Longwall Retreat and Creep Measurement Based on UWB Radar Imaging Method

The measurement of longwall retreat and creep displacements is of great significance for the safety production of a coal mine. In order to reliably and accurately obtain the longwall retreat and creep displacements, this paper proposes an ultrawideband (UWB) radar imaging method. The bolt plates fixed in the roadway coal wall are imaged as the target points. First, a signal model is built, and a modified nonlinear chirp scaling (NLCS) imaging algorithm is designed to obtain the high-resolution image. Then, the retreat and creep displacements are estimated based on the imaging results. Finally, simulation and experiment are performed. The simulation results show that the radar imaging method is theoretically feasible to measure the retreat and creep displacements. The measurement errors in the experiment are 0.058 m and 0.040 m, respectively. In the experiment, the radar velocity fluctuation and signal attenuation cause the target azimuth and range errors in the imaging results, which makes the measurement errors in the experiment larger than that in the simulation. This method requires no additional roadway information except for the bolt plates fixed in the coal wall. In addition, the signal propagation of UWB radar is rarely affected by the dust and moisture in the harsh environment.

Creep of Cement Pastes with Content of Fly Ash one Year Old

The paper discusses the creep cement pastes with addition of fly ash. The evolution of the creep was observed in age of one year, for length one month. The size of the creep is influenced by the amount the creep physically bound water. The material properties depend on the ratio of components from which the cement paste is composed. The paper presents the results of creep measurement for the ratio of cement and fly ash 70:30, 60:40 and 50:50. The basic creep and creep of the saturated cement paste were calculated from measurements.

Non-Contact Creep Measurement Based on Fourier Domain Optical Coherence Tomography

A non-contact Fourier-domain optical coherence creep tomography (OCCT) is developed and employed in real-time non-contact creep measurement. Experiments on thermal deformation were carried out by using the self-developed OCCT to measure a high-temperature structure. In the OCCT system, a high-performance spectrometer, and a thermal light are, respectively, employed as the detector and the light source. Due to the broadband of the spectrometer and light source, the system provided high robust performance with an excellent deformation measurement resolution of sub-millimeter scale. Due to the energy leakage effect of FFT, a spectrum correction technique was employed to enhance the resolution of the OCCT system. From the experimental results, the self-developed OCCT has great potential applications in non-contact real-time creep measurement of high-temperature structures.

INVESTIGATION OF UNCERTAINTY FROM CREEP AND CREEP RECOVERY OF FORCE CALIBRATION RESULT IN ACCORDANCE WITH ISO 376:2011

This paper presents an investigation of the uncertainties from creep and creep recovery of force proving instruments calibrated at NIMT in year 2012 and 2013. In this study, the NIMT's 100kN deadweight force standard machine was used as a standard to calibrate force proving instruments (from various manufacturers and models) in accordance with ISO 376:2011. The comparison of creep uncertainties calculated from creep measured at maximum load (Cmax), creep recovery measured at zero load (Czero) and reversibility errors were also investigated. The results of this study show that, for most of the calibration results (>60%), the maximum value between WCmax/WCzero and WCzero/WCmax were larger than 2. Indicating that, WCmax and WCzero could not assume to be equal. For the comparison between creep uncertainties calculated from creep error and reversibility error, more than 80% of the calibration results, the creep uncertainties calculated from reversibility were larger than 3 time of the calculated values form creep measurement. These gave conclusion that, for the unknown history of creep and reversibility characteristic of instruments, it is more appropriate to estimate the uncertainty of creep from reversibility error.