RU2301303C2 - Slab-and-pile foundation - Google Patents

Abstract

FIELD: construction, particularly slap-and-pile foundations for buildings and building structures.

SUBSTANCE: slab-and-pile comprises reinforced concrete slab or grillage and damping mats arranged between pile heads and reinforced concrete slab or grillage and made of easily deformable material. The damping mats are made of material having uniform compressibility, for instance of extruded expanded polystyrene. Designed damping mat thicknesses are 10-60 mm and increase from central and intermediate pile rows towards extreme ones and towards corner piles with 1:2:3 ratio or damping mats have equal thicknesses of 10-60 mm. Stress-strain modulus ratio of damping mats arranged over central pile rows, extreme pile rows and corner piles is 3:2:1. In the case of slab-and-pile foundation construction in non-uniformly compressible ground damping mat of easily deformable material is located under reinforced concrete slab or grillage supported by non-uniformly compressible ground. Damping mat thickness δ may be determined from δ≥[S_p.f+S_m.max-L(ΔS/L)_u]E₀/p, m, where S_p.f is maximal pile foundation settlement if mat compression is excluded, m; S_m.max is maximal settlement caused by mat compression over piles, m; p is average pressure applied to ground at slab bottom over slab area supported by incompressible ground, MPa; L is reinforced concrete slab dimension in plan view, m; (ΔS/L)_u is maximal value of relative settlement difference and E₀ is mat material stress-strain modulus in area of mat abutting upon incompressible ground.

EFFECT: increased uniformity of load distribution among piles and reinforced concrete slab or grillage and decreased material consumption.

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Description

The invention relates to the field of construction and is proposed for the device of slab-pile foundations of buildings and structures, including a reinforced concrete slab or grillage and piles.

Known pile foundation (foundation-analogue), including piles, reinforced concrete slab or grillage and damping pads above the heads of piles, in which reinforced concrete slab or grillage is involved in work under loads from buildings and structures, and after compression of the damping gaskets - piles (copyright certificate No. 947287, M. cl. ³ E02D 27/12 [1]).

For more information, see also copyright certificate No. 3112016 [3], in the book. “Studies to identify the reserve of bearing capacity of pile bushes” [4] and in the article “Ways to improve the efficiency of pile foundations” [5].

However, in the well-known pile foundation-analogue, including grillage, piles and damping pads of the same thickness, it is impossible to achieve a given load distribution between piles and a reinforced concrete slab or grillage, which would reduce the material consumption of the foundation by reducing the cost of concrete and / or reinforcement.

Known combined pile-slab foundation (prototype foundation), including piles and reinforced concrete slab or grillage, the load perception from buildings and structures which is provided by the joint work of grillage slabs and piles (SP 50-102-2003 "Design and construction of pile foundations" [2], clauses 7.4.10 ... 7.4.14).

However, in the well-known combined pile-slab foundation prototype, a reinforced concrete slab or grillage perceives only about 15% of the external load, and piles - about 85%. In addition, in the well-known pile-slab foundation, the extreme rows of piles receive a load of 2 times, and corner piles - 3 times the average load on piles in the foundation. As a result, large bending moments appear in a number of sections and especially in the marginal sections of a reinforced concrete slab or grillage, which leads to an increase in the material consumption of the foundation due to an increase in the consumption of concrete and / or reinforcement. It is also impossible to use the prototype foundation when constructing foundations on unevenly compressible soils, in particular, in the case of supporting part of the slab or grillage on incompressible soil.

The purpose of the claimed invention is:

in providing the possibility of a given, in particular more uniform, load distribution between piles and reinforced concrete slab or grillage and reducing the material consumption of the slab-pile foundation by reducing the cost of concrete and / or reinforcement;

in providing the possibility of constructing a slab-pile foundation on unevenly compressible soils.

