UPLIFT CAPACITY OF PILES SUBJECTED TO INCLINED LOAD IN TWO LAYERED SOIL. Dr. Sunil S. Pusadkar 1, Sachin Ghormode 2 ABSTRACT

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1 50 th IGC 50 th INDIAN GEOTECHNICAL CONFERENCE 17 th 19 th DECEMBER 2015, Pune, Maharashtra, India Venue: College of Engineering (Estd. 1854), Pune, India UPLIFT CAPACITY OF PILES SUBJECTED TO INCLINED LOAD IN TWO LAYERED SOIL Dr. Sunil S. Pusadkar 1, Sachin Ghormode 2 ABSTRACT Uplift forces act on the supporting piles if structures such as dry docks, basements, and pumping stations are constructed below the water table. Moreover, uplift forces may be exerted on piles due to swelling of the surrounding soils. Therefore, studying the behavior of piles under uplift forces as well as the parameters affecting the uplift capacity of piles is of most important. Chattopadhyay and Pise (1986) shows that the ultimate uplift capacity of inclined pile increases with increase in inclination of pile and decreases after reaching maximum value of α L at α=(15 to 22.5 ). Patra et al. (2004) carried out experimental investigations on the behaviour of model enlarged base piles, embedded in layered sand and homogeneous sand subjected to axial pulling loads and oblique pulling loads. The uplift capacity of the pile increases with increase in length, base enlargement. The ultimate uplift capacity was higher for medium dense over dense condition than dense over medium dense condition. The inclination at which the pile anchor offers maximum resistance to oblique pull depends on the embedment length to diameter ratio, L/d, base enlargement ratio, B/d, inclination of load and density of foundation medium. Bose and Krishnan (2009) found out net ultimate pullout capacity increases significantly with increase in length to diameter ratio. Pullout capacity also increases with increase in diameter. These studies show that an inclined pile behavior under inclined loading is lacking. The present work was focused on understanding the uplift capacity of vertical and inclined piles passing through two layered soil and subjected to the inclined loads. The study was carried out using finite element software MIDAS 3D. The foundation soil was modeled as an elasto-plastic material obeying the Mohr-Coulomb failure criterion. The parametric studies were performed by varying the angle of inclination of load (α), pile angle (θ), length of pile (L) and the soil layer which was weak over strong for the diameter (0.3m) of pile (D). The clay assumed to be resting on sand. The same soil model was used for all analysis for all parameters. The circular pile made up of concrete assumed to be linear elastic in nature was taken for the analysis. The uplift capacity of pile with inclined uplift load was observed that the uplift capacity of pile depends upon inclination of pile and load. The uplift capacity of pile varies with inclination of pile angle. The uplift capacity also varies with inclination of load. The uplift capacity increases with increase in length of pile. The uplift capacity decreases with increase in load inclination angle and then increases for 1 Dr. Sunil S. Pusadkar, Associate Professor, Department of Civil Engineering, Govt. College of Engineering, Amravati, India, ss_pusadkar@yahoo.co.in 2 Sachin Ghormode, PG Scholar, Department of Civil Engineering, Govt. College of Engineering, Amravati, India, sachinghormode24@gmail.com

2 Dr. Sunil S. Pusadkar & Sachin N. Ghormode batter angle of 5⁰ to 15⁰ and for batter angle 20⁰ to 30⁰, the uplift capacity linearly decreases. Fig. 1 shows that for vertical load the uplift capacity increases with increase in pile angle upto 15⁰ and then decreases. Fig. 2 shows that for vertical pile the uplift capacity increases with increase in load inclination angle upto 20⁰ and then decreases. It also shows that the uplift capacity increases with length of pile. Figure 1: Uplift capacity versus batter angle (θ) for D=0.3m Figure 2: Uplift capacity versus length of pile (L) for D=0.3m Keywords: Piles, Inclined Loads, Inclined Pile, Two Layer Soil, MIDAS 3D References 1. Chattopadhyay B.C. and Pise P.J. (1986): Uplift Capacity of Piles in Sand, Journal of Geotechnical Engineering, ASCE, Vol. 112, No. 9, pp Chattopadhyay B.C. and Pise P.J. (1986): Axial Uplift Capacity of Inclined Piles, Indian Geotechnical Journal, Vol.16, No. 3, pp Patra N.R., Deograthias M., and James M. (2004): Pullout Capacity of Anchor Piles, EJGE, Vol. 9, Bundle C. 4. Bose Kimi K. and Krishnan A. (2009): Pullout Capacity of Model Piles in Sand, Indian Geotechnical Society Chennai Chapter, 2009, pp

