Settlements and shear strength increase below embankments - long-term observations and measurement of shear strength increase by seismic cross-hole tomography
Swedish title: Settlements and shear strength increase below embankments - long-term observations and measurement of shear strength increase by seismic cross-hole tomography
Author Rolf Larsson, Håkan Mattsson
Series: SGI Rapport
The report deals with the settlements and shear strength increases beneath three test embankments that were constructed about 50 years ago. It also deals with the possibility of measuring this shear strength increase by seismic cross-hole tomography. The investigated embankments are three test embankments in the Institute's test fields at Lilla Mellösa and Skå-Edeby. They were constructed on natural ground without any installation of vertical drains or other measures. The embankments have different geometry and loading conditions and the settlements and consolidation processes thereby differ. The settlements and their distribution with depth as well as the dissipation of excess pore pressure and the development of the shear strength increase has been monitored since the construction, partly continuously and partly at different occasions. A new complete follow up was performed in the summer of 2002. The shear strength increase beneath old embankments can be utilised when these are to be widened or raised and when the traffic load is to be increased. However, this requires verification of the increase. Traditional geotechnical investigation require drilling through the embankment and taking of samples and/or performance of in situ tests. In many cases, and particularly for railway embankments, it is desired to use methods that do not require access to the embankment and do not interfere with the ongoing traffic. For this purpose, the method of seismic cross-hole tomography has been tried and the results show that a fairly good picture is obtained of the shear strength distribution in the soil beneath the embankments.