Sand Compaction Piles for Improving Weak Foundation Soils of Alhalfaya Bridge East Approach Embankment

Abstract

Many types of alluvial soil formed from the deposited river water are often too weak to support the loads applied on it. This paper studies the foundation soils of the River Nile eastern bank at Al Halfaya Bridge, to build a 12.0m height earth embankment with an average bulk density of 20.0 kN/m3at the Bridge’s entrance. From the soil investigation program, it is found that there is an alluvial soils consisting of a soft silty clay layer ranging from 1.0m to 3.0m depth, underlied by a very loose to medium dense silty sand soil extending considerably to a depth of15.0m. Nubian Sand Stone is found at an average depth of 15.0m from the ground level. However, if these layers are not well treated, there is a threat possibility of total settlement occurrence of about 998mm. The bearing capacity is obtained to be ranging from 53 kN/m2to 191 kN/m2 (according to Zein method used for local Sudanese soil), and the embankment requires foundation soils have allowable bearing capacity of about 240 kN/m2. The factor of safety of side slope stability is determined to be 1.43. The soil is also revealed to be having a very high possibility of liquefaction and is assumed to liquefy during earthquake. This is treated theoretically through the ‘sand compaction piles’ of 1.1m diameter, and 2.5 m interval distances in the form of square or equilateral triangular patterns. The volume of sand to be installed equals to 0.9375 m3/m depth and 0.8119 m3/m depth for the square and equilateral triangular pattern respectively. The consolidation settlement is reduced by35% and average increasing of bearing capacity of about 251.18kN/m2, achieving degree of improvement in the safety factor for side slopes equals 155%. In addition, there is an improvement in the soil properties to resist the liquefaction due to earthquakes to a degree that it became non-liquefiable, through the increase of the uniformity coefficient of particle distribution.