Advances in Reinforced Soil Structures

Table of Contents

1. Frontmatter

2. Direct Shear Testing of Sand – Geotextile Interfaces

   Ioannis N. Markou

   Abstract

   The effect of shear box size, geotextile type and properties and sand grain shape and size on the sand – geotextile interaction was investigated experimentally by conducting interface tests with conventional and large-scale direct shear equipment. Four clean uniform sands, one with subangular grains and three with rounded grains of different sizes were tested in dry and dense condition. Seven non-woven polypropylene geotextiles of various types and properties and seven woven geotextiles with or without apertures were used in the tests. The large-scale direct shear tests were conducted according to ASTM Standard D5321, using a 300 mm square shear box. The tests with the conventional 100 mm square shear box were performed using the same normal stresses and comparable shearing rate with the large-scale tests. The interface friction coefficient values obtained from the tests with the conventional and the large-scale shear box are in good agreement. Therefore, the 100 mm shear box is satisfactory for testing materials like those used in the present investigation. The values of friction coefficient, tanδ, at the sand – geotextile interface are affected by the geotextile type and range from 71% to 104% with respect to the internal friction coefficients, tanφ, of sands. Although the interface friction coefficient values are larger in the sand with subangular grains, the efficiency (tanδ/tanφ ratio) values for the sand with subangular grains are lower in comparison with the sand with rounded grains of equal size. For interfaces between sands of different grain sizes and geotextiles without apertures, the obtained efficiency values generally increase with decreasing sand grain size.

3. Consideration of Geosynthetic Tension in Interpretation of Data from Inclined Plane Tests

   Atef Ben Othmen, Mounir Bouassida

   Abstract

   The inclined plane device is specifically adapted to assess the geosynthetic interfaces friction under low confinement conditions. The lack of the standardized procedure proposed by the European standard (EN ISO 12957-2 2005) for the determination of geosynthetic interface friction properties has been proven by many recent researches available in the literature.

   These researches demonstrated the need for revising the standard displacement procedure since it seems to be poorly suited for many geosynthetics interfaces and because the high sensitivity of the determined friction angle to test conditions.

   Geosynthetics of reinforcement interface properties were determined by carrying out inclined plane tests under low confinement adapted to landfill covers conditions. Interface friction angles \( \left( {\varphi^{stand} } \right) \) were determined conformingly to the standardized displacement procedure and compared with those defined by a method known from the literature.

   Then, interface friction angles were determined according to a new method called “tension procedure” which considers the measurement of the tension developed by the geosynthetic reinforcement during inclined plane tests.

   Compared to previous data, the proposed method allows a new and more comprehensive interpretation of the inclined plane test since it pays attention to the different behavior of geosynthetics during tests.

   This research demonstrates that the consideration of reinforcement tensions allows a more suitable comprehension of the mechanical behavior of soil-geosynthetic interface and a better representation of the in-situ behavior of the geosynthetic interface.

   It appears that the mechanical behavior of the geosynthetic of reinforcement and the magnitude of the measured tension depended on the reinforcement characteristics specially the geosynthetic surface structure and the tensile stiffness (tensile modulus) J (kN/m).

   The determined friction angles, both in static \( \left( {\varphi^{stat} } \right) \) and dynamic \( \left( {\varphi^{dyn} } \right) \) inclined plane conditions, are lower than those calculated using the previous methods which allow a more accurate design of landfill cover systems.

4. Stress-Strain Behaviour of Sand with Disc Plate Shaped Reinforcement

   J. N. Jha, S. K. Shukla, A. K. Choudhary, K. S. Gill, B. P. Verma

   Abstract

   In the present study, the laboratory triaxial compression tests were carried out on soil specimens reinforced with steel and aluminium solid plates in horizontal layers. The percentages of reinforcement used were 5%, 4%, 2%, 1% and 0.5%. The solid plates were placed horizontally in five layers in all the tests. Again the triaxial compression tests were repeated by using the perforated circular aluminium plates as horizontal reinforcement instead of solid plate, but the quantity of reinforcements was kept the same as in the previous case. The diameter of the plate in all the cases was 25 mm. To alter the percentages of reinforcement, thickness of layers were varied in each case but thickness in all the five different layers were kept the same. The results show that improvement in strength of soil was not proportional to the increase in the percentage of reinforcement and residual strength ratio was also found to be less. It was also observed that there was an increase in the tangent modulus with increase in percentage of reinforcement at higher confining pressure when aluminium was used as a disc shaped plate reinforcement.

