For the rest of the book, click here. By “shells,” the Russians mean large concrete cylinder piles. Raymond Concrete Pile was developing their own prestressed cylinder piles for work in Venezuela and the Chesapeake Bay Bridge/Tunnel, with diameters up to 66″. For their part the Russians were installing working piles up to 1.55 m (61″) and experimental piles up to 3 m (118″) in diameter.
To drive shell piles into the ground, low-frequency longitudinal vibration hammers VP-1, VP-3, VP-4, VP-5, VPU-A and VPU-B are used.
For the first time in a production environment, a VP-1 vibratory driver was used to immerse shells [15]. On the initiative of the Bridge Research Institute during the construction of a bridge across the river. In Usa, instead of constructing sinkholes, foundations for river supports on reinforced concrete shell piles were designed. The river bottom is composed of alluvial deposits, consisting of layers of different-grained sands, including up to 60% gravel, pebbles and stones up to 25 cm in diameter. Below the sands, clays occur at a depth of 14 m.
The foundation of each support consisted of 8 vertical piles with a diameter of 1.2 m, a length of 10 m, and walls 80 mm thick. The weight of the shell is 6.8 tons. The design load on each shell was assumed to be 216 tons.
The shells were immersed with a vibratory loader from the bottom of the pit to a depth of 9 m. To transport the shells within the pit and installation, a crane with a lifting capacity of 15 tons was used on a railway track. The vertical position during diving was ensured by three cable braces, fixed at the head of the shell and wound on the drums of 3 ton hand winches.
The vibratory driver was fastened to the shell using a standard welded cap, similar in design to pile caps with a cone. The connection of the head cap with the shell was carried out with removable clamps. The immersion of the shells was accompanied by loosening and removal of soil from the shell cavity using a strong jet of water and an airlift.
The sequence of work was as follows. A cap was attached to the shell and an airlift and a tube for soil erosion were placed in the internal cavity, after which the pile was installed in the pit and braced with ropes from winches. Then the air and water hoses were connected, and the vibrator was installed with a crane on the head of the shell. When the vibratory driver was turned on, the shell sank into the ground for 2-3 minutes, then, due to the formation of a soil plug, the immersion stopped. After this, we began to excavate soil from the internal cavity to a depth of 40-50 cm below the shell knife. After turning on the vibratory driver, the movement of the pile was resumed until a new plug was formed, and the cycle of work was repeated.
Thus, during immersion at the beginning of each cycle, vibration primarily overcame the lateral friction on the outer surface of the shell. In addition to friction, drag resistance arose and quickly increased, stopping the forward movement of the shell into the ground. The next cycle began with the extraction of compacted soil from the shell cavity. When the shell was immersed to the designed depth, the vibratory driver was turned on for 15-20 minutes. to compact the soil around the shell and under its end.
The immersion speed of the shell when working with an airlift with a diameter of 200 mm reached 2.2 m/hour. The immersion of the shell to a depth of 9 m lasted an average of 5 hours. 37 minutes, of which the vibratory hammer worked for 1 hour 6 minutes. Preparatory work took an average of 6 hours 22 min.
The use of shell piles and their immersion by vibration made it possible to reduce the cost of support foundations by 18.2% compared to the cost of foundations on sink wells.
During the construction of a bridge across the river. In Klyazma, a VP-1 vibratory driver drove shells with a diameter of 0.92 m, a wall thickness of 60 mm, a length of 15.5 m and a weight of 6.2 tons. The calculated load on the shell was 226 tons. 11 shell piles were driven into the base of each support, of which 10 along the perimeter of the grillage with a slope of 5:1 and one – central – vertically.
The technology for driving shells was basically the same as described above. Here, a VP-1 vibratory driver was used, in which, by replacing the gears, the speed of the eccentrics was increased from 420 to 485 rpm. This ensured an increase in the dynamic force to 22.6 tons. A derrick crane with a lifting capacity of 10 tons was used as a lifting mechanism. The shell was slung 5 m from the head. After installing the shell in place, using braces to give it the design inclination, a vibratory driver was installed on it using the same crane.
The shell was immersed by vibration to 2-2.5 m without removing soil from the cavity until its forward movement stopped. Then the shell was filled with water and the airlift was turned on. By periodically turning on the vibratory loader for 2-3 minutes, with continuous operation of the airlift, the shell was immersed to the design mark.
It took about 24 hours to immerse one shell. The highest diving speed reached 10.5 m/hour.
Several vertical shell piles were subjected to static tests. Using hydraulic jacks with a lifting capacity of 500 tons, the load on the pile could not be brought to a critical value.
