CN109918721B - A kind of method of pile formula roadbed stress ratio under the conditions of acquisition Particle Breakage - Google Patents
A kind of method of pile formula roadbed stress ratio under the conditions of acquisition Particle Breakage Download PDFInfo
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Abstract
The present invention provides a kind of methods of pile formula roadbed stress ratio under the conditions of acquisition Particle Breakage, which comprises determines Particle attrition index Br;According to the Particle attrition index BrDetermine soil body particle size coefficient nd;The sagitta h of soil arch is determined according to the soil body particle size coefficient ncWith arch angle αh;According to the sagitta h of soil archcWith arch angle αhDetermine the stress ratio η of pile roadbed.The method of pile formula roadbed stress ratio can determine pile formula roadbed Pile Soil-net loading sharing situation under the conditions of Particle Breakage under the conditions of acquisition Particle Breakage of the invention, it can be used for accurately calculating pile formula post-construction settlement of subgrade, reduce the subgrade defect that soil arch damage generates, saves railroad embankment maintenance cost.
Description
Technical Field
The invention belongs to the technical field of railway tracks, and particularly relates to a method for obtaining pile-bearing type roadbed pile-soil stress ratio under a particle crushing condition.
Background
Under the action of dry-wet circulation caused by high roadbed load, dynamic train load and climate environment, roadbed fillers and foundation soil particles at the connection part of a roadbed and a foundation are easy to disintegrate and break, the strength is reduced, and simultaneously, the form and the properties of an earth arch force chain are changed, so that the earth arch in the pile-supported roadbed is damaged, the settlement of the road foundation after line operation is difficult to control, the smoothness of a track is reduced, and the repair of the earth arch in the operation period is very difficult. Therefore, accurate calculation of the soil stress of the foundation pile plays a crucial role in laying the track.
The existing pile-supported roadbed pile-soil stress ratio determination method mainly comprises three methods: firstly, the method is determined by adopting a field full-scale model test or an indoor scale model test; secondly, determining by adopting a finite element or discrete element numerical simulation method; and thirdly, determining by adopting an analytical solution method. Compared with the former two methods, the pile-supported roadbed design is simpler and more convenient to calculate and design by adopting an analytical solution method.
However, the analytical solution method is to determine the load sharing proportion and stress distribution of the pile-soil-net three on the basis of the assumed soil arch shape in the pile-supported roadbed. The existing soil dome state is mainly assumed for homogeneous soil, and does not relate to dome variation caused by particle characteristic change. In the actual working process of the pile-supported roadbed, particle crushing often causes particle size refinement and uneven particle group distribution, causes larger contact force chain density change angle and arch height of an arch foot of the soil arch, increases the load of the upper roadbed shared by soil among piles, causes the loading efficiency of a pile body and the geogrid to be passively reduced, and obviously increases the reinforcing failure risk of the pile-supported roadbed.
The existing pile-supported roadbed pile soil stress ratio determining method does not fully consider the particle crushing condition, has low accuracy of post-construction settlement calculation of the pile-supported roadbed, and increases the line operation and maintenance cost for roadbed diseases caused by soil arch damage.
Disclosure of Invention
Aiming at the technical problem, the invention provides a method for obtaining the pile-soil stress ratio of a pile-supported roadbed under the condition of particle crushing.
A method of obtaining pile-bearing subgrade pile-soil stress ratio under particle crushing conditions, the method comprising:
determination of the particle breakage index Br;
According to the particle breakage index BrDetermining the soil particle size coefficient nd;
Determining the arch height h of the soil arch according to the soil particle size coefficient ncAnd arch angle alphah;
According to the height h of the soil archcAnd arch angle alphahAnd determining the pile-soil stress ratio eta of the pile bearing roadbed.
Determining the particle breakage indicator further according to the following parameters:
the area difference of the current particle grading curve and the initial particle grading curve, and the area difference of the limit particle grading curve and the initial particle grading curve.
Further determining said particle breakage indicator B according to the following formular:
In the formula:
F0(D) is an initial particle grading curve expressed in terms of particle mass;
Fc(D) is a current particle grading curve expressed in terms of particle mass;
Fu(D) is a limit particle grading curve expressed in terms of particle mass;
S0,Scand SuAreas corresponding to the initial, current and limit particle grading curves, respectively;
△Sc0the area difference corresponding to the current particle grading curve and the initial particle grading curve is obtained;
△Su0the area difference corresponding to the limit particle grading curve and the initial particle grading curve is obtained;
d is the particle diameter;
Dmis the minimum particle size of the sample;
DMis the maximum particle size of the sample.
Further according to the particle breakage index BrDetermining the soil particle size coefficient ndThe method specifically comprises the following steps:
in the formula:
S0the area corresponding to the initial limit grading curve,
Suthe area corresponding to the initial limit grading curve,
d is the particle diameter;
Dmis the minimum particle size of the sample;
DMthe maximum particle size of the sample;
initial particle size coefficient n of roadbed filling0Taking 0.95-1.0, limit gradation nLThe value is 0.1 to 0.15.
