Performance of D-bolts Under Static Loading

D-bolt is a type of energy-absorbing rock bolt. It is made of a smooth steel bar with anchors spaced along the bolt length. A typical section between adjacent anchors is approximately 1-m long, but it can be adjusted to adapt to the rock conditions. The bolt is fully encapsulated with either cement or resin grout in a borehole. The anchors are firmly fixed into the grout, while the smooth bolt sections can freely deform to absorb deformation energy. Full-scale static pull tests were carried out at different testing facilities in two laboratories. The tests show that a smooth bolt section between anchors may elongate by 110–167 mm depending on the section length. Field trials of the D-bolt were conducted in deep metal mines. The measurements showed that the D-bolts were equally loaded within every anchor-between section, avoiding load peaks and premature bolt failure due to stress concentrations caused by fracture/joint opening. The field trials of rebar and D-bolts in a largely deformed mine tunnel showed that the D-bolts behaved satisfactorily, with only a few failed bolts, while a number of the rebar bolts failed at the thread.     

Innovative constant resistance large deformation bolt for rock support in high stressed rock mass

Bolt supporting is a major technology used in highly stressed surrounding rock support. Although significant developments of new patterns of bolts have been documented, the stiffness problem which causes the bolt to cannot adapt to the large deformation of surrounding rock was still unsolved. Hence, a novel bolt with constant working resistance and steady large deformation was developed to bear creep deformation and impact load. The constant resistance large deformation bolt (CRLD bolt) was composed of constant resistance element, bolt rod, baffle plate, and tightening nut, which would efficiently control the engineering disasters such as collapse and rock blast. The results of static tensile tests indicated that the CRLD bolt could provide constant resistance ranging from 120 to 130 kN, and the maximal elongation length was 1100 mm without bolt breaking at tensile rate of 10, 20, and 100 mm/s, respectively. Tensile rate has no obvious relationship with constant resistance force. Dynamical impact tests showed that bolt resistance property and its absorption capacity of impact energy were stable, and the dynamic constant resistance changed from 90 to 120 kN, with the impacting height for drop hammers of 10 and 1000 mm. It has also been proved that this kind of bolt has good performance in practical application such as in Qing Shui coal mine. The in situ monitoring results indicate that the CRLD bolt is able to retain rock mass stability and prevent the surrounding rocks from being destructed due to its large-scale deformation. Overall, CRLD bolt is suitable for large deformation, constant resistance, and energy absorption.     

Three-dimensional numerical modelling of falling rock protection barriers

This paper presents a new numerical strategy for the design and verification of flexible falling rock barriers: passive protection measures for risk mitigation of potentially unstable rock slopes. The key point of the proposed approach is that notwithstanding the complexity of the simulated phenomenon, the resulting highly non-linear, dynamic model is simple and produces an accurate prediction of all the relevant parameters for barrier design, such as anchorage forces, net panel elongations and residual heights.The modelling procedure has been assessed using detailed experimental data obtained from a set of full-scale tests on three barrier prototypes with various energy absorption capacities (5000 kJ, 3000 kJ and 500 kJ). By comparison with the experimental results, the numerical model has shown to be reliable in capturing very accurately the barrier response to a block impact. Consequently, this method can be extended to investigate the behaviour of flexible falling rock protection barriers under conditions different from those encountered in full-scale tests. Therefore, the numerical procedure can be regarded as an effective tool used for designing and testing these structures.     

Proton migration in portlandite inferred from activation energy of self-diffusion and potential energy curve of OH bond

