RU2494194C2 - Method to construct buildings, structures on unevenly compressible soils - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: method to construct preferably high and high-rise buildings and structures on unevenly compressible soils, according to which, after erection of another group from one or several floors of the building, they measure subsidence of foundations, average inclinations of the upper slab above this group of floors and average inclinations of upper slabs above all previously erected groups of floors. On the basis of measurement results and their analysis they decide on deformations of the base and strain stress behaviour of the building at the moment of measurements and until completion of the building, and also on the necessity to impact the soil or the foundation. At first the foundation is erected as designed not for a full load from the building, but for its part, for instance, from the half of the building, in process of erection of this part of the building they measure deformations of foundations and inclinations of slabs, they are used to assess actual characteristics of soil deformability, strain stress behaviour of the building at the moment of measurements and for its completion, and also the necessity to increase the bearing capacity of foundations. Afterwards, if necessary, works are performed to increase the bearing capacity of the foundations by means of increasing of foundation size, strengthening of soils under foundations, for instance, by means of injection of setting solutions, addition of a solid reinforced concrete board to the previously erected foundations, or pressed, screwed or bored piles. The bearing capacity of foundations is increased only in that part, that volume and at that level of height of the constructed building or structure, which provide for safety and permissible level of building deformations until its completion.

EFFECT: increased accuracy of assessment of soil compressibility characteristics in a foundation base in process of erection of a building, a structure, increased validity of analysis of strain stress behaviour of a structure during erection and upon completion of construction, reduced labour intensiveness.

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Description

The present invention relates to the field of construction and is used in the construction and analysis of the stress-strain state of predominantly tall and tall buildings and structures under construction on unevenly compressible soils.

A known method of construction of buildings, structures on unevenly compressible soils (analogue method), including measuring deformations or stresses in the main and additional structural elements, evaluating the compressibility of soils at the base of the foundation and the stress-strain state of the structure at the time of measurement and on the full erection of the structure, assessment of the need, methods and volumes of impact on the soil to improve its properties, if necessary, the implementation of the required impact on the soil and the continuation of the construction structure Ia (Patent RU №2169238 «Method of construction of buildings and structures on uneven ground compressible" [1]).

The disadvantage of the analogue method is the lack of accuracy in assessing the compressibility of soils, since the foundation, designed for full load from the structure, at the time of measurement at the level of 1 / 3-1 / 2 of the height and for the same part of the load from the structure, creates relatively small stresses in soil and the corresponding small precipitation of the foundation.

The closest to the claimed on the basis of essential features adopted as a prototype is the method of building buildings, structures on unevenly compressible soils (prototype method), according to which, after the construction of the next group of one or more floors of the building, measurements are made of the foundations of the foundations, the average slopes of the upper floor above this group floors and the average slopes of the upper floors above all previously constructed groups of floors, and based on the results of measurement and analysis they judge the deformations of the base and the stress-strain state of the structure at the time of measurement and until the structure is completely erected, as well as the need to affect the soil or foundation (Application for a patent “Method for the construction and analysis of the stress-strain state of buildings, structures and other vertically extended objects on unevenly compressible soils ". - FIPS Notification of May 26, 2011 [2]).

The disadvantage of the prototype method as well as the analogue method is the lack of accuracy in evaluating the compressibility of soils, since precipitation and stress in the soil at the base of the foundation at the time of measurement are relatively small.

The purpose of the invention is, first of all, to increase the accuracy of assessing the characteristics of the compressibility of soils at the base of the foundations during the construction of a building, structure and, as a result, to increase the reliability of the analysis of the stress-strain state of the structure during its construction and after completion of construction.

The goal is achieved by the fact that in the method of building buildings, structures on unevenly compressible soils, at first, the foundation of the structure is constructed not based on the full load of the structure, but on its part, for example, on half of the structure, in the process of constructing this part of the structure, measurements of the deformations of foundations and slopes floors, they evaluate the actual characteristics of the deformability of soils, the stress-strain state of the structure at the time of measurement and its full erection, after which, if necessary and they perform work to increase the bearing capacity of foundations by increasing the size of foundations, hardening soils under foundations, for example, by injecting fixing mortars, supplementing previously constructed foundations with a solid reinforced concrete slab, pressed, screwed or bored piles, and increasing the bearing capacity of foundations is carried out only in that part , in that volume and at that level of the height of the building under construction, structures that provide safety and an acceptable level of deformation with trip to its complete completion.

During construction according to the proposed method, the following is achieved.

