Study on Open and Closed end Pile Foundation (Comparative Study in Open and Closed end Pile Foundation)

Study on Open and Closed end Pile Foundation (Comparative Study in Open and Closed end Pile Foundation)

Ravindra Kumar, Vinod Kumar Kumawat

Department of Civil Engineering Poornima University

Jaipur, India

AbstractThis Research paper is a live study on the above mentioned title Study on Open and Closed end Pile Foundation. Steel pipe piles are highly durable, provide reliable foundation, have shorter construction period and can be driven into such medium where other piles cant like boulder medium. Steel pipe piles are economical for long piles into deeps loose soil. Till now most of research has been directed towards the response of individual piles to vertical loads. Both the driving response and static bearing capacity of open-ended piles are affected by the soil plug that forms inside the pile during pile driving. In order to investigate the effect of the soil plug on the static and dynamic response of an open-ended pile and the load capacity of pipe piles in general, field pile load tests were performed on instrumented open- and closed-ended piles driven into sand. For the open-ended pile, the soil plug length was continuously measured during pile driving, allowing calculation of the incremental filling ratio for the pile.

Keywords Pile Foundation, pile cap, bearing capacity, pile group, pile load tests, piles driving.

1. INTRODUCTION

   Pile foundations have been used as load carrying and load transferring systems for many years. Pile foundations are the part of a structure used to carry and transfer the load of the structure to the bearing ground located at some depth below ground surface. The main components of the foundation are the pile cap and the piles. Pipe piles can be either open-ended or close-ended. It has been documented that the behavior of open-ended piles is different from that of closed-ended piles. At the earlier time, the capacity of pile groups was taken as equal to the sum of the capacities of the individual piles. However, in practice, when piles are placed close to each other, the stresses transmitted to the soil through neighboring piles will overlaps, resulting in a considerable change of the group capacity.

2. EASE OF USE

   It is known that a short open-ended pile has lower load capacity than an equivalent closed-ended pile. However, as pile length or penetration depth increases, the load capacity of the open ended pile approaches that of the equivalent closed- ended pile. This is due to the greater degree of soil plugging with larger penetration depth the settlement of an open-ended pile is greater than that of a closed-ended pile under the same load and soil conditions. However, the difference in load

   capacities varies within a wide range, depending on the degree of soil plugging during driving.

3. OBJECT

   There are a lot of studies and researches are done in past in same topic but further study was also necessary for better improvement. other research results Mc Cammon and Golder (1970), Lu (1985), Smith et al. (1986); Brucy et al. (1991) have shown that the mode of pile driving is an important factor in driving resistance. If a pile is driven in a fully coring or fully unplugged mode, soil enters the pile at the same rate as it advances. On the other hand, if a pile is driven under plugged or partially plugged conditions, a soil plug finally attaches itself to the inner surface of the pile, preventing additional soil from entering the pile.

4. MATERIALS AND METHODS

   The research work was divided into different headings as determination of index properties of loose sands, procurement of pile cap material, steel piles, sand etc, preparation of test model, testing of pile and pile groups and finally evaluation and comparison of test results.

   1. Materials

      • Sand: The sand used in the investigations has been collected from the banks of river Banas from a village near Tonk district of Rajasthan. The physical and engineering properties of Banas sand have been summarized in table below.

      • Steel pile: It is usually desirable from economical and practical considerations that the smallest model should be used. At the same time the model pile should be slender and also wide enough so that the effect of individual soil grains is negligible. The piles were used having 2 cm diameter and the total length of pile was 50 cm with an embedded length of 40 cm.

      • Mild steel plates: Mild Steel Plates can come in various sizes and grades. Thicknesses available range from 3mm up to as thick as 150mm. The plate used in making of pile caps is of 12 mm thickness which is cut according to the required dimension of pile caps.

        The spacing between the piles in each group was

        2.5 times of pile diameter. The size of pile cap varied according to the number of piles in a group. A minimum cover of approximately half the pile spacing

        was provided around the outer piles. The length of embedment of piles was kept as 40 cm in all the tests. Total thirteen tests were performed in which five circular groups were also tested. The details of the pile groups are shown in the Appendix A.

   2. Methods

      • Single Pile Testing: The single pile was driven into the sand. The proving ring was attached to the lower end of screw jack. Two dial gauges were fixed at the top of pile cap. These Batty dial gauges (least count

   0.01 mm and 25 mm travel) were supported on a cross angle sections through magnetic bases. The average of dial gauge readings was taken as the average settlement under a particular load. The load was applied in small increments. Load was maintained constant after an increment, till the settlement was constant. When there was no movement of dial gauge readings were recorded. Next increment was applied and the process was repeated till failure i.e. when the pile started setting rapidly. Graph below shows the load-settlement curve obtained from the Appendix B.

   • Pile Group Testing: The proving ring was attached to the screw jack. Two dial gauges were suitably mounted on the pile cap at opposite corners. It was checked by tapping that the dial gauges were securely fixed. The load is than applied at the centre of pile cap by turning the screw jack. After each increment, the load was maintained constant till the settlement was constant. After the settlement was complete, the next increment of load was applied and the process continued till the pile group started sinking. From the recorded readings of proving ring and dial gauges, the values of load settlement were computed. The load settlement curves obtained for various pile groups are shown in Appendix B.

   • Theoretical pile group Efficiency: The efficiency of

   • Experimental Pile Group Efficiency: The spacing of piles is usually predetermined by practical and economical considerations. The design of a pile foundation subjected to vertical loads consists of

   1. The determination of the ultimate load bearing capacity of the group Qgu.

   2. Determination of the settlement of the group, Sg, under an allowable load Qga.

5. RESULTS AND DISCUSSION

   The data obtained from tests on open end pile groups and closed end pile groups at various spacings is presented and interpreted in the following sections.