A fundamental mechanism on the atomic level for self-diffusion in the proton layer of portlandite, Ca(OH)₂, was investigated by conducting hydrogen–deuterium (H–D) exchange diffusion experiments and by deriving potential energy curves of OH vibrations from optical absorption measurements. Synthetic single crystals of portlandite were used in H–D experiments between 250 and 450°C at 150 MPa. Arrhenius parameters for proton diffusion perpendicular to the c-axis gave a frequency factor of 1.0 × 10⁻¹⁰ m²/s and activation energy of 0.61 eV (58.5 kJ/mol). The activation energy corresponds to the height of the potential barrier between two oxygen atoms across an interlayer. The potential barrier height was also theoretically estimated using the OH potential energy curve (OH-PEC) determined by optical absorption measurements. Experimental and theoretical results suggest that the potential barrier height cannot be simply determined by overlapping two OH-PECs. The potential barrier derived theoretically was 3.11 eV. This is too high for the activation energy of the proton diffusion. It implies that the interaction between a diffusing proton and the vacancy of a proton site, and the shortening of interlayer oxygen distance by thermal vibration reduce the potential barrier.     

冲击荷载下玄武岩纤维水泥土吸能及分形特征

为研究玄武岩纤维对水泥土冲击破坏过程中能量吸收及碎块块度分布特征的影响,采用Φ50 mm变截面霍普金森压杆（split Hopkinson pressure bar,简称SHPB）试验装置对不同玄武岩纤维掺量的水泥土进行了冲击压缩和动态劈裂试验,分析了冲击荷载作用下玄武岩纤维掺量与水泥土吸收能、破坏形态和分形维数 的关系,试验结果表明：随着玄武岩纤维掺量的增加,水泥土吸收能呈先增大后减小的趋势,超过最佳掺量后,由于纤维-纤维薄弱面的存在,水泥土吸收能减少;冲击破坏后水泥土破碎块度分布是具有统计意义上的分形,冲击压缩试验中水泥土破碎块度平均粒径随玄武岩纤维掺量的增加而不断增大,对应的 值总体上呈现不断减小的趋势;在动态劈裂试验中,玄武岩纤维掺量在0～2.0%范围内,水泥土破碎块度平均粒径呈现上升趋势, 值不断减小,玄武岩纤维掺量超过2.0%后,平均粒径有所降低,对应 值增大。玄武岩纤维水泥土吸收能和 值之间有着密切的联系,冲击压缩试验中,吸收能在分形维数为2.20～2.26范围内呈先增大后减小的趋势,而在动态劈裂试验中,吸收能在分形维数为1.85～2.20范围内总体呈现下降趋势,两者具有一定的负相关性;合适掺量的玄武岩纤维对水泥土动态特性起着积极作用,通过试验得出玄武岩纤维的合适掺量为1.5%～2.0%。     

Paleoseismological analysis of an intraplate extensional structure: the Concud fault (Iberian Chain,eastern Spain)

The Concud fault is a 13.5 km long, NW–SE striking normal fault at the eastern Iberian Chain. Its recent (Late Pleistocene) slip history is characterized from mapping and trench analysis and discussed in the context of the accretion/incision history of the Alfambra River. The fault has been active since Late Pliocene times, with slip rates ranging from 0.07 to 0.33 mm/year that are consistent with its present-day geomorphologic expression. The most likely empirical correlation suggests that the associated paleoseisms have potential magnitudes close to 6.8, coseismic displacements of 2.0 m, and recurrence intervals from 6.1 to 28.9 ka. At least six paleoseismic events have been identified between 113 and 32 ka. The first three events (U to W) involved displacement along the major fault plane. The last three events (X to Z) encompassed downthrow and hanging-wall synthetic bending prompting fissure opening. This change is accompanied by a decrease in slip rate (from 0.63 to 0.08–0.17 mm/year) and has been attributed to activation of a synthetic blind fault at the hanging wall. The average coseismic displacement (1.9–2.0 m) and recurrence period (6.7–7.9 ka) inferred from this paleoseismic succession are within the ranges predicted from empirical correlation. Such paleoseismic activity contrasts with the moderate present-day seismicity of the area (maximum instrumental Mb = 4.4), which can be explained by the long recurrence interval that characterizes intraplate regions.     

