Recalling the body of experience gathered in the collieries of the Upper Silesian Coal Basin, the

increased risk of seismicity and rockburst occurrences in confined conditions including the exploitation of

remnants were identified. This study investigates geomechanical aspects of longwall mining in the areas

affected by old excavations aimed at relaxation of a multi-bed deposits within a thick coal seam or a group

of seams. It is assumed that high-energy seismicity is another factor determining the rockburst hazard

alongside the state of stress. A case study is recalled, describing a colliery where mining-induced seismic

activity of a de-stressed coal seam remained at the level comparable to or higher than it was experienced

in the de-stressed seam operations. An analytical model was used to study the stress state and potential

loss of structural continuity of an undisturbed rock body surrounding the longwall panel being mined

beneath or over the abandoned workings. Recalling the developed model of the system involving nonlinear

functions demonstrating the existence of abandoned mine workings within the rock strata, computer

simulations were performed to evaluate the rockburst hazards along the face area. Discussions of results

are based on observations of immediate roof convergence and the vertical stress concentration factor at

the longwall face zone. Computational data of the modelled mining situations demonstrates that despite

using the de-stressing method of mining, the occurrence of events impacting on mine working beneath

and over abandoned workings cannot be precluded. Here the scale of rockburst hazards is determined by

local mining and geological conditions, such as the type and extent of abandoned workings, their age and

vertical distance between them and the coal seam currently mined.

Synthetic aperture (SA) technique is a novel approach to present day commercial systems and has previously not been used in medical ultrasound imaging. The basic idea of SA is to combine information acquired simultaneously from all directions over a number of emissions and to reconstruct the full image from these data.

The paper presents the multi-element STA (MSTA) method for medical ultrasound imaging. The main difference with the STA approach is the use of a few elements in the transmit mode in contrast to a single element aperture. This allows increasing the system frame rate, decreasing the number of emissions, and provides the best compromise between the penetration depth and lateral resolution. Besides, a modified MSTA is proposed with a corresponding RF signal correction in the receive mode, which accounts for the element directivity property.

In the experiments a 32-element linear transducer array with 0.48 mm inter-element spacing and a burst pulse of 100 ns duration were used. Two elements wide transmission aperture was used to generate an ultrasound wave covering the full image region. The comparison of 2D ultrasound images of a tissue mimicking phantom obtained using the STA and MSTA methods is presented to demonstrate the benefits of the second one.