5. Swelling and Shrinkage Behaviour of Expansive Soil Blended with Lime and Fibres

   Mayakrishnan Muthukumar, S. K. Sekar, Sanjay Kumar Shukla

   Abstract

   Expansive soils are considered to be highly problematic because of their capacity to significant volume change. They swell during the rainy season as they absorb water and shrink when water evaporates from them during the summer season. Because of this dual swell-shrink behaviour, an expansive soil causes severe distress to many civil engineering structures. Several mitigating techniques are adopted to counteract the problems posed by the expansive soils, either by modifying the properties of the soil by adopting stabilization techniques using lime, cement, fly ash, calcium chloride etc. or by adopting special foundation technique such as construction of belled piers, under-reamed piles, etc. In recent years polymeric fibres have also been used to stabilize the soil as well as to improve the strength of the expansive soils. Hence in the present study lime and fibres have been used in different proportions to study the swelling and shrinkage behavior of expansive soils. Swell tests were performed by varying the fibre content and lime with expansive soils. Tests were also conducted by blending fibres and lime together with expansive soils. In a similar way, shrinkage tests were also performed for the various proportions. The test result show that swelling tends to decrease slightly with an increase in the fibre content, whereas shrinkage tends to decrease significantly upon addition of fibres. Both swelling and shrinkage tends to decrease significantly with increasing lime content. The optimum content of fibre was found to be 2%. So the expansive soil specimens blended with 2% fibres and with varying lime content was tested. It is found that blending 2% fibres and 15% lime together in expansive soils is considered to be more effective in controlling the swelling and shrinkage behaviour.

6. Feasibility of Utilization of Metalized Plastic Waste in Cohesionless Soil

   Siddharth G. Shah, Ankur C. Bhogayata, Sanjay Kumar Shukla

   Abstract

   This paper presents the test results of shear strength of cohesionless soil reinforced with macro-sized metallized plastic waste (MPW). The soil samples were collected from Rajkot city of Gujarat state, India. The objective was to obtain the effects of addition of MPW in cohesionless soil on shear strength variation of soil. MPW was received from a local plastic packaging unit as films and shredded into flakes of 5 mm × 5 mm average size. The flakes were mixed in soil by weight fractions from 0% to 3% with an increment of 0.5%. The direct shear test was performed on each specimen. Soil specimen containing 0% MPW was regarded as reference soil. The test results revealed that inclusion of MPW improved the shear strength of soil for MPW dosage up to 1.5% by weight. Beyond 1.5% of addition of MPW flakes reduced the shear strength. However, the experimental study demonstrated the feasibility for a sustainable utilization of MPW in cohesionless soil. Soil reinforced with MPW could be used for the civil engineering applications where shear strength enhancement is required.

7. Comparison of Geotextile-Reinforced and Geogrid-Reinforced Flexible Pavements by Numerical Analyses

   Nadjet Bouacha

   Abstract

   Over the past three decades, geosynthetics have been used successfully around the world in many areas of civil engineering, and are now a well-accepted building material. Their use provides excellent economic alternatives to conventional solutions to many engineering problems. Therefore, students and practicing engineers need exposure to the fundamentals of geosynthetics as a building material. The Geosynthetics is a generic term for all synthetic materials used in conjunction with the soil, rock and/or other-related civil engineering material as an integral part of a project, structure or system. Geomembranes are used to distinguish their sealing qualities or permeability and geotextiles used for their mechanical functions. This study is to analyze the behavior of the pavement structure reinforced with layers of geotextiles. This analysis is done through a numerical modeling with the code PLAXIS V8. The latter is based on the principle of finite elements, this criterion will help us to better understand the behavior of the pavement structure and the ground vis-à-vis the parameter analysis of stress and strain. The principle of this analysis is based on a comparison designed pavement with and without geotextiles and will focus on the radial stresses settings, vertical stresses and displacements for two types of materials processed bitumen treated materials bitumen structures and materials treated with hydraulic binders.

