Factors affecting the wall displacements and soil settlements which is behind the wall in deep excavations

Because of rapid growth in urban development, numerous deep excavation projects for high rise buildings and subway lines are being executed and more projects are scheduled in the future. During excavation, an in situ wall system is constructed to provide stability and to minimize movements of the adjacent ground. Obviously, improper design of an in situ wall system constructed in an urban area may not only impose serious lead to loss of life in extreme cases. Therefore, consideration must be given to wall and adjacent ground movements for a given wall system during the design phase in order to ensure a successful excavation work. Deep excavations having huge importance in geotechnical engineering are so complex topics. Deep excavations including lots of factors can be constituted with vertical and horizontal supporting members. Constituted systems earth pressure, water pressure and also surcharge loads should be calculated for the design of the system. Loads acting on system are safely transferred with horizontal and vertical supporting members to soils. Design of an deep excavation supporting system requires a lateral earth pressure distribution behind the wall for final wall height to estimate support loads and wall bending moments. For deep excavation supporting systems constructed from the ''top down,'' the deformation pattern is complex and not consistent with the development of a theoretical Rankine or Coulomb earth pressure distribution. Evaluating earth pressures for deep excavation supporting system, the apparent earth pressure envelopes are more frequently used than other methods primarily because of expediency in practical application. These apparent earth pressure envelopes were originally developed by Terzaghi and Peck (1967) and Peck (1969) to provide loadings for conservative design of struts in internally braced excavations, based on field measurements of strut loads from various excavation sites. Since 1969, several modifications to the original envelopes have been proposed. Another important point is displacement of wall to do. Wall displacement is important because displacement of wall and displacement shape is affect the soil settlement quantity and shape behind the wall. Deep excavation systems should be designed according to quantity of settlement which must be acceptible limits range. These acceptable limits range of the soil settlement can change with respect to structures property or aim of the utilization of structures being behind of the wall. For instance, a historical buildings' or a nuclar reactors' allowable settlement is different than a residential buildings'. Ground movements adjacent to an excavation are influenced by a number of factors. Deformation behavior of a braced excavation may be affected the excavation width and depth, wall stiffness, strut spacing, stiffness and preloading, depth to an underlying hard stratum, soil stiffness and strength distribution, dewatering operation, adjacent surcharge, soil consolidation and creep, and workmanship. Some of these factors are difficult to access or quantify. Thus, it is difficult to consider all the relevant factors in a detailed analysis of the deformation of deep excavations. In this thesis, 21 factors affecting wall displacement with related to lots of articles is mentioned under its own subtitle. Several empirical and semiempirical methods are available for estimating the excavation-induced maximum wall deflection (Mana and Clough 1981; Wong and Broms 1989; Clough and O'Rourke 1990; Hashash and Whittle 1996; Addenbrooke et al. 2000) and the surface settlement profile (Peck 1969; Mana and Clough 1981; Clough and O'Rourke 1990; Ou et al. 1993; Hashash and Whittle 1996; Hsieh and Ou 1998). In this thesis lots of articles about deep excavation systems deflection and soil settlement is used to understand of soil movement behaviour on the half of interpretting behaviour of used together different vertical and horizontal support members. Different vertical and horizontal supporting members can be evaluated together for calculating wall displacement and soil settlement. This evaluation can be done with some equations including wall bending moment, vertical distance between two support members and soil stiffness. Therefore used different vertical and horizontal support members in different articles can be evaluated together using some equations named generally system stiffness. Choosing the most appropriate stiffness for an excavation support system is crucial to minimizing excavation related damage to adjacent structures. The stiffness of an excavation support system is a complex function of the flexural rigidity of the wall element, the structural stiffness of the support elements, and the type of connections between the wall and supports, and the vertical and horizontal spacing of the supports. Previous Studies on the relationship between stiffness of support system and movements Clough et al. (1989) introduced a design chart for estimating the magnitude of the maximum lateral wall movement based on the system stiffness (ρs) and the factor of safety against basal heave (FOSheave) in soft to medium clays. Addenbrooke et al. (2000) demonstrated via finite element analyses that the displacement flexibility number (Δ) can be used to define wall and ground movements in undrained deep excavations in stiff clay. They suggested that this parameter can be utilized to derive an economical support system in retaining wall designs. The results of the finite element analyses illustrate a clear relationship between the stiffness of the support system and movements (lateral wall deflection, vertical, and horizontal ground movements). Finite element method is often employed to model complex soil structure interaction problems such as braced excavations. Although the deflection of the braced wall can generally be predicted well using a finite element analysis. In this thesis, PLAXIS 2D 2018 finite element program is used to investigate the 5 factors which affect the displacement and settlement. In this parametric study, anchor inclination, vertical and horizontal distance between anchors and anchor unbonded zone lenght is adopted as constant values and 12 m excavation is investigated depends on pile embedment depth, prestressed force, number of strand wire and anchor bonded zone lenght with PLAXIS 2D 2018 finite element computer program. For the investigation of these factors influencing wall displacement, initially a supporting system is created for loose sand. The reason for choosing of the created system for loose sand is that finding the maximum displacement of the wall to occure in loose sand and dense sand. Supporting system to be designed for loose sand can be used for dense sand but supporting system to be designed for dense sand can not be used for loose sand because supporting system designed for dense sand fails in loose sand when not to be given maxsimum displacement of the wall. But this thesis another aim is to compare displacement and soil settlement according to soils. In the first section in this thesis, why deep excavations is needed and importance of deep excavations is mentioned. In the second section, vertical and horizontal supporting systems is mentioned. Mentioned systems in this section is helpful to introduce the systems and advise to use Turkish equivalent word which can be easily used among the society. Again in this section, supporting systems and their rigidity, earth pressures acting on anchored systems and calculating the earth pressures according to system rigidity, forces acting on anchors and anchor design is explained. Third section mention about calculating methods of deep excavation systems, affect of different wall types on wall displacement, factors affecting the wall displacement and soil settlement behind the wall, displacement and settlement shape and finally ways of calculating the displacement and settlement advised in literature. Also in this section maksimum observed wall displacement and soil settlement quantity is given for different soil types in literature and where the maksimum soil settlement location occure is given in the thesis. In the fourth section, PLAXIS 2D 2018 computer program is introduced to reader. Also in this section, equations which is used to calculate soil and structure elements' parameters are presented. At the end of this section to model the soil most appropriately, the soil constitutive models is mentioned. Program modes to create the model is introduced and which modes is used for this thesis to constitute the soils and structures is mentioned in this section. For he importance of soil constitutive model, in this section some soil constitutive model and which constitutive model can be used in specify soil is expressed. In the fifth section, the systems being in this thesis are handled. At the first, systems feature which is selected for this parametric study is mentioned. After than systems stability is handled. Finally how soil parameters was selected with compliance according the lots of source in literature is mentioned also pile and anchor parameters is presented. At this section, the procedure of system stability calculations is given according to BS 8081 factor of safety coefficient. In sixth section, value of soil settlement and wall displacement gained from program analyses results for this five factors is presented in the form of tables and graphics. In seventh and final section, results gained from PLAXIS 2D 2018 computer program is interpreted and writers' suggestion is mentioned. In the literature, when pile radius is increased the displacement of wall is decrease is mentioned under the system rigidity topics. But this thesis, in 12 m excavation performed in loose and dense sand with 4 row anchors system, wall displacement and soil settlement doesn't decrease everytime when pile radius is increased. This case is investigated in this thesis for different pile embedment depth and prestressed force according to pile radius. When prestressed force and embedment depth is over specific values than wall displacement and soil settlement decrease. This finding is the most important point for this thesis. Other factors which influence displacement of wall and soil settlement is in harmony with limited source in literature. As a result of, if prestress force, embedment depthof pile, anchor bond lenght and anchor strand wire is augmented, wall displacement and soil settlement is generally decrease. Also wall displacement and soil settlement is decrease when soil stiffness is increase, this stiffness is relevant to sand soil density in this thesis.