Mechanical properties and supporting effect of CRLD bolts under static pull test conditions

A device for supporting soft rock masses combined with a constant resistance structure characterized by constant resistance and large deformation at the end of a steel bar, known as the constant resistance and large deformation（CRLD） bolt, has recently been developed to counteract soft rock swelling that often occurs during deep mining. In order to further study the mechanical properties of the CRLD bolt, we investigated its mechanical properties by comparison with the conventional strength bolt（rebar） using static pull tests on many aspects, including supporting capacity, elongation, radial deformation, and energy absorption. The tests verified that the mechanical defects of the rebar, which include the decrease of bolt diameter, reduction of supporting capacity, and emergence and evolution of fracture until failure during the whole pull process, were caused by the Poisson＇s ratio effect. Due to the special structure set on the CRLD bolt, the bolt presents a seemingly unusual phenomenon of the negative Poisson＇s ratio effect, i.e., the diameter of the constant resistance structure increases while under-pulling. It is the very effect that ensures the extraordinary mechanical properties, including high resistance, large elongation, and strong energy absorption. According to the comparison and analysis of numerical simulation and field test, we can conclude that the CRLD bolt works better than the rebar bolt.

Development of the rolling extrusion rock bolt with constant resistance and large deformation

With the increasing excavation depth of underground engineering,engineering problems such as large deformation and rock burst caused by high geo-stress brings new challenges to the excavation and reinforcement of surrounding rock in deep underground engineering.The traditional rock bolt is prone to brittle fracture under high geo-stress due to its low elongation.Therefore,this work aims to develop a novel energy-absorbing bolt with constant resistance and large displacement to reinforce the surrounding rock with a risk of large deformation or rockburst.The novel energy-absorbing bolt refereed as rolling extrusion rock bolt(RE bolt)is mainly consists of sleeve tube with a variable cross-section,energy absorption slider with steel balls embedded,steel bar connected with the energy absorption slider.The rolling extrusion is adopted to produce the resistance force of the RE bolt,which avoids the sudden attenuation of resistance force and the abrasion of the energy absorption slider.The static pull test is conducted to study the resistance force and deformation characteristics of the RE bolt with different specifications.Results imply that the RE bolt has higher resistance force,larger deformation capacity and energy absorption capacity.The work of this study provides an effective solution for the reinforcement of surrounding rock in deep rock engineering.

Sea Experiments of the Underway Conductivity-Temperature-Depth Prototype Made in China

A new instrument for upper ocean survey, namely the UCTD （Underway Conductivity-Temperature- Depth）, which combines some of the advantages of other underway instruments, is introduced in this paper. The Introduction section presents a description of the construction and function of the UCTD, and the experiments conducted in the South China Sea on board the R/V Dong Fang Hong 2 in July 2007 and August 2008. The UCTD system, with pressure and temperature sensors in the probe, is con- veniently portable, cost-effective and environment-friendly. It is hopefully suitable for future cruises. An intercomparison based on regressing with the experiment temperature data from both SeaBird plus911 CTD and the UCTD showed that the standard deviation is 0.88~C and the correlation coefficient is 0.96, achieving the goals set for the current oceanography uses. In the hydrodynamic experiments, the descending velocities and depths were calculated for different ship speeds. A pulling test was designed with a tensiorneter to measure the magnitude of the pull. The maximal tension of the line was found to be 66.2 kg, which is far lower than the bearing limit of the Hollow Spectra line. Finally, some improvement suggestions are put forward for future experiments and production.

EVALUATION OF ADHESION AND PLASTICITY OF PVD FILMS

Evaluation of adhesion of PVD Ti and TiN films on steel A_3 was carried out with constant rate pulling test(CRPT)at 0.05 mm/min under simultaneous SEM observation. As a criterion,the critical elongations of the film/substrate system for the initial cracking and spelling of the film may be applied to evaluate the plasticity and adhesion of the film to substrate.The conventional scratch test was also made for evaluation of the adhesion for the same systems.Both methods give the coordinate assessment for all the systems. In addition,the influence of the films on the ultimate yield strength of the substrate was discussed and another criterion of conherent work was proposed for the evaluation.

A review on the performance of conventional and energy-absorbing rockbolts

This is a review paper on the performances of both conventional and energy-absorbing rockbolts manifested in laboratory tests. Characteristic parameters such as ultimate load, displacement and energy absorption are reported, in addition to load-displacement graphs for every type of rockbolt. Conventional rockbolts refer to mechanical rockbolts, fully-grouted rebars and frictional rockbolts. According to the test results, under static pull loading a mechanical rockbolt usually fails at the plate; a fully-grouted rebar bolt fails in the bolt shank at an ultimate load equal to the strength of the steel after a small amount of displacement; and a frictional rockbolt is subjected to large displacement at a low yield load. Under shear loading, all types of bolts fail in the shank. Energy-absorbing rockbolts are developed aiming to combat instability problems in burst-prone and squeezing rock conditions. They absorb deformation energy either through ploughing/slippage at predefined load levels or through stretching of the steel bolt. An energy-absorbing rockbolt can carry a high load and also accommodate significant rock displacement, and thus its energy-absorbing capacity is high. The test results show that the energy absorption of the energy-absorbing bolts is much larger than that of all conventional bolts. The dynamic load capacity is smaller than the static load capacity for the energy-absorbing bolts displacing based on ploughing/slippage while they are approximately the same for the D-Bolt that displaces based on steel stretching.

Influence of sand content on the flow characteristics of soft soil under cyclic and high-frequency vibration

The flow characteristics of foundation soils subjected to train loads can present engineering hazards in highspeed railways.In order to verify the feasibility of blending coarse sand in modifying soft subsoil,undrained pulling sphere tests were carried out and the train loads were simulated through localized and cyclic vibration at various frequencies.Laboratory testing results indicate that the fl ow characteristics of soft soil can be signifi cantly enhanced by high-frequency vibration;meanwhile the continuous increase in fl ow characteristics caused by cyclic vibration may be an important reason for the long-term settlement of soft subsoil.The infl uence of sand content on fl ow characteristics is also studied in detail,and it is shown that the addition of coarse sand can weaken the fl ow characteristics of soft soil induced by sudden vibration at lower than 50 Hz.Under the condition of cyclic vibration,the growth of the fl ow characteristics of sand-clay mixtures is mainly caused by the fi rst-time vibration in the cycle,and the increase in sand content can make the fl ow characteristics present a faster convergent tendency.

Bonding between Aggregates and Cement Pastes in Concrete

This investigation was carried out to study the effect of aggregate roughness on ITZ （interfacial transition zone） at same water/cement ratio and the influence of silica fume on the bond strength. On the experimental side, two types of aggregates （limestone and granite） were used, which were prepared with broken surface. Cement （Type I） was used with same w/c ratio for all batches. In order to study the effect of silica fume on the bond, the same mixes were produced with 8% silica fume. Three different tests were performed： ＂pull a part＂, Brazilian test and compressive strength test. The specimens for Brazilian and compressive strength were tested after 28 days, while the ＂pull a part＂ specimens were tested after 29 days. The result showed that the bond strength is influenced by the surface roughness of aggregate. For the same mix, limestone recorded higher bond strength than granite. Moreover, the bond strength is increased by adding the silica fume.