8. Study on Square Footing Resting on Prestressed Geotextile Reinforced Sand

   S. Kumar, C. H. Solanki, J. B. Patel, P. B. Sudevan, P. M. Chaudhary

   Abstract

   This paper presents the results of laboratory model tests carried out on square footing resting on geotextile reinforced sand. The model steel tank of size 120 cm × 50 cm × 50 cm and square footing of size 10 cm are used. The effect of reinforcement with geotextile of sizes 20 cm × 20 cm, 30 cm × 30 cm and 40 cm × 40 cm below footing at different depth of placement were studies through a series of laboratory model tests. The effects of prestressing the geotextile on bearing capacity improvement and settlement reduction of a reinforced sand bed are also being investigated. The study also highlights the effect of size of geotextile and placement of geotextile below footing on load-settlement characteristics.

9. Numerical Studies on Ground Improvement Using Geosynthetic Reinforced Sand Layer

   G. Sanoop, Satyajit Patel

   Abstract

   Clayey soils exhibit high shrinkage and compressibility characteristics as well as low shear strength. Engineering projects in clayey soils requires construction of deep foundations or use of ground improvement techniques. Soil reinforcement is a popular and widely used ground improvement technique. Shallow foundations resting on geosynthetics reinforced sand layer is a cost effective and feasible construction technique. Since the geosynthetics are placed in sand or granular layer compaction can be easily performed to achieve the design density and adequate friction between sand and the geosynthetics. The performance of strip footings resting on geosynthetics reinforced sand layer overlying clay layer is investigated using finite element software MIDAS GTS NX. A number of numerical models were analyzed and the effect of various parameters such as type of geosynthetic material, depth of sand layer, critical depth of reinforcement below base of footing, number of reinforcement layers, spacing between multiple layer of reinforcement and width of reinforcement layer on the load-settlement behavior of strip footings was studied. The optimum values of these parameters were also determined. Laboratory models of clay underlying sand layer with and without geosynthetics reinforcement were prepared in a steel tank of size 84 * 25 * 50 cm and monotonic load was applied through a steel plate of width 8 cm up to failure. The model test results were compared with the finite element analysis results. Design charts were developed which can be used to determine the depth of sand layer and number of reinforcement layers for a target bearing capacity.

10. Bearing Capacity Prediction of Inclined Loaded Strip Footing on Reinforced Sand by ANN

    R. Sahu, C. R. Patra, N. Sivakugan, B. M. Das

    Abstract

    Laboratory model tests have been conducted on a strip foundation resting over multi-layered geogrid-reinforced dense and loose sand subjected to inclined load. Based on the laboratory model test results, a neural network model is developed to estimate the reduction factor for bearing capacity. The reduction factor obtained by ANN can be used to estimate the ultimate bearing capacity of a strip foundation subjected to centric inclined load from the ultimate bearing capacity of the same foundation under centric vertical loading. A thorough sensitivity analysis was carried out to find out the important parameters affecting the reduction factor. Emphasis was given on the construction of neural interpretation diagram, based on the weights developed in the neural network model, to determine the direct or inverse effect of input parameters to the output. An ANN model equation is developed based on trained weights of the neural network model. The results from artificial neural network (ANN) were compared with the laboratory model test results and these results are in good agreement.

