lateral load carrying capacity of model pile · pdf filelateral load carrying capacity of...

Lateral load carrying capacity of model pile groups.Karsan R. Hirani *

* (PG-structure student), B.V.M. Engineering college,Gujarat Technological University,

Vallabh Vidhayanagar, India.Email ID:*[email protected]

A. K. Verma#

# Professor and Head of structure engineering department,B.V.M. Engineering College, Gujarat Technological

University, Vallabh Vidhayanagar, India. Email ID: #[email protected]

Abstract— The pile group in loose to medium dense sand has found popular application world-wide. The behavior of batter pile group buried in sand and subjected to lateral loads is investigated. This paper is an attempt to examine the effect of batter angle of a pile group on its ultimate lateral load carrying capacity and load deflection behavior. The results are compared with vertical and batter pile group, and optimization for battered pile group is done.

KEY WORDS: Batter pile group, loose sand, ultimate lateral load carrying capacity, model test, batter angle.

I. INTRODUCTION

The quick growth of main offshore structures in the last two decades all over the world led to a rapid increase in the number of offshore structures even in unfavorable ground condition. The foundation of offshore structures on such unfavorable subground presents a challenge for both geotechnical and structural engineers.

Pile foundations are generally preferred when heavy structure loads have to be transferred through weak subsoil to hard strata. These foundations in some situations are subjected to significant amount of lateral loads besides vertical loads. Lateral forces may be due to impact of ships during berthing and wave action in the case of off shore structures. Piles are commonly used to support bridge structures, tall buildings, and transmission line towers. Towers and offshore structures are usually subjected to overturning moments due to wind, wave pressure and ship impact. These overturning moments transferred to the foundation of the structure in the form of horizontal and vertical loads. The type of foundation usually recommended for such loading conditions is combination of vertical and batter piles. In practice piles are used in groups and are connected by a cap at the pile heads. The spacing between the piles, arrangement of piles, their batter, and direction of load has an important role in the assessment of load deformation behavior of pile groups under lateral loads.

When the piles are inclined at an angle to the vertical they are called as batter piles. Batter piles are quite effective for taking lateral load. The usual assumption in design of a batter pile is that the pile is capable of resisting the same axial load as a vertical pile of the same type and size and driven to same stratum.

LITERATURE REVIEW

Ultimate lateral Resistance of Piles GroupsThe behavior of laterally loaded pile groups has

generally analyzed using the concept of subgrade modulus or considering the soil as an elastic continuum. Meyerhof and Yalcin (1992) investigated behavior of single free headed model flexible vertical and batter pile under central inclined loads in two layered soil. The ultimate capacity of pile is found to depend on the layered soil, load displacement of flexible batter piles are presented on the basis of resultant influence factors that are related to better angle, load inclination, and distribution of soil modulus with depth. Patra and Pise (2001) have investigated load-displacement response, ultimate resistance and group efficiency with proposed to predict the ultimate lateral capacity of single pile & pile groups. Zang, et al(2005) developed a method for determination of ultimate soil resistance to piles including frontal side resistance and side shear resistance in cohesionless soil.

Load-Deflection behavior of Piles and Piles GroupsStudies on deflection of single better piles and pile

groups are reported by Murthy (1965). He investigated the behavior of model instrumented piles subjected to horizontal load. He has developed non dimensional solution for the case of lateral loads acting at ground level for better piles. Ooi and Duncan (1994) presented a simple method for estimating pile group deflection and maximum bending moments based on the theories of Poulos (1971) and Focht and Koch (1973). Lateral deflection and maximum bending moment are calculated using the group amplification procedure. Juvekar and pise (2008) developed a group amplification factor group efficiency of battered pile subjected to lateral loading.

II. SCOPE OF STUDY

Laboratory model tests on batter pile group (3×1) have been carried out in uniform sand under horizontal loads. The qualitative and quantitative influence of parameters such as configuration of the pile group, batter angle, and direction of loading on ultimate horizontal resistance and difference between vertical and batter pile group.

National Conference on Recent Trends in Engineering & Technology

13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India

III. EXPERIMENTAL SET UP AND TESTING PROGRAMME

A. FoundationDry local river sand was used as foundation medium in

modal tank of size 650mm x 600mm x 700mm deep. The specific gravity and uniformity coefficient of sand were 2.59 and 3.5 respectively. The placement density of sand during testing was 1.60 g/cc, corresponding to relative density of 39.03% and angle of shearing resistance Ф was 36°.

