土釘加勁邊坡靜動態行為分析

Dynamic and Static Behavior of Nailed Soil Slopes

范峻崇(Jien-Chung Fan)

指導教授 ： 洪勇善

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.2005.00276

摘要

土釘應用於邊坡加勁主要利用土釘抗張之特性對邊坡產生約束作用，以提高整體邊坡的穩定性。近年來已逐漸作為永久支撐結構，因此完善的設計除靜態分析外，動態特性也必須加以考量。然而，現今動態穩定分析仍沿用傳統邊坡之擬靜態分析法，對於土釘邊坡受震之行為與耐震能力至今鮮少相關文獻。故土釘邊坡的耐震特性與土釘-土壤間的互制機制，為當前土釘應用於邊坡整治所需探討的重點。
本研究主要以數值分析方式模擬現地土釘邊坡受靜、動態外力作用下之力學行為，並進行各項影響參數之研究。在靜態分析方面，首先針對坡度30°~80°之邊坡探討上部載重作用時土釘受力的行為，以瞭解土釘加勁機制及破壞型態。此外，為增加土釘實務性的應用，亦探討土釘傾角及長度對邊坡的影響，並經由極限力平衡分析建議完整的設計參考圖表。
在動態分析方面，則先以洪勇善等人(2002)之振動台試驗結果為佐證，建立與模型相近之平面應變數值模式，經分析比對確立動態數值模式之正確性與適用範圍。接著，由數值模型建立坡高6m之真實邊坡，進行土釘加勁後的動態行為參數研究。研究發現如下：(1)8倍坡高的後邊界及1.5倍坡高之前邊界為不影響動態數值分析結果之適當邊界範圍；(2)土釘耐震之最佳傾角隨著坡度減緩而增大，於坡度30°~80°邊坡，最佳傾角介於30° ~ 13°；(3) 土釘最有效釘長在動態外力小時，約為坡高的0.67倍，動態外力較大時，則隨著外力增加而最有效釘長呈線性增加；(4)對土釘邊坡而言，垂直地震較水平地震之影響小許多，若忽略垂直地震之作用，邊坡的反應行為並無明顯不同；(5)加勁區內的土壤因受震時土釘有效發揮抗張能力，經由摩擦阻抗機制提供土壤圍束應力以降低加勁區內土壤之破壞勢能；(6)地震加速度的大小與方向對邊坡穩定性有極大的影響，變形的產生皆由入坡面方向加速度所造成，而出坡面加速度則影響不大，入坡面方向加速度導致坡體慣性力向坡外作用，此對邊坡之穩定性最為不利。

關鍵字

土釘 ； 邊坡 ； 設計圖表 ； 數值模擬 ； 動態分析

並列摘要

Soil nailing has been used successfully in temporary and permanent applications of the new and remedial construction, and in rural and urban settings. The soil nailing concept involves obtaining a stable composite material by reinforcing the soil with nails. The reinforcing mechanism is accomplished by transferring tensile force from the nails into the soil mass through friction mobilized at the soil-nail interface. In recent years, soil-nailing techniques have been used widely in soil excavation and slope stabilization. However, most of the researches focus on the nailed soil structure under static condition. The aim of this study is to investigate the response of nailed slopes under seismic loading as well as their failure mechanism and nail behavior. The mechanical behavior of nailed slopes under static and dynamic loading respectively is obtained by numerical modeling. Parameters study also to discuss the effect on the nailed slopes behavior. In the static analysis, the nail mechanical behavior and failure mechanism are to realize through a uniform surcharge was gradually applied to the slope ground surface for slope angle between 30° to 80°. To increase applied practicability, design charts of nailed slopes are also accomplished based on limit equilibrium approach.
In dynamic aspect, the experimental results of shaking table model test conducted in the previous research (Hong et al., 2002) revealed that soil nailing is effective in increasing stability of steep slopes under seismic load. However, a comprehensive understanding of slope response regarding the force variation of nails along their length, distribution of earth pressure in soil mass, and development of failure mechanism are difficult to obtain from model test. The numerical method can overcome the deficiency of the model tests and is employed in this study. Build-up the numerical model of an experimental nailed slope with the finite difference program, and compare the results with the measured data to conform the adequate of numerical model. A series of parameters study to discuss the effects on the 6-meter nailed slopes behavior during seismic shaking. Research result shows that: (1) The facing displacement maintains constant value when the back and front horizontal boundary up to the 8 and 1.5 times slope height respectively. (2) The nail optimum inclination increases with the decreasing slope angle. When slope angle is between 30° and 80° then the nail optimum inclination is between 30° and 13°. (3) From economical viewpoint, the most effective nail length is about 0.67 times slope height under lower seismic acceleration. When peak acceleration is greater the most effective nail length linear increase with the increasing peak acceleration. (4) The effects of vertical component smaller than horizontal earthquake can be neglected when analyzing nailed slope structures. (5) The nailed soil mass decreases the failure potential due to the nails mobilized tensile force through the friction at nail-soil interface. (6) When the acceleration direction is toward the interior reinforced zone caused slope unsafely during shaking.

並列關鍵字

soil nailing ； slopes ； dynamic analysis ； numerical modeling

參考文獻

1. 何嘉浚（1996），「土釘擋土牆結構設計方法之探討」，碩士論文，國立台灣大學土木工程研究所，臺北。

9. Bathurst, R. J. and Hatami, K.(1998), “Seismic Response Analysis of a Geosynthetic-Reinforced Soil Retaining Wall,” Geosynthetics International, Vol. 5, Nos. 1-2, pp. 127-164.

13. Bruce, D. A. and Jewell, R. A.（1986）, “Soil Nailing : Application and Practice – Part 1,” Ground Engineering, November, pp. 10-15.

14. Bruce, D. A. and Jewell, R. A.（1987）, “Soil Nailing : Application and Practice – Part 2,” Ground Engineering, January, pp. 21-38.

20. Hatami, K. and Bathurst, R. J. (2000), “Effect of Structural Design on Fundamental Frequency of Reinforced-Soil Retaining Walls,” Soil Dynamics and Earthquake Engineering, April, pp.137-157.