ABSTRACT:

The improvement of superficial sand layers has frequently been used in the city of Recife, Brazil, through the execution of compaction piles of sand and gravel. This technique has been facilitated the adoption of superficial foundations in buildings with up to 25 stories together with the consideration of the effects of the soil-structure interaction. Some aspects of design, execution and control are presented and discussed in this work.

INTRODUCTION

The city of Recife, Brazil, is located in a fluvial-marine plain of recent sediments not consolidated and presents difficulty subsoil conditions for foundations of buildings. Its typical subsoil is constituted by layers of fine to medium loose sand, followed by soft organic clay and very dense sand. The presence of thick deposit of organic clay makes deep foundation to reach more than 30 m with very high cost. Because of that, since the 1950Õs, one has been used successfully the technique of surface compaction of sandy soils with compaction piles of sand and gravel. The technique has been allowing the adoption of surface foundations in places that request deep foundation. This work presents some aspects of design, execution and control of this technique.

IMPROVEMENT OF SURFACE SANDY LAYERS

The technique consists of the execution of a square or triangular mesh of compaction piles of sand and gravel. Figure l shows the results of the penetration resistance of SPT tests made at different distances of a group of compaction piles. It is observed that the execution of a pile makes the compaction of the surrounding soil in a ray of influence of 2 to 2.5 times the diameter of the pile (Figure 2). As the material is going to be compacted, the tube is going to be lifted until the surface of the terrain is reached.

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