Effect of grain size, gradation and relative density on shear strength and dynamic cone penetration index of Mahi, Sabarmati and Vatrak Sand

Transcription

1 Discovery ANALYSIS The International Daily journal ISSN EISSN Discovery Publication. All Rights Reserved Effect of grain size, gradation and relative density on shear strength and dynamic cone penetration index of Mahi, Sabarmati and Vatrak Sand Publication History Received: 7 August 2015 Accepted: 13 September 2015 Published: 9 October 2015 Citation Mehul kumar P Katakiya, Ami D Parekh, Samir P Parmar. Effect of grain size, gradation and relative density on shear strength and dynamic cone penetration index of Mahi, Sabarmati and Vatrak Sand. Discovery, 2015, 40(185), Page356

2 EFFECT OF GRAIN SIZE, GRADATION AND RELATIVE DENSITY ON SHEAR STRENGTH AND DYNAMIC CONE PENETRATION INDEX OF MAHI, SABARMATI AND VATRAK SAND Mehul kumar P. Katakiya Dept. of Civil Engineering, Charutar University of Science and Technology, Anand, India. Ami D. Parekh Dept. of Civil Engineering, Dharmsinh Desai University, Nadiad, India. Samir P. Parmar Dept. of Civil Engineering, Dharmsinh Desai University, Nadiad, India. ABSTRACT:The present papermainly focus on behaviour of dynamic cone penetration resistance with respect to angle of internalfriction (dry and submerged conditions), various relative density (Rd) and different gradationof sand (C c & Cu) of cohesionless soils. The series of dynamic cone penetration test,relative density test, direct shear test and sieve analysis test carried out on Mahi sand,sabarmati sand and Vatrak sand. Results of dynamic cone penetration test (DCP Index) arecor related with respective relative density and values for each three poorly graded andthree well graded sand to understand dynamic penetration resistance behaviour with varyinggradation of sand. Keywords: Sand, Dynamic cone penetration test, direct shear test, Relative density, Gradation. 1 INTRODUCTION Sand is required for many purposes, for example, backfill of earth retaining structures, backfill in foundation trenches, reclamation of low lands and construction of road embankments etc. In all these situations good compaction of fill should be ensured to avoid future subsidence, failure of foundation and moreover liquefaction. Relative density is the most appropriate index to control the compaction of Sand. The term used to indicate the strength characteristics in a qualitative manner is relative density (D R ) which describes the state condition of cohesion-less soils. So, relative density is a very important index for a sandy soil. The density of granular soil varies with the shape and size of grains, the gradation and the manner in which the mass is compacted. Relative density is 0% for loosest condition of sand and 100% for densest condition of sand. Relative density of cohesion-less soil can be determined from IS: 2720 (Part 14) On the other hand, extensive information on the behavior of sandy soils has been obtained from laboratory tests on reconstituted and undisturbed samples. In these laboratory studies, the relative density (D R ) is commonly identified as a principal factor influencing the deformation and strength characteristics of sands. No any available soil compaction measuring devices provide direct readout of soil density values which is main parameter to control soil compaction performance. Most of these devices are strength or stiffness measuring devices which monitor the change of in-place engineering properties due to the application of impact or vibrating force on the soil. Their output, however, provide a measure of soil densification and they can be used satisfactorily in compaction control when they are calibrated to soil relative compaction and moisture content. In order to establish the relationship between the readings of these devices and soil relative compaction, there is a need to evaluate the sensitivity of the measured strength or stiffness parameters to the changes of soil types, and compaction efforts. Dynamic Cone Penetrometer (DCP) is one of those devices and is performed on sand of known relative densities in calibration chamber. The Dynamic Cone Penetration Test ( DCPT) is a simple ground investigation technique in which a solid penetrometer is driven into the ground and the number of blows required to drive it to a given depth is recorded. During the past decade, the DCP test has been correlated to many engineering properties such as the CBR, shear strength of granular materials, and most recently, the subgrade Resilient modulus (MR) Elastic Modulus (Es) and soil classification. 1.1 Experimental Setup It include laboratory investigations for dynamic cone penetration resistance as well as relative density. Page357