1) Increasing the reliability of assessing the characteristics of compressibility of soils at the base of foundations and, as a result, increasing the reliability of the analysis of the stress-strain state of a structure during its construction and after completion of construction. Improving the reliability of evaluating the compressibility characteristics of soils is achieved by the fact that the foundation according to the proposed method is not based on the full load of the structure, but only on its part, for example, from half the structure, as a result of which the foundation initially has smaller dimensions, for example, equal to half the area sizes usually calculated for the full load of the building. If a pile-slab foundation is designed, then at first it is constructed as a slab without piles, but holes (nozzles) are provided in the slab so that, if necessary, the piles are immersed.

2) Therefore, during the construction of a part of a building, for example, a multi-story building - up to half its height, stresses and precipitation occur under the foundations, corresponding to stresses and precipitation from a full load. In other words, when constructing a building according to the proposed method, for example, up to half its height, soil is tested with a higher load, which will occur only at the end of the building.

3) Soil loading with full design load allows you to specify the soil deformability characteristics by removing the uncertainty associated with non-linear features of soil behavior under loads, since non-linear effects are fully manifested only as a result of the full design load acting on soils.

4) When implementing the proposed method, the existing contradiction is overcome between the compressibility characteristics of soils obtained from laboratory and field tests and the same characteristics actually calculated from the measurements of deformations of buildings under construction and built: actual deformation modules characterizing the compressibility of soils, in the vast majority of cases significantly higher. This is explained by the caution of survey organizations, which a priori believe that the assignment of low values of the deformation modulus is safer and guarantees higher reliability of design and construction. At the same time, the commonly practiced underestimation of the compressibility characteristics leads to more costly and material-intensive technical solutions of the base-foundation-building system.

5) When constructing a multi-story building, for example, up to half its height, while the foundation is still not needed for the building to the full extent, according to the proposed method, a soil test is actually carried out with a load from the full height of the house, and the obtained values of the soil deformation modules, different for different sections foundation, allow you to evaluate the stress-strain state of the structure to its full height, i.e. on his virtual state in the already built form. It is important that there is no need to establish exactly the deformation modules here - it is enough to calculate the values of the direct parameters used in the calculation of foundations together with the above-ground structure, the bed coefficients at each specific location of the foundation foundation and enter them directly into a computer program for subsequent analysis. There is also no need to use computational models of the theory of linearly deformable bodies, through which they usually pass to the values of bed coefficients.

6) Clarification of the actual characteristics of soils allows minimizing the amount of work to increase the bearing capacity of foundations (by increasing the size, hardening of soils, supplementing foundations with slabs, etc.), as a rule, only in that part, in that volume and at that height level of the building under construction, construction , which ensure the safety and the acceptable level of deformation of the structure until its completion.

An analysis of the prior art did not reveal an analogue characterized by features identical to all the essential features of the proposed solution, i.e. It meets the requirements of novelty. Also, no signs that are distinctive in the claimed solution, i.e. It meets the requirement of inventive step.

The invention is illustrated by drawings (figure 1-9), which schematically shows the plans and vertical sections of an 8-story building with a basement floor 3.0 m high with external walls 1, reinforced concrete frame (columns 2, floors 3). The dimensions of the house in terms of 36 m (in axes 1-6) × 24 m (in axes A-D), height H = 36.0 m; the first three floors of commercial use with a height of 4.0 m, the five upper floors of administrative purposes - 3.6 m.

Figure 1 and 3 shows the engineering and geological structure of the construction site. Below the soles of the foundations are eluvial loams, which according to the initial design assumptions have a specific gravity of 18 kN / m ³ , a design resistance of R = 0.28 MPa = 280 kN / m ² , a deformation modulus of E = 12 MPa, and the loam layer wedges out so that under the foundations along axis 1, its thickness is 2 m, and along axis 6 - 8 m. Below are low-compressible soils - semi-rock varieties of medium-strength porphyrites.

Figure 1 and 2 shows a vertical section of the building (figure 1) and a plan of its foundations (figure 2) at the time of its construction on 3 above-ground floors. The columnar foundations of 4 columns 2 have dimensions I × b = 2.7 × 2.7 m and are designed to absorb the load from the most loaded columns of 2 middle rows along axes 2-5:

- from three floors - N ₃ = 1200 kN (taking into account the weight of the foundations, but excluding the useful and part of the constant load from floors, partitions and finishes);

- complete from eight floors - N ₈ = 2350 kN.

Foundations 4 after the construction of the 3rd floor transmit the average pressure to the soil (taking into account the coefficient Y _fcp . = 1.15 for calculations on deformations) p ₃ = N ₃ / (Y _fcp . · I · b) = 1200 / (1.15 · 2.7 · 2.7) = 145 kN / m ² , and after the construction of the eighth - p ₈ = 280 kN / m ² , which do not exceed the calculated resistance of the loam layer (R = 280 kN / m ² ). Figure 2 shows the concrete preparation 5. For measuring deformations (sediments and slopes of the floors), grades 6, geodetic rails 7 and level I of class 8 are provided.