11. Soft Soil Improvement with Conventional and Geogrid-Encased Stone Piles Under an Embankment

    Mohamd B. D. Elsawy

    Abstract

    Construction on natural soft soil is considered a risk due to its low shear strength and permeability as well as its high compressibility. Stone piles technique have been utilized in soft soil to increase the bearing capacity and accelerates the consolidation. To improve the reinforcement and the drainage functions of the stone piles, the geosynthetic are used as encasement. In the current research, a case history of an embankment constructed on the reinforced soft soil with conventional stone piles has been chosen from the past research to be simulated. 3-Dimension, plane strain and axisymmetric techniques are used to simulate the embankment parts. The stone piles are reinforced by geogrid material to imply the influence of the encasement on the behavior of the stone piles-soft soil foundation. The consolidation analysis is applied to investigate the long-term behavior of the clay. There is a good agreement between the FEM results and the field measurements of the reinforced soft soil with conventional stone piles. The 3D and the axisymmetric models induces better agreement with field measurements than that of the plane strain model. The reinforced soft soil with encased stone pile has a smaller settlement and a shorter consolidation time than those of the reinforced soft soil with conventional stone piles. The reduction in the settlement is more significant with developing consolidation time. The dissipation of the excess pore water pressure in the reinforced clay with encased pile consumes shorter time in comparison with the reinforced clay with conventional piles. The effective vertical stress and the stress concentration in the encased piles are higher than those in the conventional piles. The encasement also causes reduction in the total stress of the surrounding clay which participates in the acceleration of the consolidation.

12. Analysis and Design of Piled Geogrid-Reinforced-Earth Embankment

    Nasr O. Sheta, Rudolph P. Frizzi

    Abstract

    A pile-supported geogrid-reinforced-earth embankment was designed and constructed to serve as an access road for heavily loaded cranes and pile-installation rigs for constructing a major bridge between New York and New Jersey in the United States. The road is to also serve as an access to maintain the bridge during its service life. Subsurface investigations performed along the proposed access road alignment revealed subsurface conditions typically consisting of surficial fill underlain by a highly compressible organic clay and/or peat overlying marine sand underlain by glacial till. A limiting-settlement criterion set forth by the crane engineer together with settlement and slope-stability analyses indicated a conventional embankment could experience non-tolerable settlement and slope instability where thick organic soils were encountered. A ground-improvement program was carried out using geogrid reinforcement, a load transfer platform (LTP), and timber elements to control settlement and enhance slope stability. Where thinner organic soils were encountered, staged construction and a monitoring program were implemented to design and construct the proposed embankment.

13. Case Study on GeoTrel® Reinforced Earth® Steepened Slopes on Soft Founding Soils for the Approach of Major Bridge Over River Kaljani at CoochBehar in West Bengal, India

    Sumonto Banerjee, Atanu Adhikari, Saikat Chatterjee, Dhananjoy Das

    Abstract

    The paper focuses on a particular case study involving the construction of full height steep reinforced slope walls with an inclination of 70° with the horizontal for the approach of major bridge over river Kaljani in West Bengal, India. The maximum height of the steep slope walls is 9m at the abutment location. The soft founding soil has been improved by soil replacement at a requisite design depth followed by providing inclusions of Geostrap® basal reinforcement at intermediate layers. The case study covers the design, engineering, construction methods and challenges that were overcome during the construction of this project. Another key feature in utilizing this technology over concrete panel or block facing was savings in construction time span and known as ‘ready to install’ technology. The project has saved the client time and money over conventional rigid retaining wall structures in such cases.

14. Prediction of Ultimate Bearing Capacity of Eccentrically Loaded Rectangular Foundations Using ANN

    B. P. Sethy, C. R. Patra, N. Sivakugan, B. M. Das

    Abstract

    Extensive laboratory model tests were conducted on a rectangular embedded foundations resting over homogeneous sand bed and subjected to eccentric load to determine the ultimate bearing capacity. The depth of embedment varies from 0 to B with an increment of 0.5B; where B is the width of foundation and the eccentricity ratio (e/B) was varied from 0 to 0.15 with increments of 0.05. Based on the laboratory model test results, a neural network model has been developed to estimate the reduction factor (RF). The reduction factor can be used to estimate the ultimate bearing capacity of an eccentrically loaded foundation from the ultimate bearing capacity of a centrally loaded foundation. A thorough sensitivity analysis has been carried out to determine the important parameters affecting the reduction factor. Importance was given on the construction of neural interpretation diagram, and based on this diagram, whether direct or inverse relationships exist between the input and output parameters was determined. The results from artificial neural network (ANN) were compared with the laboratory model test results and the agreement is good.

15. Backmatter