CN110485455A - Loess hidden holes area bridge pile foundation vertical bearing capacity and correction factor calculation method - Google Patents
Loess hidden holes area bridge pile foundation vertical bearing capacity and correction factor calculation method Download PDFInfo
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- CN110485455A CN110485455A CN201910792471.3A CN201910792471A CN110485455A CN 110485455 A CN110485455 A CN 110485455A CN 201910792471 A CN201910792471 A CN 201910792471A CN 110485455 A CN110485455 A CN 110485455A
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D27/00—Foundations as substructures
- E02D27/10—Deep foundations
- E02D27/12—Pile foundations
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D27/00—Foundations as substructures
- E02D27/32—Foundations for special purposes
- E02D27/42—Foundations for poles, masts or chimneys
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D33/00—Testing foundations or foundation structures
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Abstract
The invention discloses a kind of Loess hidden holes area bridge pile foundation vertical bearing capacity and correction factor calculation methods, are obtained under different operating conditions by experiment, bridge pile foundation ultimate vertical bearing capacity P when around pile body without dark cave0And bridge pile foundation ultimate vertical bearing capacity P when having dark cave around pile bodyj, j=1,2；When Loess hidden holes are at Bored Pile of Bridge side, bridge pile foundation ultimate vertical bearing capacity is denoted as P1；When Loess hidden holes are at Bored Pile of Bridge bottom, Bored Pile of Bridge bearing capacity is denoted as P2；Calculate Bored Pile of Bridge bearing capacity disturbance degree αVj,Then the Bored Pile of Bridge bearing capacity disturbance degree α obtained according to step 1VjCalculate Bored Pile of Bridge vertical bearing capacity correction factorζvj=1- αvj；According to beam Vertical Bearing Capacity of Pile Foundation correction factorBored Pile of Bridge vertical bearing capacity can be calculated.The Vertical Bearing Capacity of Pile Foundation being calculated is more nearly Loess hidden holes area Bored Pile of Bridge actual carrying capacity, avoids the incidence of engineering accident.
Description
Technical field
The invention belongs to civil engineering Bridge Design and technical field of construction, and in particular to Loess hidden holes area bridge pile foundation is perpendicular
To bearing capacity and correction factor calculation method.
Background technique
As highway industry continues to develop, bridge acts on increasingly significant in highway construction, and Bored Pile of Bridge is bridge
One of main base form in beam engineering.Bridge upper load is transferred in ground by pile foundation, Bored Pile of Bridge carrying
Power is mainly provided by pile side friction and end resistance jointly, and Pile Bearing Capacity shares how many points according to its pile side friction
For friction pile and end-bearing pile.When Pile Bearing Capacity is mainly provided by pile side friction, it is called friction-type pile foundation at this time
Plinth is called end-bearing pile when Pile Bearing Capacity is mainly provided by end resistance.In existing highway Bored Pile of Bridge mostly
The profound pile foundation of number is based on friction pile, and for friction pile, its side friction mainly passes through pile body side surface area and stake week ground
Body interaction, pile foundation can generate a downtrend relative to pile peripheral earth since pile top load is acted on, pile foundation by
Pile foundation is supported to bear upper load to the upward side friction of stake week Rock And Soil offer.
The Bored Pile of Bridge bearing capacity intact for foundation condition is calculated according to existing specification and corresponding Pile Bearing Capacity
Formula calculates.But loess is since its own is with very strong collapsibility, and loess easy to form is dark under current scour effect
Cave 2, the presence in dark cave lack the stake side of pile foundation 1 or the soil around pile 3 at stake end, the higher loess foundation of script bearing capacity, secretly
Cave generates large effect to Pile Bearing Capacity, and shown in Fig. 1 a and Fig. 1 b, dark cave is horizontal in the side of pile foundation and pile foundation
There are different influences to Bored Pile of Bridge bearing capacity from the vertical distance of pile foundation in pile foundation bottom to distance, pile foundation.But mesh
The preceding Loess hidden holes area Bored Pile of Bridge bearing capacity that is directed to is still without specific calculation formula, still according to conventional Bridge Pile
Basic vertical bearing capacity calculation formula calculates its Pile Bearing Capacity, specifically such as formula 1-1 and formula 1-2.
(1) friction pile
(2) embedded rock pile
The Loess hidden holes Bored Pile of Bridge limit is calculated using this general bridge Ultimate Bearing Capacity of Pile Foundation calculation formula to hold
Power is carried, bearing capacity is not conform to the theoretical value presence actual, Bored Pile of Bridge bearing capacity formula acquires by the level land
Following disadvantage:
(1) calculated value found out is higher than actual bearer ability, makes Loess hidden holes area Bored Pile of Bridge bearing capacity system safely
Number reduces, and easily causes traffic accident.
(2) difficulty is brought to Bored Pile of Bridge design, is acquired according to the calculating of traditional common Pile Bearing Capacity calculation formula
Bearing capacity is higher, none relatively accurate bearing capacity value, is not easy to pile foundation during Bored Pile of Bridge Design of Bearing Capacity
Plinth design.
(3) it is be easy to cause the waste of material, increases design and construction cost.It is calculated in the design according to general equation
Bearing capacity ratio is actual big, then big how much none relatively accurate value actually, then designer then can be for safety by stake
Key dimension, arrangement of reinforcement etc. blindly increase, and may actually have more than is needed so much material, and engineering cost is be easy to cause to increase.
Summary of the invention
To solve the above-mentioned problems, the present invention provides a kind of Loess hidden holes area bridge pile foundation vertical bearing capacity and amendment systems
Number calculating method, the Vertical Bearing Capacity of Pile Foundation being calculated are more nearly Loess hidden holes area Bored Pile of Bridge actual bearer
Power avoids the incidence of engineering accident.
