Vibration Hammer Principle
The vibration hammer is designed using resonance theory. When the forced vibration frequency of the pile coincides with the vibration frequency of the soil particles, the soil particles resonate. At this time, the soil particles have the largest amplitude, and the sufficient vibration velocity and acceleration can quickly destroy the adhesion between the pile and the soil. The transition from the compacted state to the instantaneous separation of the soil, the resistance of the pile, especially the side of the resistance quickly reduced, the pile under the effect of heavy subsidence. As the vibration hammer to reduce the friction between the pile and the soil to achieve the purpose of piling, so the friction between the pile and the soil to reduce the situation, you can use a slightly larger than the pile and pile force can pull up the pile The Therefore, the vibration hammer is not only suitable for piling, but also suitable for piling. Pile piles, pull pile efficiency is very high.
The main parameters: amplitude A, excitation frequency ω, eccentric moment M, shock force F, vibration weight Q, power N
1. Determination of vibration power N. The vibration power N is calculated as: N = K · M · n / 9550 (kw) where n is the rotational speed and K = 1.25.
2. Determination of eccentric moment M. The greater the eccentricity of the vibrating hammer, the stronger the ability to overcome the hard soil layer. When the known amplitude and the total weight of the vibrator Q (the weight of the pile and the weight of the vibration hammer), the eccentric moment can be calculated: M = Q · A M)
3. Determination of excitation frequency ω. The vibration frequency of the vibration hammer is closely related to the natural frequency of the vibration system. When the excitation frequency is close to the natural frequency of the vibration system, the vibration pile is maximized. The natural frequency of the vibration system is not only related to the parameters of the vibration hammer, but also related to the parameters of the soil. The natural frequency of the soil in different strata is very different. The following table is based on the experience of the different layers of vibration hammer the best frequency range. The experimental results show that the increase of the vibration frequency can accelerate the liquefaction of the saturated sand and the corresponding decrease of the soil resistance, which can improve the acceleration of the pile more effectively than the increase of the amplitude, so that the pile efficiency can be improved significantly , But the excitation frequency is too high will cause the output power is too large, so determine the excitation frequency should also be considered.
4. Determination of vibration weight Q. Vibration hammer in addition to the necessary amplitude and acceleration, but also must have a certain vibration weight to overcome the resistance when the pile, the pile in the soil of the static resistance R and soil penetration into the standard value of N and cross-sectional area S between The relationship is: R = 4N · S (KN)
Therefore, when the pile is subjected to vibration and the friction force is significantly reduced, the pile can be sunk to the pile end resistance equal to the weight of the vibration, that is, Q = 4N · S
5. Determination of excitation force F. The exciting force F is a parameter that reflects the comprehensive capacity of the vibration hammer. The exciting force F must be larger than the static friction force between the pile and the soil, and it will decrease sharply under the action of the exciting force. When the vibration between the pile and the soil friction between f 'said, then: F ≥ f' = μf (KN) where μ is the vibration force when the friction coefficient of reduction, mainly by the vibration acceleration of the size of the control. Experiments show that the vibration acceleration of more than 10 times the acceleration of gravity, μ changes are very small, μ and f 'tend to set value.
6. Determination of amplitude A. The larger the amplitude, the greater the sink speed. When the amplitude is very small, the pile will not sink, only the amplitude is greater than a certain value, the pile may sink, this value is called the starting amplitude A0, with the amplitude increases, the pile speed is also accelerated until the trend Of the limit value Ac, so the range of amplitude is: A0 <A <Ac. The starting amplitude A0 can be used to calculate the standard value of soil N, calculated by the formula:
Standard penetration of soil
Soil type N value
Very loose sand 0-4
Loose sand 4-10
Medium density of sand 10-30
Dense sand 30-50
Very dense sand> 50
Soft clay 2-4
Medium hardness clay 4-8
Hard clay 8-15
Very hard clay 15-30
Very hard clay> 30