Indian Geotechnical Conference (December 18-20, 2003) s12

Behaviour of Laterally Loaded Piles in Layered Soil Deposits IGC 2009, Guntur, INDIA

BEHAVIOUR OF LATERALLY LOADED PILES IN LAYERED SOIL DEPOSITS

J. Sherin Nisha P.G Student, Division of Soil Mechanics and Foundation Engineering, Department of Civil Engineering, Anna University Chennai, Chennai–600 025, India. E-mail: [email protected] M. Muttharam Assistant Professor, Division of Soil Mechanics and Foundation Engineering, Department of Civil Engineering, Anna University Chennai, Chennai–600 025, India. E-mail: [email protected]

ABSTRACT: A model pile of diameter 19 mm was used to find the lateral capacity of pile with L/D ratios of 12, 18 and 24 embedded in clay bed of consistencies 0.2, 0.35 and 0.5 underlain by sand layer of relative density 60% by varying the thickness of clay bed to 0.25, 0.5 and 0.75 times the length of pile. Further, tests for lateral capacity are performed with uniform clay layer thickness of 0.25, 0.5 and 0.75 times the length of pile equal to 18D = 342 mm. Experimental results of pile subjected to lateral load showed that the ultimate lateral load of pile increases almost linearly with increase in consistency and embedded length of the pile in layered soil. For L/D ratio12, the ultimate lateral load of pile for uniform clay layer thickness is less than the ultimate lateral load of pile for varying clay layer thickness and for L/D ratio 24, the ultimate lateral load of pile for uniform clay layer thickness increases. However, the lateral load capacity increases with increase in L/D ratios of pile, consistency of clay bed and decrease in clay layer thickness.

1. INTRODUCTION consistency of clay bed, L/D ratio of pile and relative thickness of clay to sand bed. Laterally loaded piles are commonly used in engineering practice. Many structures, such as some bridges and other transportation structures, oil production platforms, 2. MATERIALS transmission towers, high-rise buildings, earth retaining In coastal areas the top soil is of soft clay in nature and this structures, quays, wharfs and jetties transfer lateral loads to can be laid over sandy stratum. River Sand collected from the ground. Wind gusts are the most common cause of lateral locally available area was used in all the experiments. Clay loads that a pile must support. Wind loads are important for sample collected from Siruseri, Chennai, India was used in tall buildings and transmission towers. Lateral loads are also all the experiments. An open pit was dug at the site and the caused by seismic activity. Horizontal ground shaking during bulk of clay soil samples were collected at a depth of 2 m. earthquakes generates lateral forces that piles must This soil was air dried, powered and passed through required withstand. In the case of bridge abutments and piers, IS sieve to carry out respective experiments. A steel circular horizontal forces are caused due to traffic and wind tank of diameter 400 mm and height 500 mm was used to movement. Dams and lock structures have to withstand water prepare the layered soil bed for conducting experiments. pressures that transfer as horizontal forces to the supporting Hollow aluminum piles with an outer diameter of 19 mm and piles (Indian department of transportation 2007). Analysis thickness of 1mm plugged at both ends was used. The length relating to behavior of piles under lateral loads forms an to diameter ratio L/D of the piles of 12, 18, and 24 were important aspect in the design of piles (Basu & Salgado selected to study the behaviour of laterally loaded piles. In 2007). The design of the laterally loaded pile is mainly the present study, piles with L/D = 12 is classified as short, governed by the property of the soil present at the proximity piles with L/D = 18 as intermediate and piles with L/D = 24 of top of the pile. In many situations the pile terminated at as long flexible pile as per the recommendations of Terzaghi strong sandy stratum can be overlain by soft clay stratum. (1955). Uniformly graded clean river sand was used for Therefore it is essential to study the performance of lateral conducting the experiments. To characterize the soil, tests for load carrying capacity of piles founded in layered soil for the index properties are conducted as per BIS procedure. The safe and economical design of pile foundation. In this paper, grain size distribution obtained from sieve analysis as per IS: attempts are made to understand the behavior of laterally 2720 part IV (1970) is presented. The sand composed of 20% loaded piles founded in a layered deposit i.e., clay layer coarse sand, 66% medium sand and 14% fine sand. As per underlain by sand for varying various parameters such as the Indian soil classification system the sand is classified as poorly graded sand (SP). The index properties of the soil are

