本研究規劃設計一套可以改善長期溫度效應，直接觀測基樁負摩擦力之模型試驗，利用模型計測樁來探討壓密沉陷對基樁負摩擦力之影響，以及壓密完成後負摩擦力是否會發生變化。在模型樁受力同時，藉由模型計測樁內之應變規量測模型樁體受力反應，配合樁尖及樁頂之荷重計讀數，可求得模型樁在不同深度之受力，進而推算樁身表面負摩擦力，並以此為依據，探討基樁負摩擦力之行為。由試驗結果得知，負摩擦力之歷時曲線與土壤壓密之歷時曲線相似，其生成主要集中在主要壓密階段，之後隨時間趨於緩和。隨著覆土應力的增加，樁身之負摩擦力也會跟著增加。

This paper presents a model pile test system which was designed to measure the negative friction behavior of a pile when its surrounding ground consolidated in multi-stage. The design overcame the temperature effect on the strain gauges which were pasted in the interior wall of the model pile, with an inner diameter of only 17mm by a half-bridge connection and a dummy model pile. The system has successfully measured the time dependent response of downdrag force of the pile. The time-dependent negative friction along the pile was deduced. The neutral point is at the location of 90% thickness of the compressible layer. The development of the downdrag force is closely related to the consolidation behavior of the compressible layer. The variation trends with time are almost the same for the downdrag force and the consolidation settlement. The negative frictions at the upper and lower parts of the compressible layer are larger than that of the middle part due to the larger consolidation rate at both ends of the layer.

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