Technical Note
Geotechnical performance of waste tires for soil reinforcement from chamber tests

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Abstract

This paper presents reinforcing effects of the newly devised ‘Tirecell’, made from treads of waste tires, in sand. Parametric studies of the number of connection bolts between Tirecells, relative density of sand, embedded depth, the number of reinforced layers, and the width of Tirecell were performed by using plate load tests. The number of connection bolts used was enough to maintain the given pressure. Both the bearing capacity increased and the settlement reduction was the highest at the lowest density of sand, and the reinforcing effect of sand was obtained when the embedded depth was within 1.0B, where B is the loading width.

Higher bearing capacity was achieved by adding the Tirecell-reinforcement layers within 1.0B. Especially, the bearing capacity increased remarkably at one layer of the reinforcement, and the degree of increase was small from one-layer reinforcement to two layers. The Tirecell width that did not change the bearing capacity was smaller than that of geocell because of the high stiffness of the Tirecell. The reinforcing effect of Tirecell, in general, was more prominent than that of a commercial geocell.

Introduction

Waste tire disposal has become a major environmental issue in many countries. Each year more than 250 million used tires are stockpiled in the United States (Rma, 2004) and Canada generates over 28 millions of passenger tires per year (Garga and O’Shaughnessy, 2000). Korea has generated approximately 20 millions of waste tires per year since 1998, and some of the tires are utilized for rubber tiles and blocks or for cement materials. However, the cost of making rubber powder from a tire is very high. Therefore, several beneficial uses of waste tires have been proposed in the last decade, and some of them have already been applied in construction. Waste tires are desirable as construction material because of their excellent mechanical properties and durability. Fine-ground tire powders can be used as partial replacement for asphalt in asphaltic concrete; tire chips can be used for lightweight fill (Humphrey and Manion, 1992; Foose et al., 1996; Humphrey et al., 1998; Reid et al., 1998); tire treads can be used as a form of grid (Yoon et al., 2004); whole tires or tires with one sidewall removed (Garga and O’Shaughnessy, 2000; Nguyen, 1996; Ecoflex, 2006) can be used. In some cases, environmental assessments of toxic compounds in the tire-embedded earth fill were performed previously (O’Shaughnessy and Garga, 2000; Humphrey and Katz, 2000, Humphrey and Katz, 2002; Moon, 2003). In these assessments, the effluents were field monitored and the results indicated that toxic compounds had no significant adverse effects on ground water quality over a period of 5 years.

In this research, tire sidewalls were removed and a shallow, large diameter, cylinder tire was folded to make small two cells forming an Arabic number 8 type (called Tirecell). Many units of cells can be combined to complete a Tirecell, which can be used in the same way as a commercial geocell (Dash et al., 2001). A large number of plate load tests were performed to study reinforcement effects on the bearing capacity increase and settlement reduction in a test chamber filled with sands.

Section snippets

Tirecell

Tirecell used in this research was developed by combination of treads only after elimination of the sidewalls, as shown in Fig. 1. Tirecell may be used as (1) underlying material over unstable ground surfaces, (2) reinforcing elements between soil layers for embankment, (3) soil reinforcement of foundations, and (4) materials for retaining walls, etc. Fig. 2 shows the plane figure of Tirecell. The concept of soil confinement is the same as that of a commercial geocell system. The Tirecell units

Test chamber

The plate load tests for this research were carried out in a test chamber of 2.0 m width, 2.0 m length, and 1.5 m height. The chamber was placed under a loading frame and was filled with sand up to the depth of 1.2 m. Hydraulic cylinder, dial gages, and a measuring system were involved in the test (Fig. 5). The chamber had rigid boundaries, and its size was determined by finite element analysis, which checked the boundary influence. No boundary influence was confirmed from the pilot-plate load

Plate load tests

Plate load tests were conducted in a chamber as described in Section 3.1, and a 350 mm load plate was used. Before the main tests for the parametric study, plate load tests for both geocell and Tirecell were conducted at a certain relative density to confirm the reinforcing effect of Tirecell on the bearing capacity. Four parameters related to the bearing capacity and the settlement of reinforced sand were investigated. The parameters included relative density of the sand, Dr; number of layers

Conclusions

This study presents a newly devised method by use of waste tires called ‘Tirecell’ for soil improvement. To confirm soil improvement by Tirecell, plate load test results were compared with the results obtained from plate load tests using geocell. From the comparison, Tirecell reinforced the sand to produce higher bearing capacities and lower settlements. Tirecell reinforcement was effective within the depth of plate width, and the BCR was higher at lower densities. BCR in loose sand was more

Acknowledgments

The authors express their sincere thanks to KICTTEP (Korea Institute of Construction & Transportation Technology Evaluation and Planning) for the financial assistance. Thanks are also extended to Mr. Kyung-Soon, Choi for his much help.

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