B. Model PilesStainless steel pipe piles of 32.3mm outer diameter and

1.65mm wall thickness were used as a model piles. The embedment length-to-diameter ratio of vertical pile was 10. The pile flexibility factor, Krs is expressed as Krs = EpIp / nh (L5) (Poulos and Davis, 1980). Where, Ep = modulus of elasticity of pile, Ip = moment of inertia of pile. EpIP of the pile was 3742 x103 kg-cm2. Length of pile, L was 323mm. Coefficient of horizontal subgrade reaction, nh, was 0.21 kg/cm3 [Terzaghi. (1955) for medium dense sand]. Krs of the test pile was found to be 0.506 kg/cm. It indicates that the test piles were rigid piles.

The relative stiffness factor. T = [Eplp / nh]^1/5: T = 28.19cm L/T of the pile was 1.145 < 2; and so the piles were short and rigid.

C. Loading PlateLoading plate is used for applying horizontal load and

to measure pile head displacement. Length of the loading plate was 380mm and width 80mm. On the loading side one hole is drilled at the center of loading plate to attach wire rope which passes over frictionless pulley for applying horizontal load.

D. Angle Fixing PlatesTo make optimization in fabrication for experimental

programme one types of angle fixing vertical plates were fabricated to change the batter angle between -100 to +30° for the piles. Figure1 show angle fixing plates and its arrangement.

Fig.1 Angle Fixing Plate

E. Model TestsModel test were carried out on 3-pile groups

configuration (3x1). Spacing between piles was 3d. The piles and pile groups were subjected to horizontal load which was applied at the center of loading plate through wire rope passing over frictionless pulley as shown in Figure 2. The tests were carried out in medium sand (R.D. = 39.03%). Table 1 shows the testing programme.

Table 1 Testing programme.

Test Batter angle in dig No. of test (0, 0,0) 1

(-10, 0,+10), (-20,0,+ 20), (-30,0,+ 30)

3

(0,0, +10),(0, 0,+20), (0, 0,+30)

3

(-10, 0,0), (-20, 0,0), (-30,0, 0)

3

F. Experimental ProcedureThe schematic diagram of test set-up, loading

arrangement and model pile group with loading plate is shown in Figure 2.

Loading plates of stainless steel were fabricated for pilegroups (3 x 1) for spacing 3d. After placing the piles with the loading plate and angle fixing plates in the tank, sand was poured in the tank through sand raining technique the height of fall 400 mm similar to Patra and Pise (2001).

The horizontal load was applied to the loading plate through a pulley arrangement with flexible wire attached to the plate. The other end was attached to the loading pan. The loads were applied by dead weight over the loading pan starting from smallest with gradual increase in stages to get the load-deflection response. Mechanical magnetic base dial gauges having sensitivity of 0.01 mm were used for measuring horizontal displacement.

1. Loading Plate2. Angle Fixing Plate3. Dial Gauge4. Model Test Pile Group5. Pulley6. Non Extensive Wire Rope7. Loading pan

Fig.2 Model Testing Tank and Loading Arrangement.



IV. TEST RESULT

Horizontal load / Horizontal displacement diagrams.The basic observations from the tests were applied

horizontal loads and corresponding horizontal displacement and also plotted graph for each pile groups. Typical diagrams of horizontal load vs. horizontal displacement in medium dense sand are shown in fig.3 to 5.

Fig. 3 Comparison between vertical pile group and various batter pile groups (00,00,00)(-100,00,+100)(-200,00,+200)

Fig. 4 Comparison between vertical pile group and various batter pile groups (00,00,00)(00,00,+200)(00,00,+300)

Fig. 5 Comparison between vertical pile group and various batter pile groups (00,00,00)(-200,00,00)(-300,00,00)

COMPARISON OF RESULTS

The results are compared with Vertical pile group and batter pile group. Finding out ultimate lateral load corresponding to 6mm horizontal displacement from the graph.

V. CONCLUSONThe following conclusion is drawn from the present

study:The horizontal load – horizontal displacement curves

are practically non-linear.Batter pile groups (00, 00, +100) to (00, 00, +300) and

(-100, 00, +100) to (-300, 00, +300) offer 40-55% more resistance as compared to vertical pile group.

Batter pile groups (00, 00, -100) to (00, 00, -300) offer 10-15% more resistance as compared to vertical pile group. This is similar to vertical pile groups.