3 50 th IGC 50 th INDIAN GEOTECHNICAL CONFERENCE 17 th 19 th DECEMBER 2015, Pune, Maharashtra, India Venue: College of Engineering (Estd. 1854), Pune, India UPLIFT CAPACITY OF PILES SUBJECTED TO INCLINED LOAD IN TWO LAYERED SOIL Dr. S. S. Pusadkar, Associate Professor, Dept. of Civil Engineering, GCOE, Amravati, Sachin Ghormode 2, PG Scholar, Dept. of Civil Engineering, GCOE, Amravati, ABSTRACT: The present work was focused on understanding the uplift capacity of vertical and inclined piles passing through two layered soil and subjected to the inclined loads using MIDAS 3D. The foundation soil was modeled as an elasto-plastic material obeying the Mohr-Coulomb failure criterion. The pile was driven through a soil layer weak over strong. The uplift capacity of pile with inclined uplift load was observed that the uplift capacity of pile depends upon inclination of pile and load. The uplift capacity increases with increase in length of pile. The uplift capacity decreases with increase in load inclination angle and then increases for batter angle of 5 to 15⁰ and for batter angle 20 to 30⁰ the uplift capacity linearly decreases. INTRODUCTION Uplift forces acts on the piles if structure such as dry docks, basements and pumping stations are constructed below the water table. Additionally, transmission line towers, tall chimneys, submerged platforms, jetting structures, masts, and similar constructions on pile foundations are usually subjected to overturning moments due to wind effects, seismic events, wave actions or ship impacts. Uplift forces may be acts on piles due to swelling of the surrounding soils. Therefore, studying the behavior of piles under uplift forces as well as the parameters affecting the uplift capacity of piles is of most important. When the piles are inclined at an angle to the vertical they are called as batter piles. Batter piles are quite effective for taking inclined load. A number of investigations had been performed numerically as well as experimentally to determine the uplift capacity of piles. They used numerical methods such as limit equilibrium approach, curved failure surface, finite difference and finite element methods or conduct laboratory model experimental tests to study the uplift capacity of single pile and pile groups under compressive loads and pure uplift loads. Chattopadhyay and Pise [1] shows that the ultimate uplift capacity of pile increases with increase in pile inclination angle of 15º to 23º and after that it decreases. Patra et al. [2] carried out an experimental investigations on the behaviour of model enlarged base piles, embedded in layered sand and homogeneous sand subjected to axial pulling loads and oblique pulling loads. The uplift capacity of the pile increases with increase in length, base enlargement. The ultimate uplift capacity was higher for medium dense over dense condition than dense over medium dense condition. The inclination at which the pile anchor offers maximum resistance to oblique pull depends on the L/d, B/d, and inclination of load and density of foundation medium. Abdullah [3] carried out experimental study on uplift capacity of model piles under different percentages of compressive loads. It was observed that the percent of compressive loading was significant parameter influencing the net uplift capacity of the pile. Also the net uplift capacity decreases with the increase in the percent of compressive loading. Bose et al. [4] found out net ultimate uplift capacity increases significantly with increase in length to diameter ratio. Uplift capacity of also increases with increase in length of pile. Shankar et al. [5] used semi-empirical method of analysis based on the conventional limiting equilibrium approach for predicting the

