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Project Title: Behaviour of reinforced embankments supported by piles improved soft soils under repeated loading conditions

  • PhD Student: Khaled Aqoub
  • Supervisors: Dr Mostafa Mohamed and Dr Therese Sheehan

Background

These days weakness of soil is one of the biggest problems in many regions around the world because it directly effects constructions such as roads, buildings and bridges. Recently, using layers of reinforcement with groups of piles to support embankments are widely utilised in many civil engineering works. Using reinforcement with piles helps to improve the bearing capacity and strength of soils and to reduce total and differential settlement under engineering construction. In addition, using this system in many applications provides economic and effective solutions.

Most of the previous research studied the behaviour of embankments under their weight only (static loads) because the weight is large compared with the other loads carried by the embankment. This behaviour may be changed if the load carried by the embankment is very large compared with the weight of the embankment. Also, the effect of repeated loading and cyclic loading on the body of the embankment can become more significant when the height of embankment is very small.

Aims

In this study the behaviour of shallow reinforced embankments supported by groups of piles and the improvement provided for soft soils under repeated loading conditions will be investigated and analysed experimentally and numerically. These samples consist of clay and layers of granular material with different thicknesses and different properties which are placed above the clay soil. This study will be conducted on samples with and without piles.  Also, the effect of many parameters such as properties of granular materials, thickness of granular materials, reinforcement stiffness, number of reinforcement layers, reinforcement layer spacing, pile stiffness, pile size and number of cycles of loading will be investigated and analysed.

Significance of research

Many countries around the world have problems with weakness of soil. Using alternative materials which have good quality is very important. But getting these materials in many countries is very difficult because these materials are very expensive, are not available or are very far away from the sites. However, using new materials which are not expensive and which meet the appropriate requirements is becoming more common. In this study using reinforcement and piles can reduce the amount of granular material which is used because these materials can transfer the loads directly to underneath the soil. Also, using these materials can significantly affect the cost and period of construction. In addition, using reinforcements can significantly reduce the effect of cyclic loading.

Methodology

The repeated load California bearing ratio (RLCBR) test which will be carried out in the laboratory in order to investigate the improvement of strength of reinforced soils. The RLCBR test will be applied on samples consists of clay, granular materials and layers of geotextile reinforcement which are placed at different depths within the samples. The results which will be collected from the RL CBR test for both reinforced and unreinforced samples will be analysed and compared.

The large model of repeated load tests will be conducted on samples consisting of clay soil, granular materials, layers of geotextile reinforcement, which are placed at different depths of the samples, and groups of piles. This test will be carried out experimentally and numerically. The results, which will be collected from experimental and numerical models, will be analysed and compared.

RL-CBR test   Sample of soil after the test.

References

Asha. M. N. and Latha, G. L. (2012). Strength behavior of reinforced soil-aggregate systems under repeated and cyclic loading , GeoCongress, 2012 : state of the art and practice in geotechnical engineering, Oakland, California USA, American society of civil engineers.2012, 1513-1522

Hello B. L. and Villard. P. (2009) Embankments reinforced by piles and geosynthetics-Numerical and experimental studies dealing with the transfer of load on the soil embankment. Engineering Geology, 106, 78-91.

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