(7) The equation of state and the equation of flow of gas in the upper chamber of
hydraulic hammer are, respectively,
p u0 V
n
u0 ¼ p u V
n
u
ð12:45Þ
Q u ¼
dV u
dt
¼ À
V u
np u
dp u
dt
¼ A u
dy
dt
ð12:46Þ
where
p u0 ; V u0 Inflation pressure and volume of air chamber of hydraulic–pneumatic
composite hammer;
V u
Volume of air chamber of hydraulic–pneumatic composite hammer when
working.
(8) Strike energy of hydraulic hammer: Assuming that the friction loss of hydraulic
hammer and the energy loss during impact are not considered, the kinetic
energy of falling hammer is converted into strike energy, and the energy satisfies the following equation:
E ¼
1
2
m
dy
dt
2
g
ð12:47Þ
where g—Pile efficiency of absorbing strike energy, i.e., pile driving efficiency.
12.4.3 Influencing Factors of Rapid Piling
From the above mathematical model Eqs. (12.37)*(12.47), the influence of length
and diameter of oil return pipeline and low-pressure accumulator on the descending
process and strike energy of hydraulic hammer can be calculated.
12.4.3.1 Influence of Diameter and Length of Oil Return Pipeline
(1) If the length and diameter of the pipeline are different, and the inflatable
pressure of the low-pressure accumulator is different. The inflatable pressure of
low-pressure accumulator is generally 0:8 $ 0:85 times of the working pressure.
The length and diameter of oil return pipe directly affect the pressure loss along
the oil return pipeline, but have little influence on the local pressure loss.
12.4 Rapid Piling Process of High-Speed Pneumatic–Hydraulic Composite Hammer
303