A large number of reinforced concrete shells were successfully embedded in sandy soils during the construction of the Wuhan Bridge in the People’s Republic of China [54]. For this purpose, vibratory hammers VP-1, VP-3 and VP-4 were used here.
The shell piles had an outer diameter of 1.55 m, a wall thickness of 100 mm and a link length of 9 m. The weight of such a link was approximately 10 tons. Metal flanges were installed at both ends of each link, with the help of which the links could be connected to each other. The lower links of the shells were equipped with metal tubular knives. Special metal frames were used as guides for installing and immersing the shells.
The shells were installed in separate sections using floating cranes with a lifting capacity of 30 tons. The sections were joined on the upper platform of the frame. After winding, the shell section was suspended from the frame with special clamps; the next link was installed on the hanging shell. The mating flanges were then bolted together and the shell was lowered onto one link and suspended again to connect to the next link. The height of the assembled shells on individual supports ranged from 27 to 36 m.
The shells were immersed by vibration through the thickness of the sand to the rock. With a layer thickness of up to 8 m, the dive was relatively easy without jetting. When the sand was thicker, external washing was used or washing was carried out simultaneously from outside and inside the shell. Practice has shown that this method is more rational than removing sand during immersion from the shell cavity using an airlift.
The vibratory hammers were connected to the shells using a flange adapter.
The experiments carried out by Chinese and Soviet specialists on vibration immersion of large-diameter shells into various soils are of great scientific and practical importance [21].
The experiments consisted of immersing shells with a diameter of 1.55 3 and 5 m into sandy, clayey and gravelly soils using vibratory hammers of the VP-3, VP-4 and VP-5 types. We present the main results of the experiments in the form of tables.
Table 42 shows the results of an experimental immersion of a shell with a diameter of 1.55 m into clay soils. The total dive time was 177 minutes. at an average speed of 10.1 cm/min.
| Type of Vibratory Driver | Depth Achieved, m | Power required to operate the vibrator, kW |
| VP-3 | 11.5 | 60 |
| VP-4 | 16.3 | 100 |
| VP-5 | 17.9 | 220 |
The immersion of a shell with a diameter of 3 ohms into clayey soils (Table 43) was carried out with periodic removal of soil from its cavity.
| Type of Vibratory Driver | Depth Achieved, m | Power required to operate the vibrator, kW |
| VP-3 | 8.0 | – |
| VP-4 | 16.0 | 170 |
| VP-5 | 17.8 | 180 |
The total time spent immersing the shell to a depth of 17.8 m was 207 minutes. Average speed – 8.6 cm/min.
A prefabricated reinforced concrete shell with a diameter of 5 m, a length of 18 m and a weight of 91 tons was immersed in clay soil (with its removal from the cavity) with a VP-4 type vibratory driver to a depth of 10 m and with a VP-5 type vibratory driver – up to rock to a depth of 16.5 m A total of 180 minutes were spent on the dive. The average immersion speed is 9.2 cm/min. The required power for operation of the VP-5 vibratory hammer was 140 kW.
Then experiments were carried out on immersing the shells in sandy soils.
A shell with a diameter of 1.55 m, a length of 46.2 m, and a weight of up to 51 tons was immersed in fine-grained sands at a depth of 35 m in 56 minutes. with an average speed of 62.5 cm/min (Table 44.)
| Jobsite Conditions | Shell Length, m | Shell Weight, tons | Immersion Depth of Vibratory Driver, m | |
| VP-3 | VP-4 | |||
| Without jetting or excavation | 21 | 23.2 | 12.3 | – |
| With jetting with one inner tube (pressure 17 atmospheres) | 33 | 36.3 | 14.6 | – |
| With jetting with one internal and four external tubes (pressure 15 atmospheres) | 33 | 36.3 | 20.4 | – |
| 42 | 46.2 | – | 26.9 | |
| Same, soil removed by an air lift to the level to the shell head | 46.6 | 50.8 | – | 35.0 |
A similar experiment of immersion in fine-grained sands was done with a shell with a diameter of 3 m (Table 45.) Such a shell, 42 m long and weighing 126 tons, was immersed with a VP-4 type vibratory loader to a depth of 23 m in 14 minutes.
| Jobsite Conditions | Shell Length, m | Shell Weight, tons | Immersion Depth of Vibratory Driver, m | Total Immersion Time, minutes |
| Without jetting | 18 | 54 | 10.8 | 5 |
| With jetting with one internal and four external tubes | 30 | 90 | 19.4 | 9 |
| Jetting with four external tubes, soil removed by an air lift to the level to the shell head | 42 | 126 | 23.0 | 14 |
An experimental immersion of a shell with a diameter of 3 m was carried out in gravelly-sandy soils containing inclusions of large cobblestones up to 40 cm in size. The soil from the shell cavity was removed first after 2 m, and then after every 1 m of depth.
