Monitoring tectonic movements in the Simitli Graben, SW Bulgaria

Long-term in situ monitoring of slow tectonic movements has been applied to a seismoactive region of SW Bulgaria, within the epicentral zone of one of the strongest earthquakes in Europe (4 April 1904, M=7.8). The region has been found the most seismoactive in Bulgaria being of interest to many scientists. Three spatial extensometers were installed here in carefully selected sites to reflect fault movements on fissures. The extensometer TM-71 used here, enables three-dimensional detecting of even very slow movements with the accuracy of 0.01 mm and high stability over time. After 17 years of measuring, the rates of tectonic movements were established at all three monitoring points. Movements recorded at point B6 located in the seismoactive Kroupnik fault zone are of a relatively high rate. Locally, they show left-lateral strike–slips at rates of ca. 2.7 mm year⁻¹, as well as thrusting with a mean rate of 1.9 mm year⁻¹. Monitoring point K7 located in a fissure of the same zone on a steep slope affected by recent earthquakes has shown an uplift tendency of the block W of the Strouma Fault, with a result of gradual slope subsidence occurring from time to time. Monitoring point K5 located in a fissure of Strouma Fault zone became increasingly active during the last 2 years after 8 years of relative quiescence. Before that, only low left-lateral movements could be observed. Long-term fissure monitoring has shown quite a number of details interpretable to the dynamics of a broad region. Permanent shear displacements were found to develop after earthquakes. It was established that only a certain distinct part of local earthquakes provide such a displacement reaction at the monitoring points showing particular seismic connections.     

Design and performance of a compacted clay barrier through a landfill

This paper presents the construction and performance details of a compacted London Clay barrier that was designed to prevent any leachate or methane penetrating a stretch of the cut and cover box section tunnel of the London Heathrow Express Rail Link. The barrier was constructed with London Clay that was spoil from concurrent bored tunnelling operations on adjacent sites. Laboratory investigations carried out on the compacted London Clay are presented in the paper. These indicated that it was possible to design the clay surround to function as a barrier protecting the structure from the ingress of the leachate. Field monitoring using magnetic extensometer gauge measurements indicate that the consequent ground movements are lower than that predicted by the laboratory tests.