Two-dimensional model tests and elastoplastic finite element analyses for excavation problems with a braced wall are performed to investigate the influence of construction history, wall friction, wall stiffness and the struts on the ground movements and the earth pressures on the wall. Test results show that the surface settlements of the backfill and earth pressure on the wall depend on the deflection process of the wall, even if the final wall deflections are the same. The wall friction, wall stiffness and the position and stiffness of strut significantly affect the earth pressure on the wall and the ground movement including the surface settlements. The computed results, in which mechanical behavior of soil and structure, behavior of interface between soil and wall and the process of excavation were properly taken into consideration, describe wall the results obtained in the model tests. Such influence on the deflection of the wall, the earth pressure on the wall and the ground movements has not been evaluated properly in the present design practice.

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A cylindrical earth retaining wall 144 m in diameter was adopted for the excavation works of a 500 kV large-scale underground substation building. Various in-situ measurements, which comprised approximately 1, 100 measuring points, were carried out throughout the excavation works. Following the examination of the measured data, it was ascertained that the retaining wall behaviour was largely influenced by wall temperature variations in addition to lateral pressures. This paper presents the earth retaining wall behaviours based on the measurement results and the practical analysis methods by introducing the retaining wall temperature variations.

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A test apparatus was designed for studying seepage failure of soil behind sheet piles, and the mechanism of seepage failure was described through experiments on sand models with D_r≈50%. Sand models are in a stable state at an early stage of a small hydraulic head difference H between up-and downstream sides. The model sand is subjected to an irreversible deformation, that is to say, upstream subsidence and downstream rise near sheet piles after the hydraulic head difference at deformation, H_y, is reached. It is proved that the value of H_y is effectively estimated as the hydraulic head difference at which a certain prism of soil loses the equilibrium of forces using the Prismatic failure concept. As the hydraulic head difference H increases, the sand model is subjected to large rearrangement and/or movement of sand particles rather than infinitesimal deformation of the sand. The upstream subsidence and downstream rise of the soil surface increase with the increase in H. When the hydraulic head difference at failure H_f is reached, the soil model finally collapses. The sand model has approximately 10% free board between H_y and H_f i.e. H_f-H_y=0.1×H_y. The be haviour of the soil model in this part could be a self-healing phenomenon.

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During shield tunnelling operation, a shield machine is driven forward by applying mechanical jack forces behind the machine tail and excavating the soil in front of the machine with its cutting face. In this study, the advancement and excavation processes of the shield tunnelling operation are modelled using the finite element method in order to investigate the effect of these construction processes on the ground response. A new excavating finite element, which models the disturbed soil in front of the cutting face, is introduced. The operation of shield advancement and of soil excavation is simulated using the finite element remeshing technique at each time step of the analysis. The accuracy of the finite element remeshing technique is discussed by analysing one-dimensional consolidation of an isotropic elastic medium. The proposed modelling techniques of shield tunnelling construction are applied to simulate a tunnelling project in Tokyo and the numerical results are compared with the field measurements. The soil deformation mechanism associated with the shield tunnelling operation is examined in detail.

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In recent years, because of the development of the technology in shield tunneling, deformation due to shield tunneling is mainly contributed by these occurring while a shield is passing and by subsequent deformations. Though a few methods have been proposed to predict the deformation in numerical, statistic and empirical ways, it is hard to say these methods can be used with confidence. Based on the accumulated measurement data of shield tunneling, it is known that the ground deformation when a shield is passing is mainly caused by the stress release at the cutting face and the tail. It is also known that the subsequent deformation is dependent on the maximum deformation that occurred during the shield passing and the liquidity index I_L which is related to the sensitivity. The total deformation due to shield tunneling is divided into the two parts mentioned above. These are evaluated with the proposed prediction method in practical ways respectively based on accumulated measurement data.

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The need for accurate predictions of tunnelling-induced ground movements has led to increased research activity over the past 30 years. However, there has been very little investigation into the problem of tunnelling in multi-layer ground or the associated subsurface movements. This paper presents data from a series of centrifuge model tests aimed specifically at investigating the effect of stiffness of an overlying layer on ground movements above tunnels driven in clay. Results of the tests indicate that the stiffness of the upper strata has a significant influence on the distribution of movements in the lower clay layer and current design methods of settlement prediction may then under-estimate the width of the subsurface settlement troughs.