193 Behaviour of Laterally Loaded Piles in Layered Soil Deposits presented. The soil is composed of 6% fine sand, 18% silt Table 1: Ultimate Lateral Load of Piles with Varying Clay and 76% clay. The liquid limit of the soil is 86%, plastic Layer Thickness limit is 29% and plasticity index is 57%. As per the Indian Thickness Consistency Ultimate lateral load (N) soil classification system the soil is classified as high of clay I C L/D = 12 L/D =18 L/D = 24 plasticity clay (CH). layer 0.2 96.21 124 141 3. METHODS 0.25L 0.35 127.16 148.98 159.57 0.5 155.24 174.52 190 In the analysis of laterally loaded piles, the main parameters involved are ultimate lateral capacity and lateral 0.2 41.22 60.45 76.98 displacement. Lateral capacity has to be obtained 0.5L 0.35 63.27 71.51 88.87 corresponding to a certain level of deflection from load 0.5 82.60 88.09 110.04 deflection curves. Ultimate lateral load capacity governs the 0.2 10.94 18 25.02 behavior of short and rigid piles. Ultimate capacity of a 0.75L 0.35 16.58 26.46 36.34 laterally loaded pile is usually fixed based on same deflection 0.5 22.23 33.52 46.22 criteria. The two widely used criterions are suggested by Broms (1964) and Meyerhof (1980). As per Broms (1964), 3.2 Experimental Procedure ultimate capacity is taken as the load corresponding to a The schematic representation for laterally loaded pile in deflection equal to 20% of the diameter of the pile. As per layered soil deposits with relative thickness of clay to sand Meyerhof (1980), ultimate lateral capacity is that one at bed of 0.25, 0.5 and 0.75 times length of the pile. Experiments which the portion of load-deflection curve becomes straight. were conducted with consistencies of 0.2, 0.35 and 0.5. The The criterion suggested by Meyerhof has been used in the required quantity of air dried clayey soil is blended with present investigation. For laterally loaded piles, Broms water content corresponding to the above mentioned (1965) developed a simplified solution based on the consistencies. After conditioning the required quantity of soil assumptions of i) shear failure in soil, which is the case for it is kept for two days before it is placed in the test tank. short piles and ii) bending of pile governed by plastic yield Enough care has been taken to control the moisture at the resistance of the pile section, which is applicable to long desired consistency and density in all the cases. The sand piles. Piles may be treated as rigid if the soil mass layer is filled from the bottom of the tank and compacted surrounding the pile fails in shear and rotation of pile occurs using vibrator to the desired height and the conditioned under lateral loads. On the other hand, when the surrounding clayey soil is then filled in the tank in layers from the bottom soil is relatively stiff and the piles are long and slender, there of the tank up to the desired elevation by adopting kneading is a possibility of bending of pile prior to the shear failure in compaction technique. The pile is then placed vertically in soil and in such cases piles are referred as flexible. This position and preparation of layer is continued up to the top aspect is further explained using some non-dimensional level of the tank. To facilitate lateral loading, pile was terms as suggested by earlier researchers (Broms in 1964, connected to loading frame using high-tension wire. The Matlock & Reese in 1956, Poulos & Davis in1980). displacement at pile head was measured using dial gauge. After placing the pile in position, it was loaded laterally at 3.1 Experimental Programme load increment of 5.5N for clay layer thickness of 0.25L and 0.5L and a load increment of 1.4N for clay layer thickness of The prime objective of this investigation is to determine the 0.75L. The displacement at the top of the pile for each load behaviour of laterally loaded pile in layered soil. The effect increment was noted at pre- determined time intervals (i.e for of consistency of clay, L/D ratio of pile and relative 15 minutes). From the values obtained load deflection curve thickness of clay to sand bed are the main variable is drawn and the procedure is continued for different parameters in this study. Tests are performed on piles of L/D parameters to determine the behaviour of pile in layered soil. ratios of 12, 18 and 24 embedded in clay bed of consistency 0.2, 0.35 and 0.5 underlain by sand layer of relative density 4. RESULTS AND DISCUSSIONS 60% by varying the thickness of clay bed to 0.25, 0.5 and 0.75 times length of the pile. Further, the performance on The shape of lateral load versus displacement curve is piles of L/D ratios of 12, 18 and 24 are tested for their lateral generally convex upward initially followed by gradual capacity embedded in clay bed of consistency 0.2, 0.35 and increases in load with displacement for single pile. 0.5 underlain by sand layer of relative density 60% by uniform clay layer thickness of 0.25, 0.5 and 0.75 times 4.1 Lateral Load versus Displacement Behavior of Pile length of the pile equal to 18D = 342 mm. Table 1 shows the Embedded in Clay Bed of Thickness 0.25L Followed various experimental programme conducted in the present by Sand Layer study. Figure 1 shows the lateral load versus displacement relationship for a single pile of L/D ratio 12 embedded in sand bed of relative density 60% and clay bed of various

