Chapter 12 Subsidence – chalk mining

Old chalk and flint mine workings occur widely across southern and eastern England. Over 3500 mines are recorded in the national Stantec Mining Cavities Database and more are being discovered each year. The oldest flint mines date from the Neolithic period and oldest chalk mines from at least medieval times, possibly Roman times. The most intensive period for mining was during the 1800s, although some mining activities continued into the 1900s. The size, shape and extent of the mines vary considerably with some types only being found in particular areas. They range from crudely excavated bellpits to more extensive pillar-and-stall styles of mining. The mines were created for a series of industrial, building and agricultural purposes. Mining locations were not formally recorded so most are discovered following the collapse of the ground over poorly backfilled shafts and adits. The subsidence activity, often triggered by heavy rainfall or leaking water services, poses a hazard to the built environment and people. Purpose-designed ground investigations are needed to map out the mine workings and carry out follow-on ground stabilization after subsidence events. Where mine workings can be safely entered they can sometimes be stabilized by reinforcement rather than infilling.

Field performance of a peat railway subgrade reinforced with helical screw piles

Rail tracks on peat subgrades can experience significant deflections, some of which have led to derailments. A potential ground stabilization strategy is to use screw piles to reduce rail displacements; however, limited research has been undertaken to investigate the effect of these piles and their performance under cyclic train loading. A field site was instrumented and monitored before and after screw pile installation. The piles were instrumented with strain gauges, piezometers were installed in the peat, and high-speed cameras were used to measure track and subgrade displacements. The load carried by each instrumented pile was approximately 50–60 kN 3 weeks after installation, but reduced to approximately 30 kN after 6 months. Although 1 year’s worth of piezometric data were collected before installation of the piles, it is difficult to conclusively attribute the changes in pore pressures to the piles, particularly because the piezometric data collected after the pile installation were only available for the 7 months that exhibit the period of greatest seasonal fluctuations. The track support system deformations showed no significant difference pre- and post-pile installation. Therefore, based on the monitoring data at this site, it appears that the designed transfer of load from the ties to the piles through arching within the ballast layer was not realized.

The Influence Of Radar Picture Stabilization Type To Anti-Collision Manoeuvre Planning Accuracy

The problem of the accuracy of anti-collision manoeuvres planning and executing at different radar picture stabilization methods (sea or ground stabilization) is described in the article. The analysis of performance standards elaborated for the radar equipment and the results of the simulation are presented. The obtained research results could be the base of discussion on the need to correct the radar equipment performance standards for easier and more appropriate interpretation of information. Basic radar utility use (for example trial manoeuvre) should be more clearly described in manuals for better and proper radar use.