Deep mixing (DM) is the modification of in situ soil to increase strength, control deformation, and reduce permeability. Multi–axis augers and mixing paddles are used to construct overlapping columns strengthened by mixing cement with in situ soils. This method has been used for excavation support to increase bearing capacity, reduce movements, prevent sliding failure, control seepage by acting as a cut–off barrier, and as a measure against base heave. DM is effectively used in excavations both in conjunction with and in substitution of traditional techniques, where it results in more economical and convenient solutions for the stability of the system and the prevention of seepage. Although DM is currently used for excavation control in numerous projects, no standard procedure has been developed and the different applications have not been evaluated. As this technique emerges as a more economical and effective alternative to traditional excavation shoring, there is a need for guidelines describing proven procedures for evaluation of design, analysis and construction. The main objective of this research is to develop a methodology to design retaining systems using deep mixing technology. The method will be evaluated using numerical analysis of one selected case history.

Deep mixing (DM) is the modification of in situ soil to increase strength, control deformation, and reduce permeability. Multi–axis augers and mixing paddles are used to construct overlapping columns strengthened by mixing cement with in situ soils. This method has been used for excavation support to increase bearing capacity, reduce movements, prevent sliding failure, control seepage by acting as a cut–off barrier, and as a measure against base heave. DM is effectively used in excavations both in conjunction with and in substitution of traditional techniques, where it results in more economical and convenient solutions for the stability of the system and the prevention of seepage. Although DM is currently used for excavation control in numerous projects, no standard procedure has been developed and the different applications have not been evaluated. As this technique emerges as a more economical and effective alternative to traditional excavation shoring, there is a need for guidelines describing proven procedures for evaluation of design, analysis and construction. The main objective of this research is to develop a methodology to design retaining systems using deep mixing technology. The method will be evaluated using numerical analysis of one selected case history.

Due to space limitations in urban areas, underground construction has become a common practice worldwide. When using deep excavations, excessive lateral movements are a major concern because they can lead to significant displacements and rotations in adjacent structures. Therefore, accurate predictions of lateral wall deflections and surface settlements are important design criteria in the analysis and design of excavation support systems. This research shows that the current design methods, based on plane strain analyses, are not accurate for designing excavation support systems and that fully three-dimensional (3D) analyses including wall installation effects are needed. A complete 3D finite element simulation of the wall installation at the Chicago and State Street excavation case history is carried out to show the effects of modeling: (i) the installation sequence of the supporting wall, (ii) the excavation method for the wall, and (iii) existing adjacent infrastructure. This model is the starting point of a series of parametric analyses that show the effects of the system stiffness on the resulting excavation-related ground movements. Furthermore, a deformation-based methodology for the analysis and design of excavation support systems is proposed in order to guide the engineer in the different stages of the design. The methodology is condensed in comprehensive flow charts that allow the designer to size the wall and supports, given the allowable soil distortion of adjacent structures or predict ground movements, given data about the soil and support system.

Development in urban areas around the world has steadily increased in recent years. This rapid development has not been matched by the ever decreasing open space commonly associated with urban centers. Vertical construction, thus, lends itself a very useful solution to this problem. Deep excavation is often required for urban construction. Unfortunately, the ground movements associated with deep excavation can result in damage to adjacent buildings. Thus, it is critically important to accurately predict the damage potential of nearby deep excavations and designing adequate support systems. A new design method is proposed, as an attempt, to address the problem. The method is semi-empirical and directly links excavation-induced distortions experienced by nearby buildings and the components of the excavation support system. Unlike, the traditional limit equilibrium approach, the method is driven by the distortions in adjacent buildings. It goes further to propose a preliminary cost chart to help designers during the design phase. The benefit is that initial cost is known real time and will help speed up making business decisions. A new design flowchart is proposed to guide the designer through a step-by-step procedure. The method is validated using 2D Plaxis (the finite element program) simulation. Though the nature of deep excavation is three-dimensional, a plane strain condition is valid when the length of the excavation is long. Hence, two-dimensional finite element simulation was considered appropriate for this effort. Five hypothetical cases were compared and the model performed very well. The lack of available literature on this approach made verification difficult. It is hoped that future case histories will be used to ascertain the veracity of the deformation-based design method.