An experimental study on static and dynamic bending behaviour of piles in soft clay

Static and dynamic lateral load tests were carried out on model aluminium single piles embedded in soft clay to study its bending behaviour. Model aluminium piles with length to diameter ratios of 10, 20, 30 and 40 were used. Static lateral load tests were conducted on piles by rope and pulley arrangement upto failure and load–deflection curves were obtained. Dynamic lateral load tests were carried out for different magnitudes of load ranging from 7 to 30 N at wide range of frequencies from 2 to 50 Hz. The load transferred to the pile, pile head displacement and the strain variation along the pile length were measured using a Data Acquisition System. Safe static lateral load capacity for all piles is interpreted from load–deflection curves. Dynamic characteristics of the soil–pile system were arrived from the acquired experimental data. The soil–pile system behaves predominantly in nonlinear fashion even at low frequency under dynamic load. The displacement amplitude under dynamic load is magnified by 4.5–6.5 times the static deflection for all piles embedded in soft clay. But, the peak magnification factor reduces with an increase in the magnitude of lateral load mainly because of increase of hysteretic damping at very soft consistency. The maximum BM occurs at the fundamental frequency of the soil–pile system. Even the lower part of the pile affects the pile head response to the inertial load applied at the pile head. The maximum dynamic BM is magnified by about 1.5 times the maximum static BM for model piles in tested consistency of clay. The maximum dynamic BM occurs at a depth of about 1.5 times the depth of maximum static BM for model piles, which indicates an increase of active pile length under dynamic load.     

深部破碎软岩巷道围岩稳定性分析及控制

针对深部破碎软岩巷道围岩稳定性控制难题,以邢东矿-980车场巷道为研究对象,采用现场调研、数值模拟、井下试验及现场观测等方法分析围岩变形破坏特征,揭示其破坏机制,针对性地提出了以高强锚杆密集支护、新型喷层结构护表、滞后注浆加固为主体的多层次锚喷网注联合支护系统,详细阐明了具体支护措施的围岩控制机制,并用数值方法分析了锚杆间距、喷层厚度对于围岩应力场和位移场的影响规律。研究表明：（1）随着锚杆间距减小（0.7 m→0.3 m）,锚杆承压拱和喷层结构的承载能力呈幂函数增长趋势,锚固区围岩压应力呈线性增长趋势,围岩变形量明显降低;（2）随着喷层厚度增大,喷层结构承载能力近似线性增长,锚固区围岩压应力亦呈增长趋势,各部位围岩位移量显著降低;（3）当喷层厚度达到200 mm时,非锚固区内围岩大部分处于压应力状态,拉应力区大幅减少。基于上述研究,结合现场地质、生产条件确定试验巷道围岩支护方案,并进行现场应用。工程实践表明,多层次锚喷网注联合支护技术可有效控制深井破碎软岩巷道围岩大变形,实现深井巷道围岩的稳定性控制。     

Low T heat capacity measurements and new entropy data for titanite (sphene): implications for thermobarometry of high-pressure rocks

The accepted standard state entropy of titanite (sphene) has been questioned in several recent studies, which suggested a revision from the literature value 129.3 ± 0.8 J/mol K to values in the range of 110–120 J/mol K. The heat capacity of titanite was therefore re-measured with a PPMS in the range 5 to 300 K and the standard entropy of titanite was calculated as 127.2 ± 0.2 J/mol K, much closer to the original data than the suggested revisions. Volume parameters for a modified Murgnahan equation of state: V _P,T  = V ₂₉₈° × [1 + a°(T − 298) − 20a°(T − 298)] × [1 – 4P/(K ₂₉₈ × (1 – 1.5 × 10⁻⁴ [T − 298]) + 4P)]^1/4 were fit to recent unit cell determinations at elevated pressures and temperatures, yielding the constants V ₂₉₈° = 5.568 J/bar, a° = 3.1 × 10⁻⁵ K⁻¹, and K = 1,100 kbar. The standard Gibbs free energy of formation of titanite, −2456.2 kJ/mol (∆H°_f = −2598.4 kJ/mol) was calculated from the new entropy and volume data combined with data from experimental reversals on the reaction, titanite + kyanite = anorthite + rutile. This value is 4–11 kJ/mol less negative than that obtained from experimental determinations of the enthalpy of formation, and it is slightly more negative than values given in internally consistent databases. The displacement of most calculated phase equilibria involving titanite is not large except for reactions with small ∆S. Re-calculated baric estimates for several metamorphic suites yield pressure differences on the order of 2 kbar in eclogites and 10 kbar for ultra-high pressure titanite-bearing assemblages.     

