本研究主要是模擬基樁貫入軟弱土層中，受地表均佈荷載造成之負摩擦力行為。基樁承載方式主要是以點承樁型式為主，藉由比較不同之試驗參數與加載方式，觀察瞭解影響負摩擦力發展機制之各項因素。研究項目有(1)黏土層預壓密應力之影響；(2)有限均佈荷載面積大小之影響；(3)樁頭荷載與地表均佈荷載施加先後順序之影響；(4)薄層黏土壓縮層對負摩擦力之影響。 試驗結果得知，施加超載超過預壓密應力之地表沉陷量與負摩擦力均較未超過土體預壓密應力之情況大；有限均佈荷載試驗中，荷載面積較小時，中立點位置會較接近於土表，且其負摩擦力亦較小；荷載施加順序試驗中，以先加樁頭荷載再加地表均佈荷載會有較大之負摩擦力；薄壓縮層試驗中，發現樁底點承於砂土中，其上只要有一薄層黏土，就容易產生負摩擦力，且其總摩擦力大小視薄層黏土上部土層之摩擦強度而定。 This research is mainly to simulate behavior of negative skin friction by applying surface loading on the soft soil layer. The type of pile foundation is end bearing pile. By varying different test parameters and loading sequence. The factors influencing negative friction development have been observed. The research put focus on four influencing factors which are the pre-consolidation stress of clay, the area of loading, the order of applied loading and the existence of thin clay layer. Based on the test results, the surface settlement and the negative skin friction of NC clay are greater than those of OC clay. In case of loading of finite area, the neutral plane is more close to ground surface and the negative skin friction is smaller than that of one dimensional loading. The negative skin friction for the case of loading pile first and then applying surface load is larger than the case in a reverse loading order. The existence of thin clay layer above the bearing layer is more easily to develop negative friction and its value is dependent on the strength of soil layer above the thin clay layer.
