Soil nailing reinforcing technique has been popular in western countries, because it has merits of rapid and economic construction. However, Taiwan began to employ this technique to stabilize slopes and excavations only until ten years ago. Though it has been thirty years after the development of soil nailing technique since 1970s, the method still has some area under active research such as mechanism, design method, etc. This article compares the differences in the reinforcing principles among similar reinforcement methods at first. Then, the reinforcing characteristics, designing methods as well as monitoring program are also introduced extensively.
Soil nailing has been used successfully in temporary and permanent applications on new and remedial constructions in rural and urban areas. Therefore, the seismic resistance and failure mechanism of nailed slope are worthy of investigation to find a method of stabilizing steep slopes subjecting to seismic strike. Literature on nailed structures emphasizing the mechanical behavior of reinforcement and the interaction mechanism between nail and soil are reviewed. In addition, the seismic response and earthquake resistance of nailed steep slopes are discussed as well.
Soil nailing is normally designed with uniform length and equal spacing for the soil nailed walls and slopes. Uniform arrangement of soil nailing on the retaining walls and slopes may meet the requirement of stability. However, it may not be the optimum design in terms of the economic concern. Factors affecting the stabilization of soil nailed structures and slopes are investigated through: (1)inclination of soil nailing; (2)bending stiffness of soil nailing; (3)length of soil nailing at different elevations; (4)location of soil nailing on the outward surface of the walls or slopes. Investigation of mechanical behavior of soil-nail interaction is carried out in this study. Effect of deployment and bending stiffness of soil nailing on the contribution of stabilization of walls and slopes are assessed in terms of factor of safety, analyzed with the nonlinear finite element methodology. Findings of this study are helpful to the optimum design of retaining walls or slopes stabilized with soil nailing.
A rapid growing of slope development and deep excavation in Taiwan reflects the need of increasing population and transportation. From the engineering point of views, the challenge to satisfy this need is the slope stability analysis and mitigation design. With the progress in computer techniques, the common engineering practice of slope stability problem is using the Limit Equilibrium Analysis and the Working Stress Analysis. However, engineers usually fail to use the proper fundamental judgment on the theoretical background and parametric definition, which leads to an unavoidable misleading. For this purpose, this article introduces a two-dimensional analytical approach on the design of soil nail and soil reinforcement, especially focusing on the interaction between soil and soil nail. By using SLOPE/W and PLAXIS, this article will also use example sites, such as a slope in U.S.A. and two excavation sites in Northern Taiwan, to demonstrate a proper procedure. This procedure provides a proper method of defining parameter values and interpretation of computational results.
THE APPLICATION AND CASE STUDIES OF SOIL NAILING FOR SLOPE EXCAVATIONS
本文將以美國聯邦高速公路局(Federal Highway Administration,簡寫為FHWA)所提出土釘加勁工法之“最佳可用設計法”(Best Available Design Method)設計斜坡開挖配合土釘加勁與噴凝土護坡方式，作為地下室開挖之臨時性擋土結構或整地修坡之永久性擋土及護坡結構。文中除簡述“最佳可用設計法”之設計原則及設計方法外，並以此“最佳可用設計法”之實際施工及完工案例說明土釘加勁工法應用於斜坡開挖擋土護坡之情形，希望能提供各位讀者及工程先進參考。惟上述工程案例皆無配置相關觀測儀器，故無法提供實際觀測行為以資參考比較，實屬可惜。
Based on FHWA’s Best Available Design Method of Soil Nailing, this article describes the principle of Best Availlable Design Method and presents two design cases for slope and basement excavation. In these cases soil nailing and shotcrete were adopted. In the slope excavation case galvanized steel bars were used as inclusions for permanent slope retaining system. Descriptions of several in-situ works are also presented for reference. It is unfortunate that no instrumentation was installed in presented cases. No comparisons can be made for further study. But it proves FHWA’s Best Available Design Method of Soil Nailing is satisfactory.
Soil nails were first designed and installed in field in France. Because of their advantages in construction efficiency, cost, and application in both temporary as well as permanent structures, soil nails have been used for various stabilization purposes and the technology has been significantly advanced since their first application. In addition to the use in earth retaining structures, soil nails have been designed for the slope stabilization in public civil works. This paper presents the advantages of using soil nails for slope stabilization and the application restrictions. An example was used to demonstrate the design methodology.
The site geological condition investigating project for more than 600 strong ground motion stations was conducted by National Center for Research on Earthquake Engineering (NCREE) in corporation with Central Weather Bureau (CWB) since 2000, therefore the geological properties could also be considered in strong ground motion records analysis. Suspension PS Logger was used in the investigation to measure stratum velocity profile. For PS Logger, the receivers that detect the wave, and the source that generates the wave, are moving as a unit in the borehole. The elapsed time between arrivals of the waves at the receivers is used to determine the average velocity of a 1-meter-high column of soil around the borehole. Source to receiver analysis is also performed for quality assurance.
Great discrepancies are often found between the evaluated results, when using various simplified SPT-N methods to evaluate soil liquefaction potential. Therefore, it is important to know which simplified method is more suitable for use. However, this problem is not solved yet. Using a total of 302 liquefied and non-liquefied cases during Chi-Chi earthquake, this paper proposed two assessment indices, prediction success rate and at-least safety factor error, to appraise the suitabilities of the five simplified SPT-N methods currently used in Taiwan. Success rate is an index that represents the accuracy of a method in predicting whether liquefaction occurs or not. On the other hand, at-least safety factor error is an index to indicate the relative error of the calculated safety factor by a method. Based on the appraisal, it is found that among the five methods, the success rates of NCEER’97 and Seed’85 methods are the highest and their at-least safety factor error are also the lowest, thus, these two methods can be considered to be most suitable methods. The performances of T-Y’83 and JRA’96 methods are the second. The JRA’90 method has the worst grade, therefore, it is believed to be an unsuitable method.