A Simplified Mechanism for the Vertical Permeability Test of Geo-textile

Transcription

1 International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol:10 No:02 25 A Simplified Mechanism for the Vertical Permeability Test of Geo-textile Kamrun Nahar, Md. Wahid Ferdous, Dr. Syed Abdul Mofiz and Khaleda Ferdous Abstract Now-a-days geo-textile materials have been used worldwide for solving geotechnical engineering problems associated with soil and water conservation work. Among the various properties of the geo-textile, the hydraulic properties are of major importance from the engineering point of view. This paper presents a simplified mechanism for the design and fabrication of vertical permeability test apparatus to determine the vertical permeability of geo-textile. The vertical permeability test apparatus has been fabricated and installed as per ASTM standard D The test apparatus has been manufactured in the department of civil engineering using locally available materials. After installation of the apparatus, the cross-plane permeability test for the geo-textile material has been performed. The permeability of geo-textile for different thickness obtained from this apparatus satisfies the standard values of permeability. Index Term Geo-textile. Vertical permeability, Fabrication, Rotating discharge, Head measuring, Lower unit, Upper unit. I. INTRODUCTION Geo-textiles can be simply defined as a textile material used in a soil (geo) environment and include woven and nonwoven polymeric materials and natural materials, such as jute, manufactured using textile processes. As observed by Theisen (1992) Geo-textiles are used with foundation, soil, rock, earth, or any other geotechnical engineering-related material as an integral part of a human-made project, structure, or system. Due to very wide ranges of application and the tremendous variety of available geo-textiles having widely different properties, selection of particular geo-textile for the particular place is very critical decision. The decision must be made before the actual mechanism of the geo-textile material started 1 Kamrun Nahar, Lecturer, Department of Civil Engineering, Rajshahi University of Engineering & Technology, Rajshahi 6204, Bangladesh. ( knahar47@yahoo.com). 2 Md. Wahid Ferdous, Lecturer, Department of Civil Engineering, Rajshahi University of Engineering & Technology, Rajshahi 6204, Bangladesh. ( wf_jewel@yahoo.com). 3 Dr. Syed Abdul Mofiz, Professor, Department of Civil Engineering, Rajshahi University of Engineering & Technology, Rajshahi 6204, Bangladesh. ( samofiz@gmail.com). 4 Khaleda Ferdous, Department of Biotechnology and Genetic Engineering, Islamic University, Kustia, Bangladesh. ( khaleda_ferdous@yahoo.com). on the applied place. That s why for the particular selection of a geo-textile, the properties of the geo-textile material should be correctly measured. Among the various properties, the hydraulic properties of the geo-textile material which include (i) Porosity (ii) Percent open area (iii) Apparent opening size(calhoun, 1972 developed a test for equivalent opening size). (iv) Permeability are of major importance. These properties are interrelated such as opening pore size) of the fabric controls the filtration performance of geo-textitle as observed by Ogink (1991) Being a growing industry, the geo-textitle currently does not have a completely unified set of worldwide standards and test methods. Yet the activity toward such an ultimate goal is very intense (Koerner, 1997). As observed by Koerner, a many of the test methods are not fully standardized as far as their test procedures are concerned. In the U.S., the ASTM has a standards committee specifically organized for geosynthetics (D35): however. there are also worldwide organizations. Few of them are: International Organization for Standards, German Standards Committee for Geo-textiles, British Standards Institution etc.geotextiles tests can be divided into two categories: Index tests and Design tests. Index tests are relatively simple to perform and provide basic properties primarily for purpose of quality control. Such properties are also of value for classifying geo-textiles, however, and in some cases they have been empirically related to engineering behavior (Yeo, K.C. 2008). Design tests attempt to model the anticipated field conditions and frequently involve a combination of geo-textiles and the proposed fill material in an appropriate manner. Such tests generally employ relatively complex apparatus and are often both expensive and time consuming. This paper focus on the vertical permeability of geotextile and presents a simplified mechanism to fabricate an apparatus for the vertical permeability test of geo-textile material and is designed and fabricated according to the ASTM D The fabrications of the apparatus consist of using locally available materials having component parts of upper unit, lower unit, rotating discharge, head measuring. The permeability value obtained from this apparatus and a comparison between the standard value and the values obtained from other expensive apparatus are also presented and discussed in this paper.

