STUDY OF RIVER BANK EROSION CONTROL BY SOIL NAILING AND GEOSYNTHETICS

Abstract

The dissertation aims at using the nailing technology and geosynthetics in river bank protection work. With a view to suggest the technique, analytical work and field experiment with flexible polymer ropes in controlling river bed erosion have been carried out and presented in different chapters of this report. An effort has been made in Chapter-I of this report to describe advantages, application, construction sequences, component of nailing, limitation etc. for easy understanding regarding the nailing technology. In Table -1.2 of the same chapter some investigated information have been presented with a view to justify how confidently soil nailing technique can be used to solve different types of geotechnical related problem. In Chapter-II, chronological developments of soil nailing technology made by different researchers are presented. Several methods are available for stability analysis of nailed structure, namely the limit equilibrium method, limit analysis method and the finite element method. Among all these, the limit equilibrium method has attracted the attention of the researchers because of its simplicity,, reasonable accuracy and popularity among the practicing engineers. Although these are not correct from the viewpoint of mathematical theory of plasticity for their incorrectly oriented slip surfaces, these have acquitted themselves quiet well for their reasonable accuracy and predictions. These are not very much off from the solutions obtained through more rigorous applications. No universally accepted standard method for design of such structures without any controversy could yet be developed. Chapter-III represents the summary of design methods available. Chapter —IV deals with how to analyze a soil nailed wall considering circular type wedge failure. In this analysis friction circle method for c-4 soil has been adopted. Soil nail interface friction angle has been considered as 2/3 of angle internal friction. Since this angle has to be measured from pullout test under in-situ field condition, it does not guarantee accurate analysis. The analysis includes the role of bending stiffness in factor of safety. This chapter results in an equation for computing factor of safety. With the help of computer program, the effect of variation of design parameters such as nail length, nail diameter, nail inclination, wall inclination, wall height, angle of internal friction as well iii as cohesion of soil in factor of safety can be determined. At the end of this chapter some graphs are plotted to have a look at the variation of factor of safety with the variation of different design parameters. The dissertation aims at how to use the technology in river training works. It can be concluded that this technology can be used in riverbank protection work above HFL i.e. in free board zone successfully. It can also be used in rainfall eroson control. In hilly region where riverbank level is too high and it has a tendency to slide, this technology may be more suitable. It can also be mentioned here that due to turbulence, velocity and ground water effect the technology may not be suitable under water. Uses of geosynthetics in water resources projects are increasing day by day. Due to wide range of uses of this material, some basic properties as well as selection criteria are presented in Chapter-VI in order to make it more popular among the water resources engineers. Emphasis has been given only on the use of the material. Additional attention has been put on the use of geo-jute and it can be added that it may be a suitable alternative of geo-synthetics in riverbank erosion control as a filter material. Theoretical background of different approaches for designing the bank protection work is presented in Chapter-VII. This may be treated as an over view of design procedure so far available in literature. Some formulae for determination of roughness of bed material especially in gravel stage river and the same for scour depth are also presented here. One `Case Study' of Beas river regarding bank protection work has been presented in Chapter-VIII. Different alternative methods are designed and finally best suitable method has been recommended for implementation depending upon many factors. Field experiment for performance study of flexible polymer rope in gabion boxes in riverbank protection work is conducted in the river Beas located in Himachal Pradesh. Behavior of polymer rope was observed. Since observational time period was limited, preliminary assessments that were observed in the field are presented here..