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In this study centrifuge model tests of a vertical excavation in normally consolidated soft clay were carried out using a newly developed test system, in which the construction sequence of a double propped wall for an open excavation can be properly simulated in flight. Settlements of the ground surface behind the wall, earth pressures on the wall, strains along the wall and pore water pressures in the ground were measured during the test. Effects of propping and embedment of the retaining wall into the bottom sand layer on the behaviour of the wall and ground were carefully studied. It was found that only 1 m embedment into the bottom sand could increase significantly the stability of excavation. Under the condition with the embedment into the bottom sand layer, deformation became a main concern instead of stability against failure. The deformation after a certain excavation depth was mainly determined by the mechanical properties of the sand, i.e., stiffness or stress-strain relationship. Propping can prevent marked increase in the settlement ; however, it is very difficult to recover the settlement and deformation once it occurs by increasing the strutting force (i.e., preloading). Hysteresis and non-linear behaviour of the soil is considered to be one of the main reasons of the irrecoverable deformation.

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In this paper, simulation methods and measurement systems for earth retaining structures during deep excavation work in Shanghai, China are discussed. Comparisons between the measured and simulated data are made, and the inverted construction method for underground works is also evaluated. The main results are as follows : (1) The maximum wall displacement was more than 10 cm in the first excavation stage, and reached a value of approximately 13 cm in the final stage excavated to a depth of 18 m below G.L. (2) In the simulation analysis, the stiffness of the ground on the excavation side was reduced to model the presence of vertical voids induced from the installation of plastic-board drains and other pre-excavation construction. The stiffness of the earth retaining wall was also reduced due to the cracks in the concrete. With these modifications, the results of the simulation analysis showed values quite similar to the measured data. (3) The measuring system worked flawlessly except for minor problems in the installation of the sensors and occasional breakdowns of the inclinometers. (4) During the excavation, real time simulations were conducted by using the most current measurement results to predict behavior in subsequent excavation stages. Consequently, the originally planned No. 4. temporary struts were eliminated, and the excavation was successfully completed to the designed depth.

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This paper describes monitoring results of ground movements due to slurry shield tunnelling on the Docklands Light Railway Lewisham Extension (hereinafter referred to as DLR). The DLR tunnels (twin bored tunnels) run from Island Gardens Station to Greenwich Station in East London, passing under the River Thames, a distance of around 4.2 km. The construction of the tunnels, which were at shallow depth, needed an extensive appraisal of the potential damage induced by ground movements to the overlying and underground structures. Therefore, in order to effectively minimize the ground movements, a slurry shield machine with a diameter of 5.85 m was employed. Careful control of excavation was carried out during shield tunnel construction. As a result, the slurry shield tunnelling method in Woolwich and Reading Beds by well controlled monitoring was successfully conducted, leading to volume losses less than 1.0%. This paper focuses on the ground surface movements, particularly the transverse and longitudinal settlement profiles, and volume losses during shield tunnel construction, in relation to the ground conditions. Based on the monitoring results, combined with previous centrifuge model test results and other field monitoring data, practical methods to appropriately predict ground movements due to shield tunnelling are proposed.

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This paper presents the results of a detailed field instrumentation program conducted on an Earth Pressure Balanced (EPB) shield driven tunnel for the construction of the Shanghai Metro Tunnel-Line 2 in China. A twin 6.2 m diameter precast, concrete-segmental tunnel system was constructed in a soft silty clay, which is compressible, sensitive, saturated and with low permeability. In order to study the response of the soft clay and the ground movement during and after the advance of the tunneling machine, the surface and subsurface ground displacements, pore water pressure changes, and earth pressure development around the concrete lining were monitored during construction. Based on the field results, the influences of tunnel construction control processes on the resulting ground responses are interpreted and discussed in this paper. Correlation between the ground response and surface settlement are developed taking into consideration the control factors in the excavation process as well as the grouting process. Particular attention is also given to the development of correlations between the construction control processes and the associated tunnel performance under both short-term and long-term conditions.

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