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Any tunnel construction inevitably causes differential soil movements, resulting in additional adverse effects on existing pipelines. Although there are many jointed pipelines in practice, previous studies commonly simplified existing pipelines as continuous structures. In this study, centrifuge tests were designed and conducted to investigate the influence of joint stiffness on pipeline response due to tunnel excavation. Along the longitudinal pipeline direction, upward and downward pipe–soil relative movements were identified. Because of relatively flexible joints causing a reduction in the pipeline flexural stiffness, tunneling-induced maximum settlement in the jointed pipeline was much larger than that in the continuous pipeline. Tunnel excavation caused bending moment in the continuous pipeline only, while bending moment and joint rotation occurred simultaneously in the jointed pipeline. As a result of joint rotation, tunneling-induced maximum bending strain in the jointed pipeline was less than 42.4% of that in the continuous pipeline. If a jointed pipeline is assumed as a continuous structure, tunneling-induced pipeline settlement is underestimated, while bending strain is grossly overestimated. All the centrifuge test results were adopted to verify the validity of calculation charts for estimating tunneling-induced maximum bending strain and joint rotation in existing pipelines. [ABSTRACT FROM AUTHOR]

• Model tests are conducted to explore pipe response to tunnel passive face instability. • Pipe experiences settlement first, followed by heave due to tunnel face passive instability. • Pipes located at 0.7 D -1.2 D ahead of tunnel face experience excessive deformations. • Dimensionless graphs are proposed for estimating pipe bending strains due to ground heave. Earth pressure balanced shield tunnelling is commonly used to alleviate soil disturbance and adverse effects on existing infrastructures. If soil excavation or discharge rate is not properly controlled, soil pressures acting on tunnel face may increase or decrease rapidly. However, current studies mainly concentrated on pipeline deformations caused by tunnel excavation and active face instability. In this study, physical model tests together with numerical parametric study are conducted to explore pipeline deformation mechanisms due to progressively passive instability of tunnel face. Because of soil localised failure mechanisms, ground and existing pipeline experience settlement first, followed by heave as an increase in tunnel face horizontal movement. Moreover, the measured limiting pressure against passive face instability is much smaller than the upper bound solutions considering soil blowout mechanisms. For tunnel cover-to-diameter ratios (C/D) of 1.0 and 1.5, pipelines experience maximum deformations when they are located at 0.7 D and 1.2 D ahead of tunnel face, respectively. For these two C/D ratios, face passive instability induced longitudinal deformation zone ahead of tunnel face are 1.5 D and 2.0 D , respectively. By varying C/D ratio from 1.0 to 1.5, the maximum heave and bending strain indued in the pipeline are reduced by up to 83.4% and 73.4%, respectively. The maximum bending strain of pipeline along its vertical direction is 24.3%-43.0% larger than that along its horizontal direction. Two dimensionless groups are proposed to develop dimensionless graphs, which can effectively calculate pipeline bending strain under arbitrary ground heave, pipeline dimension and soil property. [ABSTRACT FROM AUTHOR]

• Physical tests are conducted to explore pipe response to tunnel active face failure. • Pipe deformations reach maximum values at normalized horizontal distance of 0.1 D. • Effect of C/D ratio on pipe deformations is less prominent than that of H/D ratio. • Measured results verify calculation chart for estimating pipe tensile strain. In congested urban areas, earth pressure balance (EPB) shielding is commonly adopted to alleviate tunneling effects on surrounding structures. Tunnel active face instability can cause excessive ground movements, which threaten the serviceability of nearby underground pipelines. However, previous studies mainly focused on tunnel face support pressure and tunnel face failure induced ground movements, while pipeline deformations due to tunnel active face instability are seldomly explored. In this study, a series of physical model tests are designed and conducted to investigate the effects of tunnel cover to diameter ratio (C/D) and normalized horizontal distance (H/D) between tunnel face and existing pipeline on three-dimensional pipeline deformation mechanisms. Tunnel active face instability induces excessive settlements and tensile strains in the existing pipeline when it is located at 0.1 D ∼ 0.3 D in front of tunnel face. By increasing H/D ratio from 0.1 to 0.5, the maximum settlement and tensile strain of the existing pipeline decrease by up to 64.8% and 59.9%, respectively. But the maximum settlement and tensile strain of the pipeline only decrease by up to 14.9% and 7.3%, respectively, as C/D ratio increases from 1.0 to 1.5. Obviously, the effects of C/D ratio on pipeline response are less prominent than that of H/D ratio. The measured results are used to verify calculation charts for directly predicting maximum tensile strains of existing pipelines due to tunnel face active instability induced differential ground movements. [ABSTRACT FROM AUTHOR]

