CHAPTER 4 EXPERIMENTAL WORK 4.1 GENERAL

Transcription

1 CHAPTER 4 EXPERIMENTAL WORK 4.1 GENERAL In the present chapter engineering properties of subgrade soils, moorum and aggregate used in the investigation are presented. The details of geotextiles and geogrids used are also been presented. 4.2 SUBGRADE SOILS Two locations with different clay subgrades are selected for investigation in Kurnool city of Andhra Pradesh, India. The expansive clay (CH group) used in the investigation is procured from a site opposite to More Market, Near C Camp center, Kurnool. The non expansive clay (CI group) is procured from a site opposite to Govt. General Hospital, Kurnool. Both the soils are collected at different depths ranging from 0.3 to 1m and mixed after pulverization. Laboratory investigation are carried out on the proposed clay surfaces to determination the engineering properties of the soils. 46

2 IS light compaction test are conducted to evaluate the compaction characteristics of the clay soils. Swell pressure is determined from swell under load method. Percent swell is determined as the ratio of swell under surcharge load of 5 kg to that of initial thickness of expansive soil. Using the OMC and MDD values of I.S. light compaction CBR specimens are prepared and soaked and tested to determine the soaked CBR values. The Engineering properties of the clay subgrade under study determined from laboratory tests were presented in the Table 4.1. Table 4.1 Engineering Properties of Expansive Clay Subgrade S. No. Engineering Property Soil 1 (black clay) Soil 2 (brown clay) 1. Specific Gravity Grain Size Analysis a) Gravel (%) b) Sand (%) c) Fines (%) 3. Atterberg Limits a) Liquid limit (%) b) Plastic limit (%) c) Shrinkage limit (%) 4. Compaction Characteristics (I.S. Light Compaction Test) a) Optimum Moisture content (%) b) Maximum Dry Density (g/cc) 5. Undrained Shear Parameters a) Cohesion (kn/m 2 ) b) Angle of internal friction o 15 o 6. Soaked C.B.R. Value (%) Differential Free Swell (%) Swell Pressure (kn/m 2 )

3 4.3 MOORUM The moorum used as cushion material to suppress the swelling of expansive soil. The moorum used in the study is procured from a local quarry near Ulindakonda, Kurnool district. The various properties of moorum determined from the laboratory tests are presented in the Table 4.2 Table 4.2 Engineering Properties of Moorum Soil S. No. Engineering Property Moorum 1. Specific Gravity Grain size Analysis a)gravel (%) b) Sand (%) c) Fines (%) 3. Atterberg Limits a) Liquid limit (%) b) Plastic limit (%) c) Shrinkage limit (%) I.S Classification Symbol SC-SM 5. Compaction Characteristics (I.S. Light Compaction Test) a) Optimum Moisture content (%) b) Maximum Dry Density (g/cc) 6. Undrained Shear parameters a) Cohesion (kn/m 2 ) b) Angle of internal friction o 7. Soaked C.B.R. Value (%) AGGREGATE The aggregate used in the research study are procured from a quarry located at Thammarajupalli, Kurnool District, Andhra Pradesh, India. The gradation characteristics and engineering properties of aggregate are presented in the Table 4.3 (a) and 4.3 (b). 48

4 Table 4.3 (a) Gradation of Aggregate used in WMM IS Sieve Designation (mm) Percent by Weight Passing Table 4.3 (b) Engineering Properties of Aggregate S. No. Property Value 1. Specific Gravity Crushing Value (%) Impact Value (%) Abrasion Value (%) Flakiness & Elongation Index OMC (%) MDD (g/cc) REINFORCING MATERIALS In the present study woven geotextile and geogrid are used as reinforcing material in flexible pavement design. The details of reinforcing material used are given below Geotextiles In the present work two woven polypropylene geotextiles of different tensile strengths as stiffness are used as reinforcing material in the swell studies. The geotextiles are procured from Garware Wall Ropes, Pune. The tensile strength of the geotextile at different strains as obtained from the warp and weft tension test are presented in the Fig. 4.1 to

5 Figure 4.1 Tension Test Results of woven geotextile 2 in warp direction Figure 4.2 Tension Test Results of woven geotextile 2 in weft direction Figure 4.3 Tension Test Results of woven geotextile 1 in warp direction Figure 4.4 Tension Test Results of woven geotextile 1 in weft direction 50

