Keywords: tunnels, structure, construction, building, foundation, cost, soil.

A tunnel project with buildings of varying dimensions over the tunnel line in the city of Amsterdam, in the Netherlands led to feasibility and engineering studies of alternative support systems. The buildings could be positioned separately or combined with the tunnel construction. The three feasible construction systems are buildings supported on top of, through or over (a combined system) or to the sides of the tunnel (separated). Combined building-tunnel structures are scarce. Very few examples of combined building-underground infrastructures are found in the Netherlands. In the few examples found buildings mainly span over the tunnel via a bridge girder support with minimum building-tunnel interaction.. Examples of the other systems where tunnel and building form one unit (on top and through options) are not available in the Netherlands. For the tunnel project Axis-south such options were open for investigation. The investigation posed questions on the technical feasibility and cost consequences for all options including those where no previous local experience was available.

This paper describes the various facets of the problem and provides an approach that is of potential interest to researchers as well as planners and designers in tunnelling. The novelty of the study is in computationally coupling geotechnical, structural, and cost models using the concept of "surplus bearing capacity" (SBC) [1]. The carrying capacity of the tunnel foundation is used to calculate and reduce costs of additional works and materials. The height of the buildings, dimensions of the piles, soil bearing capacity and the tunnel dimensions are considered. Girder support between the tunnel and buildings is found necessary at certain building heights depending on the tunnel and soil strength. The requirements for the structural strength and of the girder construction are found to have the most significant effect on building costs but this could be optimized using the surplus bearing capacity of the tunnel-piles foundation system. The soil, structural, cost and foundation components are separate modules that form the engineering-cost model capable of calculating sizes and material qualities for cost estimations. The coupled modules can process data inputs for the design of different tunnel dimensions and foundations in addition to the structural engineering design of the girder.

This study is confined to investigating variations in the material costs due to increased building heights, ground water pressures in the soil and pile lengths. The study presents cost comparisons of the three technically feasible design alternatives of the building-tunnel combinations over, through, and on top options. In essence the approach involves modelling the effect of foundation alternatives and ground conditions on the construction process variables. This type of multi-disciplinary research takes the variables encountered in construction project-management problems (cost, time, risk, site, etc.) into the modelling of engineering decisions [2]. The problem described in this paper will present preliminary results using this approach. The results of this study demonstrate the potential for early planning and design decisions of modelling structural strength with bearing capacity of the tunnel foundations and cost relationships. Moreover the work couples, computationally, geotechnical, structural, and cost calculations using the novel concept of "surplus bearing capacity".

1

U.F.A. Karim and M.M.J.D. Slijkerman "Cost and technical study of building on top of, through, or over a tunnel in the city of Amsterdam", Int. conf. on Geotechnics in cities GeocityNet, University of Lille press, France, 2005.

2

J.F. van den Adel, S.H.S. Al-jibouri, U.F.A. Karim and M. Mawdesley, "An expert system for foundation design of buildings: case demonstration of a GCPM-integrated prototype system", B.H.V. Topping and B Kumar (Ed), Proc. 6th Int. conf. on the Applications of Artificial Intelligence to Civil & Structural Eng., Civil-Comp Press, Stirling, UK, paper 10, 2001. doi:10.4203/ccp.74.10

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