1. O.M. Beketov National University of Urban Economy in Kharkiv
Ukraine
Kharkiv
O.M. Beketov National University of Urban Economy in Kharkiv
THE METHOD OF DETERMINING BORED PILES LOAD-BEARING CAPACITY, TAKING INTO ACCOUNT OF THE DIRECTION OF VERTICAL LOADING IN WATER-SATURATED SOILS
PRESENTING AUTHOR
Sergii Tabachnikov, Ph.D
Department of Soil Mechanics,
Foundations and Engineering Geology

2. LABORATORY AND THEORETICAL STUDIES
THE METHOD OF DETERMINING BORED PILES LOAD-BEARING CAPACITY, TAKING INTO ACCOUNT OF THE DIRECTION OF VERTICAL LOADING IN WATER-SATURATED SOILS
LABORATORY AND THEORETICAL STUDIES
Using a patented method (patent UA 96859, Tabachnikov and Samorodov 2015), the nature of the distribution of skin friction forces in sandy soil was identified for a multisection model pile of length L at rest T0, with no consideration of vertical load.
Figure 1. Diagram of the installation at rest for a fill height H of 1.0 m: 1) rotating mechanism with motion sensor; 2) model pile; 3) pivoted rod; 4) cover plate; 5) tank; 6) sand
Figure 2. Installation during the experiment: 1) tank (1000×1500 mm); 2) rotating mechanism with motion sensor; 3) model pile; 4) sand; ) loading container for transfer of moment effort through the pulley
Figure 3. Design of the pivoted mechanism: 1) metal disk; 2) cell with thrust bearing inside; 3) pin; 4) pulley with a developed tubular part; 5) metal cable Ø2.0 mm; 6) pivoted rod; 7) model pile
Figure 4. Design of the section of model pile: 1) fluoroplastic section 46mm, h=50mm; ) pivoted rod

3. LABORATORY AND THEORETICAL STUDIES
THE METHOD OF DETERMINING BORED PILES LOAD-BEARING CAPACITY, TAKING INTO ACCOUNT OF THE DIRECTION OF VERTICAL LOADING IN WATER-SATURATED SOILS
LABORATORY AND THEORETICAL STUDIES
Calibration of the installation. Determination of frictional forces between each section of model pile under the influence of its own weight in the absence of send in the tank.
Figure 5. Construction for calibration: 1) boards with holes; 2) model pile; 3) fastening bolts; 4) rotating mechanism

4. LABORATORY AND THEORETICAL STUDIES
THE METHOD OF DETERMINING BORED PILES LOAD-BEARING CAPACITY, TAKING INTO ACCOUNT OF THE DIRECTION OF VERTICAL LOADING IN WATER-SATURATED SOILS
LABORATORY AND THEORETICAL STUDIES
The influence of downward and upward loading on pile skin friction capacity in sandy soil was also determined within the experiment scope.
Figure 6. Experiment of influence of downward loading on pile skin friction capacity: 1) model pile; 2) pass construction; 3) stop shim; 4) hanger for transmission a vertical load

5. THE METHOD OF DETERMINING BORED PILES LOAD-BEARING CAPACITY, TAKING INTO ACCOUNT OF THE DIRECTION OF VERTICAL LOADING IN WATER-SATURATED SOILS
RESULTS OF THE TESTS
A series of experiments was carried out for different ratios of model pile length to diameter (L/d), which enabled the identification, after statistical processing, of the qualitative nature of the depth distribution of pile skin friction forces at rest and to approximate it with the relation:
It was determined that the ratio of load-bearing capacity due to skin friction forces for downward loading Fd,f and upward loading Fdu,f lies in the interval 2.2 < Fd,f /Fdu,f < 2.9, depending on the pile length-to-diameter ratio L/d.
Figure 7. a) Distribution of friction forces in sandy soil at rest T0 on depth z (z/d): 1) experiment; 2) dependence; b) Dependence of stress attenuation coefficient.
Figure 8. Dependence of kf on L/d in response to downward loading

6. THE METHOD OF DETERMINING BORED PILES LOAD-BEARING CAPACITY, TAKING INTO ACCOUNT OF THE DIRECTION OF VERTICAL LOADING IN WATER-SATURATED SOILS
NEW METHOD FOR DETERMINING THE LOAD-BEARING CAPACITY OF BORED PILES IN WATER-SATURATED SOIL
The proposed method, which is based on a differentiated approach to determining pile skin friction capacity, permits the examination of shear along the pile shaft using a "ground to ground" scheme (bored, driven, etc.) and to determine:
the overall friction forces along the pile shaft at rest T0, depending on the stressed state of the soil
near a pile and the physico-mechanical properties (γ, ν, φ и с) of soil layers;
additional compression force Tdu in response to vertical loading;
the pile skin friction capacity in response to upward Fdu,f and downward Fd,f loads.
(1)
(2)
(3)
kc is a component that takes account of reduced adhesion to soil resulting from shear and set depending on soil consistency (Gorbunov-Posadov 1985)
Figure 9. Analytical model for determining overall friction force T0

7. THE METHOD OF DETERMINING BORED PILES LOAD-BEARING CAPACITY, TAKING INTO ACCOUNT OF THE DIRECTION OF VERTICAL LOADING IN WATER-SATURATED SOILS
NEW METHOD FOR DETERMINING THE LOAD-BEARING CAPACITY OF BORED PILES IN WATER-SATURATED SOIL
An analytical model (Fig. 10) is proposed for determining additional soil compression force Tdu in response to upward loading, in which the distribution of vertical stress resulting from shear forces along the pile shaft while forming the reference foundation base is taken in accordance with DBN V , Rev. 1, Structure Bases and Foundations
(4)
(5)
σA=T0 /πl2tan2(φ/4)
(6)
express (6) as:
(7)
where
(8)
C=T0 /πγ tan2(φ/4)
As a result, the pile skin friction capacity is:
(9)
By analogy with (DBN V , Rev. 1. and
SP ), the pile capacity is written in the form:
(10)
Figure 10. Analytical model for determining additional compression force Tdu due to uniformly distributed upward load T0/l.

8. THE METHOD OF DETERMINING BORED PILES LOAD-BEARING CAPACITY, TAKING INTO ACCOUNT OF THE DIRECTION OF VERTICAL LOADING IN WATER-SATURATED SOILS
CONCLUSION
Experiment results show that the direction of vertical loading is one of the principal factors impacting the stressed state of the soil near a pile, and is of fundamental significance when determining pile skin friction capacity.
A proposal was made for the first time to identify pile skin friction forces due only to the formation of a stressed state near the pile that is due to the soil own weight without the influence of vertical loads, i.e., at rest, for our purposes.
A theoretical solution was obtained for the consideration of additional compressive force on the pile skin resulting from an upward load, and consideration of these forces for downward loads was empirically proposed.
A procedure was proposed for determining pile skin friction forces that consider the direction of vertical load, enabling a significant improvement in calculation accuracy in comparison to the procedure of (DBN V , Rev. 1. and SP ); that said, the mismatch with the results of in situ pile tests is within 10%.

9. THANK YOU FOR ATTENTION
THE METHOD OF DETERMINING BORED PILES LOAD-BEARING CAPACITY, TAKING INTO ACCOUNT OF THE DIRECTION OF VERTICAL LOADING IN WATER-SATURATED SOILS
THANK YOU FOR ATTENTION
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