Numerical modelin of floating prefabricated vertical drains in layered ...

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I. IKHYA & H. F. SCHWEIGER: NUMERICAL MODELING OF FLOATING PREFABRICATED VERTICAL DRAINS IN LAYERED SOIL Degree of Consolidation Degree of Consolidation Degree of Consolidation Model II-A (Single Drained) 1 10 100 1000 10000 100000 0 0.1 0.2 0.3 L/H=1.0 (Full Penetration) L/H=0.9 0.4 L/H=0.8 0.5 L/H=0.7 0.6 Soil Layer I L/H=0.6 E1&k1 L/H=0.5 0.7 Without PVD 0.8 k2>k1 0.9 1 Soil Layer II E1&k2 Time (days) Model II-B (Single Drained) 1 10 100 1000 10000 100000 0 0.1 0.2 0.3 L/H=1.0 (Full Penetration) L/H=0.9 0.4 L/H=0.8 0.5 L/H=0.7 0.6 Soil Layer I L/H=0.6 E1&k1 L/H=0.5 0.7 Without PVD 0.8 E2>E1 0.9 1 Soil Layer II E2&k1 Time (days) Model II-C (Single Drained) 1 10 100 1000 10000 100000 0 0.1 0.2 0.3 L/H=1.0 (Full Penetration) L/H=0.9 0.4 L/H=0.8 0.5 L/H=0.7 0.6 Soil Layer I L/H=0.6 E1&k1 L/H=0.5 0.7 Without PVD 0.8 E2>E1 & k2>k1 0.9 1 Soil Layer II E2&k2 Time (days) Figure 13. Settlement curves for two soil layers and single drainage condition for varying PVD penetration depth. where the first layer is stiffer and more permeable than the second layer (model 3; IIIA, IIIB, IIIC), the drain length can only be reduced by about 10% without affecting the consolidation process (L/H = 1.0–0.9). Based on this numerical study it can be concluded that for single drainage conditions, only model 2, i.e., if the second layer is stiffer and more permeable than the first layer, can the use of floating PVDs be recommended. 5 CONCLUSIONS Numerical results from a study of floating PVDs in two soil layers for double and single drainage conditions were examined to determine the optimum penetration depth for the PVDs. It is interesting to note that the differences in stiffness and permeability in the two-soil-layer condition, especially in the unimproved area below the PVD tip, have an influence on the optimum penetration depth 34. ACTA GEOTECHNICA SLOVENICA, 2012/2 Degree of Consolidation Degree of Consolidation Degree of Consolidation Model III-A (Single Drained) 1 10 100 1000 10000 100000 0 0.1 0.2 0.3 L/H=1.0 (Full Penetration) L/H=0.9 0.4 L/H=0.8 0.5 L/H=0.7 0.6 Soil Layer I L/H=0.6 E1&k2 L/H=0.5 0.7 Without PVD 0.8 k2>k1 0.9 1 Soil Layer II E1&k1 Time (days) Model III-B (Single Drained) 1 10 100 1000 10000 100000 0 0.1 0.2 0.3 L/H=1.0 (Full Penetration) L/H=0.9 0.4 L/H=0.8 0.5 L/H=0.7 0.6 Soil Layer I L/H=0.6 E2&k1 L/H=0.5 0.7 Without PVD 0.8 E2>E1 0.9 1 Soil Layer II E1&k1 Time (days) Model III-C (Single Drained) 1 10 100 1000 10000 100000 0 0.1 0.2 0.3 L/H=1.0 (Full Penetration) L/H=0.9 0.4 L/H=0.8 0.5 L/H=0.7 0.6 Soil Layer I L/H=0.6 E2&k2 L/H=0.5 0.7 Without PVD 0.8 E2>E1 & k2>k1 0.9 1 Soil Layer II E1&k1 Time (days) (L/H) in order to achieve the same consolidation time. It was found in this study that for double drainage conditions in a homogeneous soil layer (model 1), the drain length can be reduced by up to 20% without significantly affecting the consolidation process (L/H = 0.8). For a two-soil-layer condition where the second layer is stiffer and more permeable than the first layer (model 2; IIA, IIB, IIC), the drain length can be shortened by 30–40% (L/H = 0.7–0.6). In contrast, for a two-soil-layer condition where first layer is stiffer and more permeable than the second layer (model 3; IIIA, IIIB, IIIC), the drain length can be reduced by only 10–20% (L/H=0.9–0.8). For single drainage conditions it is possible to use a floating PVD only if the second layer is stiffer and/or more permeable than the first layer. This study has shown that a good agreement between field measurements and numerical predictions for settlements in both full and partial penetration conditions
can be achieved. For the presented case study the drain length could be reduced by up to 30% without significantly affecting the consolidation process (L/H = 0.7). ACKNOWLEDGEMENTS The authors wish to thank PT. Soilens, PT. Doosan Heavy Industries Indonesia, PT. Cirebon Electric Power, PT. Tripatra Engineers and Constructors for providing the case-study data in this paper. The authors would also like to thank Ir. Padmono, P.E., (PT. Soilens Bandung) for his time during a detailed discussion of the site conditions and parameters. The work reported in this paper was supported by North-South-Dialogue scholarship programme from Österreichische Akademische Austauschdienst (ÖAD) for the first author as part of a