6 The details of tests performed on geotextile are described below Table 4.4 Physical Properties Property Geotextile 1 Geotextile 2 Specific Gravity Thickness (mm) Weight(g/m 2 ) Table 4.5 Mechanical Properties Property Test Method Geotextile 1 Geotextile 2 Tensile Warp Strength Weft IS:1969: (kn/m) Puncture Strength ASTMD (N) Trapezoid Warp Tear Weft ASTMD4533 Strength (N) Geogrid For the present work to study reinforced mattress concept in CI soils Geogrid material used was procured from the Geosol associates, Hyderabad. The properties geogrids are presented in the Table 4.6 Table 4.6 Properties of Geogrid Property Base Polymer Geogrid High Tenacity Polymer Mass per Unit Area (g/m 2 ) 472 Thickness (mm) 1.9 Tensile strength(kn/m) 120 Elongation at Break (%)

7 4.6 INTERFACIAL SHEAR PARAMETERS OF CLAY SUBGRADES AND MOORUM WITH WOVEN GEOTEXTILE Studies on geotextile friction evaluation (Venkatappa Rao and Pandey, 1988) revealed that the pullout tests gave higher values of friction angle than that obtained from modified shear box tests. So the values of friction angle determined from modified shear box tests are to be used in the design of reinforced soil structures, though the values are conservative, but lead to a safe design. So in the present study, modified shear box tests are conducted as per the procedure given by Hussaini and Perry (1978) to determine the interfacial friction angles of moorum with synthetic woven geotextile under study. The test involved filling the upper half of shear box with fill material and lower half with wood to support reinforcing fabric so as to cause shearing between fill material and reinforcing fabric during testing. The shearing of the specimens is done in a manner similar to conventional box shear testing at different normal pressures. The strength envelopes are drawn and the interfacial shear parameters of clay subgrade and moorum are determined and are presented in Table 4.7 Table 4.7 Interfacial shear parameters of clay subgrades and moorum with woven Geotextiles. Material Interfacial Shear Parameters Geotextile/ Geogrid Adhesion (kn/m 2 Angle of Internal ) Friction Expansive Clay Woven Geotextile o Non Expansive Clay Woven Geotextile o Moorum Woven Geotextile 8 20 o Geogrid - 35 o Note: For geogrid, the interfacial friction angle with moorum is equal to the angle of internal friction. 52

8 4.7 EVALUATION OF MOORUM CUSHION TO SUPPRESS SWELLING OF EXPANSIVE CLAY Generally as the thickness of cushion material increases over expansive soil, its effectiveness to absorb the volume changes also increases. The swelling of underlying expansive soil on to the pavement structural layer thus depends mainly on the nature of cushion material. So, in the present work effectiveness of moorum proposed as sub base material over expansive soil for control of swell has been evaluated. Expansive soil is compacted in CBR mould up to different heights (0.5H, 0.6H, 0.67H, 0.75H and 0.8H) at a dry density of 1.55 g/cc and at a moisture content of 23.2%. The remaining volume is filled with the cushion material. Moorum was compacted under heavy compaction condition at water content of 8.2% and a dry density of 2.04 g/cc. The specimens are subjected to a surcharge of 5.0 kg and are soaked in water for a period of 96 hours and the swell is recorded. The values of the percent swell are calculated as the ratio of swell observed at the surface of specimens to the potential thickness of expansive soil. The percentage reduction in the value of percent swell with cushion materials has been determined in accordance with the percent swell value of expansive soil alone. The results of the tests are presented in Table 4.8.The reduction in percent swell of expansive soil with increase in thickness of the cushion material has been presented. The reduction of percent swell with increase in thickness of moorum cushion is shown in Fig.4.5. Table 4.8 Effect of Cushion Material on Swelling of Expansive Soil Pavement thickness option (cm) Moorum sub base Thickness (cm) Cushion to expansive soil ratio Percentage reduction of Swell

9 Figure 4.5 Reduction of percent swell with cushion to expansive clay ratio It may be seen from the results of the swell studies presented in Table 4.8 that the swell controlled by cushion material increases with increase in the cushion thickness. It may be noticed that percentage reduction in percent swell has been higher initially with increase of cushion thickness and later decreases. The better cushioning effect of moorum can be attributed to cohesion present in it in addition to frictional characteristics and dense packing of particles. 4.8 SUMMARY In the present chapter, the properties of clay subgrades chosen for study, moorum and aggregate proposed for use in pavement design and test tracks studies are presented. The properties of synthetic reinforcing materials namely woven geotextile and geogrid, determined from laboratory tests are presented. The results of interactive study of woven geotextile with soils under study are summarized. Also the swell suppressing ability of moorum cushions is discussed based on small scale laboratory studies. 54