苏州地区深基坑锚杆支护的应用实例

苏州地区地层多为粉质粘土夹粉土,含水量较大,呈软塑至流塑状态,对深基坑支护极为不利。苏州世茂运河城深基坑支护工程选用护坡桩＋土层锚杆方案。锚杆设计为三层,间距为1.5m,承载力分别为250、280和220kN,有效锚固段长度分别为13、14.4和14m,杆体选用1860级75mm钢铰线。每层锚杆施工完成后,均进行了验收试验。试验结果表明,各层锚杆的承载力完全满足设计要求,而且安全储备很大,证明锚杆在软塑土层中的应用是可行的。     

Influence of different transition zones on the dynamic response of track–subgrade systems

A railway track–subgrade system is modeled using the finite element method (FEM). Two different transition zones between a bridge and an ordinary subgrade, usually used for high speed passenger lines in China, are investigated. Both the calculated vertical displacement and acceleration of the rail and the slab and the calculated vertical displacement and the stress of the subgrade surface of the two transition zones are compared. The dynamic response of the two-part transition section is better than that of the inverted trapezoid transition section, and a 30-m length of both transition sections is recommended. The dynamic response of the track–subgrade system changes abruptly after the first 3 m of the transition section, measured from the bridge abutment. Special attention should be given to this critical zone during construction.     

Electrical conductivity of amphibole-bearing rocks: influence of dehydration

We investigated the electrical conductivity of amphibole-bearing rocks under the conditions of the middle to lower crust. Alternating current measurements were performed in the frequency range of 10–10⁶ Hz in a cubic-anvil high-pressure apparatus at 0.5–1.0 GPa and 373–873 K. The electrical conductivity of these rocks is weakly temperature dependent below ~800 K with modest anisotropy and relatively low conductivity (~5 × 10⁻³ S/m at ~750 K with the activation enthalpy of 64–67 kJ/mol). However, the electrical conductivity starts to increase with temperature more rapidly above ~800 K (activation enthalpy of 320–380 kJ/mol). The infrared spectroscopy observations indicate that dehydration occurs in this high temperature regime. The observed high activation enthalpy and the reproducibility suggest that the enhanced conductivity is not due to the direct effect caused by the generation of conductive fluids. Dehydration of amphibole is associated with the oxidation of iron (from ferrous to ferric), and we suggest that the increased conductivity associated with dehydration is caused by oxidation. This effect may explain high electrical conductivity observed in some regions of the continental crust.     

Examination of loose saturated sands impacted by a heavy tamper

This article examines the densification effects on the loose saturated sands impacted by a heavy steel tamper dropped from a great height (i.e., deep dynamic compaction, DDC). This examination was achieved by carrying out a series of piezocone penetration test (CPTu) soundings before and after the DDC impact. The depths at which densification took place ranged from 6.5 to 9.5 m below the ground surface (BGS) after one pass of DDC, and from 7.5 to 11.0 m BGS after two passes. The propagation of the surface waves generated in DDC disturbed the top 0.3–1.3 m soils. Directly below this disturbed layer, it was the most densified soil layer at the depths of 1.7–4.5 m BGS. The existence of the residual soft peat pockets reduced the densification effects substantially. Both the strength and the stiffness of the loose saturated sands were significantly improved after the DDC treatment. After two passes of impact, the liquefiable soils were densified to the level of unliquefiable along with dramatic reduction in liquefaction probabilities when subjected to earthquake motions.     