In order to achieve the above objectives, the calculating of Bored Pile of Bridge vertical bearing capacity correction factor in Loess hidden holes area of the present invention
Method, comprising the following steps:
Step 1 is obtained under different operating conditions, bridge pile foundation ultimate vertical bearing capacity when around pile body without dark cave by experiment
P0And bridge pile foundation ultimate vertical bearing capacity P when having dark cave around pile bodyj, j=1,2；When Loess hidden holes are in Bored Pile of Bridge
When side, bridge pile foundation ultimate vertical bearing capacity is denoted as P1；When Loess hidden holes are at Bored Pile of Bridge bottom, Bored Pile of Bridge
Bearing capacity is denoted as P2；Calculate Bored Pile of Bridge bearing capacity disturbance degree αVj,
Step 2, the Bored Pile of Bridge bearing capacity disturbance degree α obtained according to step 1VjCalculate Bored Pile of Bridge vertical bearing capacity
Correction factor ζvj, ζvj=1- αvj。
Further, it in step 1, is tested by loess cave area Bored Pile of Bridge centrifugal model, measures following work
Bored Pile of Bridge ultimate vertical bearing capacity under condition:
1) when Loess hidden holes are at Bored Pile of Bridge side, measure different Bored Pile of Bridge stakes and dark cave horizontal space with
And the Bored Pile of Bridge ultimate vertical bearing capacity P under different dark cave distributed depths1；
2) when Loess hidden holes are below Bored Pile of Bridge, the Bored Pile of Bridge measured under different dark cave distributed depths is perpendicular
To ultimate bearing capacity P2。
Further, in step 1, taking displacement at pile top is that be the corresponding load of 6%D perpendicular as Bored Pile of Bridge for vertical displacement
It is the diameter of Bored Pile of Bridge to ultimate bearing capacity P, D.
Further, it for the dark cave distribution situation that do not tested, is carried out in linear according to obtained reduction coefficient
It inserts and calculates.
Further, for the dark cave distribution situation that do not tested, pass through linear interpolation, numerical simulation and laboratory test
Three reduction coefficients are obtained, take in three reduction coefficients reckling as final reduction coefficient.
A kind of calculation method of Loess hidden holes area Bored Pile of Bridge vertical bearing capacity, the Loess hidden holes area Bridge Pile of friction pile
Base bearing capacity [Ra1] calculation formula are as follows:
The Loess hidden holes area Bearing Capacity of Pile Foundation [R of embedded rock pilea2] calculation formula are as follows:
In above formula, ζvjIt is repaired for the Vertical Bearing Capacity of Pile Foundation that any one of claim 1 to claim 5 is calculated
Positive coefficient；Rα1The Loess hidden holes area Bearing Capacity of Pile Foundation feasible value of-friction pile；Rα2The Loess hidden holes area bridge of-embedded rock pile
Beam bearing capacity of pile foundation feasible value；c1- end resistance the mobilization factor depending on the factors such as borehole cleaning situation, catalase degree；
Ap- stake end section area；λ-correction factor；m0- clear bottom coefficient；[fa0The basic feasible value of bearing capacity of soil at]-stake end；
k2- allowable bearing with depth correction factor；γ2It is more than-stake end that each soil layer is weighted and averaged severe；It buries at h-stake end
Set depth；frk- stake end rock saturation uniaxial compressive strength standard value, frkiFor i-th layer of frkValue；c2i- according to borehole cleaning feelings
The side of i-th layer of rock stratum depending on the factors such as condition, catalase degree hinders mobilization factor；The stake of each soil layer of u-or each rock stratum part
Body perimeter；hi- stake is embedded in the thickness of each rock stratum part, does not include severely-weathered layer and completely decomposed layer；M-rock stratum the number of plies, is not wrapped
Include severely-weathered layer and completely decomposed layer； ζsThe collateral resistance mobilization factor of-coating soil；li- each the thickness of the layer；qik- stake side
I-th layer of native collateral resistance standard value, preferably uses single pile frictional resistance test value, when no experimental condition, presses highway for drilled pile
Bridges and culverts design specification value；N-soil layer number of plies, severely-weathered and fully weathered rock stratum consider according to soil layer.
Compared with prior art, the present invention at least has technical effect beneficial below:
(1) the Bored Pile of Bridge vertical bearing capacity correction factor for being measured and being calculated under different operating conditions by experiment, obtains
To correction factor may be directly applied under identical operating condition, after obtained bearing capacity will be calculated multiplied by the correction factor, stake
Basic vertical bearing capacity is more nearly Loess hidden holes area Bored Pile of Bridge actual carrying capacity, reduces the incidence of engineering accident,
Through analogue simulation, the Bored Pile of Bridge vertical bearing capacity being calculated using the correction factor meets engineering allowable error.
(2) after considering the correction factor, Loess hidden holes Bored Pile of Bridge vertical bearing capacity is more accurate, sets in pile foundation
The precision that design can be improved in meter reduces uncertain factor bring design alteration in engineering.
(3) after multiplied by correction factor, Design of Foundation is more nearly actual value, reduces waste of material, reduces pile foundation and applies
Work cost.
Further, it for the dark cave distribution situation that do not tested, is carried out in linear according to obtained reduction coefficient
It inserts and calculates, such method can calculate the correction factor under new operating condition quickly according to known corrections coefficient.
Further, for the dark cave distribution situation that do not tested, pass through linear interpolation, numerical simulation and laboratory test
Three reduction coefficients are obtained, take in three reduction coefficients reckling as final reduction coefficient.Such method is compared with the above method
It is cumbersome, but obtained correction factor can guarantee safety to greatest extent.
