|Abstract: ||摘要:鑽掘式場鑄鋼筋混凝土基樁,一般因地質、地層及施工方法等因素之影響,經常引致樁身產生蜂窩、龜裂及縮頸等缺陷,這些缺陷常影響基樁之正常功能,對這種有問題的基樁而言,若能事先加以檢驗出來且予以修補,對整個基礎工程之安全,將非常有助益,且更節省許多工程經費。 本文研究之主要目的在於使用衝擊法非破壞性檢測鋼筋混凝土模型基樁之完整性,利用1.2m*1.2m*2.0m之試驗槽內置高1.5m之乾砂模擬大地,依樁身可能發生之斷面變化,預製六根鋼筋混凝土模型基樁,(其中四根圓型模型基樁,另二根為方型模型基樁)將應變計、加速計與位移計(LVDT)三種感應元件設置在近樁頭處量測基樁在衝擊過程中之受力、速度和位移訊號對時間之關係,藉此訊號關係,分析預測基樁斷面變化情形,進而探討基樁之完整性。 研究結果顯示,因有土壤摩擦力影響,預測斷面積值必比實測斷面積值最大。另衝擊能量愈大,樁身位移因摩擦之向上部分回升及因樁址貫穿土壤之向下沈陷將增大。利用TNO法分析,較適用於圓形基樁分析,其他斷面較不適合。由CASE法分析,僅能檢測出樁身第一個結構缺陷,其下缺陷恐難預測得知。|
abstract:Generally speaking, the reinforced concrete piles of bored type are usually of the defective physiognomy of honeycomb, crack and shrinkage which are influenced by the factors of geology, soil layer and construction method. These defects often affect the normal function of pile foundations. For the pile with flaw, if one can before hand predict the defect of pile and repair it then one will save a lot of on engineering expenditure. In addition, it is very good for the safety of the whole foundation. The main purpose of this investigation is to detect the integrity of reinforced concrete model pile by means of impact method. The test tank with length 1.2m, width 1.2m and high 2.0m is filled with dry sand about 1.5m depth for simulating ground. Design and construct six reinforced concrete model pile with different cross sectioned area. The LVDT, strain gauge and accelerometer are installed the shaft nearly the pile head. The signals of force, velocity and displacement versus time are acquired at the hammer impact pile head. Using these signals, one can predict the variation of cross sectional area of pile. This method is generally to study the pile integrity. From this study, one gets some important conclusions shown as following: (1) the predicted area of pile cross section is larger than the real ones. This is due to the effect of soil frictional resistance around pile shaft. (2) The more impact energy of hammer the larger of displacement of pile due to the arise of upper shaft friction and toe penetrating into soil mass. (3) The TNO method is suitable for analyzing the pile integrity with circular cross section. The other cross section area of pile is not convenient. (4) The Case method only can detect the first flaw of pile shaft. Under the first flaw of pile, it is very difficult to predict the defect of pile structure by using the Case method.