4 Dr. Sunil S. Pusadkar & Sachin N. Ghormode uplift capacity of pile groups embedded in sand. Verma et al. [6] carried out experimental investigation of single piles, group of piles and enlarged based piles of different material. It was observed that G.I. Pipe resists higher amount of uplift load than concrete pile and PVC pipe pile. Chae et al. [7] carried out numerical simulation on uplift capacity of belled piles in weathered sandstone via finite element analysis (MIDAS GTS) in which experimental data was compared to FEA software. It was observed that, the shape and size of the bell influences the loaddisplacement behaviors of belled piles. Gaaver [8] carried out experimental model tests on single piles and pile groups embedded in cohesionless soil and subjected to pure uplift loading. It shows that at a particular upward displacement, the magnitude of the net uplift load of a single pile improves with an increase in the relative density of sand. Also it shows that the pile embedment depth has a major influence on the net uplift capacity of single piles The limited studies observed in the area of uplift capacity of vertical and inclined pile with inclined loading condition. Therefore, this paper attempts for detailed study of uplift capacity of vertical pile and inclined pile in two layer strata subjected to inclined uplift load for different lengths of pile. The present work provides results of vertical and inclined pile analyzes under different lengths for load displacement and uplift capacity under vertical and inclined uplift loads. PROBLEM DEFINITION The uplift capacity of vertical piles and inclined piles subjected to inclined load are determined by using MIDAS 3D which works on finite element approach. Two layer soils assumed to be made of clay resting on sand. The thickness of clay layer was assumed to be half the length of pile and thickness of sand layer was extended 5m below the bottom of pile from clay layer. The properties of clay and sand used in the MIDAS 3D analysis are shown in Table 1, while the pile properties are shown in Table 2. Table 1: Soil properties Sr. No Properties Clay Sand 1 Unsaturated unit weight (kn/m 3 ) Dry unit weight (kn/m 3 ) Cohesion (c) (kn/m 2 ) Poisson s ratio (ν) Young s modulus (E) (kn/m 2 ) Angle of internal friction (φ) 0º 35º 7 Material model 8 Type of material behavior Mohr Coulomb Undrained Mohr Coulomb Drained Table 2: Pile properties Sr. No Parameter Values 1 Young s modulus (E) (kn/m 2 ) 2x Dry unit weight (kn/m 3 ) 25 3 Poisson s ratio (ν) 0.15 The soil model, pile and load on pile are shown in Fig. 1. The soil model of size 15m X 15m was used in the analysis. Fig. 1 shows the inclined pile driven in sand and clay subjected to uplift inclined load. Fig. 1: Problem satement model The circular pile with 0.3m diameter was considered for the analysis. The other parameters such as length of pile, inclination of pile and loads are given in Table 3.

5 50 th IGC 50 th INDIAN GEOTECHNICAL CONFERENCE 17 th 19 th DECEMBER 2015, Pune, Maharashtra, India Venue: College of Engineering (Estd. 1854), Pune, India Table 3 : Parameters for study Case Parameters Remarks 1 Length of piles L = 5, 10, 15m 2 Inclination of pile 3 Inclination of load θ=0⁰, 5⁰, 10⁰, 15⁰, 20⁰, 25⁰, 30⁰ α=0⁰, 5⁰, 10⁰, 15⁰, 20⁰, 25⁰, 30⁰ ANALYSIS The analysis of pile in two layered soil mass was carried out using MIDAS 3D. The Mohr-Coulomb constitutive soil model was used for MIDAS 3D analysis. The pile was taken as beam structure made of concrete and assumed to be a linear elastic material. The analysis was carried out on weak over strong soil where upper soil layer was taken as half the length of pile. Fig. 2 shows the soil model, pile geometry model and mesh generated in MIDAS 3D software. The MIDAS is compatible with the MS-Excel. The extract result window and uplift capacity found from Load displacement curve are shown in Fig The same soil model was used for all analysis for all parameter studied. (a) (b) Fig. 2: Soil (a) and pile (b) geometry model Fig. 3: Extract result window Fig. 4 : Load displacement curve RESULTS AND DISCUSSION The analysis was carried out in MIDAS 3D using soil model and soil properties as discussed above for uplift capacity of pile subjected to inclined load in two layered soil. The results were plotted between uplift capacity obtained from load displacement curve and inclination of load with vertical (α) for different pile angle (θ) and also for uplift capacity versus batter angle (θ) for various lengths. Effect of Pile Inclination The effect of pile inclination (θ) on uplift capacity of pile are shown in Fig. 5 (a) to (g). For vertical load the uplift capacity increases with increase in pile inclination angle upto 15⁰ and then decreases (Fig 5a). For load inclination angle of 5⁰ to 15⁰ the uplift capacity decreases for certain pile inclination then increases or remains constant (Fig 5 b-d). However, for pile inclination 20⁰ - 30⁰ the uplift capacity continuously decreases (Fig 5 e-g).

