Dynamic analysis of new type elastic screen surface with multi degree of freedom and experimental validation

A feasible method was proposed to improve the vibration intensity of screen surface via application of a new type elastic screen surface with multi degree of freedom(NTESSMDF). In the NTESSMDF, the primary robs were coupled to the main screen structure with ends embedded into the elastomers, and the secondary robs were attached to adjacent two primary robs with elastic bands. The dynamic model of vibrating screen with NTESSMDF was established based on Lagrange's equation and the equivalent stiffnesses of the elastomer and elastic band were calculated. According to numerical simulation using the 4th order Runge-Kutta method, the vibration intensity of screen surface can be enhanced substantially with an averaged acceleration amplitude increasing ratio of 72.36%. The primary robs and secondary robs vibrate inversely in steady state, which would result in the friability of materials and avoid stoppage. The experimental results validate the dynamic characteristics with acceleration amplitude rising by62.93% on average, which demonstrates the feasibility of NTESSMDF.

When traditional ground support techniques aren’t enough–Chemical injections can solve complex problems

Broken and jointed ground is extremely hazardous and requires unique stabilization techniques to protect workers and critical entries.Bolting techniques,even the most advanced pre-load to create roof compression,can leave large gaps of unconfined and separated roof.This roof can also be susceptible to water inflows which only exacerbate the support problem.These types of conditions existed on long-term development main entry accessing several future longwall panels.The geotechnical assessment identified well defined jointing systems that also permitted water to flow between the roof separations,which"lubricated"the roof material and minimized any frictional advantages.Chemical injections of polyurethane materials,Minova Carbopur WS,was placed beyond the bolted horizon to move the water to the rib lines and reinforce the fractured and broken roof.The injection materials permitted the effective use of bolting patterns and helped ensure long-term stability of critical entries.The paper describes the evaluation techniques,design patterns,basis for chemical selection and application,and results and recommendations.

CORROSION FATIGUE OF HSLA STEELS IN SALT SPRAY

The corrosion fatigue propagation behaviour of high strength low alloy Cr-Ni and Si-Mn steels has been investigated in 3.5 %NaCl solution spryly at the frequencies of 0.1 and 5.5 Hz. It was shown that the fatigue crack initiation resistances of the two steels are significantly re- duced in salt spray;the fatigue crack growth rates of steels increase with the decrease of fre- quency and are much higher in salt spray than in air within low ΔK range.A critical stress in- tensity factor was observed for each steel and the crack growth stoppage will occur if the ΔK values are lower than it.It was found that the active dissolution makes great contribution to the fatigue crack growth within low ΔK range.

Interpretation of pipe-jacking and lubrication records for drives in silty soil

In recent years,there has been an increased resort to microtunnelling/pipe-jacking as a means of constructing underground conduits(for water,sewage,gas,and other utilities)to avoid on-street disruption in urban areas.In this paper,technical details of two 1200 mm internal diameter microtunnels in silty sand totalling over 550 m in length are discussed.While average skin friction values are extremely low for both drives suggesting effective lubrication practice,differences in normalised bentonite volumes appear to be responsible for differences in skin friction.Full or near full buoyancy of the pipeline has been demonstrated for the majority of the drive.The frictional stress increase after a stoppage is shown to depend on not only the stoppage duration but also on the normalised lubrication volume.Interpretation of data in the manner presented in the paper is an important means of assimilating experience of microtunnelling in different ground conditions.