A kind of calculation method of Loess hidden holes area Bored Pile of Bridge vertical bearing capacity, will calculate obtained bearing capacity multiplied by
After the correction factor, Vertical Bearing Capacity of Pile Foundation is more nearly oblique abrupt slope area Bored Pile of Bridge actual carrying capacity, avoids work
The incidence of journey accident.After considering the correction factor, oblique Steep Slope Bridge Vertical Bearing Capacity of Pile Foundation is more accurate, in pile foundation
The precision that design can be improved in plinth design, reduces uncertain factor bring design alteration in engineering.It is multiplied by amendment
After number, Design of Foundation is more nearly actual value, reduces waste of material, reduces pile foundation construction cost.
Detailed description of the invention
Fig. 1 a is Loess hidden holes area pile foundation schematic diagram of the dark cave in stake bottom；
Fig. 1 b is Loess hidden holes area pile foundation schematic diagram of the dark cave in stake side；
P-S curve when Fig. 2 a is stake and the variation of dark cave horizontal space；
Pile foundation vertical ultimate bearing capacity schematic diagram when Fig. 2 b is stake and the variation of dark cave horizontal space；
Pile foundation vertical ultimate bearing capacity disturbance degree schematic diagram when Fig. 2 c is stake and the variation of dark cave horizontal space；
Fig. 2 d is pile foundation P-S curve when dark cave distributed depth changes；
Fig. 2 e is pile foundation vertical ultimate bearing capacity schematic diagram when dark cave distributed depth changes；
Fig. 2 f is pile foundation vertical ultimate bearing capacity disturbance degree schematic diagram when dark cave distributed depth changes；
Fig. 2 g is the P-S curve of the dark cave vertical interval variation in stake bottom-；
Fig. 2 h is pile foundation vertical ultimate bearing capacity schematic diagram when the dark cave vertical interval in stake bottom-changes；
Fig. 2 i is pile foundation vertical ultimate bearing capacity disturbance degree schematic diagram when the dark cave vertical interval in stake bottom-changes；
Fig. 3 is the geometry numerical model schematic diagram of loess cave area bridge pile foundation；
In attached drawing: 1, pile foundation, 2, Loess hidden holes, 3, soil around pile.
Specific embodiment
The following describes the present invention in detail with reference to the accompanying drawings and specific embodiments.
In the description of the present invention, it is to be understood that, term " center ", " longitudinal direction ", " transverse direction ", "upper", "lower",
The orientation or positional relationship of the instructions such as "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outside"
To be based on the orientation or positional relationship shown in the drawings, be merely for convenience of description of the present invention and simplification of the description, rather than indicate or
It implies that signified device or element must have a particular orientation, be constructed and operated in a specific orientation, therefore should not be understood as
Limitation of the present invention.In addition, term " first ", " second " are used for description purposes only, it is not understood to indicate or imply phase
To importance or implicitly indicate the quantity of indicated technical characteristic.Define " first " as a result, the feature of " second " can
To explicitly or implicitly include one or more of the features.In the description of the present invention, unless otherwise indicated, " more
It is a " it is meant that two or more.In the description of the present invention, it should be noted that unless otherwise specific regulation and
It limits, term " installation ", " connected ", " connection " shall be understood in a broad sense, for example, it may be being fixedly connected, be also possible to detachable
Connection, or be integrally connected；It can be mechanical connection, be also possible to be electrically connected；It can be directly connected, it can also be in
Between medium be indirectly connected, can be the connection inside two elements.For the ordinary skill in the art, can have
Body situation understands the concrete meaning of above-mentioned term in the present invention.
1 Pile Bearing Capacity correction factor proposes
According to the relative positional relationship between pile foundation and Loess hidden holes, by Loess hidden holes to Bored Pile of Bridge bearing capacity
Influence is divided into three kinds of situations and considers: first is that when Loess hidden holes are at Bored Pile of Bridge side, then between pile foundation and Loess hidden holes
Horizontal distance size can to Bored Pile of Bridge generate Different Effects；The second is Loess hidden holes are at Bored Pile of Bridge side,
Distributed depth changes the influence to Bored Pile of Bridge vertical bearing capacity；The third is Loess hidden holes are at Bored Pile of Bridge bottom, this
When Bored Pile of Bridge and Loess hidden holes vertically apart from size can to Bored Pile of Bridge bearing capacity generate Different Effects.By extensive
Field research, distributed depth be 20m dark cave it is most commonly seen.Based on this, by Loess hidden holes to Bored Pile of Bridge bearing capacity shadow
Ring from it is above it is several in terms of consider, propose Bored Pile of Bridge capacity correct coefficient in varied situations respectively.
2 Pile Bearing Capacity correction factors solve
By front analysis as can be seen that loess cave area Bored Pile of Bridge bearing capacity is held with no cave Bored Pile of Bridge
It is differentiated for carrying power, therefore asks its capacity correct coefficient can be convenient and calculate pile foundation in the reality in loess cave area
Bearing capacity designs the Bored Pile of Bridge centrifugal model test of loess cave area, finds out its Pile Bearing Capacity disturbance degree, in turn
Bored Pile of Bridge correction factor in the case of finding out its loess cave from different places according to formula 1-3.
Analysis of experiments scheme under 2.1 vertical uniform load qs
According to field condition, a diameter 2.5m, the long 35m of stake are taken.Loess hidden holes distributed areas pile foundation is carried in model test
The research of characteristic is provided with following operating condition of test altogether, and details are as follows:
Loess cave Pile Bearing Capacity centrifugal model test operating condition under table 1-1 different situations
Note: the centrifugal model test likelihood ratio is 100:1.