3 Figure 1 Dynamic Cone Penetrometer Where, 1 : Reading Edge 2 : Handle 3 : Top edge of lower shaft 4 : Upper shaft (d = 16 mm) 5 : Lower shaft (d = 16 mm) 6 : Bottom of measuring scale 7 : Hammer (8 kg. weight) 8 : Cone (d = 20 mm, 60 0 angle) 10 : Measuring scale All dimensions are in mm. Dynamic cone penetration tests were carried out in Plexiglas tank (60 cm 60 cm 75 cm) on three different poorly graded and three different well graded sand at different relative density of 30, 50, 65, 75 %. Dry sand has been filled in tank up to 70 cm height of tank. Whole 70 cm of height is divided into 14 different layers of 5 cm height. Uniformly distributed compactive efforts were applied at each layer of sand with tamping rammer (30 cm 30 cm 1 cm) of 9.5 kg weight to achieve required density. Desired depth of penetration is 60 cm. Dynamic cone penetration tests were performed according to ASTM D After assembling DCP, dynamic cone penetrometer is held vertically at center of the tank with one hand placed at the top of the handle. Set the instrument is such that the wildest part of the cone is flushing with the surface of the sand. In data sheet, record the current shaft reading as the starting point for blow number zero. With one hand placed on the top handle, use other hand to seat the cone by dropping the hammer from a partial height until the widest part of the cone is below the reference surface. Do not record penetration during the seating operation. Establish a reference for reading the penetration of the shaft after each blow. The reading edge is a reference level that must remain constant for accurate depth readings. On the data sheet,as shown in figure 1 record the current shaft reading as the starting point for blow number zero. Raise the hammer and let it fall freely on the anvil with height of fall 575 mm. Note down the shaft reading after each number of blow to the nearest of millimeter. Record the reading and blow count by reading the shaft to the nearest millimeter if using a metric scale. Record this as penetration for blow number 1. Operation is continued until the total penetration is less than 3 mm/blow for ten consecutive drops or 60 cm depth is reached. Page358

4 Cumulative No. of Blows Table 1 Sample sheet for DCPT Record Sheet Penetration Depth (mm) DCP Index (mm/blow) Relative density of sand samples were determined according to IS : 2720 (Part 14) RESULTS A graph of cumulative number of blow vs. depth is prepared. Some unreliable data up to top 30 cm depth is neglected due to lower confinement pressure at the top of sand deposit. Such kind of graph is shown in figure 2 below. No. of blows penetration depth (mm) y = 34.86x Figure 2 Depth of penetration vs. No of blow It is observed that cumulative number of blows increases linearly with depth. DCP Index was calculated from the average slope of the cumulative number of blow vs depth plot. DCP Index for the graph shown in figure is mm/blow. Dynamic cone penetration test has been performed on three different sand samples collected from different region of Gujarat viz. Mahi Sand, Vatrak Sand, Sabarmati Sand at different relative density of 30%, 50%, 65% and 75%. Three well graded sand samples were prepared by mixing different proportions of sand samples collected. Properties of sand samples collected (Poorly Graded Sand) and Well graded sand is shown in table below. Page359

5 Table 2 Properties of poorly& well graded sand Mahi Vatrak Sabarmati Combination Combination Combination Sand Sand Sand % G % C S % M S % F S % S & C D 60 (mm) D 30 (mm) D 10 (mm) Cu Cc Sp.Gty, G max (g/cc) e min min (g/cc) e max Composition of three well graded sample is given below. Combination 1 (250, 100, 50): This combination is having 250 kg. of Mahi Sand, 100 kg. of Vatrak Sand and 50 kg. of Sabarmati sand for 400 kg. mass of Sample. Combination 2 (137, 168, 95): This combination is having 137 kg. of Mahi Sand, 168 kg. of Vatrak Sand and 95 kg. of Sabarmati sand for 400 kg. mass of Sample. Combination 3 (180, 143, 77): This combination is having 180 kg. of Mahi Sand, 143 kg. of Vatrak Sand and 77 kg. of Sabarmati sand for 400 kg. mass of Sample. Results of DCP Index for each poorly graded samples are given in table 4 and table 5 below. Table 4 Values of DCP Index at Different Relative density for poorly graded sand Mahi Sand DCP Index (mm/blow) Vatrak Sand Sabarmati Sand Table 5 Values of DCP Index at Different Relativedensity for well graded sand Combination 1 DCP Index (mm/blow) Combination 2 Combination Page360

