Improvement of soft fat clay using rigid inclusions and vertical drains

Proceedings of the 18 th International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013Nevertheless, below the embankment, there is no concrete slabor rigid structure like for the foundation of the bridge.Reinforced earth with galvanized steel was designed to hold thelarge horizontal forces of active earth pressure. Because of thelarge geotextile deformations during the consolidation period, asshown in the following monitoring results, the decision wasmade to use a stronger more rigid construction with nearly nodeformation. Compared with plastic geotextiles, the steel gridmaterial has only very small elastic deformations, and as aresult limiting the horizontal deformations of the embankment.Through the addition of some gravel in parts of the sandy loadtransfer platform LTP, the friction between LTP and CMC wasgreatly increase and nearly no deformation was necessary tomobilize the friction of the LTP.5.2 Controlled Modulus Columns CMCSeveral measurement systems were installed between the CMCand the reinforced earth in the load transfer platform. Theinstruments show an almost perfect full stress concentration ofthe load on the CMC and less than one centimetre of horizontaldeformation. Figure 10 shows the cross section and the 5vertical deformation measurements over a period of 2 years.The horizontal inclinometer was laid across six marked CMCcolumns(figure 1 and figure 9). A settlement of one centimetreof the top of the CMCs and two centimetres in-between CMC inthe reinforced earth steel construction were measured. Therewas a good agreement between the calculated values of thesettlement and the results of the monitoring.5 MONITORING RESULTS5.1 Wick drainsFigure 10. horizontal inclinometer results with arround 1 cm of CMCsettlements and 2 cm of reinforced earth settlementsFigure 8. measurement at the settlement plates SP 9 und SP10.6 SUMMARY AND CONCLUSIONSSoft and fat clay were found at the B5 / B202 road crossing.Additional soil investigations and laboratory tests wereperformed to be able to complete a proper design, regardingstability and consolidation time.Oedometer consolidation tests allowed to precisely predict themovements during the consolidation processes that wereaccelerated by the use of vertical drains at different spacings.Large deformations of up to 1.5 m of settlements and 27 cm ofhorizontal displacement were experience and closely match thecalculations and show that it was the right decision not to placethe highest embankment directly on the softest soil beside thebridge over the running traffic on the highway B5.Vibration free CMC in combination with reinforced earthallowed to construct this high embankment with less than twocentimetre differential settlements to the piled bridge.With a careful planning of the work within the overallconstruction schedule, detailed design combined with anextensive monitoring program, economic soil improvementtechniques can be combined with deep foundations in oneproject even on very soft soil can be treated successfully.7 REFERENCESFigure 9. vertical inclinometer results at the 7 m high damm with drainsand 600 kN/m vowen geotextileThe measured settlements during the consolidation process infigure 8 follow very closely the predictions shown in figure 7.An additional strong geotextile layer of 600 kN/m tensilestrength between the embankment and the vertical drains had27 cm of deformation measured with vertical inclinometers.DIN Deutsches Institut für Normung, 2002, DIN 4094-4: Subsoil –field testing – part 4 : Field vane test.DIN Deutsches Institut für Normung, 2001, DIN EN 12699: Executionof special geotechnical work - Displacement piles; German versionJ-L Chaumeny, J.F.Kirstein, S. Varaksin, 2008, An experience ofconsolidation of extremly soft mud for one of Europe’s largestprojects “The AIRBUS A-380” factory in Hamburg, Glasgow.2516