Following content is studied respectively according to above-mentioned operating condition:
(1) research stake and dark cave horizontal space are to pile foundation vertical bearer properties affecting laws；
(2) dark cave distributed depth range is studied to pile foundation vertical bearer properties affecting laws；
(3) the dark cave vertical interval in research stake bottom-is to pile foundation vertical bearer properties affecting laws.
2.2 test results and analysis
According to above-mentioned operating condition, carries out large centrifugal model test, verified phase between Pile Bearing Capacity and loess cave
Mutual changing rule, it is specific as follows.
1) correction factor that pile foundation vertical ultimate bearing capacity changes with stake and dark cave horizontal space
Stake changes the P-S curvilinear motion rule of lower pile foundation as shown in Figure 2 a with dark cave horizontal space.From Fig. 2 a it can be seen that
P-S curve does not have apparent inflection point, therefore taking stake top vertical displacement is 6%D (1.5mm) corresponding load as pile foundation vertical pole
Bearing capacity P is limited, the ultimate vertical bearing capacity calculating achievement of pile foundation is shown in Table 1-2 when stake and dark cave horizontal space change.Wherein αVFor
Bearing capacity disturbance degree,P0Pile foundation vertical ultimate bearing capacity when for around pile body without dark cave；P is stake
There is pile foundation vertical ultimate bearing capacity when dark cave around body.Stake is with the variation of dark cave horizontal space to the shadow of vertical bearing capacity
It rings as shown in Fig. 2 b, Fig. 2 c.
1-2, table are summarized with pile foundation vertical ultimate bearing capacity when the variation of dark cave horizontal space
By table 2-2 and Fig. 2 b, Fig. 2 c it can be seen that the presence in stake week dark cave weakens pile foundation vertical ultimate bearing capacity, and
With the reduction of stake and dark cave horizontal space, weakening effect is gradually increased.Stake with dark cave horizontal space be respectively 1.0D, 0.5D,
When 0.2D, 0.1D, pile foundation vertical ultimate bearing capacity is respectively 8444kN, 8187kN, 7981kN, 7856kN, than stake week without dark cave
The case where when distribution (pile foundation vertical ultimate bearing capacity is 8943kN), reduces 5.6%, 8.5%, 10.8% and respectively
12.2%.
As the above analysis, the presence in stake week dark cave reduces pile foundation vertical ultimate bearing capacity, therefore is determining loess
It should be reduced according to stake is corresponding with the progress of the size of dark cave horizontal space when the area An Xue pile foundation vertical ultimate bearing capacity.Stake with it is dark
The ultimate vertical bearing capacity that pile foundation vertical ultimate bearing capacity when cave horizontal space changes is compared when being distributed with stake week without dark cave is repaired
Positive coefficient ζV(ζV=1- αV) it is shown in Table 1-3.
Ultimate vertical bearing capacity correction factor when 1-3, table changes with dark cave horizontal space
| Stake and dark cave horizontal space (× D) | 0.1 | 0.2 | 0.5 | 1.0 | Without dark cave |
| Correction factor ζV(%) | 87.8 | 89.2 | 91.5 | 94.4 | 100.0 |
Table 2-3 can be seen that the increase with stake and dark cave horizontal space, pile foundation vertical ultimate bearing capacity correction factor by
It is cumulative big.
2) correction factor that pile foundation vertical ultimate bearing capacity changes with dark cave distributed depth
The P-S curvilinear motion rule of pile foundation is as shown in Figure 2 d in the case of different dark cave distributed depths.Different dark cave distributions are deep
The bearing capacity calculation achievement of pile foundation is shown in Table 1-4 in the case of degree.Influence variation of the dark cave distributed depth variation to bearing capacity of pile foundation is such as
Shown in Fig. 2 e, Fig. 2 f.
Pile foundation vertical ultimate bearing capacity summarizes when the dark cave distributed depth of table 1-4 changes
By table 1-4 and Fig. 2 e, Fig. 2 f it can be seen that
(1) with the increase of dark cave distributed depth, pile foundation vertical ultimate bearing capacity is gradually reduced.Dark cave distributed depth difference
When for 5m, 10m, 15m, 20m, 30m, pile foundation vertical ultimate bearing capacity be respectively 8814kN, 8381kN, 8093kN, 7981kN,
7759kN, when than without dark cave the case where, reduce 1.4%, 6.3%, 9.5%, 10.8% and 13.2% respectively.
(2) as dark cave distributed depth continues growing, the fall of pile foundation vertical ultimate bearing capacity gradually slows down.This master
If deep with continuing growing for dark cave distributed depth because pile foundation side friction is smaller in pile body middle and lower part performance degree
Though dark cave is distributed in place's soil layer, influence of the soil body to pile foundation side friction is smaller within the scope of this, though so dark cave distributed depth
It continues growing, but the influence to pile foundation vertical ultimate bearing capacity has been gradually reduced, so as to cause pile foundation vertical ultimate bearing capacity
Fall gradually slowing down.
As the above analysis, the dark cave being distributed within the scope of pile soil horizon certain depth reduces pile foundation vertical ultimate bearing
Power, therefore should be carried out according to the depth bounds of stake week dark cave distribution when determining Loess hidden holes area pile foundation vertical ultimate bearing capacity
Corresponding reduction.Pile foundation vertical ultimate bearing capacity under dark cave distributed depth variation operating condition is compared with stake week is without the distribution of dark cave
Capacity correct coefficient ζV(ζV=1- αV) it is shown in Table 1-5.
