Application of the Vibration Method Near Existing Structures

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Work on the reconstruction of existing enterprises occupy a significant place in construction, and their volume is constantly increasing. This determines the need for building foundations near existing structures by high-performance methods, which include the vibration] method.

It should be noted that in the conditions of close development of Japanese cities, vibration technology is used much more often than pile driving.

At the same time, during vibration immersion near existing structures, as well as with other types of dynamic impacts on a submerged element, there is a danger of their uneven settlement and damage, disruption of precision equipment and harmful effects on people.

Currently, there are no effective ways to protect buildings from vibrations. There is only one reliable way – to reduce the initial level of vibrations that occur during vibration immersion or extraction.

Experimental studies were carried out at VNIIGS in order to determine the effect of the following factors on the level of ground vibrations: vibrational parameters of submerged elements and their sizes, formation of a soil plug during submersion, change in the direction of vibrations of a submerged element, extraction of soil from the cavity of a submerged tubular element (leading and advanced excavation), run-out after turning off the electric motor of the vibratory driver.

Experimental studies were carried out when a pipe with a diameter of 377 mm was immersed in sandy soil with four types of vibrations: longitudinal, longitudinal-rotational, helical and rotational (M. G. Zeitlin, G. G. Azbel, V. O. Izofov, I. V. Smirnov, 1979). Along with experimental studies, field observations of vibrations of the surrounding soil were carried out during vibration driving of shell piles, metal sheet piles, construction of filled piles and trench foundations using vibration technology. The results of experimental studies allowed us to draw the following conclusions.

With the same value of the driving force, an increase in the frequency of vibrations and a decrease in the static moment of the mass of unbalances lead to a decrease in the level of vibrations of the surrounding soil. With the same parameters of the vibratory driver, with an increase in the cross-sectional area of the submerged element, the level of vibrations of the surrounding soil increases.

Vibratory immersion of tubular elements without excavation is characterized by two maxima of soil vibration amplitudes: at the maximum amplitude of vibrations of the submerged pipe (at the beginning of immersion) and when creating a soil plug (before the end of immersion) (Fig. 76.) The excavation reduces the level of vibrations of the surrounding ground. The maximum level of vibrations of a submerged tubular element is observed during longitudinal vibrations, the minimum during rotational vibrations (M. G. Tseitlin, G. Azbel, V. O. Izofov, 1983).

The influence of the frequency of the vibrator on the level of vibrations of the soil surface was clarified at the site, where reinforced concrete piles-shells with a diameter of 1600 mm were immersed in clay soils with a vibrator VP-170. It has been established that the level of ground vibrations decreases with an increase in the frequency of vibrations of the shell pile (Fig. 77).

Fig. 76. Dependence of the change in the amplitudes of the longitudinal vibrations of the pipe Atp and soil Aгp on the depth of immersion; Aгp y , Aгp z, Aгp x – components of the amplitudes of oscillations of the soil surface; AгpyΣ geometric sum of oscillation amplitudes
Fig. 77. Change in the amplitudes of vibrations of the pile-shell AcB and the surrounding soil Aгp with an increase in the frequency of vibrations

The influence of the vibration exciter run-out on the ground vibrations was studied during the construction of the sheet piling of the underground passage. The ShK-I sheet pile was driven by the VPS-32/19 straightening unit. It was found that resonant oscillations are excited on the soil surface during the run-out, the amplitude of which is 1.7 times higher than the amplitude of the EO oscillations of the soil surface at the nominal operating mode of the vibration exciter.

At present, experience has been gained in the use of vibration equipment for the manufacture of filled piles and trench foundations (N.A. Makovskaya, B.B. Rubin, V.E. Trofimov, 1983 ), some of which were erected near existing buildings and communications.

Measurements of the amplitudes of ground vibrations, as well as an assessment of the state of buildings located in the immediate vicinity of the work site, showed that when driving piles using VNIIGS vibration machines using certain technological operations and methods, dynamic impacts on existing structures do not pose a danger to their integrity.

So, when immersing shell piles (M. G. Zeitlin, E. G. Godes, V. M. Klementyev, 1976), it became possible to significantly reduce the level of ground vibrations due to the installation of a leading well with a vibrating grapple. The amplitudes of ground vibrations, measured when the vibratory grapple was operating at distances from 0.7 to 46.8 m from the submerged shell, had values from 30 to 2.6 microns, respectively, and did not pose a danger to surrounding buildings.

The analysis of the data obtained also made it possible to conclude that it is possible to reduce ground vibrations due to the limitation of the depth of immersion of the soil intake and the reduction of the time of operation of the grab at the bottom. Further work confirmed the safety of using vibrating grabs near buildings and structures.

In Minsk, a trench wall with a length of about 40 m, a depth of 6-9 m of a complex section in plan was erected with a vibrating grapple PV-500 (VE Trofimov, 1978). The wall was made using the split-hole method in the immediate vicinity of existing buildings (the distance from the trench axis to the building wall did not exceed 1.5 m). Observation of the building during the operation of the vibrating grapple and its subsequent examination showed the absence of any damage.