194 Behaviour of Laterally Loaded Piles in Layered Soil Deposits consistencies 0.2, 0.35 and 0.5 with clay layer thickness By analysing the data presented in Table 1 it can be inferred equal to 0.25 times length of the pile.The shape of lateral that, though the lateral load carrying capacity of piles load versus displacement curve is generally convex upward increases with increase in length of pile and consistency of initially followed by gradual increases in load with clay bed, the rate of increase in ultimate capacity decreases displacement for single pile. Similar trend of behaviour was as the thickness of clay layer increases. When the lateral load obtained for pile of L/D ratios 18 and 24 as shown in Figure is applied to the pile, the soil infront of the pile towards the 2 and Figure 3 respectively. direction of deflection gets compressed and is in the passive state. The lateral capacity mainly depends on the plastic resistance developed and this in turn depends upon the type of soil. For the clayey soil the passive resistance developed is much lesser than that of the same in sandy soil. As the thickness of clay layer increases, the thickness of sandy stratum in contact with the pile is reduced. This leads to the reduction in the lateral load capacity.

4.3 Comparison of Lateral Load Capacity of Piles of Various Consistencies for Various L/D Ratios with Uniform Clay Bed Thickness Figure 3 shows that lateral load versus displacement at the Fig. 1: Variation of Lateral Load and Displacement at Pile pile head for 0.2, 0.35 and 0.5 consistencies with 0.25L clay Head for Pile with L/D = 12, Dr = 60%, Clay Layer layer thickness. Thickness = 0.25L

4.2 Ultimate Lateral Load for Clay Layer of Thickness 0.5L (D = 19 mm, L = 18D = 342 mm)

In Figure 2 the variation of ultimate lateral load with the ) N ( consistency of clay bed is plotted for pile with L/D ratios of d a

12,18 and 24. For the pile of L/D ratio 12 embedded in clay o L bed of consistencies 0.35 and 0.5 the ultimate capacity is l a r e

respectively 1.53 and 2.00 times the ultimate capacity at t a consistency of 0.2. For the pile of L/D ratio 18 embedded in L clay bed of consistencies at 0.35 and 0.5 the ultimate capacity is respectively 1.18 and 1.45 times the ultimate capacity at consistency of 0.2. For the pile of L/D ratio 24 embedded in clay bed of consistencies 0.35 and 0.5 the ultimate capacity is respectively 1.08 and 1.21 times the ultimate capacity at consistency of 0.2. Displacement at pile head (mm)

Fig. 3: Comparison of Load versus Displacement Response of 0.2 Consistency with 0.25L (L = 18D = 342 mm) Clay Layer Thickness for Different L/D Ratios

4.4 Ultimate Lateral Load for Different L/D Ratios of Piles The ultimate lateral load capacity of pile increases with increase in L/D ratio of piles for all the cases. The rate of increase in ultimate lateral load capacity is nearly linear for single pile with increase in length of pile. Comparison of Fig. 2: Variation of Ultimate Lateral Load with the ultimate lateral load for different L/D ratios of piles and Consistency for Clay Layer Thickness = 0.5L consistencies for constant clay layer thickness is as shown in (L = 18D = 342 mm) Figure 4. The ultimate lateral load capacity of piles with uniform clay layer thickness is tabulated in Table 2.