In this experiment (Table 46), a shell 18 m long was immersed to a depth of 16.3 m in 113 minutes. with an average speed of 14.4 cm/min.
| Type of Vibratory Driver | Length of Shell, m | Weight of shell, kg | Immersion depth Achieved, m | Maximum power required to operate the vibrator, kW |
| VP-3 | 12 | 36 | 6/5 | 160 |
| VP-4 | 18 | 54 | 16.3 | 250 |
The experimental installation made it possible to establish that:
a) when using vibratory hammers of appropriate power and removing soil from the cavity, shells with a diameter of up to 5-6 m can be immersed to great depths in various soils;
b) removal of soil from the cavity of the shells helps to increase the speed and depth of immersion;
c) removing sandy soils from shells using an airlift is more economical than using erosion, which requires significant energy consumption;
d) when immersing shells in difficult soil conditions (clays, loams, gravel), it is advisable to use grabs to remove soil;
e) the power of vibratory hammers of the VP-4 and VP-5 types cannot be increased if necessary, which causes certain difficulties; their design does not allow soil to be removed from the shells with a grab without removing the vibratory hammer.
Let’s consider two more examples of vibration immersion of shell piles.
When reconstructing one of the embankments, the Sevzapmor Hydrostroy Trust used reinforced concrete shell piles with a diameter of 0.96 m instead of metal gantry piles. The design of the pile and the welded joint between the individual links was developed by VNIIGS.
Initially, the 24 m long shells, open at the bottom, were driven with a VP-3 vibratory loader using a crawler crane. The connection of the vibratory driver to the shell was made using a welded cap with a conical pin (Fig. 102.)
If there were soft soils at the base of the structure, the open shells sank at high speed without additional impacts on the soil. The shells were immersed to a depth of 14-17 m in 12-15 minutes, and the soil in the cavity rose above the ground level outside the shell by 2-2.5 m.
Static tests of the shells showed that their critical resistance does not exceed 150-250 tons. In order to increase the load-bearing capacity, several piles were driven with conical tips closed at the bottom. The driving went much slower (Fig. 103.) However, as static tests have shown, the use of conical tips closing the shell from below did not provide an increase in load-bearing capacity.
1 – open at the bottom; 2 – closed with a conical bottom
At another site, reinforced concrete prefabricated shell piles were used as a deep pile foundation for bridge piers instead of a low grillage on wooden piles. The design of the piles and their dimensions were the same as at the previously indicated object. Each pile, 24 m long, consisted of four links of equal length, which, as they were buried in the ground, were joined together by welded seams. The immersion of the shells was carried out using a VP-3 vibratory loader using an E-505 crane.
To install the piles and direct their movement at the beginning of the immersion, guides were installed, consisting of wooden piles immersed by vibration to a shallow depth, and two tiers of horizontal logs connected by bolts to the wooden piles (Fig. 104.)
The connection of the vibratory driver to the shell was carried out not with a conical head, but with a flange adapter, which turned out to be more convenient. To secure the adapter to the shell, threaded studs were welded to the end steel ring. Installation of the vibratory loader on the studs and screwing in the nuts was carried out by two workers located on suspended scaffolds. The workers climbed onto the scaffolding and descended from it along a light metal folding ladder. During the immersion of the next link, the scaffolding was removed from the vibrator by a crane.
During the construction of the bridge, as well as during the reconstruction of the embankment, there was a rise in the soil level inside the shell by 1.5-2 m above the river bottom, and the upper layers of soil in the pile cavity were in a liquefied state after immersion. In this regard, loosened soil to a depth of 10 m was removed from the shell with a special grab (Fig. 105) and instead of weak soil, the cavity of the shell was filled with sand to the freezing level, and above this level with concrete.
From the above two examples it is clear that for weak clayey soils characteristic of Leningrad, vibratory driving of shells with a diameter of 0.96 m using a VP-3 vibratory driver gave quite satisfactory results.
In general, the available data from industrial experience give grounds to recommend the method of vibratory driving of thin-walled piles and shell wells for widespread use in construction, where these highly economical prefabricated reinforced concrete structures can be used to construct the foundations of industrial hydraulic engineering and transport facilities, as well as as fencing for underground structures – water intake wells, deep reservoirs, etc.
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