Settlement Behavior Of Pile Foundation In Wenzhou Soft Ground

In recent years, a lot of high-rise buildings and large structures have been constructed in Wenzhou , in which pile foundation are mostly employed . However, as one kind of very typical soft soils, it is noted as thick layer, high water content and high compressibility. With the performance in engineering design in Wenzhou for about 20 years, the author has achieved abundant practical experience in design of multi-layer and high-rise building.The engineering geological features of Wenzhou soil shows, that the lithology of the upper portion(within the range of 40 - 60m) of Wenzhou plain is obviously different from the lower/middle portion's, where the upper portion is mainly made of muddy clay and silt, while the lower/middle portion mainly consists of the lithology of coarse particle. Therefore, in Wenzhou, the long piles and super-long piles are always applied. Based on the analysis of several pile types in common use, the designer should choose the type of piles properly considering safety, economy, structural type, the load action level and the bearing layer characteristics.The following factors are measured in the static load test of three piles, these factors include the settlement of pile top and pile toe, pile top load, so as to analyze the axial force of pile and the distribution principle of friction resistance against the pile shaft. According to the relations between the friction resistance and the relative displacement of soil, the friction resistance is proportionally developed with the increasing of the relative displacement. While the fixed value(critical displacement) is obtained by the relative displacement, the friction will be close to the fixed value. The critical displacement value of pile soil in Wenzhou soil is listed in this text.On the base of monitoring data of three building, the relations of the settlement, the differential settlement, the load and the time are analyzed. The development of building settlement is divided into three stages as follows: Geostatic stress, additional stress and constant stress. the first two stages is one kind of construction settlement, whose proportion will effect on the value of overall settlement, however, the main factor working on the proportion of the construction settlement is the bearing layer of the pile toe, therefore, the bearing layer of the pile toe is the key factor to effect on the pile settlement.Many kinds of settlement computing methods are analyzed and compared in this text, the theoretical results are compared with the measured settlements. The settlement computing method suitable for Wenzhou soft soil is developed with comprehensive statistic method, as well as the important regional soil parameter. This formula are applied in calculating the settlement of pile foundation on the basis of the measured settlement value by the writer of 50 Wenzhou representative built buildings. The results show that it is very suitable for the pre-estimation of the pile settlement in preliminary design.