Design On Limit Equilibrium Of Foundation Reinforced With Geosynthetics And Research Of Material In Reinforcements

For engineering purposes, soil is defined as the uncemented aggregate of mineral grains and decayed organic matter (solid matter) with liquid and gas in the empty spaces between solid particles. Sometimes it is necessary to use two or three-dimensional medium to improve the entirety, the tensile and shear strength of the soil. Geosynthetics meet these requirements quite well. The present development of soil reinforcement (RS) was initiated by a French engineer named Vidal (1966) and even treated as a revolution in civil engineering in recent years. Geosynthetics have been used to improve bearing capacity of poor foundation in different practical engineerings, such as foundation of embankment, sea wall, oil tank and building. This reinforced earth is made up of single layer or several layers of reinforcements horizontally placed in the soil or sand cushion under the foundation. A great number of model tests and practical engineering show it has the advantages of improving settlement and bearing capacity of foundation.However, in spite of extensive applications of reinforced soil and vast literature on the subject, the understanding of RS is still insufficient. The rapid development of RS technology has been accompanied by somewhat slower development of the methods enabling its rational analysis and design. There continues to be a lack of mature formulas which can be adopted in standard or code. Based on the domestic and overseas achievements in RS research, this thesis have done some studies on the foundation reinforced with geosynthetics about determination of bearing capacity, design method and development of new type geosynthetics (EKG) etc. The main contents include the followings:1. The families of geosynthetics and their functions are outlined at first, and the domestic and overseas amount of geosynthetics application is evaluated too. Then, an overview of reinforced soil is presented. The developments and studies of the foundations reinforced with geosynthetics are analyzed here, including some existing problems.2. The type of reinforcements and their characteristics are analyzed. The principles on how to select them and the soil used as the fill material are evaluated too.3. New types of geosynthetics EKG are studied including the conductive materials which have been considered for EKG, and the conductive methods, the conductive patterns, the electric corrosion and so on. Results of the model tests show that EKG can be used to improve the drainage property and increase the undrained shear strength of cohesive fill, and conductive plastics can get rid of the corrosion that happened in metal electrode. Field applications are required to further studies.4. Available empirical results indicate that the creep of reinforcement strongly influences the overall behavior of RS structures, which is demonstrated by excessive deformations. Different creep tests are discussed and the test methods to obtain the two kinds of creep curves are compared in this thesis. The methods of how to determine the reduction factor according tolong-term strength of creep or allowable strain during the services life are presented.5. The design methods of foundation reinforced with geosynthetics mainly include the followings: 1) Analysis of stresses in reinforcement and soil by Boussinesq's solution (Binquet and Lee, 1975), 2) Formula of improving Terzaghi ultimate bearing capacity (Yamanouch and Gotoh, 1979). Both of them for analysis of bearing capacity of strip foundation have some shortcomings. Many assumptions have been used in these methods. Combined with Code for design of building foundation and Code for foundation treatment (in China) these two methods are replenished here.6. This paper deduced the formula of ultimate bearing capacity based on the principle of limit equilibrium and the formula of determining the length of reinforcement based on equilibrium of anchoring segment outside shear failure lines by analyzing two limit equilibrium modes, those are limit breaking and pullout of reinforcement.