靜態側向反覆荷載下單柱式橋墩與群樁裸露基礎之研究

A study of piled pier and scoured groups of piles under statically lateral cyclic loading

鄧爵明(Chueh-Ming Teng)

指導教授 ： 張國鎮

國立臺灣大學/工學院/土木工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201701686

摘要

本研究探討單柱式橋墩與群樁基礎模型受沖刷導致基礎裸露後，在反覆側推試驗下的結構行為、破壞機制、群樁效應與樁土互制之變化。試驗使用大型雙軸向剪力試驗盒、結構模型試體以及砂土試體。結構模型試體之上部結構為單柱式橋墩，由120 mm×120 mm×20 mm的千斤頂接合面，直徑40 mm、高度200 mm之實心鋼棒，搭配150 mm×150 mm×15 mm鋼製基礎板所構成。下部結構則為群樁基礎試體，由200 mm×200 mm×15 mm鋁製底部轉接板以及150 mm×150 mm×30 mm 鋁製基礎板，搭配d25 mm×8.25 mm ×800 mm之2×2群樁所組成。試驗規劃分為純結構模型與基礎沖刷模型，純結構模型者是將純結構試體固定於剪力試驗盒內，在沒有砂土的情況下進行試驗；基礎沖刷模型者同樣將試體固定於剪力試驗盒內，並以裸露深度0倍、3倍、6倍的基樁直徑作為沖刷深度之分組，以探討基礎於不同裸露深度之下的影響。砂土試體採用相對密度50%之乾性石英砂。試驗過程當中，進行不同位移大小的反覆側推試驗，位移由小到大依序為±1 mm、±5 mm、±10 mm、±15 mm、±20 mm、±30 mm、±40 mm、±50 mm，其中小位移±1 mm ~ ±20 mm進行三次循環，而大位移±30 mm ~ ±50 mm則進行了兩次循環，並於過程當中，記錄結構之位移、角度以及應變之反應，並經由應變計量測數據計算出試驗過程中彎矩與軸向力的變化。
試驗結果，位移的部分：隨著土壤裸露深度越多，基礎板之位移越明顯。角度的部分：側推高程的角度變化與基礎板的角度變化並非一致，表示橋柱並非完全的剛性體，相同位移之下，隨著土壤沖刷深度的增加，旋轉角會隨之下降。應變的部分：觀察到應變大的位置產生在基樁頂部以及基樁底部，也由於應變較大的緣故，應變計容易於試驗過程當中，在該處產生滑移、鬆脫、損壞之現象，使得該位置之應變值較容易出現異常。軸向力的部分：隨著砂土沖刷深度越多，基樁之軸向力會隨之下降。彎矩的部分：純結構模型第一個降伏點產生在基樁底部；基礎沖刷模型第一個降伏點出現在基礎頂部。遲滯迴圈的部分：隨著砂土沖刷深度越多，勁度下降，力量隨之下滑。

關鍵字

反覆側推試驗 ； 樁基礎 ； 破壞機制 ； 群樁效應 ； 沖刷效應 ； 土壤結構互制 ； 土壤彈簧

並列摘要

This study investigated the structure behavior and soil-structure interaction of single-column pier and the group piles model through lateral cyclic loading test. A large biaxial laminar sand box was used to set the model specimen and sand. The upper part of the structure is a single-column pier consisting of a 120 mm×120 mm×20 mm joint face connected with actuator, a solid steel pier with a diameter of 40 mm, 200 mm high and a 150 mm×150 mm×15 mm base plate made by steel. The lower structure is a group pile foundation specimen, consisting of 200 mm×200 mm×15 mm aluminum bottom adapter plate, 150 mm×150 mm×15 mm aluminum base plate with d25 mm×8.25 mm ×800 mm 2 × 2 group pile composition. The experiment divide into pure structure model and model of scouring. The pure structural model is fixed to the shear box and experiment with no sand. The scouring model also fixed the specimen in the shear box and the model with specified exposed length of pile foundation, as a ratio of pile diameter D, from 0D, 3D to 6D to explore the foundation of different depth of exposure. The sand property of dry fine silica sand is controlled by relative density of 50%. In the course of experiment, the lateral displacement of the different sizes is ±1 mm、±5 mm、±10 mm、±15 mm、±20 mm、±30 mm、±40 mm and ±50 mm. In the ±1 mm ~ ±20 mm for three cycles and ±30 mm ~ ±50 mm for two cycles. Among the experiment, the displacement, angel and strain response are recorded. Furthermore, the strain gauge can calculate the value of bending moment and axial force.
The results of the experiment. Displacement: With the depth of the soil exposed, the displacement of the base plate is more obvious. Angle: the angle variation of the actuator elevation is different from that of the base plate, indicating that the pier is not a rigid body. Under the same displacement, as the depth of scouring increases, the rotation angle decreases. Strain: It can be observed that the position of the strain is large at the top and bottom of the pile. In the large strain area, the strain gauge is easy to slip, loose and even damage in the experiment process, so that the strain value of the large position is more prone to abnormal. Axial force: As the souring increase, the axial force of the pile will decrease. Moment: Pure structure, the maximum bending moment is generated at the base of the foundation. The maximum moment of the scouring model appears at the top of the foundation. Hysteresis loop: As the exposed depth increase, the force will decrease.

並列關鍵字

Lateral cyclic loading test ； Pile foundation ； Failure mechanism ； Group pile effect ； Scouring effect ； Soil-structure interaction ； Soil spring

參考文獻

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