195 Behaviour of Laterally Loaded Piles in Layered Soil Deposits linearly with increase in consistency and embedded length of the pile in layered soil.  For L/D ratio 12, the ultimate lateral load of pile for varying length founded in clay bed of uniform thickness decreases for clay layer thickness equal to 0.25L, 0.5L and0.75L. The lateral loaded piles showed that as the clay layer thickness increases the ultimate lateral load decreases.  For L/D ratio 18, the ultimate lateral load of pile for varying length founded in clay bed of uniform thickness and in clay bed of varying thickness remains constant for clay layer thickness equal to 0.25L, 0.5L and 0.75L since the clay layer thickness is uniform for both cases.  For L/D ratio 24, the ultimate lateral load of pile for varying length founded in clay bed of uniform thickness increases for clay layer thickness equal to 0.25L, 0.5L Fig. 4: Comparison of Ultimate Lateral Load for Different and 0.75L. L/D Ratios of Piles and Consistencies for Constant 0.25L  From the results it is inferred that, lateral loaded capacity (L = 18D = 342 mm) Clay Layer Thickness increase with increase in L/D ratios, consistency of clay bed and decrease in clay layer thickness. Table 2: Ultimate Lateral Load of Piles with Uniform Clay Layer Thickness REFERENCES Thickness Consistency Ultimate lateral load (N) Alem, A. and Benamar, A. (2002). “Graphs for the Design of of clay I C Laterally Loaded Piles in Clay”, Electronic Journal of layer L/D= L/D =18 L/D= 24 Geotechnical Engineering, 7B, 2002. 12 Ashour, M., Pilling, P. and Noriss, G. (2004). “Lateral 0.25L 0.2 64.40 124 254.58 Behavior of Pile Groups in Layered Soils”, Journal of (L=18D) 0.35 78.80 148.98 275.67 Geotechnical and Geoenvironmental Engineering, ASCE, 0.5 109.85 174.52 301.69 Vol.130 (6), pp. 580–592. 0.5L 0.2 35.59 60.45 157.51 Basu, D. and Salgado, R. (2007). “Elastic Analysis of (L=18D) 0.35 50.08 71.51 171.36 Laterally Loaded Pile in Multi-layered Soil”, Journal of 0.5 70.14 88.09 190.72 Geotechnical and Geoenvironmental Engineering, ASCE, 0.75L 0.2 8.35 18 88.21 Vol. 2 (3), pp. 183–196. (L=18D) 0.35 13.76 26.46 99.23 Charles, W.W. Ng, Limin Zhang and Dora, C.N. (2001). 0.5 20.82 33.52 110.10 “Response of Laterally Loaded Large-Diameter Bored Pile Groups”, Journal of Geotechnical and The data presented in Table 2 brings out that for the uniform Geoenvironmental Engineering, ASCE, Vol. 127 (8), thickness of clay layer, the ultimate load carrying capacity pp. 658–669. again increases with increase in length of the pile and Davisson, M.T. and Gill, H.L. (1963). “Laterally Loaded Pile consistency of clay bed. It is also observed that the thickness in Layered Soil System”, Journal of Soil Mech. and of clay layer plays major role in governing the lateral Foundation Engg. ASCE, Vol. 89 (3), pp. 63–94. capacity of pile compared to the other parameters like consistency and length of the pile. The increase in lateral George Mylonakis and George Gazetas (1999). “Lateral capacity with increase in pile length for the constant Vibration and Internal Forces of Grouped Piles in Layered thickness of clay bed is attributed to the fact that as the Soil”, Journal of Geotechnical and Geoenvironmental remaining length of the pile beyond the clay layer is founded Engineering, ASCE, Vol. 125 (1), pp. 16–25. in sand layer which offer higher passive resistance against Muttharam, M. and Ilamparuthi, K. (2005). “Lateral Load lateral pull thus lead to the higher lateral pile capacity. Behavior of Pile and Pile Groups Founded in Soft Clay”, Indian Geotechnical Conference, pp. 19–22. 5. CONCLUSIONS Zhang, L. Ernst, H. and Einstein, H.H. (2000). “Nonlinear Analysis of Laterally Loaded Rock-Socketed Shafts”, The following conclusions may be drawn from this study, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 126 (11), pp. 955–968.  Experimental results of pile subjected to lateral load, showed that the ultimate lateral load increases almost