The ultimate vertical bearing capacity correction factor of the different dark cave distributed depths of table 1-5
| Dark cave distributed depth (cm) | Without dark cave | 5 | 10 | 15 | 20 | 30 |
| Correction factor ζV(%) | 100.0 | 98.6 | 93.7 | 90.5 | 89.2 | 86.8 |
Table 1-5 can be seen that the increase with dark cave distributed depth, and pile foundation vertical ultimate bearing capacity correction factor is in reduction
Trend, but the influence due to stake week upper soil horizon to pile side friction is more obvious than lower part soil layer, so the lower range of decrease of correction factor
Degree is gradually slowing down.
3) correction factor that pile foundation vertical ultimate bearing capacity changes with the dark cave vertical interval in stake bottom-
The dark cave vertical interval in stake bottom-changes the P-S curvilinear motion rule of lower pile foundation as shown in Figure 2 g.Though there is curve in Fig. 2 g
Obvious inflection point, but since stake top vertical displacement when there is inflection point is larger, to take stake top vertical displacement still convenient for analysis
Pile foundation for the corresponding load of 6%D (1.5mm) as pile foundation vertical ultimate bearing capacity P, when the dark cave vertical interval in stake bottom-changes
Bearing capacity calculation achievement is shown in Table 1-6.Influence variation of the dark cave vertical interval variation in stake bottom-to pile foundation vertical ultimate bearing capacity is such as
Shown in Fig. 2 h, Fig. 2 i.
Pile foundation vertical ultimate bearing capacity when the dark cave vertical interval in 1-6 bottoms-of table changes summarizes
By table 1-6 and Fig. 2 h, Fig. 2 i it can be seen that with the dark cave vertical interval in stake bottom-reduction, the pile foundation vertical limit holds
Power is carried also to be gradually reduced.Pile foundation vertical ultimate bearing capacity is affected by the dark cave vertical interval variation in stake bottom-, when stake bottom-is dark
When cave vertical interval is 2m, pile foundation vertical ultimate bearing capacity is 3602kN, reduces 59.7% without dark cave situation compared with stake bottom；And
When stake bottom-, dark cave vertical interval increases to 8m, pile foundation vertical ultimate bearing capacity increases 8081kN, compared with stake bottom without dark cave
Situation reduces 9.6%.This explanation, when the dark cave vertical interval in stake bottom-is smaller, the bearing capacity of pile-end soil body is smaller, stake top
When load is gradually increased, end resistance is also being gradually increased, when end resistance is greater than the bearing capacity of pile-end soil body, stake bottom
Dark cave is destroyed, pile-end soil body loss of stability, so that the ultimate vertical bearing capacity of stake be caused to decline.As the dark cave in stake bottom-is hung down
The increase of straight spacing, the bearing capacity of pile-end soil body increases with it, so that pile foundation vertical ultimate bearing capacity be made also to increase with it.
As the above analysis, the dark cave of stake bottom distribution reduces pile foundation vertical ultimate bearing capacity, therefore is determining loess
It should be reduced accordingly at a distance from stake bottom according to dark cave when the area An Xue pile foundation vertical ultimate bearing capacity.The pile foundation vertical limit
Bearing capacity increases the capacity correct coefficient ζ compared with without the distribution of dark cave with the dark cave vertical interval in stake bottom-V(ζV=1- αV) become
Change, is shown in Table 1-7.
Ultimate vertical bearing capacity correction factor when the dark cave vertical interval in 1-7 bottoms-of table changes
| The dark cave vertical interval (cm) in stake bottom- | 2 | 3 | 5 | 8 | Without dark cave |
| Correction factor ζV(%) | 40.3 | 64.2 | 79.1 | 90.4 | 100.0 |
It can be seen that the increase with the dark cave vertical interval in stake bottom-, pile foundation vertical ultimate bearing capacity amendment system from table 2-7
Number is in increase tendency.
It can be obtained by above-mentioned experiment:
1) stake and dark cave horizontal space change the influence to pile foundation vertical bearer properties
When dark cave distributed depth certain (20m), pile foundation vertical ultimate bearing capacity when stake and dark cave horizontal space change and
The ultimate vertical bearing capacity correction factor ζ compared when stake week is without the distribution of dark caveV(ζV=1- αV) it is shown in Table 2-1.
Ultimate vertical bearing capacity correction factor when 2-1, table changes with dark cave horizontal space
(1) D indicates pile foundation diameter in table.
Wherein αVFor bearing capacity disturbance degree, P0Pile foundation vertical ultimate bearing capacity when for around pile body without dark cave；P is to have secretly
Pile foundation vertical ultimate bearing capacity when cave.
2) dark cave distributed depth changes the influence to pile foundation vertical bearer properties
Pile foundation vertical ultimate bearing when stake is with dark cave horizontal space certain (0.2D), under dark cave distributed depth variation operating condition
Power is with stake week without the capacity correct coefficient ζ compared with the distribution of dark caveV(ζV=1- αV) it is shown in Table 2-2.
The ultimate vertical bearing capacity correction factor of the different dark cave distributed depths of table 2-2
3) the dark cave vertical interval in stake bottom-changes the influence to pile foundation vertical bearer properties
Capacity correct coefficient of the pile foundation vertical ultimate bearing capacity with the dark cave vertical interval in stake bottom-compared with without the distribution of dark cave
ζV(ζV=1- αV) variation, it is shown in Table 2-3.
