Compaction control of a soil improvement with powder columns

Compaction control has been performed by means of crosshole measurements. The soil consists of an inhomogeneous coal mining deposit. Powder columns consisting of fly ash have been installed as soil improvement by the Keller Grundbau GmbH using a modified Vibroreplacemenl technique. Crosshole measurements before and after the column installation have been applied to monitor the improvement of the soil. Shear wave velocities have been measured along three different lines in two depths. The obtained results are the earth pressure coefficients determined with normalised stresses and the void ratios using an empirical correlation. K0-values before the installation of the powder columns decrease considerably after the installation and void ratios changed from 0.9 to 0.4, showing an impressive soil improvement due to the powder columns. A comparison of the crosshole results with density measurements from borehole logs and with earth pressure measurements yields a good agreement.