Microsoft Word 223 Ph?m THanh Tùng doc Tuyển tập Hội nghị Khoa học thường niên năm 2019 ISBN 978 604 82 2981 8 122 BEHAVIOR OF PILE UNDER PUSH AND PULL FORCE USING SMALL SCALE MODEL Phạm Thanh Tùng1,[.]
Tuyển tập Hội nghị Khoa học thường niên năm 2019 ISBN: 978-604-82-2981-8 BEHAVIOR OF PILE UNDER PUSH AND PULL FORCE USING SMALL SCALE MODEL Phạm Thanh Tùng1, Masato Saitoh2 Thuyloi university, email: tung.kcct@tlu.edu.vn Saitama University INTRODUCTION The application of deep pile foundation is highly recommended in many designs of high rise building Such types of pile foundation are well known for tensile resistance and compressive resistance due to the impact of variety type of loading such as earthquake and wind loads Since then, many researchers have focused on the research on new type of pile foundation for not only high-rise building, but also another type of building such as towers, bridges Pile foundation is one of solution for it The bearing capacity of pile foundation can be discovered by on-site test This process is often costly, particularly for large-diameter pile One of solution for it is using small scale experiment, which is carried by Meyerhof and Adams (1968) The experiment process will reduce the cost of testing at construction site, while we can discover characteristic of pile foundation There are researches about the behavior of pile under static loadings, but there are few experimental about dynamic behavior of the pile under dynamic excitations Therefore, this study will focus on the behavior of pile for both cases in order to confirm the bearing capacity of the pile METHODOLOGY a) Scale model: Model belled pile was design based on the law of similitude of Kokusho T and Iwatate T (1979), and scaling ratios between the model and the prototype were taken as 1/20 The detail of model was given in Table Table Relationship between model pile and prototype Objects Soil Pile Parameter Abbr Scale factor Factors Value a 0.05 Prototype Model 20 Target 1.00 Achieved 1.00 1.46 1.46 85.48 95.72 Objects Layer of soils H Density g b 0.81 1.8 Shear wave velocity v b-1/4a1/4 0.50 171.5 Natural frequency f b-1/4a-3/4 9.97 2.14 21.33 23.93 Hz Length L a 0.05 12 0.60 0.60 m Diameter d a 0.05 0.8 0.04 0.04 m Density g b 0.81 2.4 1.94 1.21 T/m3 Young's modulus E b1/2a1/2 0.20 122 2.50E+07 5.03E+06 3.20E+06 m T/m3 m/s kN/m2 Tuyển tập Hội nghị Khoa học thường niên năm 2019 ISBN: 978-604-82-2981-8 b) Setting up experiment: The pile is supported to set up at the middle of the shear box test However, with the intention of acting the vertical force at the pile head, so that a space about 50mm from the bottom of the pile head to soil surface is reserved In addition, to measure the vertical data accurately the impact between the top of the pile and the bottom of the shear box should be minimize Thus the pile will be set at appropriate position with the required distance from the bottom of the shear box, as shown in Figure Pairs of strain gauge were put on the surface of the pile at the determined positions in order to measure the axial strain of the pile during experiment period The expected position of the strain gauges was shown in Figure The dry Gifu sand will be employed in this study to investigate behavior of pile soil interaction, Table According the plan drawing, the sand will be placed at the maximum high level of the shear box during installing process The vibration created by bottom actuator is necessary in order to make the sand reach to designed density Moreover, for a realistic model, a rough (or adhesive) interface is required between the pile shaft and the soil Also it is noted that the material produced model pile had no friction angle Thus, covering the surface of the pile with the same typed of sand is used to generate the shaft friction In this study three types of loading were applied: monotonic static loading, triangular cyclic loadings and dynamic loadings All of the cases are shown in Figure - In case of monotonic compressive force and tensile force, the controlled displacements were determined to increase linearly until reach to mm (10 % of base diameter of the pile) - In case of triangular cyclic loading, it was established on static loading, but the different is the repetition with five cycles in each step of displacement: 1mm, 2mm, 3mm and 4mm - The dynamic loading with frequencies Hz, Hz and Hz also used in this study Table Properties of Gifu sand Expla nation Units Specific gravity (γs) 2.643 - Maximum diameter 0.84 mm 60% diameter 0.35 mm 30% diameter 0.31 mm 10% diameter 0.22 mm Coefficient of uniformity (Cu) 1.59 - maximum void ratio (emax) 1.126 - Minimum voids ratio (emin) 0.717 - 27.5 deg Parameter 123 Internal angle of friction (ɸ) Figure Schematic for setting up of the pile Tuyển tập Hội nghị Khoa học thường niên năm 2019 ISBN: 978-604-82-2981-8 1) 3) 5) 2) 4) Cyclic loadings: case 3, 4, 6) Dynamic loadings: case 6, 7, 7) 8) Figure Loading cases: 1,2 – static loading; 3,4,5 – triangular cyclic loading; 6,7,8 – dynamic loading (1, 3, 5Hz) RESULTS AND DISCUSSION The curves of force-displacement relationships were used to present the uplifting and compressive resistance of pile, and the results were shown in Fig In the static cases, the uplift resistance decreased slightly when the experiment is repeated from 0.5kN to 0.47kN, while the compressive capacity of pile increased slightly -5.4kN to -6.3kN For the cyclic case, the tensile capacity of pile was significantly lower than static case, but the compressive figure reached the highest value at -7.31kN in the full cyclic case Dynamic case saw a degree trends when the frequency increased At frequency of 1Hz, the figure was highest at 0.53kN for tensile case and -7.15kN for compressive case Thus, the differences in the bearing capacity of pile for both static and dynamic cases showed little differences Static loadings: case 1, Figure Load – displacement relationship curve: 1,2 – static loading; 3,4,5 – triangular cyclic loading; 6,7,8 – dynamic loading (1, 3, 5Hz) REFERENCES [1] Kokusho, T and Iwatate, T (1979) Scaled model tests and numerical analyses on nonlinear dynamic response of soft grounds Proceedings of Japanese Society of Civil Engineers (285), pp 57-67 [2] Meyerhof and Adams (1968), “Comparison of short-term and long-term pull-out tests in clay.” (Reproduced by permission of the National Research Council of Canada from the Canadian Geotechnical Journal, Vol 5, 1968, pp 225-244) [3] Poulos, H and Davis, E (1980), “Pile Foundation Analysis and Design”, John Wiley and Sons 124 ... and Iwatate, T (1979) Scaled model tests and numerical analyses on nonlinear dynamic response of soft grounds Proceedings of Japanese Society of Civil Engineers (285), pp 57-67 [2] Meyerhof and. .. dynamic loading (1, 3, 5Hz) RESULTS AND DISCUSSION The curves of force- displacement relationships were used to present the uplifting and compressive resistance of pile, and the results were shown in... The pile is supported to set up at the middle of the shear box test However, with the intention of acting the vertical force at the pile head, so that a space about 50mm from the bottom of the pile