2 International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol:10 No:02 26 II. DESCRIPTION OF THE APPARATUS A. Component parts Upper unit Lower unit Rotating discharge Head measuring B. Fabrication The apparatus for the vertical permeability test of geo-textile material is designed and fabricated according to the ASTM D The fabrications of the apparatus consist of using locally available materials. The materials required for the fabrications of the apparatus are 1. A 6 inch diameter plastic for the lower unit. 2. A 3.14 inch diameter plastic for the upper unit. 3. A rotating discharge of 1 inch for the measurement of outflow. 4. A ½ inch diameter plastic for head measurement. 5. Two metal plates, the bottom one being perforated to the diameter required for the sample to be pasted. All the materials discussed above are collected and the apparatus has been fabricated as per ASTM designation. A schematic drawing and the photographic view of the apparatus confirms to all of the above requirements and are shown in the Fig.1 to Fig.5. Fig. 2. Different parts of the vertical permeability test apparatus Fig. 3. Upper unit of the vertical permeability test apparatus Water inlet Overflow outlet Funnel Rotating discharge Air bleeder valve Top view Overflow outlet Sample holder Water inlet Reservoir Vernier Overflow outlet drain Gauge for falling head test Backboard Rotating discharge Air bleeder valve Vernier for rotating discharge Overflow outlet drain Fig. 4. Lower unit of the vertical permeability test apparatus. Front view Fig. 1. Schematic diagram of constant and falling head permeability apparatus

3 International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol:10 No:02 27 Fig. 5. Photographic view of the vertical permeability test apparatus C. Installation The installation of the apparatus to fit it for the vertical permeability test consists of the following arrangement: 1. The upper unit consists of a stand of diameter mm (3.14 inch) and the lower unit consists of a diameter mm (6 inch) have been fastened together with the help of collars made of metal plates. The inflow and the outflow connections are checked in order to avoid leakage. 2. The head measuring has been checked so that it can work accurately. 3. Scaling has been done on the face for the head measurement. With the help of this apparatus the permeability of geo-textile materials either in constant head and falling head cam be easily obtained. The important test considerations for this test are preconditioning of the fabric, temperature and the use of de-aired water. III. METHODOLOGY A. Sampling In order to obtain a representative value of permeability, a specimen of 1m 2 (1yd 2 ) is taken. as per Fig.6 four specimens A, B, C, and D are selected. Specimen A is taken from the centre of the sample, B is taken at one corner (centre located 200mm (8in) from the corner), C is taken from midway between A and B, and D is taken from the distance from A as C. located on aline with A, B and C. The diameter of the cut specimen is considered as 76.2 mm (3in) so that it fits the testing apparatus. The specimen is conditioned by soaking in a closed container of de-aired water, at room conditioned, for a period of 2 hour. The minimum specimen diameter is to be 50mm (2in). 1m D C Fig. 6. Sampling of geotextile from different location B A 1m The permeability test described so long, has the geo-textile test specimen under zero normal stress, a situation rarely encountered in the field. To make the test more performance oriented, numerous attempts to construct permeability under load device have been made. Generally a number of layers of geo-textile (2 to 5 layers) are placed upon one another with an open mesh stainless steel grid on top and bottom. Thus normal stress of 2 kn/m 2 is imposed on the geo-textile by the stones, but the flow is only nominally restricted. Loading by soil itself (which would definitely affect flow) is completely avoided. B. Constant Head Test 1. The apparatus has been assembled with the specimen in place. The geo-textile specimen of diameter 76.2mm (3 in) is to be positioned in bottom of the upper unit. The sample is pasted on the grooving portion which allows to check the side flow 2. A pressure of 2 kn/m 2 as per the field requirements has been applied by the stone chips. 3. The system through the stand or discharge or discharge has been backfilled with de-aired water. Backfilling in this manner forces any trapped air out of the system and the geo-textile. 4. Water is allowed to flow into the system through the water inlet, adjusting the discharge along with the rate of water flowing into the apparatus to obtain a constant head of water on geo-textile. 5. The value of time (t) and the quantity of flow (Q) as collected from the discharge have been recorded. Three Readings per specimen has been taken and the average value of permeability per specimen is determined. C. Falling Head Test The apparatus has been assembled with the specimen in place. The geo-textile specimen of diameter 76.2mm (3 in) is to be positioned in bottom of the upper unit. The sample is pasted on the grooving portion which allows to check the side flow. 1. A pressure of 2 kn/m 2 as per the field requirements has been applied by the stone chips. 2. By increasing the flow from the water supply, a head of 150mm is adjusted. When the water level is reached to a head of 80mm, the stop watch is started and the time required to reach the water head to 20mm is recorded. 3. By recording the inside diameter of upper unit (d), the diameter of the exposed portion of the specimen (D), falling head permeability is obtained. 4. The above procedure has been repeated for calculating the permeability for the remaining specimen. D. Equation for the calculation of permeability of geotextile The constant head permeability is given by the formula, [1] q k AI