The goal is achieved in that in a slab-pile foundation, including piles and reinforced concrete slab or grillage, damping gaskets between the heads of piles and reinforced concrete slab or grillage of easily deformable material, damping gaskets of material with uniform compressibility are made of extruded polystyrene foam, and the calculated thickness of the damper laying is accepted in the range from 10 to 60 mm with an increase in the direction from the central and middle rows of piles to the extreme rows of piles and corner piles with a ratio of 1: 2: 3 , or have the same thickness in the range from 10 to 60 mm, and the ratio of the deformation modulus of the gasket material over the heads of the middle rows of piles, the extreme rows of piles and over the corner piles is taken as 3: 2: 1, and when the slab-pile foundation is installed on unevenly compressible soils, under a part of a reinforced concrete slab or grillage, supported by incompressible soil, a damping pad of easily deformable material is installed, the thickness of which δ is determined from relation (1):

where S _St. - settlement of the pile foundation, excluding gasket compression, m;

S _pr.max - maximum draft from compression of gaskets over piles, m;

p is the average pressure on the soil at the bottom of the plate in the place of bearing on incompressible soil, MPa;

L is the size of the reinforced concrete slab in plan, m;

(ΔS / L) _u is the limit value of the relative difference of sediments;

E _about - the module of deformation of the gasket material in the place of bearing on incompressible soil.

The adoption of the thickness of the gasket according to formula (1) eliminates the formation of uneven deposits of individual parts of the plate or grillage in the case of supporting part of the plate or grillage on incompressible soil, and part of the plate or grillage on piles.

The above thickness of the damping pads δ is determined as follows. It is known that the load-bearing capacity of piles is almost completely realized with pile deposits ranging from 10 to 20 mm (see, for example, the book: “Piles in hydraulic construction” [7], Fig. 4.36). In addition, it is known that the maximum pile upset at which the transferred load is taken as the calculated one is 40 mm (see SNiP 2.02.03-85 [6], clause 5.5). Therefore, for inclusion in work under loads of piles, it is necessary to create their vertical movement in the range from 10-20 cm to 40 mm. A zero value of the thickness of the damping gaskets (δ = 0 mm) is required when it becomes necessary to load part of the piles (for example, piles of middle rows) from the first stages of applying an external load.

When choosing damping gaskets, the permissible precipitation of the pile foundation and the bending of the reinforced concrete slab or grillage are taken into account, which depend on the compressibility of the soil, the stiffness of the reinforced concrete slab or grillage, the compressibility of the gasket material and on the distribution of loads between piles and reinforced concrete slab or grillage (for example, according to the technical solution of the foundation prototype [2]).

It is proposed to use extruded polystyrene as a material for damping pads, manufactured by a number of Russian (Penoplex and others) and foreign (Styrofoam and other) companies, having a deformation modulus from E _o = 0.5 MPa to E _o = 2-3 MPa .

The advantage of extruded polystyrene foam over other similar materials is that it has closed pores, has great water-, frost-, and bio-resistance and has a fairly high initial strength (0.1 MPa ... 0.5 MPa). The last property of polystyrene foam allows you to completely save the specified initial height of the gaskets δ _about at relatively small loads that occur when concreting a reinforced concrete slab or grillage. In addition, the manufacture of gaskets with strictly parallel surfaces ensures reliable contact quality of the pile heads with a reinforced concrete slab or grillage after the formation of a complete draft of the slab or grillage.

For loads on piles in the composition of the slab-pile foundation from N = 200 kN to N = 400-600 kN and a cross section of piles from 0.2 × 0.2 m to 0.4 × 0.4 m in the material of deformable gaskets above the heads of piles (after receiving a reinforced concrete slab or grillage precipitation) stresses occur in the range from 1.0 to 10.0 MPa. Considering that with an increase in the load on the plate-pile foundation, these stresses will lead to a decrease in the thickness of the damped gaskets from the initial value δ _о to the value δ, which is 80-90% of δ _о (depending on the density of the gasket material and the actual load on the pile), the active (“selected” under load) damping pad thickness, as noted, should be no more than δ = 60 mm, and the initial thickness should be no more than δ _о = 70 mm.

The proposed solution for the slab-pile foundation does not contradict the requirements of chapter SNiP 2.02.03-85 [6], according to clause 7.4 of which pivotable joints of the pile with the grill and pile heads with the closure of the pile head into the grill by 5-10 cm are allowed, and according to the note to Clause 7.6, with pile loads of 400 kN or less, piling the pile head into the grillage is not required.

The totality of the proposals formulated ensures the achievement of the goal - the possibility of a given load distribution between piles and a reinforced concrete slab or grillage, which ensures a reduction in the material consumption of the foundation by reducing the cost of concrete and / or reinforcement.

In the analysis of the prior art, no analogue has been identified, characterized by features identical to all the essential features of the proposed solution, i.e. It meets the requirements of novelty.

Not detected are also signs that are distinctive in the claimed solution, i.e. It meets the requirement of inventive step.

The essence of the invention is illustrated by drawings (figure 1-4), which illustrate: figure 1 - plate-pile foundation in plan, and figure 2 is the same in the context of "aa"; figure 3 shows the node And the cantilever section of the plate, taking in bb section the bending moment from the loads on the piles of the extreme rows and from the corner piles, and the dimensions of the damping pad before (δ _o ) and after (δ) the load transmitted by the corner pile; figure 4 - plate-pile foundation, partially based on incompressible soil.

Figures 1 and 2 show a slab-pile foundation, including a reinforced concrete slab 1 with a length of L = 9.50 m and a width of B = 5.0 m and piles 2-4 with a cross section of 0.25 × 0.25 m and a length of 5 m each. Of these, 10 are the central piles 2, 14 piles of the outermost rows 3 and 4 of the corner piles 4. The foundation is based on compressible soils represented by fine medium-density sand, characterized by a porosity coefficient e = 0.73, specific gravity γ = 18 kN / m ³ , and deformation modulus E = 7.0 MPa and an angle of internal friction of φ = 28 °.

Damping pads made of extruded Penoplex polystyrene foam having a deformation modulus E _о = 1.0 MPa were installed above the pile heads: above the central piles 2, with an estimated thickness of δ = 2.0 cm (item 5); above the piles of the extreme rows 3 - δ = 4.0 cm (not shown in Fig. 2), above the corner piles 4 - δ = 6.0 cm (pos. 6). Accordingly, the initial thickness of the gaskets 5, 6 is δ _о = 2.5 and 7.0 cm.

The foundation is loaded with vertical forces N ₁ -N ₃ , moments M ₁ -M ₃ and distributed loads q ₁ -q ₂ . The total vertical component of the external load ΣN = 10200 kN, taking into account the weight of the reinforced concrete slab 1 and piles 2-4. The average load on each of the piles is N _cf. = 364 kN.

In the well-known combined pile-slab foundation prototype [2], the external load ΣN is distributed as follows: on a reinforced concrete slab N _pl. = 1530 kN (15% of the value of ΣN), on piles N _St. = 8670 kN (85% of ΣN). The load per pile N _St. = 8670 kN, in turn, is distributed unevenly between the piles: the piles of the central rows 2 perceive the load N ₂ = 173.4 kN, the piles of the extreme rows 3 - N ₃ = 346.8 kN, the corner piles 4 - N ₄ = 520.2 kN. As a result, a bending moment arises in the “bb” section (see FIGS. 1-3), equal to M _bb = 2 (N ₃ + N ₄ ) I = 2 (346.8 + 520.2) 1.05 = 1820.7 kN · m, according to which lower reinforcement of reinforced concrete slab (I = 1.05 m - the size of the basement console 1, see figure 3).

From the calculation in accordance with the instructions of SNiP 2.02.01-83 * [8] it follows:

- the average pressure on the soil under the sole of plate 1 would be p = 0.215 MPa;

- the sediment of the plate 1 in the absence of piles 2-4 would be S _PL = 12.3 cm, and the compressible thickness N _c = 9.7 m from the bottom mark of plate 1;

- settlement of the pile foundation according to the instructions of SNiP 2.02.03-85 [6] (as a conditional foundation 7, the contours of which are shown in figure 2 at an angle of inclination of the face of the conditional foundation to the vertical equal to ψ = φ / 4 = 28/4 = 7 ° ), would be S _St. = 9.6 cm, compressible zone H _with = 7.9 m below the ends of piles 2-4, i.e. 12.9 m from the bottom of plate 1.

The proposed slab-pile foundation (figure 1, 2) works as follows. At the initial stage, the loads from the building are transferred to the slab-pile foundation directly to the soil located under the sole of the reinforced concrete slab 1. The resulting precipitation of the slab 1 first causes the loading of the central piles 2, over which damping pads 5 of smaller thickness are installed (δ = 2.0 cm) , then, as the loads on the plate 1 increase, gradual compression of the damping gaskets of the extreme row 3 piles and the corner piles 4 (pos. 6), having an estimated thickness δ = 4.0-6.0 cm.

When the settlement of reinforced concrete slabs equal to S _pl. = 2.0 cm (active thickness δ of damping pads 5), a reinforced concrete slab perceives a load of N _pl. = αΣN, where α = S _pl. / S _pl.f. = 2.0 / 12.3 = 0.162 is a coefficient characterizing the fraction of the achieved precipitation with respect to the estimated settlement of plate 1 without piles 2-4, i.e. a load equal to 16.2% of the total load on the slab-pile foundation.

When the settlement of reinforced concrete slab 1, equal to S _PL. = 3.0-4.0 cm, a part of the external load is transferred to the central piles 2. In this case, the proportion of the load perceived by the plate 1 continues to increase and reaches α = S _square. / S _pl.f. ranging from 0.244 to 0.325 (i.e., from 24.4 to 32.5%).

During subsequent settlement of plate 1, sequential loading of piles of extreme rows 3 occurs (with a draft of S = 4.0-5.0 cm), then of corner piles 4 (with a settlement of plate S of more than 7.0-8.0 cm). With a full load on the foundation, slab 1 takes up 50% of the total load on the foundation (N _pl. = 0.5 · 10200 = 510 kN), and the rest (N _st. = 510 kN) is distributed evenly between the piles 2-4 - 182.14 kN each on each.

As a result, the bending moment in the section “bb” (see FIGS. 1-3) becomes equal to M _bb = 2 (182.14 + 182.14) 1.05 = 765.0 kN · m, i.e. decreases 2.38 times against the corresponding value in the prototype foundation [2].

The precipitation of the plate-pile foundation is composed of the precipitation of the actual plate 1 (S _pl. ), Equal to the compression value of the damping gaskets 6 (S _pr.max ), i.e. S _pl. = S _sp.max = 6.0 cm, and also from the draft of the conventional pile foundation 7 from the load N _pl. = 0.5ΣN = 0.5 · 10200 = 510 kN (S _{light St.} = 3.5 cm), total S _{square - St.} = 10.5 cm. They do not exceed the maximum permissible precipitation S _u = 15 cm (see [6], Appendix 4, taking into account Note 5).

Thus, the positive effect of the proposed foundation in comparison with the foundation of the prototype [2] is as follows:

- plate 1 perceives up to 50% of the external load against 15%;

- piles 2-4 perceive a uniform load; there is no need to increase the cross-section and / or length of piles of the extreme row 3 and corner piles 4 for the perception of 2- and 3-fold loads;

- the bending moment in the section “b-b” of plate 1 is reduced 2.38 times;

- precipitation of the slab-pile foundation practically does not increase (due to the perception by the slab of most of the external load ΣN on the foundation);

- the bearing capacity of piles 2-4 increases due to the compression of their side surfaces by the pressure arising from the precipitation of the plate 1 until the complete compression of the damping pads 5, 6.

These advantages lead to a decrease in the material consumption of the foundation by reducing the consumption of concrete and / or reinforcement.

Figure 4 shows a slab-pile foundation, including a reinforced concrete slab 1 and grill 2. The foundation is supported by a part of the sole on compressible soils (fine sand), and partly on incompressible (rocky) soil 8. The thickness of the damping pad 9 over incompressible soil 8 is determined from relation (1), which formalizes the condition for preventing the limiting relative difference between the sediments of individual parts of the plate-pile foundation. For the example discussed in figures 1-3, the gasket should have a thickness determined by the formula (1):

δ≥ [S _St. + S _sp.max -L (ΔS / L) _u ] E _o /p=►0.035+0.06-9.5· 0.002] 0.5 / 0.215 = 0.175 m = 17.5 cm,

where S _St. = 3.5 cm = 0.035 m - settlement of the pile foundation without taking into account the compression of gaskets 5, 6, m;

S _av.max = 0.06 m - maximum draft from compression of the strip 6 over the corner pile 4;

p = 0.215 MPa - the average pressure on the soil at the bottom of the plate 1 in the place of its support on incompressible soil 8;

L = 9.5 m - the size of the reinforced concrete slab 1 in the plan;

(ΔS / L) _u = 0.004 is the limiting value of the relative difference of sediment [8];

E _o = E ₉ = 0.5 MPa - the deformation modulus of the material of the damping pad 9 in the place of bearing on incompressible soil, MPa.

Information sources

1. Copyright certificate No. 947287, M. cl ³ E02D 27/12. The method of construction of the pile foundation / V.V. Lushnikov and I.A. Mareninov. - Publ. BI 1982, No. 28 (analogue foundation).

2. SP 50-102-2003. Design and installation of pile foundations / Gosstroy of Russia. - M.: FSUE TsPP., 2004 .-- 81 p. (prototype foundation).

3. Copyright certificate No. 3112016, M. cl. ³ E02D 27/12. The method of construction / B.M. Gil, N.S. Metelyuk and I.P. Shapoval. - Publ. BI 1971, No. 25.

4. Metelyuk N.S., Gruzintsev V.V., Kutsenko A.V. Studies to identify the reserve of bearing capacity of pile bushes // Foundations, foundations and soil mechanics, 1977, No. 6. - S.9-11.

5. Lushnikov VV Ways to improve the efficiency of pile foundations - In the book. “Proceedings of the VI International Conference on Pile Foundation Engineering, Volume III. - M .: 1998. - P.81-85.

6. SNiP 2.02.03-85. Pile foundations / Gosstroy of Russia. - M .: GUP TsPP, 2001 .-- 48 p.

7. Fedorovsky V.G., Levachev S.N. et al. Piles in hydraulic engineering: Textbook. M .: Publishing house ASV, 2003. - 240 p.

8. SNiP 2.02.01-83 *. Foundations of buildings and structures / Gosstroy of Russia. - M .: GUP TsPP, 2001 .-- 48 p.

Claims (1)

Slab-pile foundation, including piles and reinforced concrete slab or grillage, damping pads between the heads of piles and reinforced concrete slab or grillage of easily deformable material, characterized in that the damping pads of uniform compressibility material are made of extruded polystyrene foam, and the calculated thickness of the damper is accepted in from 10 to 60 mm with an increase in the direction from the central and middle rows of piles to the extreme rows of piles and corner piles with a ratio of 1: 2: 3 or the same thickness ranging from 10 to 60 mm, and the ratio of the deformation modulus of the gasket material above the heads of the middle rows of piles, the extreme rows of piles and above the corner piles is taken as 3: 2: 1, and when the slab-pile foundation is installed on unevenly compressible soils, under a part of a reinforced concrete slab or grillage resting on incompressible soil, a damping pad of easily deformable material is installed, the thickness of which δ is determined from the relation (1)

where S _{St. f} - _settlement pile foundation without taking into account the compression of gaskets, m; S _pr.max - maximum draft from compression of gaskets over piles, m; p is the average pressure on the soil at the bottom of the plate in the place of bearing on incompressible soil, MPa; L is the size of the reinforced concrete slab in plan, m; (ΔS / L) _u is the limit value of the relative difference of sediments; E ₀ - the module of deformation of the gasket material in the place of bearing on incompressible soil.

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