Stability analysis of shallow tunnels subjected to eccentric loads by a boundary element method

This paper presents the results of the shear strength（frictional strength） of cemented paste backfillcemented paste backfill（CPB-CPB） and cemented paste backfillerock wall（CPB-rock） interfaces. The frictional behaviors of these interfaces were assessed for the short-term curing times（3 d and 7 d） using a direct shear apparatus RDS-200 from GCTS（Geotechnical Consulting ＆ Testing Systems）. The shear（friction） tests were performed at three different constant normal stress levels on flat and smooth interfaces. These tests aimed at understanding the mobilized shear strength at the CPB-rock and CPB-CPB interfaces during and/or after open stope filling（no exposed face）. The applied normal stress levels were varied in a range corresponding to the usually measured in-situ horizontal pressures（longitudinal or transverse） developed within paste-filled stopes（uniaxial compressive strength, s c 150 k Pa）. Results show that the mobilized shear strength is higher at the CPB-CPB interface than that at the CPB-rock interface. Also, the perfect elastoplastic behaviors observed for the CPB-rock interfaces were not observed for the CPB-CPB interfaces with low cement content which exhibits a strain-hardening behavior. These results are useful to estimate or validate numerical model for pressures determination in cemented backfill stope at short term. The tests were performed on real backfill and granite. The results may help understanding the mechanical behavior of the cemented paste backfill in general and, in particular, analyzing the shear strength at backfillebackfill and backfill-rock interfaces.

Relationship between single and bulk mechanical properties for zeolite ZSM5 spray-dried particles

In this work typical mechanical properties for a catalyst support material, ZSM5 （a spray-dried granular zeolite）, have been measured in order to relate the bulk behaviour of the powder material to the single particle mechanical properties. Particle shape and size distribution of the powders, determined by laser diffraction and scanning electron microscopy （SEM）, confirmed the spherical shape of the spray-dried particles. The excellent flowability of the material was assessed by typical methods such as the Hausner ratio and the Cart index, This was confirmed by bulk measurements of the particle-particle internal friction parameter and flow function using a Schulze shear cell, which also illustrated the low compressibility of the material. Single particle compression was used to characterize single particle mechanical properties such as reduced elastic modulus and strength from Hertz contact mechanics theory. Comparison with surface properties obtained from nanoindentation suggests heterogeneity, the surface being harder than the core. In order to evaluate the relationship between single particle mechanical properties and bulk compression behaviour, uniaxial confined compression was carried out. It was determined that the Adams model was suitable for describing the bulk compression and furthermore that the Adams model parameter, apparent strength of single particles, was in good agreement with the single particle strength determined from single particle compression test.

Glidant effect of hydrophobic and hydrophilic nanosilica on a cohesive powder： Comparison of different flow characterization techniques

The methods used for flow characterization of a powder mass include the angle of repose （AOR）, Carr index （CI）, and powder flow tester （PFT）. The use of nanosilica as a flow modifier （glidant） is very common in industry. This study aims to compare the glidant effect of hydrophobic and hydrophilic silica on a poorly flowable active pharmaceutical ingredient （ibuprofen） by different flow characterization techniques. Different percentages （0.5, 1.0, and 2.0 wt%） of both types of mixed silica–ibuprofen powders were evaluated by the AOR, CI, bulk density, and PFT. The flow factor, effective angle of friction, and cohesion were determined to explain the bulk powder properties. The results show that different types of silica show different levels of flow property improvement, but the techniques do not equally discriminate the differences. Hydrophobic silica results in better improvement of the flow property than hydrophilic silica, probably because of its better surface coverage of silica on the host particles. Change of the bulk density with applied pressure was significant for the different powders. This study demonstrates that combining several characterization methods provides a better understanding of bulk powder flow properties with respect to powder–process relationships than a single flow indicator.