Overview
With the development of urbanization，the scale of urban construction is expanding，and the contradiction between urban development and shortage of land resources is becoming increasingly inevitable.The increase of urban population，development of industry，and popularity of automobile also bring a series of problems of space demands.In order to solve problems such as traffic congestion and population congestion，many big cities have developed urban underground space.The 21st century is“an era of development of underground space”.The utilization of underground space includes subways，underground pipe corridors，underground shopping malls，underground garages，and civil defense basements.They are characterized by diversification，integration，and large⁃scale.At present，underground space has been developed in many cities all around the world.
Within a built⁃up environment，the construction safety of a deep excavation becomes more crucial with the ever⁃increasing building density.There are many excavation accidents reported in China recent years，as shown in Table 1.1.
Table 1.1 Excavation accidents reported in China in recent years
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This book reviews state⁃of⁃the⁃art design of excavation support systems in soils.Chapter 2 is on the overall stability of excavation including basal heave stability and toe stability.It illustrates the types of factors of safety and analysis methods for basal heave including the bearing capacity method，the negative bearing capacity method，and the slip circle method，the finite⁃element method with strength reduction technique，and the Goh’s method（Goh，1994）.Push⁃in failure and overall shear failure of cantilever walls are also mentioned.
Chapters 3 to 5 analyze the response of excavation including strut force，types of retaining wall and deflection of wall，and ground movements around excavations.It is of vital importance to predict and control the ground movement of a deep excavation during construction to ensure the minimal structural damage to nearby buildings and utilities.Chapter 3 illustrates how to calculate the strut and anchor forces，and helps to understand the factors that influence the strut forces as well as the load transfer mechanism when the retaining system is subjected to one strut failure.Lateral Earth Pressure including apparent pressure diagrams（APD）is also discussed in Chapter 3.Chapter 4 introduces several types of retaining wall，such as soldier piles，sheet piles，column piles and diaphragm walls.Both of their merits and disadvantages are listed and the designs of the retaining walls can also be referred to.Stress analysis method including simplified methods，beam on elastic foundation method and finite element method are also mentioned.Chapter 5 analyzes the sources of ground movements including the wall installation，excavation in front of the wall，groundwater flow resulting in loss of ground and consolidation caused by changes in water pressures due to seepage through and／or around the wall，and other site⁃specific sources of movements.Ground movement predictions methods are presented，such as Peck’s method（Peck 1969a），Clough and O’Rourke’s method（Clough and Rourke，1990），Bowles’s method（Bowles，1998），Ou and Hsieh method（Ou and Hsieh，1993）and some new methods.In addition，the damage to buildings caused by excavation induced ground movement is also assessed and some protective measures are proposed.
Chapters 6 and 7 present the prevailing numerical analysis.Chapter 6 presents the basic principles of finite element method，and explains the determination of initial stresses，mesh generation and boundary conditions.Excavation analysis methods are also illustrated with a detailed example of excavation in sand.Chapter 7 illustrates several types of soil constitute models on their applications and limitations；the mechanism of each models are also presented，including Linear Elastic model（LE），Mohr⁃Coulomb model（MC），Hardening Soil model（HS），Hardening Soil model with small⁃strain stiffness（HSsmall），Soft Soil model（SS），Soft Soil Creep model（SSC），and Modified Cam⁃Clay model（MCC）.
Chapters 8 to 13 illustrate some practice in excavation construction，such as dewatering of excavation，jet grouting and other improvement methods，as well as the protection of adjacent buildings and instrumentation.Chapter 8 is on the dewatering methods of excavation such as open sumps or ditches，the well point method，and the deep well method.Several widely used well formulas are discussed for reference and application.Then two types of pumping tests（the step drawdown and constant rate tests）are demonstrated，and dewatering plan for an excavation is also displayed.At last，the influence of dewatering on the ground settlement is discussed.Chapter 9 presents several main methods of soil improvement in excavations such as the chemical grouting method，the deep mixing method，the jet grouting method and the compaction grouting method.Some grouting equipment are also introduced.Chapter 10 introduces methods to protect adjacent buildings near excavation during construction.Excavation⁃induced allowable settlement is discussed，and several methods of utilizing the characteristics of excavation⁃induced deformation by optimizing the design parameters are discussed，including decrease of the unsupported length of the retaining wall，decrease of the creep influence，taking full advantage of corner effect，increase of stiffness of the retaining⁃strut system，and understanding of the characteristics of ground settlement.Building protection by utilizing auxiliary methods as well as the method of underpinning and the building rectification methods is also presented.Chapter 11 illustrates a monitoring system used to monitor the excavation conditions and ensures the safety of excavation.The element of a monitoring system is showed，and monitoring objectives are presented with the detail application of monitoring system.Chapter 12 presents the use of method of back⁃analysis on excavation.It shows the common procedure of back⁃analysis in excavation issues，and the deterministic method is explained in detail.Probabilistic methods including maximum likelihood method，bayesian method，and first⁃order reliability method are illustrated.
At last，a brief review and analysis of the design practice and geotechnical control of excavation failure case is given in Chapters 13.
Readers are expected to be familiar with the basic concepts of Soil Mechanics and Foundation Engineering.The target audience is mainly the undergraduates and graduate students，faculty and practicing professionals in the fields of Civil and Geotechnical Engineering.