In this study, an extensive numerical parametric study is conducted in sand to investigate the effectiveness of countermeasures (i.e., methods used to alleviate tunnel deformation) to reduce tunnel response due to overlying basement excavation. Centrifuge test results were adopted to calibrate soil parameters and numerical modeling procedures. It is found that the maximum heave and tensile strains (i.e., transverse and longitudinal) of tunnel decrease as an increase in the wall penetration depth. But the reduction in the maximum heave and tensile strains of tunnel is less than 20% when the wall penetration depth is increased by three times. Using a 2 m thick diaphragm wall to replace a sheet pile wall, the maximum transverse tensile strain of tunnel is reduced by up to 27%. The maximum heave and longitudinal tensile strain of tunnel decrease as an increase in the thickness of tunnel lining. However, a slight increase in the thickness of tunnel lining causes an increase in the maximum transverse tensile strain of tunnel. By further increasing the lining thickness, the maximum transverse tensile strain starts to decrease. In terms of the maximum transverse tensile strain of tunnel, a slight increase in the lining thickness may even cause adverse effects on existing tunnels. [ABSTRACT FROM AUTHOR]

For the convenience of shoppers and users, there is an increasing demand for the construction of basements in close proximity to existing tunnels. To ensure the safety and serviceability of the existing tunnels, attention has been paid to the basement-tunnel interaction. However, a simplified method for direct estimation of tunnel heave and tensile strain due to basement excavation is not available. In this paper, a systematic numerical parametric study is conducted to develop a simplified and approximate method to enable practicing engineers to estimate tunnel response due to overlying basement excavation. This method only considers the effects of excavation geometry, excavation depth, cover-to-tunnel diameter ratio and sand density on tunnel response to basement excavation. An advanced soil model, a hypoplastic sand model, is adopted to simulate soil behaviors. The soil model and soil parameters are calibrated and verified by centrifuge test results. For the tunnel crown located 0.5–1.5 D (i.e., diameter) below the formation level of the basement, calculation charts of excavation geometry versus tunnel heave and tensile strain at two relative sand densities (i.e., 68% and 90%) are developed for estimating tunnel responses due to basement excavation. Because denser sand has larger soil stiffness, excavation-induced tunnel heave and tensile strain are found to decrease almost linearly with relatively sand density ( D r ) when it varies from 30% to 90%. Thus, excavation-induced tunnel heave and tensile strain at other soil densities can be linearly interpolated by using the proposed calculation charts. An example is provided to illustrate the application of the calculation charts. The tunnel heave and tensile strain predicted from the proposed method are found to be in good agreement with the numerical results. [ABSTRACT FROM AUTHOR]

For the convenience of shoppers and users, there is an increasing demand for construction of basements in close proximity to existing tunnels. To ensure the safety and serviceability of existing tunnels, many numerical analyses have been conducted to investigate the basement–tunnel interaction. However, most of previous studies have simplified the complex interaction as a plane strain problem and often they have overlooked effects of stress path and strain dependency on soil stiffness. In this study, three-dimensional numerical parametric study is conducted to explore the complex interaction in dry sand by using an advanced hypoplastic soil model. The validity of the soil model and soil parameters is calibrated and verified by centrifuge test results. Parameters considered on tunnel responses by overlying basement excavation include excavation geometry, sand density, tunnel stiffness and joint stiffness. It is found that the basement–tunnel interaction at basement centre reaches a plane strain condition when excavation length along the longitudinal tunnel direction is longer than 9 H e (final excavation depth). Both heave and transverse tensile strain of tunnel exceed the allowable movement limit and cracking strain when excavation length is longer than 5 H e and excavation width is wider than 2 H e . At a given excavation area on plan, the longer side of basement should be perpendicular to the longitudinal tunnel direction to reduce excavation induced adverse effects on existing tunnel. Because a looser soil has smaller stiffness around the tunnel, tunnel heave and tensile strain at basement centre are increased by up to 90% and 80%, respectively, when relative sand density decreases from 90% to 30%. By increasing tunnel stiffness 100 times, induced maximum tunnel heave and tensile strain are reduced by up to 75% and 85%, respectively. This means that stiffening a tunnel can be an effective way to alleviate excavation induced adverse effects on existing tunnel. Induced tunnel heave and tensile strain at basement centre are insensitive to the presence of tunnel joint unless the joint stiffness is less than 30% of the lining stiffness. [ABSTRACT FROM AUTHOR]