THE FORMATION OF THE STRESS-STRAIN STATE OF THE BASE DURING THE ERECTION

OF FOUNDATIONS AT DIFFERENT MARKS IN A DENSELY BUILT-UP TERRITORY

Ruchkivskyi V.V., postgraduate,

Geotechnical department, Kyiv National University of Construction and Architecture

Introduction: In densely built-up territory there are situations when new foundations are arranged in close proximity to existing foundations. In these cases, protective measures are required to minimize the impact of new construction on existing building. An important factor in the developing of protective measures is to take into account the different foundation depths. The purpose of this work is to study the stress-strain state of the soil base at the erection of the foundations at different marks in densely-build up territory. As part of the study, the construction of a multifunctional complex №69 for an existing building №67 was considered (fig.1). These buildings are located in Kyiv.

Figure.1. Situation scheme

Figure.2. Existing situation today

Building №67

Building №69

Figure.3. Building №67

Existing residential building №67 was built in 1937-1939. It is a five-storey brick building with a basement floor, with overall dimensions of 81,2x14m. The building is frameless. The structural scheme is rigid, with supporting longitudinal and transverse walls. The building has a rubble stone footing. The footing depth from the of the basement floor is 1.55-2.26m, the width ranges from 1.5 to 2.4m. The base of the foundations is a soft sandy loam, plastic and fluid consistency (Е=7MПа; φ=18 °; γ =19,3kN/m ³) depth up to 17m. Floors of the building - wooden on wooden beams.

82m

18m

14m

Figure. 4. Floor plan of building №69 Fig. 5. Section of building №69

Construction of building № 69 was started in 2004 and has not been completed to date. 6 floors of 16 were built. It is currently planned to resume construction. The building is a monolithic frame. Stiffness and sustainability are ensured by rigidity diaphragms, staircase blocks and elevator shafts connected by overlapping disks. The foundations of the building are bored piles Ø 820mm, united by a 1030mm thick raft, the base of the piles is a semi-solid loam (Е=35MПа; φ=19°; γ=19,2kN/m³). During the construction of the foundation and the underground part of building №69, the pit depth was 4 m. The retaining structures of pit was made of drill piles Ø 620mm. The bottom of the pit is 128.1 m.

Figure.6. Engineering-geological conditions

The base of the shallow footing of building №67 is a soft sandy loam (Е=7MПа; φ=16°; γ=18,4kN/m³). The base of the pile foundation of building №69 is a semi-solid loam (Е=35MПа; φ=19°; γ=18,3kN/m³).

12,8mm

Figure.8. Crack opening (outside)

The main reasons for the deformation of existing buildings during construction it may be: - changes in hydrogeological conditions, including flooding, associated with barge efect during underground construction, or lowering of groundwater - increase of vertical stresses at the base under the foundations of existing buildings caused by the construction near them - arrangement of or change of plane marks - technological factors -negative processes in the soil array related to the execution of geotechnical works (suffusion). -The degree of impact of new buildings on nearby buildings is more driven by technology and quality of construction. Today, as a result of the construction of building №69 and self-willed replanning with the completion of premises in building №67 is in a state unsuitable for normal operation, significant sedimentary deformations of the building and cracks in the walls are observed.

Figure.7. Crack opening (inside)

Part of the building was recognized as an emergency. According to geodetic observations of sediments and tilts of the building, the maximum deviation from the vertical surface is 119 mm, the maximum settlement is 83 mm. As part of the elimination of this condition Today, as a result of the construction of building №69 and self-willed replanning with the completion of premises in building №67 is in a state unsuitable for normal operation, significant sedimentary deformations of the building and cracks in the walls are observed. Part of the building was recognized as an emergency. According to geodetic observations of sediments and tilts of the building, the maximum deviation from the vertical surface is 119 mm, the maximum settlement is 83 mm. As part of the elimination of this condition, the base of the building was reinforced with jet-piles, but this technology did not produce significant results.

Figure.10. Strengthening of the walls by metal elements

Figure.9. Сompletion of new premises

Figure.12. Section 1-1

1 1

Figure.11. Pile plan

2 2

Figure.13. Section 2-2

SOIL MODEL

Elastic-perfectly plastic model with limit surface, which is described by the Mohr-Coulomb criterion (Mohr-Coulomb model). This model

is the simplest non-linear model of soil. Its advantage is the simplicity of setting parameters. In describing shear deformations, this

model completely ignores the nonlinearity with volume compression, which is its main disadvantage. All deformations within the

boundary surface are elastic (inverse). In general, the model only slightly supplements the linear model, limiting the level of shear stress.

The results are close to an elastic solution.

Mohr-Coulomb (MC)

The model requires inputting the following parameters: modulus of elasticity E, the Poisson's ratio, angle of internal friction and cohesion.

Fig.14. Yeild surface defined Coulomb-Mohr criterion

Fig.15. Projection of yield surfaces into: (a) deviatoric, (b) meridian plane

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Figure.16. Existing situation (6 floors) of building №69

According to numerical simulation maximum vertical deformations were 6.7mm.

In turn, according to field observations, the deformations were 40 mm.

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Figure.17. Future situation (+13 floors) of building №69 (all 19 floors)

The superstructure of 13

floors leads to a

significant increase in

deformations - 132mm.

This value is 70% more

than the deformations

existing today.

all 19 floors

CONCLUSIONS

1. It was established the mismatch between the values of the real vertical deformations of the base and

deformations found using numerical simulation. This indicates that it is necessary to clarify the

characteristics of the soil base, also is very important the technology of the foundation structures.

2. It was shown that there is a significant mutual influence between the existing building №67 and

building №69. An additional 13 floors will lead to an increase in deformations of the base of building

№67, part of which is already in ultimate limit state.

3. Considering the influence of the superstructure of building №69, it is necessary to develop

engineering measures to eliminate this influence. Without additional measures to stabilize the

deformation of building №67, exploitation becomes impossible.

THANK YOU FOR ATTENTION!!!

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