Geophysical investigation for shallow subsurface geotechnical problems of Mokattam area,Cairo, Egypt

Nine vertical electrical soundings of Schlumberger configuration were measured with AB/2 = 1–500 m. Manual and computerized interpretation were done to detect the subsurface stratigraphy of the study area. The results show that the subsurface section consists of alternated units of limestone, clay, marly limestone and dolomitic limestone and the thickness of clay unit ranged from 10 to 40 m. Nine dipole–dipole sections have also been constructed to give a clearer picture of the subsurface at the study area. The length of each dipole–dipole section is 235 m, with a electrode spacing ranging between 5 and 25 m. The Res2Dinv software was used for processing and interpretation of field data. The dipole–dipole sections at the upper plateau display high resistivity values at most parts of the plateau. Twelve shallow seismic refraction profiles are measured at selected locations for the dipole sections to define the interface between the fractured limestone and the upper surface of the clay layer. Each profile consists of 24 geophones with a geophone spacing of 2–3 m. Interpretation of seismic data indicates that the surface layer of the upper plateau consists of fractured limestone with a velocity range of 1.16–1.56 km/s and another layer of compacted clay with a velocity range of 1.38–1.88 km/s. Furthermore, the surface layer of the middle plateau consists of marl and marly limestone with a velocity about 2.1 km/s and its underlying layer consists of massive limestone with a velocity of 4.94 km/s.     

不同围岩条件下锚杆肋间距与锚固力优化研究

为研究不同围岩条件下锚杆肋间距与锚固性能的关系,基于厚壁理论,对肋间距分别为12、24、36、48 mm的左旋螺纹钢锚杆锚固试件在套筒壁厚4.5 mm和6.0 mm条件下进行拉拔试验,通过测试拉拔力、拉拔力大于100 kN的位移量、套筒周向应变、耗能值等参数,探讨了不同围岩条件下锚杆肋间距与锚固性能的关系。试验结果表明:在不同的套筒中,即不同围岩条件下,随着肋间距的增加,锚杆拉拔力大于100 kN的位移量、套筒周向应变、拉拔耗能值相应增大;肋间距为24 mm时,锚杆拉拔力最大,相同肋间距的锚杆在围岩强度较大的条件下拉拔力较大;壁厚为4.5 mm的套筒周向应变均大于壁厚为6.0 mm的套筒,即不同围岩条件对锚杆控制其变形能力有重要影响;在不同围岩条件下,增大肋间距均可以提高锚杆的锚固性能。     

International viewpoint and news

The investigations were carried out in order to evaluate change of the beaches profile during the period 1993–2008 and to elucidate main trends of the coastal dynamics. Morphometric indicators (beach width, height and inclination) were measured every year during the period 1993–2008 in 70 measuring stations located along the coastline. It was determined that the dynamic shoreline of the mainland during 1993–2008 receded by 10.2 m and the dynamic shoreline of the Curonian Spit advanced into the sea by 8.3 m. The different morphometric beach indicators changed to varying extents over the period 1993–2008, but comparison of values for 1993 and 2008 showed that those changes were small. The average beach width increased by 1.2 m on the mainland coast and by 0.5 m on the Curonian Spit coast. The average beach height also increased negligibly: by 0.5 m on the mainland coast and by 0.1 m on the Curonian Spit coast. The average beach slope inclination increased by 0.012 (from 0.065 to 0.077) on the mainland coast and by 0.005 (from 0.073 to 0.078) on the Curonian Spit coast. The measurements show that, despite being the most dynamic elements in the coastal system, these beaches managed to retain their morphometric indicators almost unchanged during the period of observation.     

