VIBRODINAMIC MONITORING OF PILE FOUNDATION ENGINEERING ON LANDSLIDE HAZARDOUS SITE IN DENSE URBAN DEVELOPMENT CONDITIONS

An example of the application of modern regulatory requirements for the scientific and technical support of construction and monitoring of building structures for the safe arrangement of the pile foundation on a landslide hazardous building site in conditions of dense urban development in Kyiv during the installation of a Ø820 mm bored pile according to the plan of the pile field has been considered. Experimentally registered levels of vibration acceleration on the foundation wall of the building in the vertical and horizontal directions do not exceed 0.015 m/s2, which is significantly lower than the minimum permissible values of vibration acceleration for the foundations of buildings with brick bearing walls 0,15 m/s2. The research also evaluated the presence of visible damage to the building in the available places and their possible development before and after piles placement. The condition of the plaster screed on a vertical crack in the wall of the house on the 8th floor, which was installed before the start of construction work, after pile foundation installation has not changed – it remained undamaged.


Introduction
The general condition of the construction sites in Ukraine does not ensure safe living conditions for citizens and society due to the increased risk of emergencies [1]. The increase in the buildings and constructions height, break with symmetric forms, constant increase in the technogenic load on the site during construction in conditions of dense urban development enhance the likelihood of disasters conditions. First of all, it regards Kyiv where there are numerous examples of such violations: 1. In the center of Kyiv there have been another construction scandal regarding construction of "Elegant" residential development in dense urban development conditions on 118, Zhilyanskaya street [2]. At the beginning of construction process the neighboring five-storey house cracked during the pile driving, the tenants had to be resettled. As a result, an old five-story mansion and a one-storеy building next to it on 120-V Zhilianskaya street was broken down and a huge trench was dug on this site. Residents of nearby houses are afraid that the walls of their houses will collapse the cracks have already appeared on the upper floors [3].
2. Residents of houses number 3, 5, 5a, 7 on Lesya Ukrainka bvld. and three more houses along Mechnikov Street were united by one problemthe construction in their yard. Houses are built on a landslide slope. Delicate balance can be disrupted by any intervention of construction equipment. Houses on Lesya Ukrainka bvld. will simply slide down to Mechnikov Street [4].
3. On 7, Marjanenko lane crack opening in the house walls coincides with the beginning of excavation for a residential complex on 9 and 11 Mechnikova street. The state of the house was affected immediately by two construction sites -9a and 11 Mechnikov street and 12a Klovskiy uzviz street as well The above examples are just the tip of the iceberg of constantly increasing number of ground displacements and catastrophes across Ukraine both in terms of their number and in terms of economic losses scale. There is an acute need for monitoring and scientific and technical support for new constructions taking into account the fulfillment of the requirements of new regulatory documents for soil accidents prevention in future [5].
Over the past 10 years State Enterprise "State Research Institute of Building Constructions" gave much attention to both the regulatory and methodological support and to construction monitoring systems implementation. During this time, a number of regulatory documents considering building structures monitoring issues have been developed: 1. State Construction Standard DBN В.1.2-5: 2007 "The scientific and technical support of construction sites" [6].
All of the above documents were a basis for new final document National Standards of Ukraine DSTU-B B.1.2-17: 2016 "Guidance on scientific and technical monitoring of buildings and constructions" [9], which was developed under scientific supervision of prof. Yu.I. Kaliukh as well as complex of standards for buildings and constructions technical diagnostics systems [10]. Construction standards [9] include all the main methodological instructions and developments on the scientific and methodological basis, design and experimental development of construction monitoring systems [6][7][8][10][11] that were put into effect on 01.04.2017. Guidance [9] was developed in harmonic accordance with international building standards fib [12]. In [9], as in the document fib [12], the classification of construction monitoring systems is the same (see Figure 1 [12]).

Main points
Let's consider an example of modern regulatory requirements application for scientific and technical support for building structures construction and monitoring [6][7][8][9][10][11] for safe arrangement of the pile foundation on a landslide hazardous construction site in conditions of dense urban development at the address 14, Pimonenka street in Kyiv during the installation of a bored pile № 87 Ø820 mm in accordance with the pile field plan. The work area with a well for the bored pile is at a distance of 18-20 m from the nine-storеу residential brick building. The area of the construction site is below the level of adjacent to the building area, on the boundary of which there is a retaining wall made of concrete blocks in height ≈ 5 m. The mutual location of the building, the retaining wall and the construction site is presented in Fig. 1  According to the present DBN [6][7][8][9][10][11] the inspection of technical condition of the building structures of the nine-storey building was performed in advance, prior to conducting drilling works, (Fig. 1). During the study of the technical condition of building constructions, the presence of visible damage in the places available for this site and their possible development before the works beginning, during and after the installation of the piles were assessed. The monitoring of the impact on building of drilling operations was monitored not only instrumentally, but also visually, by periodic observations during the arrangement of the bored pile № 87 Ø820 mm taking into account the integrity of the chalky screed on a vertical crack in the bearing brick wall of the house on the 8th floor. The screed was installed in advance, prior to drilling operations beginning (see Fig. 2).
Well drilling was performed by the BAUER 40 BG drilling rig (Fig. 3). In the photo (Fig. 4) there is a view of the investigated building, including the retaining wall on the side of the construction site. During the research period, one drilling rig BAUER 40 BG (Fig. 3) worked on the site. The vibration sensors were located on the foundation part of the building (3 vibration sensors), fixed oriented towards X, Z and Y directions (Fig. 5); two vibration sensors that were located on the floor of the 9th floor of the house were oriented towards X, Z or Y, Z directions (Fig. 6). The change in the orientation of the vibration sensors for the measurement of vibration acceleration was conducted in concert with the moment of their registration.

Results
With the help of "Seismic monitoring" software [29] the initial experimental results were processed, that are represented in the table.         Table 2 in [30].
2. The registered levels of vibration acceleration at the level of the 9th floor slab of the building in the vertical and horizontal directions do not exceed 0.004 m/s², which is significantly lower than the permissible values of vibration acceleration for high-rise buildings of 0.08 m/s² in according with paragraph 7.2 [31].
3. In the studies, the presence of visible damags to the building in the available places and possible development before and after pile installation was also assessed. Their development was evaluated according to a plaster screed on a vertical crack in the wall of the house. The condition of the chalky screed was established prior to the beginning of vibration dynamical tests on 02/15/2017 on the vertical crack in the building on the 8th floor, on the date of research on 02/21/2017 and after the installation of the concrete pile and further entire pile foundation has not changed. It remained undamaged. This is shown in the photo (Fig. 2).
4. Based on the above mentioned, it is permissible to carry out work on pile foundation implementation with the observance of the necessary technological procedures during the operation of the BAUER 40 BG drilling rig (see Fig. 3-4).