REDUCTION OF THE VIBRATIONS CAUSED BY TRANSPORT TO THE GENERAL POST-OFFICE OF MOSCOW (part 1)

Dr. Sc. (Eng.) V.A. Ilyichev,

Dr. Sc. (Eng.) L.R. Stavnitser,

Ph. D. V.Y. Shishkin

Research Institute of Bases and Underground Structures (NIIOSP)

ABSTRACT
After the completion of base reinforcement with cast-in-place piles, instrumental analysis of foundation vibration parameters was made on the basis of the vibration survey results. The analysis showed a considerable decrease in the level of vibrations caused by transport.
In major cities and megalopolises the vibratory load caused by public transport to foundation soils has dramatically increased and keeps on increasing. As a result of this process, sandy soils often get compacted and settle unevenly. Buildings undergo deformations, load-bearing structures get cracked which hampers their further normal operation. Such buildings are subject to special measures being developed to reduce transport-related vibrations.

Lack of free space, population density growth and state financing decrease result in the development of the territories located near subway tunnels and major motorways. Expensive anti-vibration systems are used there for vibratory impact reduction.

In such cases, foundation soil improvement methods may be used as a more economically efficient alternative. One of such methods implies soil reinforcement with crushed-stone piles with the help of pneumodrilts.

A pneumodrilt is a device having the following parameters: mass – from 90 to 500 kg, diameter - from 90 to 245 mm (depending upon brand), length - approximately 1.5 m, blow energy – 60-230 kJ/min for 8-12 m3/min compressor capacity. As a rule, pneumodrilts have the back stroke capacity.

Crushed-stone piles installation technology involves the following operations:

• vertical or inclined wells construction under foundation with the help of a pneumodrilt;
  
• filling of wells with small-sized crushed stone;
  
• compaction of crushed stone with the same pneumodrilt up to the density required;
  
• cementation of all crushed-stone piles at the final stage.

The aforesaid technology application to buildings 6 and 7 at Verkhnyaya Radischevskaya street, building 16 at Pokrovka street, Rot-Front plant building (during reconstruction), and the building of the Moscow General Post-Office (26, Myasnitskaya street) made it possible not only to increase design resistance of foundation soil by 1.5-2.5 times but also to considerably reduce vibratory impact:

• by 10 times for the subway-related impact;
  
• by 5 times for the road-transport-related impact.

Examination of the Moscow General Post-Office, one of the major monuments of architecture, showed that strip and pier rubble foundations at fill-up soil require reinforcement because of non-uniform deformations development. The research showed that the deformations were caused by unfavorable impact made by the vibrations caused by the subway tunnel located under the building and heavy traffic at Myasnitskaya street. Soil deterioration was also caused by process water damping it.

The project on base soil reinforcement under the foundations of walls and columns of the Moscow General Post-Office involved crushed-stone piles installation in inclined wells with the help of  IP-4603 type pneumodrilt. This is a self-propelled machine which body driven into soil by a percussion mechanism makes a well having 130 mm in diameter. The friction between the machine’s surface and the soil prevents back stroke of the machine’s body. Reverse action device returns the body into the initial position. After pneumodrilt extraction, the well gets filled with estimated volume of sand mixed with crushed stone, then the pneumodrilt gets driven down to the bottom of the well again, pressing sand-and-crushed-stone mix into the walls of the well, thereby creating a compacted zone. The process repeats until the design compaction depth is reached. After that the well gets plugged with cement mortar. Compaction quality is controlled by soil penetration tests performed right under the bottom of the foundation.

This is a patented technology of base soil reinforcement under existing foundations (the RF Patent #2026926). The following volumes of inert materials are required in accordance with this patent (see the table below):

Table 1.
Dry soil
density after
foundation
soil
reinforceme
nt, t/m3
Unit consumption (m3) of inert materials per
1 m3 of compacted foundation soil for the
following values of soil porosity ratio before
compaction
0.8 0.9 1.0 1.1 1.2
1.5 0.02 0.05 0.08 0.10 0.12
1.6 0.06 0.09 0.12 0.14 0.16
1.7 0.10 0.13 0.15 0.18 0.20
1.8 0.14 0.17 0.19 0.22 0.24

To be continued...

REFERENCES

1. Gorbunov-Posadov M.I., Ilyichev V.A., Krutov V.I. [1985].

Bases and Underground Structures. Reference Book for a esigner. Edited by E.A Sorochan, U.G. Trofimenkov. Moscow, Stroyizdat.