4 Permeability K, (m/s) Permeability k, (m/s) International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol:10 No:02 28 Where, k = permeability in m/sec q = discharge in m 3 /sec h = constant head in cm L = total thickness in cm A = Area in cm 2 The falling head permeability is given by the formula [2] k a ho 2.3 log 10 t A t h Where, Ψ = permittivity (s -1 ) k = permeability in m/sec t = thickness of the sample in m a = area of water supply stand (m 2 ) A = total area of geotextile test specimen (m 2 ) t = time change between h o and h f h o = head at beginning of test (m) h f = head at end of test (m f h = 6 cm h = 7 cm h = 10 cm Thickness t, (cm) Fig. 7. Variation of permeability with thickness of geotextile for constant head test Thickness t, (cm) Fig. 8. Variation of permeability with thickness of geotextile for falling head test. IV. RESULT AND DISCUSSION Permeability of the geo-textile material obtained from the apparatus in both the cases of constant and falling head tests are in between the range of standard test values (8 X 10-6 to 2 X 10-3 ) which are shown in the Fig.7 and Fig.8. From the figures it is shown at smaller thickness of geo-textile the permeability is at lower value and at higher thickness of the geo-textile the permeability is of higher value. Because the permeability value is dependent on the opening pore size of geo-textile fabric not on the thickness of geo-textile. That s why geo-textile having higher thickness with higher opening size will give higher permeability on the other hand geo-textile having lower thickness with lower opening size will give lower permeability. V. CONCLUSION An experimental study has been carried out by using locally available material for the fabrication and installation of the apparatus for vertical permeability test of geo-textile in both cases of constant head test and falling head test. Based on the test results and their interpretation, the following conclusions may be drawn 1) The apparatus is properly fabricated and installed according to ASTM standard D for the measurement of permeability of geo-textile using locally available material. In comparison with other heavy apparatus it is quite light and economical. 2) The apparatus works properly as per the requirements. The permeability value obtained from the apparatus for constant and falling head tests satisfied the standard range. REFERENCES [1] Robert M. Koerner, (1997) Designing with Geosynthetics. Geo-textile Fabrics Report, June 1997 pp, [2] ASTM D (1999), Standard test method from water permeability of Geo-textiles by permitivity, American Society for Testing Materials, pp 1-6. [3] Ogink, (1991) Innovative Hydraulic Engineering with Geosynthetics, Geosynthetics world. Vol. 2, No. 4, pp [4] Calhoun, (1972), Experiment of Soil Reinforcement with Geotextitle, Use of Geo-textiles for soil Improvement, New York: ASCE, pp [5] Koerner, R.M.,(1998), Designing with Geosynthetics, pp , Prince Hall, USA. [6] ASTM committee D-35, (1995), ASTM Standard on Geosynthetics, Philadelphia, P.A., U.S., pp [7] Yeo, K.C., (2008), Properties of Geo-textiles Castco Testing Center Limited, Hong Kong, pp, 1-7. [8] Thesen.M.S.,(1992) The Role of geosynthetics in Erosion and Sediment Control: An Over View. J.Geo-textiles and Geomembranes, Vol.11, Nos.4-6, pp, Kamrun Nahar Kamrun Nahar was born in Rajshahi District in Bangladesh on 6 July She obtained the degree of Bachelor of Science in Civil Engineering from Rajshahi Univerisity of Engineering & Technology in the year 2007 and secured First Class Honors with Second Position out of One Hundred Students. She was awarded the Government Board Scholarship for four years due to her outstanding performance in the Higher Secondary Examination. She also got the best student awards in the year of 2005 and Her major fields are Civil Engineering. Just after getting his B.Sc. Degree, she joined as a Lecturer in the Department of Civil Engineering, Rajshahi Univerisity of Engineering & Technology, Rajshahi, Bangladesh.

5 International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol:10 No:02 29 Md. Wahid Ferdous Mr. Md. Wahid Ferdous was born in Harinakundu, in the district of Jhenidah in Bangladesh on 2 December He obtained the degree of Bachelor of Science in Civil Engineering from Rajshahi Univerisity of Engineering & Technology in the year 2008 and secured First Class Honors with First Position out of One Hundred Students. He is selected for the University Gold Medal for the best overall performance in the final year of Bachelor of Science in Civil Engineering Degree. He also got best student awards in the year of 2004 and His major field is Civil Engineering. Just after getting his B.Sc. Degree, he joined as a Lecturer in the Department of Civil Engineering, Rajshahi Univerisity of Engineering & Technology, Rajshahi, Bangladesh. Dr. Syed Abdul Mofiz Dr. Syed Abdul Mofiz is presently the Professor in the Department of Civil Engineering, Rajshahi Univerisity of Engineering & Technology, Rajshahi, Bangladesh. He got his B.Sc. Engineering degree from Rajshahi University; M.Sc. Engineering from BUET; & Ph.D. from Malaysia. He is an expert in Geotechnical Engineering. Khaleda Ferdous Khaleda Ferdous was born in Harinakundu, in the district of Jhenidah in Bangladesh on 10 April She obtained the degree of Bachelor of Science (Honors) from Islamic University with First Class in Now she is doing her Master program from the same university. She is interested to give her knowledge among the people for the betterment of them as well as for her country.