Ultimate vertical bearing capacity correction factor when the dark cave vertical interval in 2-3 bottoms-of table changes
| The dark cave vertical interval (m) in stake bottom- | 2 | 3 | 5 | 8 |
| Correction factor ζV(%) | 40.3 | 64.2 | 79.1 | 90.4 |
The present invention proposes the capacity correct coefficient in the case of the dark cave different location of the above pile foundation-, then can be by existing stake
Foundation bearing capacity calculation formula is modified, and obtains holding in the pile foundation of Loess hidden holes area Bored Pile of Bridge in varied situations
Carry power formula:
(1) the vertical bearing capacity calculation formula of friction pile is as follows:
(2) the vertical bearing capacity calculation formula of embedded rock pile is as follows:
In formula:
ζv- vertical bearing capacity correction factor；
Rα1The single pile axial press capacity feasible value (kN) of-friction pile, pile body self weight is with displacement soil weight (when from restatement
When entering buoyancy, replace soil weight and be also included in buoyancy) difference as load consideration；
Rα2The single pile axial press capacity feasible value (kN) of-embedded rock pile, pile body self weight is with displacement soil weight (when from restatement
When entering buoyancy, replace soil weight and be also included in buoyancy) difference as load consideration；
c1- end resistance the mobilization factor depending on the factors such as borehole cleaning situation, catalase degree, is adopted according to table 1-1
With；
Ap- stake end section area (m2), for club-footed pile, take base expanding and base expanding area of section；
λ-correction factor, see the table below 2-4:
Table 2-4 correction factor λ value
m0- clear bottom coefficient, value see the table below 2-5:
The clear bottom Coefficient m of table 2-50Value
| t/d | 0.3~0.1 |
| m0 | 0.7~1.0 |
Note: 1.t, d are the diameter of sediment of the hole bottom thickness and stake.
When 2.d≤1.5m, t≤300mm；When d > 1.5m, t≤500mm, and 0.1 < t/d < 0.3.
[fa0The basic feasible value of bearing capacity (kPa) of soil, the value are generally provided by design data at]-stake end；
k2- allowable bearing is chosen with the correction factor of depth according to supporting course great soil group at stake end；
γ2It is more than-stake end that each soil layer is weighted and averaged severe (kN/m3)；
H-stake end buried depth (m), for there is the pile foundation washed away, buried depth is started by general scour line；Nothing is washed away
Pile foundation, buried depth are counted by ground line after natively upper thread or practical excavation；The calculated value of h is not more than 40m, when being greater than 40m,
It is calculated according to 40m；
frk- stake end rock saturation uniaxial compressive strength standard value (kPa), clay matter rock take natural moisture uniaxial compressive strong
Standard value is spent, f is worked asrkIt is calculated when less than 2MPa according to friction pile；frkiFor i-th layer of frkValue；
c2iThe side of-i-th layer of rock stratum depending on the factors such as borehole cleaning situation, catalase degree hinders mobilization factor；
Each soil layer of u-or the pile body perimeter (m) of each rock stratum part；
hi- stake is embedded in the thickness (m) of each rock stratum part, does not include severely-weathered layer and completely decomposed layer；
M-rock stratum the number of plies does not include severely-weathered layer and completely decomposed layer；
ζsThe collateral resistance mobilization factor of-coating soil, according to stake end frkIt determines: as 2MPa≤frkWhen < 15MPa, ζs=
0.8；As 15MPa≤frkWhen < 30MPa, ζs=0.5；Work as frkWhen > 30MPa, ζs=0.2；
li- each the thickness of the layer (m)；
qikThe native collateral resistance standard value (kPa) in i-th layer of-stake side, preferably uses single pile frictional resistance test value, when no test bar
When part, highway bridge and culvert design specification value is pressed for drilled pile；
N-soil layer number of plies, severely-weathered and fully weathered rock stratum consider according to soil layer.
Table 2-6 coefficient c1、c2Value
| Lithosphere situation | c1 | c2 |
| Completely, more complete | 0.6 | 0.05 |
| It is relatively broken | 0.5 | 0.04 |
| It is broken, smashed to pieces | 0.4 | 0.03 |
Other parameters are chosen according to existing " highway bridge and culvert ground and foundation design code " (JTG D63-2015).
The verifying of 3 Pile Bearing Capacity correction factors
For loess cave area Bored Pile of Bridge vertical bearing capacity correction factor by establishing indoor centrifugal model test,
It is proposed and solved loess cave area Bored Pile of Bridge capacity correct coefficient under different situations, but the correction factor with
Whether loess cave area pile foundation bearing capacity is consistent in Practical Project, needs further to verify.Therefore it is being familiar with investigation now
On the basis of engineering properties condition, Numerical Simulation Analysis model is established, through the capacity correct coefficient that is calculated with before
Text derives the correction factor proposed and compares, to prove the reliability of the correction factor.
3.1 model foundation
(1) geometrical model and dividing elements
In conjunction with the characteristics of pile foundation structure stress and requirement of the FEM calculation to computing resource, by a large amount of tentative calculations, really
It is scheduled on and calculates the stake diameter range that Lateral and the stake bed rock soil body take 10 times.
A variety of computing unit types are provided in Marc Nonlinear Finite metaprogram, it is contemplated that the needs of research select eight
Node hexahedral element carry out grid dividing, when by entity discreteness at finite element unit, as far as possible encryption bridge pile foundation and
Its surrounding soil unit not only can ensure that computational accuracy, but also be easy to restrain to thin transition by close in this way, save from the near to the remote
Operation time.The geometry numerical model of loess cave area bridge pile foundation is as shown in Figure 3.
(2) boundary condition determines
Computation model is approximately the unlimited body of half space, for computation model boundary condition, by model lower part bottom surface and side
X, Y, Z-direction displacement are fixed, and apply classification load to stake top.
