International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 11 Issue: 10 | Oct. 2024
p-ISSN: 2395-0072
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Structural Lightweight Aggregate as a Backfill Material for the Retaining Structures Dr. Dada S. Patil1, Alware Azain Zafar2, Nihal Layak Ali Sayyed3 & Ayman A. Khan4 1Associate Professor, Civil Engineering Department, AIKTC, SoET, Panvel, Navi Mumbai, India 2Final Year Civil Engineering Student, AIKTC, SoET, Panvel, Navi Mumbai, India
Final Year Civil Engineering Student, AIKTC, SoET, Panvel, Navi Mumbai, India 4Final Year Civil Engineering Student, AIKTC, SoET, Panvel, Navi Mumbai, India ---------------------------------------------------------------------***--------------------------------------------------------------------3
Abstract - If structural grade lightweight aggregates
void content typical of closely controlled manufactured granular coarse aggregates, which are similar to a clean, crushed stone. Second is high pore volume enclosed within the cellular particle [1].
(LWAs) are utilized, in place of usual locally available soil, in backfill and above the soft soils for the retaining structures, they offer advantages in terms of geotechnical physical properties like increased stability, high thermal resistance, high permeability and reduced density. High angle of internal friction (angle of shearing resistance) leads to improved stability; reduced specific gravity enhances the physical properties. A closely controlled manufactured aggregate gradation leads to an open texture, which in turn results in high permeability. The porosity getting developed during the LWA manufacturing process results in improved thermal resistance. The various LWAs that can be used as backfill materials are Light Expanded Clay aggregates (LECA), Expanded Shale, Slate, Perlite, Pumice, Sintered Fly Ash LWAs, etc. LWA fills are approximately half the weight of fills consisting of common materials. The decreased load, combined with high internal friction angle lead to decrease in vertical and lateral earth forces by more than one-half. This leads to economy owing to the fact that the sizes of various parts of retaining structures are reduced, thereby resulting in saving in quantities of concrete and reinforcement steel. The paper discusses engineering and economical benefits of using LWAs as backfill materials. Few cases from the developed countries are mentioned. A need to adopt this approach on a wider scale in India is highlighted.
When slates, clays and shales are subjected to temperatures more than 11000 C in rotary kilns, a cellular structure gets formed. It comprises of non-interconnected spherical pores which are surrounded by a strong and durable ceramic matrix having characteristics same as that of vitrified clay bricks [1]. Oven dry specific gravities of LWAs vary. However, the values are between 1.25 to 1.40. High interparticle void content along with low specific gravity leads to bulk dry densities usually in the range of 720 kg/m 3 [1]. Compaction of LWAs in a way similar to that used with crushed stone results in a highly stable interlocking network. This results in development of in-place moist densities less than 1040 kg/m3 [1]. Expanded Shale, Clay and Slate (ESCS) fills need no specialized machineries or forms for their installation. Usual equipment available on site can be made use of for placing them in all weathers. They are easy to handle and more importantly, durable under extreme weather conditions [2]. They don’t need liners. They also don’t require additional measures to prevent buoyancy issues. ESCS fills are angular artificial LWAs which are freely draining and strong structurally [2]. Water moves very easily through ESCS fills. Hence, there is no need to place special drainage channels throughout the fill.
Key Words: LWA Fill, Lateral Earth Pressure, Drainage, Weight, Retaining Structure, Unit Weight, Permeability, etc.
1. INTRODUCTION
When used as a backfill material against retaining wall, LECA reduces the weight on the rear of the structure by approximately 75%, as compared to usual fill material [3]. Differential settlement between embankment fill and piled bridge abutments is minimized by using LECA [3]. Rear wall block drainage is not needed as LECA is a free-draining material.
Shales, clays and slates have been expanded in rotary kilns to manufacture structural grade LWAs for use in masonry work and concrete, for more than 8 decades. Huge quantities of these aggregates are used in structural concrete constructions, with widespread availability across USA and other developed countries [1]. An idea of utilizing these aggregates for geotechnical application originates primarily from their enhanced physical properties. The particle shapes of LWAs vary from angular to round with intrinsically high interstitial voids which are due to a narrow range of particle sizes. There are two basic requirements for LWAs to be used for the geotechnical applications. First is high interstitial
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