1、Mechanism of Vibratory Pile Sinking Vibratory pile sinking is the construction method of using vibratory hammer for pile sinking. Setting up the vibrating hammer driven by electricity, gas, water or hydraulic pressure, the eccentric hammers in the vibrating hammer rotate against each other, the lateral eccentric force cancels each other, while the vertical centrifugal force is superimposed, so that the pile produces vertical up and down vibration, which causes the pile and the soil body around the pile to be in a forced vibration state, thus the strength of the soil body around it is significantly reduced and the soil body at the tip of the pile squeezes away, destroying the bond and elasticity between the pile and the soil body, and the soil body around it greatly reduces the resistance of the Mo Yang force and the soil body at the tip of the pile, and then the soil body under self-weight and vibration force can overcome the inertia. The bond and elasticity between the pile and the soil are destroyed, and the resistance of the soil at the pile tip is greatly reduced, and the pile is gradually sunk into the soil by overcoming the inertial limit force under the action of self-weight and vibration force. Vibratory pile sinking is easy to operate, high efficiency of pile sinking, short working period, cost saving, no auxiliary equipment, convenient management, strong adaptability of construction, small lateral displacement of pile and small deformation of pile when sinking, not easy to damage the pile material, and no public harm in soft foundation into the upper quickly. However, due to the vibratory hammer's structure is more complicated, maintenance is more difficult, power consumption is large, the service life of the equipment is shorter, and large power supply equipment is needed. When the undulation of pile foundation holding layer is large, the length of pile is more difficult to adjust. The foundation is greatly affected by vibration, and it is difficult to penetrate when encountering hard foundation, and there is still the public hazard of sinking pile and squeezing soil. And by the limitation of vibratory hammer efficiency, it is difficult to sink long piles over 30m.
2、Scope of application of vibratory pile sinking method 1、Scope of application Usually, it can be applied to the straight pile construction and pile pulling construction on land, water and platform of wooden piles, reinforced concrete piles, steel piles and combined piles in loose and soft foundation. Generally not applicable to hard clay and gravel foundation.2. Construction Process The construction process of vibratory pile sinking can be divided into dry vibration construction method, vibratory torsion construction method, vibratory impact construction method, vibratory pressurisation construction method, additional spring vibration construction method, additional counterweight vibratory construction method, additional counterweight vibratory pressurisation construction method and so on.
(1) Dry vibratory construction method Dry vibratory construction method is to use only vibratory effect of vibratory hammer pile sinking, pile sinking efficiency is low. Light vibratory hammer is mainly used in soft clay foundation, pile length less than 10m, pile diameter less than 40cm short pile foundation. Heavy vibratory hammer can be used in soft clay and loose sand foundation, pile length less than 30m, pile diameter less than 50cm.
(2) Vibrating and torsion construction method Vibrating and torsion construction method, the sinking pile is not only vibrated, but also torsion by the action of force coupling. When sinking large pipe piles, it is suitable to use vibratory hammer with low rotational speed and heavy eccentric block. A vibratory hammer with high rotational speed and light eccentric block is suitable for sinking small pipe piles. This method can be applied to all kinds of hard soil foundation.
(3) Vibratory Impact Construction Method Vibratory impact construction method is to use vibration and impact joint action for pile sinking. The vibration action is beneficial to overcome the soil perimeter resistance when the pile sinks, and the impact action is beneficial to overcome the frontal resistance at the tip of the pile. Therefore, the vibration impact construction method has strong pile sinking capacity, better penetration performance and less power consumption. However, the sinking speed is often lower than that of the impact construction method. This method is suitable for all kinds of soil foundations, and is often applied to foundations with intermediate hard soil layers.
(4) Vibro-pressurised construction method Vibro-pressurised construction method is to use static pressure and vibratory hammer to sink piles. With strong sinking capacity and good penetration performance, it is often applied to the foundation construction of about 30m long with intermediate hard soil layer or a certain depth into the holding layer. (5) Additional spring vibration construction method The additional spring vibration construction method is to use vibration and additional spring pressure to act together with the vibrating hammer for pile sinking. It is characterised by the fact that the vibrating hammer is not rigidly connected to the additional load plate, but the spring is used to make the additional load plate in a static state when the vibrating machine is working without participating in the vibration, so that the amplitude of the vibrating system will not be reduced. Tests have proved that the pile vibration sinking speed is much faster than the dry vibration construction method when there is additional elastic load. In order to increase the downforce during vibration, sometimes a vibratory pressure vibrating hammer can be used. However, it should be noted that the method of increasing the downforce is not very useful for large tubular piles. This method is suitable for pile foundation construction in soft clay and loose sandy soil foundation with pile length less than 30m and pile diameter less than 50cm. (6) Additional Weighted Vibration Construction Method The additional weighted vibration construction method is to use weighted pile cap for vibration pile sinking. Generally it is only used for pile foundation construction in soft clay and loose sandy soil with pile diameter less than 40cm and pile length less than 30m. The additional weight vibration pressurisation method is a combination of the additional weight vibration method and vibration pressurisation method. Its effect is basically slightly better than that of vibratory pressurisation construction method, and it is generally less used.
Sometimes, the vibratory pile sinking method can be used in conjunction with pre-drilling method and chipping method according to the construction conditions on site, in order to improve the ability to penetrate the hard soil layer and increase the penetration depth of the pile.
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