Behaviour of Cellular Reinforced Sand Under Triaxial Loading Conditions

Cellular reinforcement is a three dimensional reinforcement used for reinforced soil structures. Behaviour of such reinforcement is important for its use in actual practice. Present paper focuses on the behavior of cellular reinforcement in sand under the triaxial loading conditions. Series of triaxial tests are performed on unreinforced and reinforced sand with single layer as well as double layers of cellular reinforcements with 75 mm sample diameter. Six different reinforcement heights of cellular reinforcements (varying from 3 to 50 mm) are used along with one sheet reinforcement of thickness 1 mm. From the experimental failure patterns of the triaxial samples, multiple zones of failure are observed as an effect of cellular reinforcement. Deviator stress–strain curves are studied for single and double layers of cellular reinforcement under three different confining pressures. Peak deviator stress is found increasing with increasing height of cellular reinforcement, which shows the confining effect of cellular reinforcement. Shear strength parameters are evaluated and are found increasing with increase in height of cellular reinforcement, also cellular reinforcement with heights 10 mm and more have showed increased shear strength parameters, as compared to 1 mm thick sheet reinforcement. This assures better behavior performance of cellular reinforcement over the planar one. Failure patterns are also visualized by finite element analysis and found in accord with experimental observations Horizontal displacement for reinforced samples visualized multi-zoned failure pattern. Finite element results for deviator stress–strain relationship are found in reasonably good accord with experimental results.     

A palaeoseismological and geoarchaeological investigation of the Eliki fault,Gulf of Corinth,Greece

Palaeoseismological and morphotectonic analyses enable us to define a 400-m-wide actively deformed zone associated with the active Eliki normal fault, central Greece, bounded on the south by a second-order fault and on the north by a composite and prominent fault scarp. This scarp is further analysed by trenching. Based on colluvium stratigraphy, displacement of distinct horizons and deposition of sedimentary layers, three faulting events have been identified along four fault strands affecting unconsolidated sediments in the trench. The two younger events, with throws of 0.93 and 1.37 m, respectively, the third event, with a throw of 0.44 m, and the penultimate 373 BC event suggest a variable seismic history.The entire alluvial plain of the Kerynitis and Vouraikos rivers, which cross the Eliki fault, has subsided at a rate of 1.4 mm/year, resulting in the burial of the Late Hellenistic–Roman occupation horizons under 3 m of fluvial and colluvial sediments in places.Extension in the broader area is accommodated by the seismically active Eliki and Egion faults. Structural and palaeoseismological analysis of those two faults indicates that they accommodate 1.5 mm/year, or about 10% of the geodetically estimated extension of up to 13 mm/year.     

Observed source parameters for dynamic rupture with non-uniform initial stress and relatively high fracture energy

We have conducted dynamic rupture propagation experiments to establish the relations between in-source stress drop, fracture energy and the resulting particle velocity during slip of an unconfined 2 m long laboratory fault at normal stresses between 4 and 8 MPa. To produce high fracture energy in the source we use a rough fault that has a large slip weakening distance. An artifact of the high fracture energy is that the nucleation zone is large such that precursory slip reduces fault strength over a large fraction of the total fault length prior to dynamic rupture, making the initial stress non-uniform. Shear stress, particle velocity, fault slip and acceleration were recorded coseismically at multiple locations along strike and at small fault-normal distances. Stress drop increases weakly with normal stress. Average slip rate depends linearly on the fault strength loss and on static stress drop, both with a nonzero intercept. A minimum fracture energy of 1.8 J/m² and a linear slip weakening distance of 33 μm are inferred from the intercept. The large slip weakening distance also affects the average slip rate which is reduced by in-source energy dissipation from on-fault fracture energy.Because of the low normal stress and small per event slip (∼86 μm), no thermal weakening such as melting or pore fluid pressurization occurs in these experiments. Despite the relatively high fracture energy, and the very low heat production, energy partitioning during these laboratory earthquakes is very similar to typical earthquake source properties. The product of fracture energy and fault area is larger than the radiated energy. Seismic efficiency is low at ∼2%. The ratio of apparent stress to static stress drop is ∼27%, consistent with measured overshoot. The fracture efficiency is ∼33%. The static and dynamic stress drops when extrapolated to crustal stresses are 2–7.3 MPa and in the range of typical earthquake stress drops. As the relatively high fracture energy reduces the slip velocities in these experiments, the extrapolated average particle velocities for crustal stresses are 0.18–0.6 m/s. That these experiments are consistent with typical earthquake source properties suggests, albeit indirectly, that thermal weakening mechanisms such as thermal pressurization and melting which lead to near complete stress drops, dominate earthquake source properties only for exceptional events unless crustal stresses are low.