等条件下大跨连续刚构桥动静荷载现场试验。试验主要包括正载及偏载两种情况,静荷载试验测试了这两种情况下的主梁应变与挠度,动荷载试验分别在20、30、40 km/h车速下,通过无障碍行车试验和刹车试验,测试了桥梁的冲击系数、自振频率及动应变。在采集处理完现场数据后,将其与有限元软件的理论计算结果进行对比分析。研究结果表明:该连续刚构桥在正载及偏载两个工况下,挠度和应变实测值均小于理论计算值,相对残余应变最大值为18.8%,相对残余挠度最大值为11.71%,均不超过20%;在动载试验中,主桥一、二、三阶竖向实测振动频率均大于理论计算值;该连续刚构桥承载能力满足要求。

基于响应面法和ARO算法的桥梁有限元模型修正

针对桥梁结构模型修正过程中计算量大、全局寻优难等问题,提出一种基于响应面法和人工兔优化算法(artificial rabbits optimization, ARO)的桥梁有限元模型修正方法。该方法通过F检验法明确对结构响应影响显著的参数并建立响应面模型作为桥梁有限元模型的代理模型进行迭代计算,然后通过静动力联合修正法基于特征响应的响应面模型计算值和试验值构建目标函数,并通过人工兔优化算法对目标函数进行迭代计算进而获得精确的有限元模型参数。采用该方法对变截面连续刚构黄河特大桥有限元模型进行修正,结果显示:基于显著性分析结果建立的桥梁响应面模型相关系数大于0.98,且平均绝对误差低于0.05;模型修正后主梁关键截面竖向位移最大相对误差由32.97%降至5.72%,平均相对误差由20.67%降至3.61%,桥梁前3阶竖向自振频率平均相对误差仅为0.18%。可见,采用所提方法修正的模型能用于评价桥梁结构实际受力性能。

多种检测方法在冲填土强夯检测中的联合应用

强夯是处理沿海滩涂冲填土地基的有效方法,而强夯加固后地基的检测是场地能否用于建设的重要依据。通过静载试验、静力触探原位测试、室内土工试验及轻型圆锥动力触探试验这4种方法联合检测强夯效果,并对4种方法进行对比分析,以供同类型工程参考。