(3) constitutive model is chosen
Finite element numerical computational solution precision depends primarily on the reasonability of constitutive model and the accuracy of calculating parameter.Bridge
Beam piling strtucture uses concrete material, uses perfect elasticity constitutive model in analysis.
For all loess formations of stake in deformation process, stress-strain relation is in non-linear relation, for tracking load history ask displacement,
The full dose of strain and stress, therefore Mohr-Coulomb yield criterion is used, constitutive relation is described using incremental form.
(4) parameter is chosen
Calculating for the consistency and science for guaranteeing Numerical Simulation result and Practical Project, in Numerical Simulation Analysis
Parameter surveys data according to Practical Project to choose, and is specifically shown in Table 3-1.
Table 3-1 Material Physics mechanics parameter
3.2 conceptual design
The vertical load that bridge pile foundation is born mainly includes the load etc. that self gravity and superstructure generate.Pile foundation is worn
It crosses soft stratum or unstable formation and vertical load is transmitted to the soil layer or rock stratum that deep is harder, compressibility is small, by having
Effect is using the side friction of the formation resistance and stake side rock mass that act on an end come vertical supporting loads.Utilize finite element analysis
Software Marc carries out simulation analysis for table 3-2 operating condition, studies the bearer properties of loess cave area bridge pile foundation, is such
The design of type bridge pile foundation provides theoretical foundation.
A diameter 2.5m, the long 35m of stake are taken, using different vertical load hierarchical loadings, is analyzed under different loess cave operating conditions
The bearer properties of bridge pile foundation, calculating operating condition, see Table 3 for details -2.
Loess cave Pile Bearing Capacity numerical simulation operating condition under table 3-2 different situations
3.3 calculating achievements and analysis
By analysis, vertical bearing capacity is mainly become by the maximum that the deformation characteristic and superstructure of stake side rock mass are allowed
Shape determines.One timing of the long and stake diameter of stake, by carrying out FEM calculation to the bridge pile foundation in the different abrupt slope gradients, point
Analyse the changing rule of bearing capacity of pile foundation.Corresponding Pile Bearing Capacity under different operating conditions is obtained according to Numerical Model Analysis result
It see the table below.
1) pile foundation vertical ultimate bearing capacity when stake and dark cave horizontal space change
Pile foundation vertical ultimate bearing capacity (numerical simulation calculation) when 3-3, table and dark cave horizontal space change
| Stake and dark cave horizontal space | 0.25m | 0.5m | 1.25m | 2.5m | Without dark cave |
| Ultimate vertical bearing capacity P (kN) | 7773 | 8051 | 8086 | 8346 | 8955 |
The capacity correct coefficient that table 3-4 is calculated acquires bearing capacity (being calculated according to table 2-1)
Table 3-5 Pile Bearing Capacity reduced value (table 3-3/ table 3-4)
Table 3-3 is by the calculated ultimate bearing capacity of numerical simulation, when table 3-4 is with obtained in table 3-3 without dark cave
Bearing capacity 8955 on the basis of, multiplied by corresponding reduction coefficient in table 2-1, and then obtain the bearing capacity in table 3-4.In table 1-2
Obtain without dark cave when bearing capacity (8943) be by experiment acquire, 8943 ≠ 8955, further illustrate numerical simulation with
There are certain errors for experimental result.It is to be verified with Numerical Simulation Results to the reduction coefficient obtained in table 2-1 herein, because
This is needed on the basis of 8955, the bearing capacity correction value in table 3-4 obtained multiplied by above-mentioned reduction coefficient and the number in table 3-3
Value simulation result compares.So the data in table 1-2, table 3-4 have a certain difference, it is reasonable.
2) pile foundation vertical ultimate bearing capacity when stake and dark cave change with dark cave distributed depth
Pile foundation vertical ultimate bearing capacity (numerical simulation calculation) when 3-6, table and dark cave change with dark cave distributed depth
The capacity correct coefficient that table 3-7 is calculated acquires bearing capacity (being calculated according to table 1-2)
Table 3-8 Pile Bearing Capacity reduced value (table 3-6/ table 3-7)
3) pile foundation and dark cave are with the dark cave vertical interval variation pile foundation vertical ultimate bearing capacity in stake bottom-
Pile foundation vertical ultimate bearing capacity (numerical simulation calculation) when the dark cave vertical interval in 3-9 bottoms-of table changes
The capacity correct coefficient that table 3-10 is calculated acquires bearing capacity (being calculated according to table 1-3)
Table 3-11 Pile Bearing Capacity reduced value (table 3-10/ table 3-11)
In above table: table 3-3,3-6,3-9 correspond to the pile foundation that numerical simulation calculation obtains under three above operating condition and hold
Carry force value, table 3-4,3-7,3-10 be according to the obtained capacity correct coefficient of experiment with without dark cave location bearing capacity of pile foundation meter
The Pile Bearing Capacity obtained, table 3-5,3-8,3-11 are corresponding numerical simulation and the Pile Bearing Capacity that calculating acquires
Ratio.Substantially all 1 or so, error fully meets engine request 5%, thus may be used data in analytical table 1% or so
To find out that Pile Bearing Capacity correction factor proposed by the present invention can be applied in practice in engineering.