In Leningrad, with the help of a vibrating grapple TV-l, a trench wall was made at the construction of the Kirov-Vyborg metro line. More than 60 m of a trench with a depth of 12.6 m was passed. The work was carried out inside a pit with a depth of 6 m in the immediate vicinity of the sheet pile wall. In the process of work, deformations of the sheet pile wall and damage to buildings located outside the pit were not observed (V.E. Trofimov, 1977).

During the manufacture of rammed piles up to 450 mm in diameter and up to 18 m in length without excavation, soil vibrations were measured near the immersed casing pipe using the PVN-l vibration plant. Measurements at distances of 4, 8 and 11 m showed that vibrations propagate along the ground with a frequency of 9 Hz. The change in the amplitudes of vibration displacements and vibration accelerations at the measurement points showed that their maximum values reach 200 µm and 310 mm/s2, respectively. Based on the results obtained, it was concluded that for these soil conditions (silty sandy loam, dusty band clays), the installation of filled piles by the PVN-l installation is permissible near buildings located at a distance of at least 8-10 m from the work site.

In Minsk, over 300 piles were manufactured by the PVN-l installation at several sites. The piles were formed in a wide range of soil conditions, including water-saturated and sinking soils. Thus, the PVN-1 installation was used in the installation of filled piles at the construction of a garage, where underground utilities located 5 m from the work site did not allow the driving of reinforced concrete piles provided for by the project. During the reconstruction of the Olympic complex, as a foundation for a lighting mast, instead of driven prismatic piles, rammed piles, manufactured by the PVN-2 vibration complex, were used. The piles were 720 mm in diameter and 14 m deep.

Filled piles were formed in alternating layers of viscous clay and gravelly sand, sometimes with an admixture of silt. The work was carried out in the immediate vicinity of the stands, which are an arched structure. At all stages of the technological cycle of manufacturing piles, measurements of the vibrational displacements of the soil were made. The sensors were installed on the soil surface 3 m from the casing pipe and 1 m from the pillars of the grandstand arches. The measurements showed that the greatest vibrations of the surrounding soil occur during the vibration extraction of a casing pipe filled with concrete, and reach 115 mkm (N.A. Makovskaya, B.B. Rubin, 1980).

An examination of the stands did not reveal any damage to them. The results obtained indicate the possibility of manufacturing filled piles and trench walls using vibration equipment near existing structures and the expediency of its use in the reconstruction of industrial enterprises.

The results of the research and industrial experience in the use of vibration equipment near buildings and structures allow us to recommend the use of vibrators with a lower static mass moment of unbalances and high frequency, vibratory hammers of longitudinal-rotational and rotational action with advanced excavation, reduction of the cross-section submersible elements, arrangement of leader wells, equipment of vibratory drivers with a system of dynamic braking of vibration exciters.

When choosing options for the designs of supports and vibration equipment in the conditions of reconstruction of existing structures, in most cases the decisive factor is the ability to conduct work at a minimum level of vibrations and ensure the design bearing capacity of the erected supports.

Taking into account the results of experimental studies and field observations, the main types of deep supports, in order of decreasing the level of ground vibrations during their installation, can be arranged as follows:

  • vibration driving of shell piles with excavation to the full depth and with subsequent filling with concrete mix;
  • production of filled piles with longitudinal and longitudinal-rotary vibratory drivers with excavation of soil from the casing pipe and concreting during its vibration extraction;
  • production of filled piles of rotary vibratory installations with excavation of soil from the casing pipe and concreting during its vibration extraction.

Thus, the safest way to install filled piles using vibration technology is to manufacture them with rapid excavation of soil from casing pipes.

Prior to the manufacture of rammed piles, the existing structures must be surveyed for potential failure of building components or individual damage.

Work on the construction of foundations from filled piles using vibration technology is started after the manufacture of two or three experimental piles, during the installation of which ground vibrations and settlement of existing structures are measured at all stages of work.

In the manufacture of filled piles at a distance of at least 20 m from the nearest structures, an assessment of the risk of vibrations for buildings can be omitted. To ensure a minimum level of ground vibrations when drilling wells with a vibrating grab, the time of its continuous operation should be no more than 1-1.5 minutes.

When working with vibration units PVN-2, VP-l, BVS-1, the minimum level of vibrations is ensured when extracting casing pipes with layer-by-layer concrete laying. The height of the concrete mix column is determined by the length of the casing pipe, but should not exceed 4 m.

The vibrators used in the construction of high-bearing supports have an operating frequency range of 5-12 Hz, which corresponds to the frequencies of natural oscillations of the surrounding structures. This determines the need to use all possible measures under these specific conditions to reduce the level of ground vibrations during vibration penetration.

Metal sheet pile vibrators have frequencies of 16-25 Hz, which are less dangerous for surrounding buildings. In this regard, when installing sheet piling, the main measure to reduce the level of ground vibrations is the use of dynamic braking when the vibrator runs out.

Due to the relatively small dimensions and the ability to work with various types of lifting devices using vibration technology, it is possible to ensure high labor productivity in cramped construction conditions.

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