To obtain a Master's degree
Civil-Soil and Foundation Engineering
March 2013
Abstract
Different methods are used to stabilize pits, among which nailing and anchoring methods are common methods and are similar in terms of implementation methods. In this research, an attempt has been made to combine the two mentioned methods and arrive at a better, safer, and more economical model for creating a pit guard structure so that it can be replaced by older, unsafe, and uneconomical methods. The purpose of this research is to provide the necessary stability for the pit through the creation of an optimal combined guard structure that has the optimal angle, length, and arrangement for soil nails and Anchor Bolts to give in a way that does not cause breakage and destructive deformation in the pit, which is done by Plexis Model software. Construction is done. For this purpose, the nailing method must be modeled first, then when the desired results are obtained, anchors are added to the nailed structure and the results of the nailing method and the combined method are compared. Anchors at depths of 9, 18, and 27 meters in homogeneous soil conditions and in the mode of driving soil nails with angles of 0, 5, 10, 15, and 20 degrees and with different lengths, 0.7, 1, and 1.2 times the height of the pit. has been investigated.
It is observed that the use of anchors in the upper part of the wall of the guard structure reduces deformations in it, and the use of soil nails in the lower parts of the wall increases the stability of the structure, while the implementation costs are reduced. It is.
Key words:
Picking, nailing, anchor, combined method, numerical analysis
First chapter
Introduction and generalities
1-1 Introduction
Nowadays, with the increase in urbanization and the construction of large structures, deep excavations have been carried out to create parking lots, warehouses, and other uses. One of the important issues in excavation is the design of a suitable guard structure and the control of displacements of the pit wall and the soil behind the pit. Various methods are used in the implementation of semi-deep and deep pits; nailing and anchoring methods are common methods.
Increasing the depth of excavation, especially in urban areas near buildings Passages are of special importance, and ensuring the stability and control of displacements of the pit wall and behind the wall must be carefully checked. In this situation, some stable methods of pit construction lose their ability to be implemented, and according to the regulations, deep excavation is allowed in conditions that do not endanger the safety of nearby structures. The type of soil, the conditions of underground water, the depth and length of excavation, the location and conditions of nearby buildings, the displacement of the pit wall, whether the structure is permanent or temporary, the problem of earthquakes, the dynamic load caused by the movement of vehicles in the vicinity of the pit, and the project implementation costs are selected. The transfer of these forces to the soil mass is safe, which depends on several parameters, including the installation method and the injection method, and the characteristics of the soil and the guard structure, which is based on the work of the nailing method in such a way that the soil nails are executed and with the excavation of greater depths, the pit wall will find some displacement, which will activate the function of the soil nails.
The execution method of anchors is similar to soil nails, with the difference that prestressing forces are created in the anchor, and these forces are transferred to the restrained part through the non-restrained part of the anchor, which causes stability and displacement control.
Due to the importance of controlling the lateral deformation of the wall, a numerical analysis software should be used, for this purpose, PLAXIS 8.2 software is used, which is a software based on the finite element method.The valid regulations for the design and investigation of stability and deformation in nailing and anchoring structures are the regulations of the Federal Highway Administration of America.
1-2 research methods
In this research, the parameters affecting the nailing method and the combined method of nailing and anchoring are investigated. Investigating the effect of the angle of the nails and the ratio of their length to the height of the pit, in pits with different depths, and the effect of each of the above parameters on the displacement and stability coefficient of the guard structure is investigated, as well as different anchoring arrangements in the case of placing the anchor instead of the soil nail for the conditions of the presence and absence of the soil nail between the anchors. Different depths and longitudinal arrangements of soil nails are investigated in a combined method and the effect of the arrangement for different pits and various longitudinal arrangements of soil nails is investigated, then the results for the nailing structure and the combined structure are compared for different angles and lengths of soil nails and different excavation heights.
1-3 Necessity of conducting research
In recent years, due to the development and expansion of cities and the increase in population density, the number of underground floors and the depth of excavation have increased. Soil stability is considered as one of the important issues in geotechnical engineering. Therefore, identifying and implementing methods that can be used to It seems necessary and necessary to solve the problems as much as possible. In some cases, the construction work requires excavation with a vertical slope. It needs a temporary maintenance system to keep the deep pit walls stable. To improve the speed and quality of the construction of the project and to ensure that possible life and financial damages do not occur. The design of deep pit retaining systems requires detailed analysis, design and monitoring of its performance. In recent years, the use of hybrid systems has been noticed, and the hybrid structure of nailing and anchoring is one of them, and the importance of this hybrid method is that in addition to providing sufficient stability and controlling the deformation of the guard structure, the implementation costs it also reduces the advantages of this method in deep excavations compared to other methods. In this research, this new hybrid system is examined.
1-4 Chapters of content
This research is presented in 5 chapters, which are as follows:
The first chapter deals with the objectives and necessity of conducting the research.
The second chapter is an overview of the studies conducted in the field of different stabilization methods by two methods. nailing and anchoring has been done, we discuss the general aspects of the nailing and anchoring method, application cases, familiarization with implementation steps, and technical and operational points.
In the third chapter, we introduce the Plaxis software and describe how to model it, then a numerical validation and a case validation are performed.
in the fourth chapter, based on the regulations, the analysis and design of the nailed guard structure and the combined structure of nailing and anchoring are described, and the modeling results are compared and analyzed under different conditions and parameters.
In the fifth chapter, the conclusions of this research are presented. We will make some suggestions for other researchers and we hope that this research will play a small role in advancing the goals of the engineering community. Chapter 2: Studies done 2-1 Introduction: All the years of the earth, landslides in some parts of The world is happening, including the recent landslides in Italy, Pakistan, Mexico, etc. He pointed out that it caused significant damages. Despite the activities to reduce the risk of instability that are planned and designed before the construction of projects, there are still uncertainties, especially related to soil knowledge. Therefore, the importance of analyzing the stability of existing roofs is revealed