Ph.D. study at Graz University of Technology, Austria. REFERENCES I. IKHYA & H. F. SCHWEIGER: NUMERICAL MODELING OF FLOATING PREFABRICATED VERTICAL DRAINS IN LAYERED SOIL [1] Barry, A.J., Rahadian, H., Rachlan, A. (2002). The Indonesian geoguides. Symposium on Geotechnical Engineering, Bangkok. [2] Runesson, K,, Hansbo. S., Wiberg, N.E. (1985). The efficiency of partially penetrating vertical drains. Géotechnique Journal, Vol. 35, No. 4, pp. 511-516. [3] Onoue, A. (1988). Consolidation of multilayered anisotropic soils by vertical drains with well resistance. Journal of The Japanese Geotechnical Society: Soils and Foundations, Vol. 28, No. 3, pp. 75-90. [4] Nakano, H., Okuie, H. (1991). Consolidation by using a long drainage wells with partial penetration. Journal of The Japanese Geotechnical Society: Soils and Foundations, Vol. 39, No. 8, pp. 23-28. [5] Tang, X.W., Onitsuka, K. (1998). Consolidation of ground with partially penetrated vertical drains. International Journal of Geotechnical Engineering, Vol. 29, No. 2, pp. 209-231. [6] Tang, X.W. (2004). Comparison of partially penetrated open and closed ended vertical drains. Proceeding of the 3 rd Asian Regional Conference on Geosynthetics: Now and Future of Geosynthetics in Civil Engineering, Seoul, pp. 291-297. [7] Indraratna, B., Rujikiatkamjorn, C. (2008). Effects of partially penetrating prefabricated vertical drains and loading patterns on vacuum consolidation, In: Reddy, K.R., Khire, M.V., Alshawabkeh, A.N. (Eds.). Proceeding of the GeoCongress: Geosustainability and Geohazard Mitigation, ASCE, Orleans, pp. 596-603. [8] Hart, E.G., Kondner. R.L., Boyer, W.C. (1958). Analysis for partially penetrating sand drains. Journal of Soil Mechanics and Foundation Division: Proceedings of ASCE, Vol. 84, No. 4, pp. 1-15. [9] Zeng, G.X., Xie, K.H. (1989). New development of the vertical drain theories. Proceeding of the 12 th ICSMFE, Rio de Janeiro, Vol. 2, pp. 1435-1438. [10] Chai, J.C., Miura, N., Kirekawa, T., Hino, T. (2009). Optimum PVD installation depth for two-way drainage deposit. International Journal of Geomechanics and Engineering, Vol. 1, No. 3, pp. 179-191. [11] Geng, X.Y., Indraratna, B., Rujikiatkamjorn, C. (2011). Effectiveness of partially penetrating vertical drains under a combined surcharge and vacuum preloading. Canadian Geotechnical Journal, Vol. 48, pp. 970-983. [12] Unsworth, R. (Eds). (2008). Marine environment report of the Cirebon IPP coal fired power station for PT. Cirebon Electric Power. Sinclair Knight Merz, Brisbane. (QE09421.02). [13] Padmono, P. (Eds). (2008a). Review of settlement instrumentation report of the 1x660 MW coal fired Cirebon power plant project for PT. Doosan Heavy Industries Indonesia. PT. Soilens, Bandung. (2238-B & 2428). [14] Padmono, P. (Eds). (2008b). Soil investigation II report of the 1x660 MW coal fired Cirebon power plant project for PT. Doosan Heavy Industries Indonesia. PT. Soilens, Bandung. (2338-B & 2428). [15] Barry, A.J., Rachlan, A. (2001). Embankments on soft soils in North Java. Proceeding of International Conference on In Situ Measurement of Soil Properties and Case Histories, Bali. [16] Barry, A.J., Rahadian, H., Rachlan, A. (2003). The embankments on North Java soft clay. Proceeding of the 12 th Asian Regional Conference, Singapore. [17] Padmono, P. (Eds). (2006). Preliminary soil investigation report of the IPP 1x660 MW coal fired steam Cirebon power plant project for PT. Tripatra Engineers and Constructors. PT. Soilens, Bandung. [18] Padmono, P. (Eds). (2007). Soil investigation I report of the Cirebon thermal power plant project for PT. Cirebon Electric Power. PT. Soilens, Bandung. (2338 & 2358). [19] Brinkgreve, R.B.J., Swolf, W.M., Engin, E. (Eds). (2010). Plaxis 2D 2010 user manual: Finite element code for soil and rock analyses. Plaxis bv., Netherland. [20] Schanz, T., Vermeer, P.A., Bonnier, P.G. (1999). The hardening soil model: formulation and verification. Proceeding of the International Symposium Beyond 2000 in Computational Geotechnics – 10 Years of Plaxis, Amsterdam, pp. 281-296. [21] Hansbo, S. (1979). Consolidation of clay by bandshaped prefabricated drains. Ground Engineering, Vol. 12, No. 5, pp. 16-25. [22] Chai, J.C., Miura, N. (1999). Investigation of factors affecting vertical drain behavior. Journal of Geotechnical and Geoenvironmental Engineering, Vol. 125, No. 3, pp. 216-226. ACTA GEOTECHNICA SLOVENICA, 2012/2 35.
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