NUMERICAL SIMULATION OF GEOTEXTILE-SAND INTERFACE USING BOX SHEAR TEST AND PULL-OUT TEST: A COMPARISON (original) (raw)
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Mechanical behaviour of sand-geotextile interface
Scientia Iranica, 2012
In this study, interface direct shear tests were undertaken to investigate improvement in the mechanical behaviour of granular soils when reinforced with geotextile inclusions. Unlike past studies, various different parameters were investigated in the same study to uncover more assuring results. As expected, the interface friction angle of the reinforced sand was found to be lower than that of the unreinforced sand. No remarkable difference was seen in the shear strength of reinforced and unreinforced sands, but in reinforced sand, there was no post-peak loss of strength, as seen in unreinforced sand. Unexpectedly, geotextile inclusions did not restrict the soil from dilating. If the geotextile content was increased in the test specimen, only then did the dilation of the sand decrease. At the end of the results, it was concluded that the interface behaviour depends on the combined effects of the surface properties and deformability of the geotextiles, and also on the index properties of the soil.
A Study on the Coefficient of Friction of Soil/Geotextile Interfaces
It is well known that soil friction parameters have a significant effect on the overall performance of reinforced soil structures. Since the Coefficient of Friction of the soil is a function of these parameters, it was desired to further investigate the Coefficient of Friction of soil/geotextile interfaces and its relation to the tensile strength of the geotextile used. Accordingly shear box tests were performed inside the laboratory using two soils; organic clay and sandy fill along with four geotextiles that have different tensile strengths to determine the cohesion and internal angle of friction of the soil/geotextile interfaces. These would be used to plot the Coefficient of Friction of these interfaces. It appears from the results of the shear box tests that the Coefficient of Friction of geotextile/organic clay interfaces reduces with the increase of normal stress and increases with the increase of the geotextile tensile strength. However geotextile tensile strength did not seem to have any significant effect on the Coefficient of Friction of geotextile/fill interfaces.
Studies on Geotextile/ Soil Interface Shear Behavior
Shear frictional behavior of soil/geosynthetic interfaces plays a pivotal role in the overall performance of geotextile-reinforced roads. Since a substantial proportion of the total land area in many Southeast Asian countries is composed of organic soils, it was seen of particular importance to investigate the shear frictional behavior of such soils when subjected to loading with geotextiles used as reinforcement. Two types of soils were used; organic silty clay and a fill material, which is a sandy type of soil. Shear box tests were performed to determine the shear strength parameters of the soils and to investigate the shear frictional behavior of the soil/geotextile interfaces. It appears from the results of the shear box tests performed that there exists a relationship between the tensile strength of the geotextile used and the shear strength of its interface with the organic clay, with the shear strength of the interface increasing with the increasing tensile strength of the geotextile. The shear strength of geotextile/fill interfaces did not show a consistent relationship with the geotextile tensile strength.
2013
The time-dependent behavior of soils has been investigated extensively using onedimensional and triaxial tests. The phenomena associated with time effects in soils are creep, relaxation, strain rate and re-arrangement effects. The engineering properties of soil are often improved significantly with the elapse of time. The objective of this paper is to investigate the time-dependent effect on the shear strength parameters of sand–geosynthetic interface using large direct shear test apparatus. For this purpose, the geotextile layer was carefully adhered to a piece of rigid block with a thickness such that half of the shear test box is occupied. The other half of the box has been filled with sand and the test performed. Three normal stresses of 30, 45, and 60 kPa have been applied in all tests. The shear stress has subsequently been applied at different times to the failure stage. In all tests, the shearing velocity has been kept the same. The results of these experiments show that the...
Sand-geotextile interface characterisation through monotonic and cyclic direct shear tests
Geosynthetics International, 2013
ABSTRACT: For the design and performance analyses of geosynthetic-reinforced soil structures under repeated loading, such as those induced by compaction, traffic and earthquakes, the understanding of cyclic soil–geosynthetic interface behaviour is of great interest. Nevertheless, experimental data concerning this type of behaviour are very scarce. A laboratory study was carried out and is described in this paper. This paper presents the behaviour of an interface between a silica sand and a high-strength geotextile under monotonic and cyclic loading conditions. A large-scale direct shear test device able to perform load- or displacement-controlled cyclic tests was used. The results obtained are presented and discussed, especially in terms of interface shear stiffness and damping ratio. Monotonic direct shear tests indicated that the coefficients of interaction for the sand–geotextile interface depend on the confining pressure. Cyclic direct shear tests indicated that the interface st...
