Behavior of pile under push and pull force using small scale model

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,[.]

BEHAVIOR OF PILE UNDER PUSH AND PULL FORCE USING SMALL SCALE MODEL

Phạm Thanh Tùng1, Masato Saitoh2

1 Thuyloi university, email: tung.kcct@tlu.edu.vn

2 Saitama University

1 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

2 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 1

Table 1 Relationship between model pile and prototype

Objects Parameter Abbr

Shear wave

Soil

Natural

Pile

Young's

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 1

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 1

The dry Gifu sand will be employed in this study to investigate behavior of pile soil

interaction, Table 2 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 2

- In case of monotonic compressive force and tensile force, the controlled displacements

were determined to increase linearly until reach

to 4 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 1

Hz, 3 Hz and 5 Hz also used in this study

Table 2 Properties of Gifu sand

maximum void ratio (emax) 1.126 - Minimum voids ratio (emin) 0.717 -

Figure 1 Schematic for setting -

up of the pile

1) 2)

Figure 2 Loading cases: 1,2 – static

loading; 3,4,5 – triangular cyclic loading;

6,7,8 – dynamic loading (1, 3, 5Hz)

3 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 3

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 5

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, 2

Cyclic loadings: case 3, 4, 5

Dynamic loadings: case 6, 7, 8

Figure 3 Load – displacement relationship

curve: 1,2 – static loading;

3,4,5 – triangular cyclic loading; 6,7,8 – dynamic loading (1, 3, 5Hz)

4 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