Soil improvement with wet deep soil mixing method

In recent years, as the result of the increasing quantity and budget of the engineering projects, many different soil improvement techniques started to be implemented. As the expropriation and existing infrastructures not effected, and location of the projects change effects the project costs as and time. The soil improvement methods have been succesfully applied in many projects. In the thesis literature was focused on commonly used soil improvement methods and explained. Information on their applications were given. All soil improvement techniques were not included in this thesis. The deep mixing method is explained in detail. Deep mixing method was used in Japan and Nordic regions in 1980's and later. At the beginning of the 1990's, it started to be applied all over the world. Deep mixing method was investigated from historical point of view, mixing methods were explained in detail, and factors effecting the soil and strength parameters were investigated. Deep mixing columns increase the stiffness of the soil, thereby, reducing the compressibility of the soil. The deep mixing method has been shown to be applicable to soils of high groundwater level, soft clay and clayey sandy grounds. The principle of the method is based on the pressure injection of the binder to the soil. The main ingredient of the binder used is Portland cement and blast furnace slabs added to the cement. The water / cement ratio by weights 1: 1 for many projects. When higher strength is required, this ratio is changed to obtain columns with high rigidity. Finite elements analysis of the wet deep mixing columns that were used as a soil improvement method in an area where a cut-cover tunnel construction is to be carried out was doned. Although the tunnel foundation soil does not have a problem in terms of bearing capacity, settlements could occur. Result of the soil investigations, the soil underneath the tunnel is determined to be 18 meters thick fill layer. The bedrock is located underneath the fill layer. After the construction of the cut-cover tunnel, a 14-meter engineering fill will be made on top of the tunnel. A wet deep mixing machine groups are three different sections. Drilling machine with high torque, circular shaft and high injection pump group. After appropriate amount of binder is prepared, the admixture is transferred to the high torque drilling machine through the powerful pump and the drilling machine mixes the soil with the rotary shaft. In application, injection pressure is range to 100-200 bar. The success of quality control is paramount for the success of wet deep mixing. After the test columns are construct, the engineering parameters has to be determined in the field and laboratory environment. The main properties to look at in the test columns are diameter control, length control and unconfined compression strength and elasticity modulus of core samples. A plate loading test can then be performed to examine the displacements under loading condition, in the composite soil. Within the scope of the thesis, a cut-cover tunnel was analyzed with a finite element program. As a result of field experimental test and engineering observations, modulus of elasticity was determined and selected by appropriate parameters present in the literature. After the elastic modulus of the soil was determined, the unconfined compressive strength of the wet deep mixing columns was taken from the literature and the modulus of elasticity of the column was determined by the appropriate approach. After the modulus of elasticty of the soil and wet deep mixing columns is determined, the composite modulus of elasticity is calculated by the area improvement ratio. In the result of analysis, it is assumed that the improvement is made homogeneously along the fill and is to the top of the bedrock. The composite modulus of elasticity used in the analyses is for the to be whole fill layer. Mohr-Coulomb and Hardening-soil models were used in the finite elements program as material models. The analyzes were carried out with the virgin loading conditions, in plan grid spaces of 2.0 m * 2.0 m, 1.0 m * 2.0 m and 1.0 m * 1.5 m, of the wet deep mixing columns. At the same time, in terms of cost control, the wet soil mixing columns were planned to be constructed after 3 meters of excavation on the tunnel base and the analysis was done by the finite element program. Most of researchers have been found that the amount of settlement achieved in the analysis results made with a Mohr-Coulomb material model is higher when compared to the actual settlement amount. In the analysis results of the analysis done was given Hardening-soil material model, has given closer results to reality. Therefore the analyses made with the Hardening-soil material model in the evaluation phase of the thesis were assumed to be the main result. According to the Hardening-soil material model under the virgin condition, the expected settlement was 25 cm and the settlement limits were exceeded in the analysis studies. Subsequently, when the center to center column distance 2.0m * 2.0m wet deep mixing method was applied, the expected amount of settlement decreased by 9 cm. If the application was made with center to center columns distance of 2.0m * 1.5m applied, the expected settlement has decreased by 6.2 cm. Because the settlement limits are exceeded, the wet deep mixing column with application range of 1.0m * 1.5m is included in the analysis and the settlement of 5.5 cm is calculated. When the costs are taken into consideration, the columns are made starting at 3 m below the tunnel base and engineering fill was done for the 3m , the settlement of the tunnel is 5 cm and it has the settlement limits. The results of the analyzes are within considered according to the expected settlement conditions in the tunnel foundation soil. The cost and time analyses are also observe, and the optimum solution is found.