6 Results of Direct shear test for each well graded samples are given in table 6 and table 7 below. Table 6 Values of at Different Relativedensity for poorly graded sand Mahi Sand Vatrak Sand Sabarmati Sand (Dry) (Submerged) (Dry) (Submerged) (Dry) (Submerged) Table 7 Values of at Different Relativedensity for well graded sand Combination 1 Combination 2 Combination 3 (Dry) (Submerged) (Dry) (Submerged) (Dry) (Submerged) ANALYSIS DCPI-PHI for Poorly Graded Sand y = 56817e -0.17x R² = DCPI(mm/blow) y = 38849e -0.17x R² = y = 26020e -0.20x R² = y = 5E+07e -0.28x y = 31819e -0.21x R² = y = 2E+08e -0.31x R² = R² = Sabarmati Sand Dry PHI Vatrak Sand Dry Mahi Sand Dry Sabarmati Sand Submerged Vatrak Sand Submerged Mahi Sand Submerged 55 Figure 3 DCP Index vsphi for Poorly graded sand Correlation follow the equation DCPI = 5E+07e (R 2 =0.9923) for dry condition and DCPI = 2E+08e (R 2 =0.9864) for submerged condition for Mahi sand. Correlation follow the equation DCPI = e (R 2 =0.998) for dry condition and DCPI = e (R 2 =0.9902) for submerged condition for Vatrak sand. Correlation follow the equation DCPI = 56817e (R 2 =0.9403) for dry condition anddcpi = 39038e (R 2 =0.9648) for submerged condition for Sabarmati sand. Page361

7 DCPI combination 1 dry DCPI-PHI for Well Graded Sand y = 4E+06e -0.24x R² = y = 2E+06e -0.23x R² = y = 97106e -0.21x y = 4E+06e -0.26x R² = y = 2E+06e -0.24x R² = R² = PHI Combination 1 submerged combination 2 dry y = 97950e -0.21x R² = Combination 2 submerged combination 3 dry Combination 3 submerged Figure 4 DCP Index vsphi for Well graded sand Correlation follow the equation DCPI = e (R 2 =0.9397) for dry condition and DCPI = 4E+06e (R 2 =0.9389) for submerged condition for Combination 1. Correlation follow the equation DCPI = 4E+06e (R 2 =0.9854) for dry condition and DCPI = 2E+06e (R 2 =0.9692) for submerged condition for Combination 2. Correlation follow the equation DCPI = e (R 2 =0.9744) for dry condition anddcpi = 2E+06e (R 2 =0.9746) for submerged condition for Combination 3. 4 CONCLUSIONS DCP Index decrease exponentially with increase in value of (both dry and submerged) for each poorly graded sand as well as well graded sand. Decrement in values of DCP Index with increase in values in dry condition is almost similar to decrement in values of DCP Index with increase in values in submerged condition for any poorly as well as well graded sand. Values of DCP Index with respect to values (both dry and submerged) is depend upon particle size for poorly graded sand. Whereas, values of DCP Index with respect to values (both dry and submerged) is almost similar regardless to particle size for well graded sand. REFERENCES [1] American Society of Testing Materials (2003). Standard Test Method for Use of the Dynamic Cone Penetrometer in Shallow Pavement Applications, ASTM D , ASTM International, West Conshohocken, PA. [2] Apurvkumar Siya (2014). Analysis of Sand Gradation Effects on Relative Density, Department of Civil Engineering, National Institute of Technology, Roukela. [3] Farshad Amini (2003). Potential Applications Of Dynamic And Static Cone Penetrometers In Mn.DOT Pavement Design And Construction, Jackson State University, Mississippi. [4] Md. Jahangir Alam, Mohammad Shahadat Hossain and AbulKalam Azad (2012). Development of correlation between dynamic cone resistance and relative density of sand, Journal of Civil Engineering (IEB), 41 (2) (2013) [5] Zaki A. Baghdadi (1990). Fouad M. Ghazali and Ahmed M. Khan, Density Prediction Using a Static Cone Penetrometer, Journal of King Abdulaziz University, vol. 2, pp Page362