   Failure load: The load settlement plot obtained for the open ended and closed ended pile groups are shown below. A glance of this figure indicates that load settlement plot approaches almost vertical tangent when the pile start sinking rapidly. The load crresponding to rapid sinking of the pile is taken as the failure load of the pile. The failure loads for the pile groups have been obtained in the similar manner.

   Comparison of Experimental Failure Load with Other Theories: The ultimate bearing capacity (Qu) of piles in granular soils is given by the following formula:

   Qu = Ap (0.5 D Nr + PD Nq) + K PDi tan Asi Where

   Ap = Cross sectional Area of Pile toe in cm2 D = Stem diameter in cm

   = Effective unit weight of soil at pile toe in Kgf/cm3

   PD = Effective overburden pressure at pile toe in kgf/cm2

   Nr and Nq = Bearing capacity Factors depending upon the angle of internal friction at toe.

   pile groups were calculated by using the pile group

   efficiency equation. There are many pile group equations. These equations are to be used very

   =1

   summmation for n layers in which pile is

   installed

   cautiously, and may in many cases be no better than a good guess. The Converse-Labarre Formula is one of the most widely used group-efficiency equations which is expressed as

   = 1-(n-1)m+(m-1)n

   90 mn

   Where:

   = Group Efficiency m = number of rows

   n = numbers of columns = tan-1 (d/s)

   s = centre to centre spacing of Piles. d = Pile diameter

   K = coefficient of earth pressure

   PDi = effective overburden pressure in kg/cm2 for the ith layer where i varies 1 to n.

   = angle of wall friction between pile and soil, in degrees (may be taken equal to )

   Asi = surface area of pile stem in cm2 in the ith layer where i varies 1 to n.

   NOTE 1 Nr factor can be taken for general shear failure as per IS: 6403-1981*.

   NOTE 2 Nq factor will depend, apart from nature of soil on the type of pile and its method of construction, for bored piles, the value of Nq corresponding to angle of shearing resistance are given in Fig. 1. This is based on Berezantseus curve for D/B of 20 up to = 35° and Vesics curves beyond = 35°.

   NOTE 3 the earth pressure coefficient K depends on the nature of soil strata, type of pile and its method of construction. For bored piles in loose medium sands, K values between 1 and 3 should be used.

   NOTE 4 the angle of wall friction may be taken equal to angle of shear resistance of soil. NOTE 5 in working out pile capacities using static formula, for piles longer than 15 to 20 pile diameter, maximum effective overburden at the pile tip should correspond to pile length equal to 15 to 20 diameters.

   Property	Results
   Specific Gravity	2.39 – 2.55
   Bulk Relative Density, kg/m3 (lb/ft3)	2590 (160)
   Absorption, %	0.45
   Moisture Content, %	0.1 – 10.1
   Clay Lumps and Friable Particles	1 – 44
   Coefficient of Permeability (cm/sec)	10-3 – 10-6
   Plastic limit/plastic index	Nonplastic

   Property	Results
   Specific Gravity	2.39 – 2.55
   Bulk Relative Density, kg/m3 (lb/ft3)	2590 (160)
   Absorption, %	0.45
   Moisture Content, %	0.1 – 10.1
   Clay Lumps and Friable Particles	1 – 44
   Coefficient of Permeability (cm/sec)	10-3 – 10-6
   Plastic limit/plastic index	Nonplastic

6. FIGURES AND TABLES TABLE : 1 PROPERTIES OF BANAS SAND

   TABLE : 2 PLOT FOR BEARING CAPACITY FACTOR VS ANGLE OF INTERNAL FRACTION

   FIGURE : 1 COMPARISION OF SINGLE CLOSE AND OPEN ENDED PILE

   FIGURE : 2 PILE TEST ON SOIL STARTA FOR BEARING CAPACITY

   FIGURE : 3 LOAD TEST ON SINGLE PILE

7. CONCLUSION

   From the model tests carried out on vertical pile groups of rectangular, square and circular in loose sand following conclusion have been drawn:-

   1. The pile group load increases as number of piles in a group are increased.

   2. The efficiency of driven pile groups in sand is maximum in square group and lesser in rectangular group.

   3. The experimental efficiency of pile groups is more than the efficiency obtained by converse-Labarre formula.

   4. The efficiency obtained by the experiment in loose sand is more than 1.

   5. The ultimate bearing capacity of circular groups is more in comparison of other two groups.

   6. The experimental failure loads for pile groups are higher than the failure loads obtained using I.S code method.

8. FUTURE RECOMMENDATIONS

   • Necessary infrastructure should also be available for testing the quality of piles foundation.

   • Project developers need to be educated on on-site waste management plans.

   • Concerned authorities need to plan an awareness campaign, using the electronic and online media to promote the virtues Pile foundations.

   • The Scope of pile foundations of bridge work should be increased as possible as.

9. ACKNOWLEDGEMENT

   The authors are thankful to Poornima University, Jaipur for providing the resources that enabled us to carry out this study. The precious support was with us at every stage of this research. The authors feel highly obliged and have immense pleasure in expressing our heartfelt gratitude to Mr.Vivek Gupta for providing help during this research work.

10. REFERENCES

1. K. Paik; R. Salgado; J. Lee; and B. Kim, Behavior of Open- and Closed-Ended Piles Driven Into Sands.

2. Meyerhof, G.G., Compaction of sands & Bearing capacity of piles (1959). JSMFD, ASCE, 85, SM 6, 1-29.

3. IS: 1498 (1970), Indian Standard Methods of Test for Soils: Classification and Identification of Soil for General Engineering Purposes, Bureau of Indian Standards.