Abstract:
Bangkok - Chonburi New Highway met a settlement problem as other roadembankment on soft clay. So prefabricated vertical drain (PVD) and preloading areused to accelerate settlement under embankment and to reach the primaryconsolidation in the construction period. This thesis evaluated the settlementperformance of the Bangkok - Chonburi New Highway in Section 3-A/2 from Sta.S2+OOO to Sta. 57+6OO after being installed with PVD in a triangular pattern with aspacing of 1.20 m. For construction of preloading the embankment, it was plannedto construct in 3 stages of loading. In the first stage, the embankment was filled to1.35 m. high and maintained for 41 days. In the second stage the embankment wasfilled to 1.95 m. high and maintained for 105 days. In the last stage the embankmentwas filled to 2.70 m. high and maintained for 9-12 months to reach 80%consolidation. The reason for construction sequence like this is to increase shearstrength and stability under embankment. However, In actual construction thewaiting period was extended because of the rate of pore pressure dissipation as wellas the factor of safety do not meet with the requirement especially in the finalstage. Geotechnical Instrument were also installed to monitor the soil behavior.The result of time-settlement from the field records was analysed to predict thecoefficient of horizontal consolidation (Ch) by Asaoka Method. It is found that theCh value in this thesis are 2.25 , 1.90 ,0.75 m2/year for the first , the second and thethird stage of loading, respectively. The Cv value for the each stage are 0.91, 0.80,0.68 m/year, respectively. The ratios of Ch/Cv for the each stage are 2.72, 2.72,1.18, respectively. The average Ch value of all stages are 1.63 m/year, Cv is 0.80miyear and the ratio Ch/Cv is 2.2 1. The result of the settlement analysis forembankment without PVD estimated by Terzaghi Method are 83-271 years (SingleDrainage) and 20-67 years(Double Drainage) for 90% consolidation. Forembankment with PVD estimated by Barron Method and Hansbo Method are125.08-408.61 days and 124.60-407.04 days for 90% consolidation.