Analysis of Technological Processes for Buildings Tilt Correction

December 15, 2014

The structure tilting often occurs during civil engineering works. It is one of the major criteria to determine serviceability. Building tilt may be generated due to significant heterogenity of soil foundation, its artificial or natural moistening, asymmetric static or dynamic load in a structure, asymmetric effect of railroad or other transport on a foundation, use of pile insertion technology that does not satisfy soil conditions of a construction site, different conditions in combination.

Over the last years the number of pre-emergency and emergency situations has increased at construction sites, these situations being driven by non-uniform deformations of foundation soils and tilts arising on this account. If tilt exceeds allowable value, then tilt stabilization is applied. As for emergency conditions, when a structure is in a state of failure, such drastic measure as tilt correction is to be applied.

Maximum allowable tilt value for different buildings is given in the below table.

At implementation of a package of measures it is acceptable to take maximum allowable tilt of residential and public buildings equal to: iu = 0.008 – for buildings without elevators and also in case if the project provides special measures on alignment of elevator shaft guide rails; i_u = 0.005 – if the mentioned measures are not provided

The current situation requires both elaboration of efficient techniques and technological process refinement

In order to improve the applicable tilt correction methods or to develop new ones, the following tasks shall be set and carried out: improve the equipment, reduce the cost of technological process and reduce the works duration

Building jacking by hydraulic cylinder jacks is one of the known building tilt correction methods. Jacks are mounted on Mega piles’ heads jacked up to more or less incompressible soils.[1] Among disadvantages of this method the following may be mentioned: significant labour intensity and high accomplishment costs because of large pre-construction activities and necessity to use special equipment; it is impossible to apply this method when foundation soils have elevated compressibility and degree of saturation

Another method is hydromechanical correction of multistory building and structure tilt by waterjet scouring and extraction of some soil from contact area of foundation slab basement. [2] This method is fulfilled by boring of holes in the foundation slab. Metallic injectors are inserted in these holes in order to transmit water under pressure to foundation soils with subsequent generation and extraction of slurry. Such extraction of soil volumes from under the foundation slab results in slab deflection both in lengthwise and crosswise directions. Technological difficulties and high method accomplishment cost as well as complexity of building position control in lengthwise and crosswise directions are the method disadvantages

Technology of horizontal drilling-out of wells under the foundation base is further used. Technological process consists in the following: excavation of a pit at the less settled side of the building, horizontal drilling of wells of varying diameter with soil excavation from under the foundation base in a local area, building’s planned-high-altitude position adjustment by means of soil moistening (softening) around the wells. [3]

The figure below shows a schematic illustration of soil softening technology under the building unsettled side by formation of horizontal wells.

Schematic Illustration of Soil Softening Technology Under The building Unsettled Side by Formation of Horizontal Wells

Works principal stages were as follows: examination of buildings and soils condition, drawing up of a flowchart for tilt correction, special production and processing features of tilt correction, strengthening of soils after building stabilization, geodetic observations of geometric position and elimination of building defects, planning works at the site

The following works are classified as the main ones: definition of building stereometry and comparison between a tilt and a specified value, characterization of foundation soils and foundations as well as of their differential settlement, identification of defects in bearing structures, works on strength test of construction materials and structures, calculation of structure bearing capacity taking into account the impact of defects and damages found during expert evaluation, development of a package of measures for damaged structure renovation and repair

Works results are summed up in a Technical Statement or an Inspection Report

The flowchart consists of the following: scope, procedures of work organization and performance, requirements to quality and acceptance of works, calculation of labour costs, machine time and wages, schedule of works, material and technical resources schedule, safety norms, technical and economic parameters

The scope of the work performance comprises the following works: dismantling of asphalt cover, mechanical pit excavation, fixation of pit walls in order to prevent caving, pit bottom leveling, laying out of horizontal well axes, installation of equipment and of power cable with knife switch, drilling of wells using the suggested equipment, geodetic observations of the building settlement, disassembly of equipment, backfilling, surveillance at all working stages

Reduction of works duration is a specific feature of tilt correction working method. For the suggested equipment tilt correction may be performed lengthwise.

The suggested drilling device being used for wells drilling differs from the one designed by Zaporizhzhia Branch of Research Institute for Building Structures (ZO NIISK). This device operates through combination of two tasks (it destructs and extracts the soil out of the well simultaneously). Geodetic marks were placed after drilling of wells in order to observe settlement of foundation characteristic points in the course of tilt correction works performance. The obtained results were used to adjust volumes of the extracted soil in certain basement points.

Wells diameters shall be calculated as follows: maximum diameter is Ø 250 mm, minimum diameter is Ø 100 mm. Peculiarity of the suggested drilling device consists in simultaneous drilling-out and extraction of soil from the horizontal well.

Drilling Machine for Horizontal Drilling of Wells

This method has been used for tilt correction of the residential house located at the address: Gudymenko street, 15, Zaporizhzhia city.

Figure below shows earthwork operation diagram during tilt correction of the building.

Tilt correction technology is based on soil extraction from under the foundation base in the area of excessive soil upheaval.

Wells were drilled under the foundation in order to destruct and extract the soil according to a calculated pattern, depending on soil stress state and soil strength.

Earthwork Operation Diagram During Horizontal Drilling-Out of Wells

Conclusion

1. Known technological processes for building tilt correction have been examined.
2. Technical rules and operating procedures on building tilt correction have been worked out.

Reference Literature

[1] V.G. Simagin, P.А. Konovalov. Basements and foundations after interruption of civil engineering works. – Petrozavodsk, Moscow: Publishing house of Association of Construction Higher Educational Institutions. – 2004, p.151.

[2] A.P. Krivorotov, A.V. Lubiagin. On tilt correction of high buildings built on mattress foundations. Novosibirsk. News of Higher Educational Institutions. Construction, 2005, No. 2. – p. 113-116

[3] Ukrainian Patent for Invention No. 65455. Methods of buildings and structures de-tilting. Authors: I. V. Stepura, V.S. Shokariev, A.V. Pavlov, A.S. Tregub, R.V. Samchenko