Effect of Grading and Grain Size on the Friction Characteristics of a Sand_Geotextile Interface
In this investigation, the interaction behaviour of geotextiles with sand is evaluated by conducting extensive laboratory interface tests both in direct shear and pull-out. A comprehensive test program was established to include a needle punched non-woven geotextile interacting with sands of different grading, grain size distributions and grain shapes namely; Cape Flats, Klipheuwel and Munich sands. The respective responses were primarily presented in terms of shear stress/horizontal displacement and pUll-out resistance/front displacement relationships; showing the frictional performance of the geotextile in these sands of different physical characteristics. Interface shear strength in both test methods was determined using Mohr-Coulomb's law. The ensuing shear strength values were compared with each other and with the direct shear strengths of the respective sands used in this investigation. Specific emphasis and detailed analyses went into the pull-out experiments in which local displacements of the geotextile specimens were measured as the test progressed. The measurements enabled the study of the stretching characteristics of the geofabric in the different sands. Applying an extrapolation procedure to approximate the constantly changing deformation modulus of the geotextile as it stretched in the respective sands, allowed the back-prediction of the pull-out force/displacement relationship, and thus enabled the study of skin friction distribution along the geotextile specimen during pull-out. The effect of the grading and grain size on the development of the interface shear stress, the peak values, and the type of interface failure could be demonstrated.
International Journal of Geosynthetics and Ground Engineering, 2017
The direct shear test and the pullout tests are two widely used test procedures for determining the properties of the soilgeosynthetic interface. It is evident from the previous literature that the interface properties obtained from these tests differ considerably. In the present study, an attempt has been made to compare the interface properties obtained from the direct shear test and the pullout tests using the numerical simulations. A nonwoven polypropylene geotextile was used in the study. Three different types of sands with different fines content were considered. The analyses were carried using finite element package PLAXIS 2D in two dimensional frameworks. Initially, the numerical model was validated with the existing literature and the validated model was used to study the interface behaviour of the sand-geotextile interface. The results revealed that the interface properties obtained from the direct shear test and the pullout tests vary significantly. The presence of the fines content in the soil reduces the frictional resistance of the soil-geotextile interface. The interaction ratio value was found to vary between 0.67 and 0.97 for different types of sand. The friction coefficient of the pullout test was about 50% of the friction coefficient value obtained from the direct shear test. The friction angles obtained from the pullout test were found to vary between 30 and 50% of the direct shear tests. However, the apparent cohesion of the pullout test was found approximately four times the cohesion value obtained from the direct shear test.
Laboratory study of geotextiles performance on reinforced sandy soil
Journal of Earth Science, 2016
This paper presents the results of triaxial tests conducted for the investigation of the influence of geotextiles on stress-strain and volumetric change behaviour of reinforced sandy soil. Tests were carried out on loose sandy soil. The experimental program includes drained compression tests on samples reinforced with different values of both geotextiles layers (Ng) and confining pressure (σ′ c). Two methods of preparation were used: air pluviation (AP) and moist tamping (MT). Test results show that the geotextiles induce a quasi-linear increase in the stress deviator (q) and volume contraction in the reinforced sand. Method of preparation significantly affects the shear strength; samples prepared by the air pluviation method and mobilized deviator stresses are significantly higher than those prepared by moist tamping method. Geotextiles restrict the dilation of reinforced sandy soil and consequently the contraction increases. The mobilized friction angle increases with increasing number of layers and decreases with increasing initial confining pressure. Samples prepared by moist tamping present mobilized friction angles significantly lower than those prepared by air pluviation method. For samples prepared by the air pluviation method, the secant modulus at ε 1 =1% and 5% decreases with increasing geotextile layers; those prepared by the moist tamping method, secant modulus at ε 1 =1% and 5% increases with increasing number of geotextile layer sand confining pressure. From 10% axial strain, secant modulus increases with increasing inclusions of geotextile layers.
Modeling of soil–woven geotextile interface behavior from direct shear test results
Geotextiles and Geomembranes, 2010
Apart from other factors, the performance of geosynthetic reinforced soil structures depends also on the characteristics and behavior of the interface between soil and geosynthetic. Experiments were conducted in a direct shear test apparatus to study the shear force-displacement behavior at the soil-geotextile interface using two differently textured woven geotextiles. Analyzing the data so obtained a non-linear constitutive model has been presented for predicting both the pre-peak and the post-peak interface behavior. The predictions made by the developed model are found to be in good agreement with experimental data obtained from direct shear tests.
Geotextile friction mobilization during field pullout test
Geotextiles and Geomembranes, 1998
Small-scale laboratory tests may not yield reliable values for soil-geotextile interface properties due to the effect of scaling. Field tests offer a better alternative to overcome this problem. In situ pullout tests were performed on a full-scale embankment built over a woven polyester geotextile sheet. The field tests were conducted using different fill heights of compacted clayey soil. The performance of the geotextile was examined when the base soil underneath the geotextile was stiff clay of high plasticity or compacted clean river sand. The test section was instrumented to monitor the geotextile movement and the applied pullout force. Results of the tests showed a linear increase in the geotextile frictional resistance with the increase in the fill height. Also, a successive movement response at different locations on the geotextile away from the loaded edge was detected during the early stages of loading. At the slippage load, a continuous rigid body translation occurred in the geotextile sheet without any further increase in the applied pullout force. The suitability of a widely used interface numerical model that consists of a zero-thickness joint element and a nonlinear elastic hyperbolic stressdeformation material model was examined using the finite element technique. The results showed the inadequacy of this model to deal with large deformation problems typically experienced in geosynthetic reinforced soils.