孔穴擴張理論應用於土釘之拉出行為研究

Application of cavity expansion theory on pull-out behavior of soil nail

蕭絢嶸(Hsuan-Jung Hsiao)

指導教授 ： 吳朝賢

淡江大學/工學院/土木工程學系碩士班/碩士(2005年)

https://doi.org/10.6846/TKU.2005.00593

摘要

土釘加勁邊坡或擋土結構中，土釘與土壤間的摩擦阻抗為一重要參數；本文利用孔穴擴張理論探討土釘之摩擦阻抗，並以實驗室之土釘拉出試驗所得結果印證本研究結果的適用性。在拉出行為中，土釘外圍土壤因膨脹效應產生擠壓，導致作用於土釘之正向力也隨之增大，進而影響土釘之拉出阻抗，因此本文的主要研究在於利用孔穴擴張理論，推導土釘拉出過程中作用於土釘上的正向應力。
本文所利用之孔穴擴張理論，其中假設土釘外圍非黏性土壤之應力-應變關係為線彈性-純塑性，且符合莫爾-庫倫降伏準則，土釘拉出過程中當周圍土壤處在彈性狀態時採用小應變理論來分析，土壤處於塑性狀態時則以大應變分析，並將土壤膨脹角引入塑性環內的應力-應變關係，利用無窮級數的迭代運算，求出作用於土釘表面之正向力。理論之推導係藉由土釘周圍土壤之剪力帶厚度的形成與發展，依據土釘之直徑尺寸、螺紋牙距之粗糙表面以及土壤顆粒粒徑等參數，進行土釘之剪力阻抗及拉出行為分析。
研究結果可得以下結論：(1) 經由與陳威志 ( 2004 ) 土釘拉出試驗結果之比對，確立本理論分析模式之適用性。(2) 當土釘螺紋牙距小於土壤平均粒徑時，土釘的粗糙表面對於驅動土壤顆粒的旋轉阻抗效果並非最佳，因此膨脹角及摩擦角需作折減之修正，而角度折減後之分析預測值更趨近於試驗值。(3) 由理論模式分析得知，視摩擦係數隨覆土應力的增加而遞減，在高覆土應力的情況下，土釘表面的應力僅覆土應力貢獻，且其剪力帶厚度幾無變化，顯示土釘在拉動過程中周圍土壤膨脹現象並不明顯。(4) 土釘直徑愈小且螺紋牙距愈大者 (土釘表面越粗糙者)，視摩擦係數愈大；反之，土釘直徑愈大且螺紋牙距愈小，其行為類似光滑土釘，故視摩擦係數並無明顯變化。

關鍵字

孔穴擴張理論 ； 土釘 ； 膨脹 ； 覆土應力 ； 粗糙表面

並列摘要

The soil-nailed structure is a retaining structure formed by hammering reinforcing inclusion into soil matrix, or by inserting inclusion into predrilled hole and grouted. Among many techniques of stabilizing natural slopes or excavations, soil nailing is an applicable one due to many advantages. The dilation of soil around the soil nail during pullout process leads to the increase of confining pressure on the nail, and subsequently, the increase of the pullout resistance. Previous literatures indicate that frictional interaction between soil and the inclusion interface provides the major reinforcing effect. However, due to the complexity of the interaction mechanism between the apparent friction coefficient and the various parameters such as surface roughness of nail, particle size, and overburden pressure on the nail surface, little work has been done theoretically to describe the relationship among the pullout resistance and those variables. An attempt is thus made in this study to derive an expression for theoretical description of the relationship among the pullout resistance and various parameters using the cavity expansion theory. Closed-form solutions for calculation of the confining pressure on the surface of the soil nail are obtained. To verify the validity of the proposed approach, the predicted results are compared with those values obtained in pullout tests.

並列關鍵字

cavity expansion theory ； soil nailing ； dilation ； overburden pressure ； surface roughness

參考文獻

6. Bolton, M. D. (1986):”The strength and dilatancy of sands,” Geotechnique, Vol. 36,No. 1, pp.65-78.

7. Carter, J. P. ; Randolph, M.F., and Wroth,C. P. (1979), “Stress and pore pressure changes in clay doing and after the expansion of a cylindrical cavity,” International Journal for Numerical and Analytical Methods in Geomechanics, Vol. 3, Nol. 4, pp 305-322.

8. Chadwick, P. (1959), “The Quasi-static Expansion of A Spherical Cavity in Metals and Ideal Soils,” The Quarterly Journal Mechanics and Applied Mathematics, Vol. 12, Part 1, pp. 52-71.

9. Chadwick, P. (1962), “Propagation of Spherical Plastic-elastic Disturbances from An Expanded Cavity,” The Quarterly Journal Mechanics and Applied Mathematics, Vol. 15, Part 3, pp. 349-376.

14. Houlsby, G. T., and Withers, N. J. (1988), “Analysis of the Cone Pressure meter Test in Clay,” Geotechnique, Vol. 38, No. 4, pp. 575-587.