6 Dr. Sunil S. Pusadkar & Sachin N. Ghormode (a) Load inclination (α) = 0º (d) Load inclination (α) =15º (b) Load inclination (α) = 5º (e) Load inclination (α) = 20º (c) Load inclination (α) = 10º (f) Load inclination (α) = 25º

7 50 th IGC 50 th INDIAN GEOTECHNICAL CONFERENCE 17 th 19 th DECEMBER 2015, Pune, Maharashtra, India Venue: College of Engineering (Estd. 1854), Pune, India capacity of vertical pile with vertical load to the vertical loaded pile. The uplift capacity of pile found to be increase with increase in length of pile, for any pile and load inclination. For pile inclination of 5º, uplift capacity increases with increase length for different load inclination. The maximum increase in the percentage variation is 40% and further increase in length may not cause much effect on uplift capacity. (g) Load inclination (α) = 30º Fig. 5: Uplift capacity for different pile inclination (θ) and load inclination (α) Effect of Length and Load Inclination Fig. 6 shows the uplift capacity for vertical pile. For vertical pile the maximum uplift capacity found at load inclination of 20º. The uplift capacity of vertical pile is reduces if load inclination is more than 20 o. Fig.6: Uplift capacity versus length of pile (L) for D=0.3m Fig. 7 shows variation in uplift capacity (% V Pu ) with respect to length of pile when pile driven in weak over strong soil. Percentage variation in uplift capacity is the ratio of difference between uplift capacity for specified case and uplift Fig. 7: Percentage variation in uplift capacity with length of pile CONCLUSIONS From the present investigation for uplift capacity of the inclined pile in two layer soils clay on sand layer, the following conclusions can be summarized: The uplift capacity of pile increases with increase in length For vertical pile the maximum uplift capacity is observed at 15º of load inclination and then it decreases. The uplift capacity varies with load inclination angle. The uplift capacity varies with inclination of pile. REFERENCES 1. Chattopadhyay B. C. and Pise P.J. (1986), Uplift capacity of piles in sand, J. Geotech. Engineering, ASCE, 112:

8 Dr. Sunil S. Pusadkar & Sachin N. Ghormode 2. Patra N. R., Deograthias M., and James M. (2004), Pullout capacity of anchor piles, EJGE, Vol. 05, pp Abdullah I. Al-Mhaidib (2009), Uplift capacity of model piles under different percentages of compressive loads, 2 nd International Conference on New Developments in Soil Mechanics and Geotechnical Engineering, May, Near East University, Nicosia, North Cyprus, pp Bose Kimi K. and Krishnan A. (2009), Pullout capacity of model piles in sand, IGS Chennai Chapter, Students Paper Competition, pp Shankar K., Basudhar P. K. and Patra N. R. (2009), Uplift capacity of pile groups embedded in sand, IGC, Guntur, INDIA, pp Verma A. K., Joshi Ronak (2010), Uplift load carrying capacity of piles in sand, Indian Geotechnical Conference, GEOtrendz December IGS Mumbai Chapter, IIT Bombay, pp Chae D., Cho W. and Hyung-Yoon Na (2012): Uplift capacity of belled pile in weathered sandstones, International Journal of Offshore and Polar Engineering (ISSN ) Vol. 22, No. 4, December, pp Gaaver Khaled E. (2013), Uplift capacity of single piles and pile groups embedded in cohesionless soil, Science Direct, J.AEJ, pp

PILE SOIL INTERACTION MOMENT AREA METHOD

Pile IGC Soil 2009, Interaction Moment Guntur, INDIA Area Method PILE SOIL INTERACTION MOMENT AREA METHOD D.M. Dewaikar Professor, Department of Civil Engineering, IIT Bombay, Mumbai 400 076, India. E-mail: