CN104164869B - Band supporting leg diaphram wall Computing Method for Vertical Bearing Capacity - Google Patents

Abstract

The present invention relates to a kind of band supporting leg ground diaphragm wall Computing Method for Vertical Bearing Capacity. First the present invention is with supporting leg diaphram wall bearing capacity composition analysis; Secondly determine the bearing capacity of supporting leg and the bearing capacity of wall section, thereby obtain being with supporting leg diaphram wall bearing capacity; Then to the vertical bearing capacity checking computations of band supporting leg diaphram wall and the checking computations of supporting leg vertical bearing capacity; Finally obtain being with supporting leg diaphram wall vertical bearing capacity. The present invention, without carrying out special geotechnical engineering investigation, can adapt to the widespread adoption of engineering.

Description

Calculation method of vertical bearing capacity of underground diaphragm wall with outriggers

technical field

The invention belongs to the field of geotechnical engineering and foundation pit engineering in civil engineering specialty, and is generally used for building (structure) basements or underground structures.

Background technique

With the expansion of the city, the number of cars increases, and the basements of high-rise buildings are deepening day by day, major cities are exploring the development of roads underground, and the development and construction of underground space is in full swing. In the process of underground space construction with increasing area and depth, deep and thick underground diaphragm wall technology has been widely used, but there are still the following problems:

1. It is mainly used as the enclosure wall of the basement, and does not consider bearing the vertical load of the main structure.

2. When the bedrock is required as the bearing layer, the construction difficulty and project cost increase when the underground diaphragm wall enters the rock.

The underground diaphragm wall with outriggers is an innovation of the underground diaphragm wall according to specific soil conditions and specific use functions. It is a special underground diaphragm wall. After the outriggers are set at the bottom of the underground diaphragm wall, because the outriggers enter the lower better bearing layer or bedrock, they can also be used as engineering piles to exert their end bearing function, and finally make the underground diaphragm wall with outriggers bear the vertical load of the main structure , and at the same time reduce the construction difficulty of the underground diaphragm wall into the rock, and reduce the project cost.

After the underground diaphragm wall with outriggers bears the vertical load, engineering piles can be reduced, and the problems of difficulty in entering the rock and high cost of the wall can be solved. Compared with common underground diaphragm walls, the social and economic benefits are remarkable.

At present, there are no related studies and reports on underground diaphragm walls with outriggers abroad. In China, only Guangdong Province has carried out construction practices similar to underground diaphragm walls with outriggers as early as the end of the last century. The project scale is small and there is no impact on the underground diaphragm walls with outriggers Conduct systematic practice and theoretical research on force and deformation characteristics, scope of application, etc.

The underground diaphragm wall with outriggers is a new type of underground diaphragm wall, and there is no corresponding design method in the current national standard. The existing pile foundation formula is suitable for round piles or square piles with a single cross section, and cannot reflect the fact that the bearing layers of the wall section and the outrigger are not consistent, and the end bearing sections of the wall section and the outrigger are not the same.

Contents of the invention

In order to enable engineering designers to determine the vertical bearing capacity of the underground diaphragm wall with outriggers according to the existing engineering survey data and data, the present invention provides the characteristic values of friction and bearing capacity of each layer of soil provided according to the engineering survey report, The calculation method for determining the vertical bearing capacity of an underground diaphragm wall with outriggers, the present invention includes:

Step 1: Compositional analysis of the bearing capacity of the underground diaphragm wall with outriggers.

Step 2: Determine the bearing capacity formula of the outrigger and calculate the vertical bearing capacity of the outrigger.

Step 3: Determine the bearing capacity formula of the wall segment, and calculate the vertical bearing capacity of the wall segment.

Step 4: From Step 2 and Step 3, calculate the bearing capacity of the underground diaphragm wall with outriggers.

Step 5: Check the vertical bearing capacity of the underground diaphragm wall with outriggers.

Step 6: Check the vertical bearing capacity of the outrigger.

Step 7: After checking and calculating in steps 5 and 6, the vertical bearing capacity of the underground diaphragm wall with outriggers is finally obtained.

Beneficial effects of the present invention:

1. The end resistance of the section of the underground diaphragm wall with outriggers and the outriggers can be exerted together, and the vertical bearing capacity of the underground diaphragm wall with outriggers can be improved.

2. Provide the calculation formula of the vertical bearing capacity of the underground diaphragm wall with outriggers similar to the calculation of the vertical bearing capacity of the pile foundation, which is convenient for designers to apply, and is simple and easy.

3. Considering the self-strength conditions of the underground diaphragm wall with outriggers, it is clear that the vertical bearing capacity of the underground diaphragm wall with outriggers and the outriggers must be checked to ensure that the strength of the underground diaphragm wall with outriggers meets the vertical load Pressurized requirements.

4. Although the underground diaphragm wall with outriggers is a special-shaped underground diaphragm wall, to determine its bearing capacity according to this calculation method, the characteristic value data of the foundation bearing capacity need to be based on the data conditions specified in the current national standards, and no special geotechnical analysis is required. Engineering survey can be adapted to a wide range of engineering applications.

Description of drawings

Fig. 1a, Fig. 1b and Fig. 1c are the three-dimensional view, the front view and the side view of the vertical bearing capacity of the underground diaphragm wall with outriggers respectively (used as engineering piles);

Fig. 2a, Fig. 2b and Fig. 2c are the perspective view, front view and side view of the vertical bearing capacity of the underground diaphragm wall with outriggers respectively (used as the outer wall of the basement);

Figure 3a, Figure 3b and Figure 3c are the bearing capacity checking diagrams when the underground diaphragm wall with outriggers is used as the outer wall of the basement, and when it is used as engineering piles and outriggers.

detailed description

The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings: this embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following the described embodiment.

When the underground diaphragm wall with outriggers bears the load of the superstructure, it is equivalent to the foundation, and its vertical bearing capacity includes two meanings: the self-bearing capacity of the underground diaphragm wall with outriggers, and the ultimate bearing capacity of the foundation soil supporting the foundation of the underground diaphragm wall with outriggers force. The latter is also referred to as the vertical bearing capacity of the diaphragm wall with legs. The present invention provides a complete calculation method for the vertical bearing capacity of the underground diaphragm wall with outriggers and outriggers, and the checking formula for the bearing capacity of the section of the underground diaphragm wall with outriggers and the self-bearing capacity of the outriggers, so as to finally determine the bearing capacity of the underground diaphragm wall with outriggers. force.

To achieve the above object, the present invention takes the following steps:

Step 1: Compositional analysis of the bearing capacity of the underground diaphragm wall with outriggers. Compared with the ordinary underground diaphragm wall, the underground diaphragm wall with outriggers increases the vertical bearing capacity of the side resistance of the outriggers and the end resistance of the outriggers. That is to say, its vertical bearing capacity is composed of the vertical bearing capacity of the wall section (side friction resistance q _sw1 , q _sw2 and end resistance q _pw ) and the vertical bearing capacity of outrigger (side friction resistance q _sl1 , q _sl2 and end resistance q _pl ). When the underground diaphragm wall with outriggers is used as a vertical load-bearing structure, the outriggers play the role of end bearing. Its vertical load-bearing characteristics are similar to friction end-bearing piles. In order to exert the resistance effect of the wall section and the end of the outrigger, the wall section and the outrigger should enter the better bearing layer.

The underground diaphragm wall with outriggers is used as a vertical load-bearing structure, which can be divided into the following two situations:

(1) Used as engineering piles to bear the load of the superstructure of high-rise buildings, see Figure 1a, Figure 1b and Figure 1c.

(2) To bear the load of the upper structure and be used as the outer wall of the basement. Because the wall segments of the underground diaphragm wall with outriggers are connected in pairs, there is no vertical displacement difference between the wall widths, which can be simplified to zero, and the lateral frictional resistance q _sw1 at both ends of the wall is zero. During the construction of the basement, the foundation pit is excavated and unloaded, which weakens the lateral restraint of the soil on the side wall above the foundation pit bottom; for safety, the side friction resistance q _sw2 of the wall in the basement area is also taken as zero, see Figure 2a , Figure 2b and Figure 2c

Step 2: Determine the vertical bearing capacity R _l formula of the outrigger, which is:

R _l =(Q _sl +Q _pl )/K(1a)

Outrigger side resistance: Q _sl = n(α·2t∑q _sl1i l _i +2b _l ∑q _sl2i l _i )(1b)

Outrigger end resistance: Q _pl ＝q _pl A _l ; A _l ＝nb _l ·t(1c)

In the formula: α——the side friction reduction coefficient of the outrigger along the length of the wall, which can be taken as 0.8～0.9;

A _l — projected area of the outrigger (m ² );

l _i —thickness of the i-th layer of soil (m);

b _l , t——width and thickness of outrigger (m);

n - the number of outriggers under the wall section (m).

Step 3: Determine the vertical bearing capacity R _w formula of the wall segment, which is:

R _w ＝(Q _sw +Q _pw )/K(2a)

Among them, wall side resistance: Q _sw = 2t∑q _sw1 l _i +2b∑q _sw2 l _i (2b)

Wall resistance: Q _pw = q _sp (A _w -A _l ); A _w = bt(2c)

In the formula: A _W —— projected area of wall section (m ² );

b, t - the width and thickness of the wall section (m);

q _sp =q _pw .

Step 4: Determine the bearing capacity R formula of the underground diaphragm wall with outriggers, and calculate the bearing capacity of the underground diaphragm wall with outriggers.

R＝ _Rw + _Rl (3)

q _sw1 , q _sw2 , q _pw , q _s1 , q _sl2 and q _pl are provided by the engineering investigation report. When the underground diaphragm wall with outriggers doubles as the exterior wall of the basement, the value of q _sw1 shall be 0, and the depth range of the basement shall be around the wall section The frictional resistances q _sw1 and q _sw2 are both zero. In formulas (1) and (2), K is the safety factor, which is consistent with the safety requirements of the national standard pile foundation bearing capacity, and K=2 is taken. According to the size of the underground diaphragm wall with outriggers, the vertical bearing capacity of the underground diaphragm wall with outriggers can be calculated by formula (3).

Step 5: Check the vertical bearing capacity of the section of the underground diaphragm wall with outriggers. The vertical load P of the superstructure on the wall section must meet the requirements of the following formula:

P≤R'＝φ _c f _c A _w +0.9f _y 'A _s '(4)

In the formula, φ _c —coefficient of the working conditions of the wall, which is the same as the bored pile, can be taken as 0.7~0.8.

_fc — design value of concrete axial compressive strength;

f _y '—design value of compressive strength of longitudinal main reinforcement;

A _s '——cross-sectional area of longitudinal main reinforcement.

Step 6: Check the vertical bearing capacity of the outriggers of the underground diaphragm wall with outriggers, see Figure 3a, Figure 3b and Figure c. The vertical load N on the top of the outrigger is:

$\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; sw</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; pw</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

In the formula, G——the self-weight of the wall section above the top of the outrigger and the vertical load of the basement shared by the wall section; when used as an engineering pile, it is the self-weight of the wall section above the top of the outrigger.

The vertical load on the top of the outrigger must meet the following requirements:

N≤φ _lc f _c A _l +0.9f _y 'A _s '(6)

In the formula, φ _lc —— the working condition coefficient of outrigger forming, which is the same as that of bored pile, and it can be taken as 0.7~0.8.

Step 7: After checking and calculating in steps 5 and 6, under the condition of satisfying the vertical bearing capacity formula (6) of the outrigger itself, take the minimum value of both formula (3) R and formula (4) R', the value That is, the ultimate vertical bearing capacity of the underground diaphragm wall with outriggers.

Claims (7)

1. The method for calculating the vertical bearing capacity of an underground diaphragm wall with outriggers is characterized in that the method comprises the following steps: Step 1: Composition analysis of the bearing capacity of the underground diaphragm wall with outriggers; Step 2: Determine the bearing capacity formula of the outrigger and calculate the vertical bearing capacity of the outrigger; Step 3: Determine the bearing capacity formula of the wall section, and calculate the vertical bearing capacity of the wall section; Step 4: Add the vertical bearing capacity of the outriggers and the vertical bearing capacity of the wall section to calculate the bearing capacity of the underground diaphragm wall with outriggers; Step 5: Check the vertical bearing capacity of the underground diaphragm wall with outriggers; Step 6: Check the vertical bearing capacity of the outrigger; Step 7: After checking and calculating in steps 5 and 6, the vertical bearing capacity of the underground diaphragm wall with outriggers is finally obtained. 2. The method for calculating the vertical bearing capacity of an underground diaphragm wall with outriggers according to claim 1, wherein the bearing capacity described in step 1 is composed of a wall section and the vertical bearing capacity of the outriggers; wherein the wall section is vertically The bearing capacity includes the side friction resistance q _sw1 at both ends, the side friction resistance q _sw2 on both sides of the wall, and the end resistance q _pw at the bottom of the wall; the vertical bearing capacity of the leg includes the side friction resistance q _sl1 along the length direction and the support The side frictional resistance q _sl2 of the leg and the end resistance q _pl of the outrigger. 3. the vertical bearing capacity calculation method of underground diaphragm wall with supporting legs according to claim 2, is characterized in that: the vertical bearing capacity R of supporting legs _The specific calculation method is: R _l ＝(Q _sl +Q _pl )/K Q _sl ＝n(α·2tΣq _sl1 l _i +2b _l Σq _sl2 l _i ) Q _pl = q _pl A _l ; A _l = nb _l t where α is the side friction reduction coefficient of the outrigger along the length of the wall; A _l is the projected area of the outrigger; l _i is the thickness of the i-th layer of soil; b _l is the width of the outrigger; t is the thickness of the outrigger ; n is the number of outriggers under the wall section; K is the safety factor. 4. the method for calculating the vertical bearing capacity of an underground diaphragm wall with legs according to claim 2, characterized in that: the specific calculation method for the vertical _bearing capacity R of the wall section is: R _w ＝(Q _sw +Q _pw )/K Q _sw ＝2tΣq _sw1 l _i +2bΣq _sw2 l _i Q _pw =q _sp (A _w -A _l ); A _w =bt In the formula, A _W is the projected area of the wall section; b is the width of the wall section; t is the thickness of the wall section; A _l is the projected area of the leg, K is the safety factor, l _i is the thickness of the i-th layer of soil, Q _sw is the wall side resistance, Q _pw is the wall end resistance, q _sp is the wall segment end resistance. 5. according to claim 3 or 4 described methods for calculating the vertical bearing capacity of underground diaphragm walls with legs, it is characterized in that: the checking calculation in step 5 is specifically: the vertical load P of the superstructure suffered by the wall section needs to meet: P≤R'＝φ _c f _c A _w +0.9f _y 'A _s ' In the formula, R' is the strength of the wall section; φ _c is the working condition coefficient of the wall; f _c is the design value of the concrete axial compressive strength; f _y ' is the design value of the compressive strength of the longitudinal main reinforcement; A _s ' is the cross-sectional area of the longitudinal main reinforcement , A _W is the projected area of the wall segment. 6. The method for calculating the vertical bearing capacity of an underground diaphragm wall with legs according to claim 3 or 4, wherein the calculation in step 6 is specifically: The vertical load N on the top of the leg must meet the following requirements: N≤φ _lc f _c A _l +0.9f _y 'A _s ' $\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}$ In the formula, φ _lc is the working condition coefficient of outrigger forming, f _c is the design value of the concrete axial compressive strength; f _y ' is the design value of the compressive strength of the longitudinal main reinforcement; A _s ' is the cross-sectional area of the longitudinal main reinforcement; G is the outrigger The self-weight of the wall section above the top and the vertical load of the basement shared by the wall section; when used as an engineering pile, it is the self-weight of the wall section above the top of the outrigger, P is the vertical load of the superstructure on the wall section, and Q _sw is the side resistance of the wall , Q _pw is the wall end resistance. 7. The method for calculating the vertical bearing capacity of an underground diaphragm wall with outriggers according to claim 5, wherein: step 7 is specifically: taking the bearing capacity of the underground diaphragm wall with outriggers under the requirement of meeting the vertical load on the top of the outriggers. The minimum value of force and R', the minimum value is the ultimate vertical bearing capacity of the underground diaphragm wall with outriggers.