AbstractAccording to its designation, horizontal jet grouting (HJG) is performed horizontally at the tunnel face in order to form a support structure of improved soil. HJG is employed to reduce the surface settlements in urban tunnelling when buildings and other infrastructure sensitive to settlements are encountered. The yet unanswered question arising from engineering practice of HJG refers to the optimal design of the jet‐grouted support structure and the underlying construction scheme. In this paper, numerical studies in the context of plane‐strain finite element (FE) analyses are presented, comparing different layouts of the support structure as well as different construction schemes. Moreover, the influence of the soil properties is investigated. On the basis of the numerical results, the optimal layout of the jet‐grouted support is identified for various soil stratifications including a homogeneous soil, a relatively soft layer of sand over a stiff layer of gravel, and the reverse situation. Sophisticated thermochemomechanical material models accounting for the strength and stiffness growth as well as chemical shrinkage and creep of cemented soil and shotcrete have been employed in the numerical investigations leading to the results reported in this work. Copyright © 2004 John Wiley & Sons, Ltd.