REFERANCES

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[2] Meyerhof, G. G. and Yalçin, A. S. “Bearing capacity of flexible batter piles under eccentric and inclined loads in layered soils”., Canadian Geotechnical Journal, Vol.30, No.2, pp. 583-590, 1994.

[3] Brown, D.A., Reese, L.C. “Lateral load behavior of pile group in sand,” Journal of Geotechnical Engineering, ASCE, Vol. 114, No. 11, pp. 1261-1276, 1988.

[4] Meimon, Y., Baguelin, F. and Jezequel, J.F., “Pile group behavior under long time lateral monotonic and cyclic loading,” Proceedings, Third International Conference on Numerical Methods on Offshore Piling, Inst. Francais du Petrole, Nantes, France, pp. 285-302, 1986.

[5] Brown D.A., Reese L.C., and O’Neill M.W., “Cyclic lateral loading of a large-scale pile group,” Journal of Geotechnical Engineering, ASCE, Vol. 103, No. 11, pp. 1326-1343, 1987.

[6] Sastry Vankamamidi, “Behaviour of Flexible Batter”. ICCES, vol.4, no.3, pp.167-170, 2007Madav Sanatkmar juvekar and probhakar jagannath pise “Behavior of rigid batter piles and pile groups subjected to horizontal load in sand”. Indian geotechnical journal 38(2), 2008, 221-242.

[7] Meyerhof, G.G. and Valsankar, A.J.: “Lateral resistance and deflection of rigid walls and piles in layered soils.” Can. Geotechnical Journal., Ottawa, 18(2), pp159-170, 1981.

[8] Mayerhof, G.G., and Yalcin A.S.: “Behaviour of flexible batter piles under inclined load in layered soil.” Can. Geotechnical journal, 30, pp 247-256, 1992.



[9] Prasad, Y.V.S.N. and Chari, T.R.: “lateral capacity of model rigid piles in cohesionless soils.” Soils and found. 39(2), pp 21-29, 1999.

[10] Awoshika, K., and Reese, L.C., "Analysis of Foundations with Widely Spaced Batter Piles," Research Report 117-3F, Project 3-5-68-117, Center Highway Research, University of Texas at Austin, February 1971.

[11] G.G.Meyerhof and Gopal Ranjan “The Bearing capacity of rigid piles under inclined loads in sand, Batter piles”. UWEX-mandison, Wisconsin, oct.8-8, 1972

[12] M.T.Liang and Y.Liu. “Analysis of three dimensional pile group” Journal of marine science and technology, vol-2, no-1, pp.47-52, 1994.

[13] V.V. R. N Sastry, T.Koumoto and F.J.Monoppo. “Bearing capacity and bending moment of flexible batter piles in homogeneous soil under horizontal loads”. Bul, fac. Agr. Saga univ. 79, 77-85, 1995.

[14] S. C. Mandavkar and P. J. Pise “Discussion on paper studies on skin friction in piles under tensile and compressive load”. IGJ, vol-34, no.3 July 2004, p.p (276-289).

[15] Ooi, P.S.K, and Dukan M.J, “Lateral load analysis of group of piles and drilled shafts”. Journal of geotechnical engg. ASCE, 120(6), 1994.

[16] Pise, P.J, “laterally loaded piles in a layered soil system”. International journal, 1(3), .1981.

[17] Sun, K. “laterally loaded pile in elastic media”. Journal of geotechnical engg. ASCE, 120(8), 1994.

[18] Lawrence B. Feagin “Lateral load test on groups of battered and vertical piles”. American society for testing material. ASTM special technical publication no.154.

[19] J. H. Lee and R. Salgado, “determination of pile base resistance in sands”. journal of geotechnical and geoenvironmental engineering / august 1999

[20] R. L. Mokwa, “mechanics of pile cap and pile group behavior”[21] Harun Kürsat Engin, “An experimental study of vertical and inclined

soil nails under footings as settlement reducers”, thesis, Middle East technical university, 2005.

[22] R. Ziaie Moayed, A. Judi and B. Khadem Rabe., “Lateral Bearing Capacity of Piles in Cohesive Soils Based on Soils' Failure Strength Control”.EJGE vol.13, Bund. D, 2008.

[23] M. J. Gajjar, A. K. Verma “Lateral load capacity of piles” Thesis, S. P. University, 2010



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