Figure 3 and 4 shows a vertical section of the building (figure 3) and the plan of the foundations (figure 4) at the time of its construction to 8 above ground floors. The same figures show a reinforced concrete slab 9, the need for the device of which arose as a result of the analysis of the stress-strain state of the building after the construction of the 3rd floor.

Figure 5-9 shows: figure 5 is a graph of the development of sediment foundations along the axes 2 and 5 (positions 10, 11 and 12, respectively); figure 6 - graphs of the development of slopes of floors 3 on the 1st and 3rd floors (positions 13, 14, 15 and 16, respectively).

7-9 show possible ways to increase the bearing capacity of the foundations 4: Fig.7 - the construction of a continuous reinforced concrete slab 9, the upper and lower reinforcement of which 21 is connected with the provided outlets of the reinforcement 22 in the foundation 4; in Fig.8 - injection of fixing solutions under the foundation 4, for which injectors 23 are used, loading plates 24 (preventing leakage of solutions up), connected to the outlets of the reinforcement 22 in the foundation 4; the increase in the bearing capacity of the foundations 4 is achieved by the formation in the soil of the areas of hardened soil 25; Fig.9 - the immersion of steel piles 26 next to the foundations 4 in accordance with the patent [3], for which there are stops 27 connected to the outlets of the reinforcement 22 in the foundation 4, jacks 28 and pump station 29. After immersion, the piles 26 are connected to the stops 27 welds 30.

In this example, during the scientific and technical support of construction in accordance with the requirements of the standards (GOST R 53778-2010 [4], GOST 24846-81 [5]), precipitation and the slopes of the floors are given in Table 1.

Tab. one Precipitation of foundations S and slopes of floors i Axes, floors Precipitation S (cm) and slopes of floors i (x1000), with the number of floors built 3 four 6 8 Axis 2 1.20 / 0.90 / - 1.30 / 1.28 / 1.28 1.60 / 1.50 / 1.50 1.80 / 1.65 / 1.65 Axis 5 4.00 / 3.00 / - 4.60 / 4.45 / 4.30 5.50 / 5.13 / 4.90 6.90 / 6.20 / 5.20 Tilt, 1st floor 1.60 / 1.06 / - 1.83 / 1.76 / 1.66 2.16 / 2.01 / 2.83 2.83 / 2.52 / 1.97 Tilt, 3rd floor 1.20 / 0.80 / - 1.30 / 1.37 / 1.25 1.46 / 1.36 / 1.32 1.70 / 1.54 / 1.50 Tilt, 8th floor - - - 2.83 / 2.12 / 1.92 Note - The numbers in the columns, for example, 4.60 / 4.45 / 4.30.6, correspond to the precipitation obtained for each floor: 1st — by calculation with the initial characteristics of the soil, 2nd — after clarification of the characteristics, 3rd — after strengthening some of the foundations by device reinforced concrete slab

Figure 1 shows that by the time of construction of the 3rd floor the building received a general inclination towards the axis 6; foundation settlement along axis 2 was S ₃ = 1.2 cm, along axis 5-S ₃ = 4.0 cm; the slope of the overlap of the 1st floor i ₁ = 0.0016, of the 3rd floor - i ₃ = 0.0012. The forecast for the 8-story state of the house is precipitation along the axis S ₂ = 1.80 cm, along the axis 6 - S ₆ = 6.9 cm, the largest slope of the floors of the 8th floor is i ₈ = 0.00283, more than that allowed by the SNiP 2.01.04-85 * [ 6] the values of [i] _u = 0.002.

Using the obtained data and calculation schemes of chapter SP 22.13350.20011 [7], the actual values of the loam deformation modulus were obtained from the values of sediments and ground pressures after the construction of the 3rd floor: E = 16 MPa, 33% higher than the calculated value E = 12 MPa . The corresponding bed coefficients change as follows: along the 2 axis - from K ₂ = 9062 (according to the initial values E = 12 MPa) to K ₂ = 12083 kN / m ³ , along the 5 axis - from K ₅ = 2719 to K ₅ = 3625 kN / m ³ (here rainfall S in meters).

Given the probability of the projected excess of the slopes of the floors 3 and the deviation of the house from the vertical by ΔH = 8.8 cm against the allowable head of SNiP 2.01-07-85 * [6] of the value [ΔH] _u = N / 500 = 36/500 = 0.072 = 7.2 cm, it is accepted a decision on engineering intervention and the implementation of the “deferred decision”.

From a set of the above methods of engineering intervention, it was decided to build near the columnar foundations 4 in the axes 3-4-6 reinforced concrete slab 9 with a thickness of 0.8 m (see figure 2). Plate 9 with an area of A. _pl . = 432 m ^{2 was} built after the construction of the 3rd floor. According to the calculation, the load on the plate creates additional pressure on the soil p = 61.1 kN / m ² .