Pile Bearing Capacity PiCalculation formula it is as follows:
No loess is calculated according to Pile Bearing Capacity calculation formula (formula 1-1 or 1-2) first in capacity correct coefficient
Vertical Bearing Capacity of Pile Foundation P when dark cave0, it is worth on the basis of this calculated value, needs to calculate under corresponding operating condition discussed above
Pile Bearing Capacity Pi, Pi=P0×ζV。
4, for the operating condition that do not tested, ultimate bearing capacity is calculated in the following manner
Listed operating condition has included the case where most commonly seen relatively broadly in table 1-1 of the present invention, such as encounters the present invention
In the operating condition do not mentioned, then carry out linear interpolation according to the reduction coefficient proposed in the present invention, and pass through numerical simulation and interior
The means of test obtain accurate reduction coefficient.Further, since the result that numerical simulation and laboratory test obtain has one
Determine the difference of degree, for guarantee Loess hidden holes area bridge pile foundation safety, it is proposed that take by linear interpolation, laboratory test and
In three kinds of methods of numerical simulation, reduction coefficient reckling as be not directed in table 1-1 to the case where corresponding reduction coefficient.
The above content is merely illustrative of the invention's technical idea, and this does not limit the scope of protection of the present invention, all to press
According to technical idea proposed by the present invention, any changes made on the basis of the technical scheme each falls within claims of the present invention
Protection scope within.
Claims (6)
1. the calculation method of Loess hidden holes area Bored Pile of Bridge vertical bearing capacity correction factor, which is characterized in that including following step
It is rapid:
Step 1 is obtained under different operating conditions, bridge pile foundation ultimate vertical bearing capacity P when around pile body without dark cave by experiment0With
There is bridge pile foundation ultimate vertical bearing capacity P when dark cave around pile bodyj, j=1,2；When Loess hidden holes are in Bored Pile of Bridge side
When, bridge pile foundation ultimate vertical bearing capacity is denoted as P1；When Loess hidden holes are at Bored Pile of Bridge bottom, Bored Pile of Bridge bearing capacity
It is denoted as P2；Calculate Bored Pile of Bridge bearing capacity disturbance degree αVj,
Step 2, the Bored Pile of Bridge bearing capacity disturbance degree α obtained according to step 1VjCalculate the amendment of Bored Pile of Bridge vertical bearing capacity
Coefficient ζvj, ζvj=1- αvj。
2. the calculation method of Bored Pile of Bridge vertical bearing capacity correction factor in Loess hidden holes area according to claim 1,
It is characterized in that, in step 1, is tested by loess cave area Bored Pile of Bridge centrifugal model, measure the bridge under following operating condition
Beam pile foundation ultimate vertical bearing capacity:
1) when Loess hidden holes are at Bored Pile of Bridge side, different Bored Pile of Bridge stakes and dark cave horizontal space and not are measured
With the Bored Pile of Bridge ultimate vertical bearing capacity P under dark cave distributed depth1；
2) when Loess hidden holes are below Bored Pile of Bridge, the vertical pole of Bored Pile of Bridge under different dark cave distributed depths is measured
Limit bearing capacity P2。
3. the calculation method of Bored Pile of Bridge vertical bearing capacity correction factor in Loess hidden holes area according to claim 1,
It is characterized in that, in step 1, it is that the corresponding load of 6%D is held as Bored Pile of Bridge vertical limit that take displacement at pile top, which be vertical displacement,
Power P is carried, D is the diameter of Bored Pile of Bridge.
4. the calculation method of Bored Pile of Bridge vertical bearing capacity correction factor in Loess hidden holes area according to claim 1,
It is characterized in that, for the dark cave distribution situation that do not tested, carries out linear interpolation calculating according to obtained reduction coefficient.
5. the calculation method of Bored Pile of Bridge vertical bearing capacity correction factor in Loess hidden holes area according to claim 1,
It is characterized in that, for the dark cave distribution situation that do not tested, obtains three by linear interpolation, numerical simulation and laboratory test
Reduction coefficient takes in three reduction coefficients reckling as final reduction coefficient.
6. a kind of calculation method of Loess hidden holes area Bored Pile of Bridge vertical bearing capacity, which is characterized in that the loess of friction pile is dark
Cave area Bearing Capacity of Pile Foundation [Ra1] calculation formula are as follows:
The Loess hidden holes area Bearing Capacity of Pile Foundation [R of embedded rock pilea2] calculation formula are as follows:
In above formula, ζvjThe Vertical Bearing Capacity of Pile Foundation amendment system being calculated for any one of claim 1 to claim 5
Number；Rα1The Loess hidden holes area Bearing Capacity of Pile Foundation feasible value of-friction pile；Rα2The Loess hidden holes area bridge pile foundation of-embedded rock pile
Bearing capacity feasible value；c1- end resistance the mobilization factor depending on the factors such as borehole cleaning situation, catalase degree；Ap- stake end
Area of section；λ-correction factor；m0- clear bottom coefficient；[fa0The basic feasible value of bearing capacity of soil at]-stake end；k2- allow to hold
Power is carried with the correction factor of depth；γ2It is more than-stake end that each soil layer is weighted and averaged severe；H-stake end buried depth；frk—
Stake end rock saturation uniaxial compressive strength standard value, frkiFor i-th layer of frkValue；c2i- according to borehole cleaning situation, catalase journey
The side of i-th layer of rock stratum depending on the factors such as degree hinders mobilization factor；Each soil layer of u-or the pile body perimeter of each rock stratum part；hi- stake
It is embedded in the thickness of each rock stratum part, does not include severely-weathered layer and completely decomposed layer；M-rock stratum the number of plies does not include severely-weathered layer and complete
Weathered layer；ζsThe collateral resistance mobilization factor of-coating soil；li- each the thickness of the layer；qikThe native collateral resistance in i-th layer of-stake side
Standard value preferably uses single pile frictional resistance test value, and when no experimental condition, drilled pile is taken by highway bridge and culvert design specification
Value；N-soil layer number of plies, severely-weathered and fully weathered rock stratum consider according to soil layer.
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