Delivered by ICEVirtualLibrary.com to: IP: 129.100.229.13 On: Tue, 17 May 2011 13:44:05 Proceedings of the Institution of Civil Engineers Ground Improvement 163 May 2010 Issue GI2 Pages 121–132 doi: 10.1680/grim.2010.163.2.121 Paper 700044 Received 02/11/2007 Accepted: 18/08/2009 Keywords: foundations/ mathematical modelling Mehdi Heidari Graduate student, Shiraz University, Shiraz, Iran M. Hesham El Naggar Professor, Department of Civil and Environmental Engineering, University of Western Ontario, London, Canada Using reinforced soil systems in hammer foundations M. Heidari and M. H. El Naggar Forging hammers produce powerful short-period impact loads. A mounting system or a properly designed foundation could be used to transmit the shock to the soil and lessen its effects on the surroundings. The supporting foundations must be designed to reduce the vibration amplitude and the forces transmitted to the soil medium in order to meet serviceability and stability requirements. Soil reinforcement may be used to improve the performance of the foundations supporting shock-producing equipment. This paper investigates the effect of soil reinforcement on the performance characteristics for different configurations of shock- absorbing foundations. The results demonstrated the efficiency of soil reinforcement in improving the performance of foundations subjected to impact load. A parametric study was conducted and a set of charts was established as practical guidance for the design of soil reinforcement schemes. 1. INTRODUCTION The act of hammering is a basic industrial process encountered in such diverse activities as the breaking up of scrap and the forging of metal. Hammers, presses and other types of shock- producing machines generate powerful dynamic effects that are quite short in duration and can be characterised as pulses. Only a part of the shock energy is utilised in the intended machine function and the rest is dissipated in the foundation causing intense vibration. Shock-absorbing foundations such as mounting systems are now used to support hammers and to reduce the transmission of the impact force to the soil. The shock is transmitted through the mounting system and foundation to the soil and surroundings. Heavy shocks imparted to the foundation can cause alignment problems (i.e. reduce operating life), neighbour complaints and prohibit proper operation of adjacent equipment. Therefore, the main objectives of the design of a foundation supporting shock- producing equipment are to reduce the vibration amplitudes and the forces transmitted to the soil and/or to minimise any disturbance to the neighbourhood and surroundings. Current practice is to install die forgers and hammers on layered elastomeric isolators or viscous spring isolators. The foundation system for forging hammers using elastomeric and spring isolators is shown in Figure 1. The impact force created by each blow of the forging hammer is absorbed by the vertical motion of the machine through viscous damping. The layered elastomeric foundation systems, as shown in Figure 1(a), and the viscous spring isolator mounting systems, as shown in Figures 1(b) and (c) are designed to allow the motion of the machine to decay below a certain level before the next impact. To ensure satisfactory performance of the machinery, the mounting system and/or the foundation should be designed such that the vibration amplitudes do not exceed the values given in Table 1 (Novak, 1983). A number of dynamic models have been developed to analyse the response to pulse loading of one-mass and two-mass foundations with springs and dampers. Using these models, the influence of various parameters of the isolator mounting system was studied (e.g. Chehab and El Naggar, 2003, 2004; (a) (b) (c) Figure 1. Isolated foundation types for forging hammers: (a) layered elastomer; (b) isolator supported inertia block; (c) direct isolator support Hammer weight: t Anvil Foundation block mm in. mm in. , 1 1 0 . 04 1 . 2 0 . 05 2 2 0 . 08 1 . 2 0 . 05 . 3 4 0 . 16 1 . 2 0 . 05 Table 1. Maximum allowable amplitude for hammer foundations Ground Improvement 163 Issue GI2 Using reinforced soil systems in hammer foundations Heidari • El Naggar 121