Manuel Matos Fernandes

Three-Dimensional Nonlinear Analyses of a Metro Tunnel in Sao Paulo Porous Clay, Brazil

Tropical residual clays with a highly porous structure react to the stress changes induced by tunneling in such a way that surface settlements can be larger than crown-level settlements along a tunnel axis. This behavior, which is not readily simulated by most numerical analyses, was also observed in the Paraiso tunnel, built for the Sao Paulo Metro, Brazil. This is a shallow tunnel driven through porous clayey soils by the sequential method. Detailed results of field monitoring are presented and discussed. 3D finite-element analyses that allowed a detailed simulation of the construction sequence have been carried out, considering two distinct constitutive models for the soil: a simple elastic-perfectly-plastic Mohr-Coulomb model, and the elastoplastic model developed by Lade. The results of these analyses are compared with the observed behavior as well as with the results from a plane strain finite-element analysis. It is shown that only the 3D finite-element analysis coupled with the more sophisticated soil constitutive model provides a full reproduction of field performance, with particular relevance for the deformations in the soil mass over the tunnel.

Influence of tension cut-off on the stability of anchored concrete soldier-pile walls in clay

A previous paper studied the stability of soldier-pile walls in clay under vertical loading using upper bound analyses. A classical Tresca yield criterion was assumed in that analysis. This paper extends that study by considering a tension truncated Tresca yield criterion in an upper bound numerical analysis of the problem. It shows that assuming zero tension soil strength has a significant influence on the values of the minimum soldier-pile resistance required to ensure stability.

Discussion of New Earth Retention System with Prestressed Wales in an Urban Excavation by Jong-Sik Park, Yong-Sun Joo, and Nak-Kyung Kim

The authors should be congratulated for the innovative retention system presented in the paper. The search for structural solutions permitting support to deep and wide excavations without using ground anchors has been a challenge for engineers, requiring a proper combination of geotechnical and structural expertise. This discussion aims to describe a solution with strong similarities to the one presented in the paper, which has been applied to support an excavation in Lisbon, Portugal, in 1982. Fig. 1 shows a plan and a cross section of the excavation, which was square in plan (39 × 39 m) and 24–29 m deep, for the construction of seven basements of a new building. The ground comprised a fill layer and Miocene sedimentary marine soils covering basalt rocks. As shown in Fig. 1(b), the retaining structure consisted of an anchored diaphragm wall supporting the upper part of the cut (corresponding to the fill and the decompressed Miocene soils) and nailing for the depths at which stiffer soils are encountered. After the construction of the first anchor level at the face adjacent to the masonry building, its owner obtained a court order prohibiting further installation of any anchors or nails under his property. Several solutions to overcome this unexpected problem were then discussed. The adopted one was conceived by Edgar Cardoso, an expert on bridge design, and was developed by the staff of the contractor, Teixeira Duarte (Lousada Soares 2003). The solution, denoted in Fig. 1 as a prestressed arch, is represented in more detail by the schemes in Fig. 2 and by the general view in Fig. 3. It consists of a polygonal tendon of 14 high-strength steel strands prestressed to 2,100 kN, coupled to a system of five steel-framed struts applying to the wall forces ranging from 300 to 350 kN. The tendon is anchored at the two corners of the cut by steel anchor plates inserted in concrete blocks linked to the diaphragm wall. The solution’s sequence of construction is described in the following: 1. Partial demolition (from the interior of the cut) of the diaphragm wall at the two corners to insert the anchor plates connected to the reinforcement of the wall;

The influence of water on the seismic response of waterfront retaining walls

Abstract Many cases of waterfront retaining wall failure, as a result of earthquakes, are caused by deterioration of soil and not by the insufficient dimensioning of the retaining structure. Softening of soil or liquefaction, when there are saturated sand deposits, taking place in wide zones causes global failures which result in significant damage. The phreatic surface position has a great effect on the structure response to dynamic action. Comparison of computer models and field and laboratory measurements can give greater insight into predicting real soil-structure response to dynamic loading and to validating numerical models. A finite element analysis representing a system of soil, water, retaining structure and interfaces between the different materials is described. The fluid elements have elastic behaviour with zero shear modulus and the real bulk modulus. A elasto-plastic stress-strain law is used in soil discretization with different treatment for volumetric and shear straining, i.e. the bulk and shear moduli are independent. Energy absorbing boundaries are used to prevent undesirable reflections of stress waves in order to simulate very large or infinite domains. Excess pore pressures are generated during the seismic loading and at every step a check is made on the values of effective stresses for eventual liquefaction that may occur.