Subsequent calculations showed that uneven precipitation and slopes of floors 3 significantly decrease against those values that could occur without the installation of slab 9. In particular, after the construction of the 8th floor, the predicted precipitation of the foundations 4 along axis 2 (S ₂ = 1.65 cm) did not change , and along the 5 axis they decreased from S ₂ = 6.9 to 5.2 cm. The slopes of floors 3 changed as follows: on the 1st floor i ₁ - from 0.0016 to 0.0019, on the 3rd floor i ₃ - from 0.0012 to 0.0015, on 8- m floor i ₈ - from 0.00283 to 0.00193.

The deviation of the top of the building from the vertical decreased from ΔН = 8.8 cm to ΔН = 4.9 cm.

All monitored parameters are within the permissible standards:

- maximum ground pressure p = 280 kN / m ² (foundations 4 in axes 1-3) and p = 145 kN / m ² (plate in axes 3-4-6) does not exceed the calculated soil resistance R = 280 kN / m ² ;

- maximum draft S _max = 5.20 <[S] _u = 10 cm;

- slopes of the floors of the 1st floor i _max = 0.0012 <[i] _u = 0.002;

- the slopes of the floors of the 8th floor i _max = 0.00192 <[i] _u = 0.002;

- the deviation of the house from the vertical ΔН = 4.9 cm <[ΔН] _u = 7.2 cm.

Thus, the advantages of the proposed method are as follows.

1) Improving the accuracy of assessing the characteristics of compressibility of soils at the base of the foundations and, as a result, improving the reliability of the analysis of the stress-strain state of the structure during its construction and after completion of construction.

2) Removing the uncertainty associated with the non-linearity of soils under loads.

3) Overcoming the existing contradiction between the compressibility characteristics of soils obtained by the test results, and the characteristics actually calculated by measuring the deformations of buildings under construction and constructed.

4) The ability to assess the stress-strain state of the structure to its full height, i.e. on his virtual state in the already built form.

5) The ability to minimize the amount of work to increase the bearing capacity of foundations, which provide safety and an acceptable level of deformation of the structure until it is completed.

List of materials used

1. Patent RU No. 2162917, MKI ⁷ E02D 3/12, 37/00. A method of fixing soils at the base of deformed buildings and structures. - Publ. 12/10/2001, Bull. Number 4.

2. Application for a patent: date of receipt 05.24.2011, input. No. 030864, reg. No. 20111120865 “Method of construction and analysis of the stress-strain state of buildings, structures and other vertically extended objects on unevenly compressible soils”. - Notification of the department №17 FIPS from 05.26.2011.

3. Patent RU No. 2037604, MKI ⁶ E02D 27/08, 37/00 E02D 27/34. A way to strengthen the foundation of a building, structure. / E.I. Mulukov and I.P. Little one. - Publ. 06/19/1995.

4. GOST R 53778-2010. Buildings and constructions. Rules for inspection and monitoring of technical condition. / Federal Agency for Technical Regulation and Metrology. - M .: Standartinform, 2010.

5. GOST 24846-81. Soils. Methods for measuring the deformation of the foundations of buildings and structures. - M .: IPK Publishing House of Standards, 1981.

6. SNiP 2.01.07-85 *. Loads and impacts. / Gosstroy of Russia. - M .: GP TsPP, 2003.

7. SP 22.13350.20011. Foundations of buildings and structures (updated edition of SNIP 2.02.01-83 *). / Gosstroy of Russia. - M.: OJSC “TsPP”, 2011.

Claims (1)

A method of constructing predominantly tall and tall buildings and structures on unevenly compressible soils, according to which, after the construction of the next group of one or several floors of the structure, measurements of foundation precipitation, the average slopes of the upper floor above this group of floors and the average slopes of the upper floors above all previously constructed floor groups , and according to the results of the measurement and their analysis, they judge the deformations of the base and the stress-strain state of the structure at the time of measurement and to the floor erection of the building, as well as the need for exposure to the soil or foundation, characterized in that at first the foundation is constructed not to fully load the building, but for its part, for example, from half the structure, in the process of constructing this part of the structure, measurements of the deformations of the foundations and slopes of the floors, they evaluate the actual characteristics of the deformability of soils, the stress-strain state of the structure at the time of measurement and its full erection, as well as the need to increase the foundation abilities, after which, if necessary, work is carried out to increase the bearing capacity of the foundations by increasing the size of the foundations, hardening the soils under the foundations, for example, by injecting fixing solutions, supplementing the previously constructed foundations with a solid reinforced concrete slab, pressed, screwed or bored piles, and increasing the bearing capacity of the foundations is carried out only in that part, in the volume and at that level of the height of the building under construction, structures that provide safety and allowable level of deformation of the building until its completion.

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