The arch angle α is further determined according to the following formulah:
In the formula:
s and snThe distance between piles and the net distance between piles are respectively;
n is the particle size coefficient of the current grading;
ndthe particle size coefficient of the roadbed filling material in the operation period;
hcis the height of the soil arch, wherein:
when H is more than or equal to s/2,
when H is present<At the time of s/2, the ratio,
h is the height of the roadbed;
psi is the deformation coefficient of the soil arch,
gamma is the subgrade filler severity;
Pdpthe dynamic stress acting on the pile top at the bottom surface of the roadbed.
Further determining the pile-soil stress ratio eta according to the following formula:
wherein,
in the formula:
d is the pile diameter;
h is the height of the roadbed;
Pdpand PdsRespectively acting on the dynamic stress of the pile top at the bottom surface of the roadbed and the dynamic stress of the top of soil between the piles;
gamma is the subgrade filler severity;
dtpthe stress diffusion diameter is the stress diffusion diameter of the pile at the bottom surface of the roadbed; dtp=d+2H/tanαh;
dtsThe diameter of stress diffusion between piles at the bottom of the roadbed; dts=s-2H/tanαh;
snThe clear distance between piles;
and s is the pile spacing.
Further determining dynamic stress P acting on pile top at subgrade bottom surface according to the following formuladpAnd dynamic stress P of top of soil between pilesds:
In the formula:
Pddynamic stress acting on the top surface of the roadbed;
Ampand AmsRespectively the dynamic stress diffusion areas of piles at the depth of 3m below the roadbed surface and among the piles;
Abpand AbsRespectively the dynamic stress diffusion areas of the bottom surface of the roadbed between the piles;
dmpand dmsThe diameters of dynamic stress diffusion between piles and piles at the position 3m below a roadbed surface are respectively.
The method for determining the pile-soil stress ratio of the pile-bearing roadbed can determine the load sharing condition of the pile-bearing roadbed pile-soil-net (soil arch grid) under the condition of particle crushing, can be used for accurately calculating the post-construction settlement of the pile-bearing roadbed, reduces the roadbed diseases caused by soil arch damage and saves the line operation and maintenance cost. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
FIG. 1 shows a basic flow chart of a method for obtaining pile-soil stress ratio of a pile-supported subgrade under a particle crushing condition according to an embodiment of the invention;
FIG. 2 shows a fragmentation index B according to an embodiment of the inventionrDefining a schematic diagram;
FIG. 3 illustrates a particle grading curve equivalence transformation graph from an actual grading curve to an equivalent grading curve according to an embodiment of the invention;
FIG. 4 shows a schematic view of soil arch parameters according to an embodiment of the invention;
FIG. 5 shows a schematic representation of the force of the earth arch according to an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a method for determining pile-bearing type roadbed pile-soil stress ratio under a particle crushing condition. The method mainly comprises the steps of respectively testing particle breakage indexes and dynamic modulus of foundation soil in a natural state or under a water immersion condition by using a circulating triaxial test, preliminarily judging an arching condition of a soil arch effect in a roadbed, determining key soil arch shape parameters, and finally calculating the pile-soil stress ratio after soil body particles are broken. As shown in FIG. 1, the method for obtaining pile-soil stress ratio of pile-supported subgrade under particle crushing condition mainly comprises the steps of determining a particle breakage index BrAccording to said particle breakage indicator BrDetermining the soil particle size coefficient ndDetermining the arch height h of the soil arch according to the soil body particle size coefficient ncAnd arch angle alphahAccording to the height h of the soil archcAnd arch angle alphahAnd determining the pile-soil stress ratio eta of the pile bearing roadbed.
The concrete calculation method of the pile-supported subgrade pile-soil stress ratio determination method under the particle crushing condition comprises the following steps:
the first step is as follows: definition of fragmentation index Br。
As shown in FIG. 2, the initial grading curve of the soil sample and the current grading curve of the soil sample after the shearing of the circulating triaxial test are respectively tested by adopting a particle test and drawn into a particle curve graph, wherein the area of the shaded part in the graph is broken particles, and the breakage rate index B can be calculated according to the broken particlesrThe calculation formula is as follows:
in the formula: f0(D),Fc(D) And Fu(D) Initial, current and limit particle grading curves, expressed in terms of particle mass, respectively; s0,ScAnd SuAreas corresponding to the initial, current and limit particle grading curves, respectively; delta Sc0Is the area difference corresponding to the current particle grading curve and the initial particle grading curve; delta Su0Is the area difference corresponding to the limit particle grading curve and the initial particle grading curve; d is the particle diameter; dmAnd DMThe minimum and maximum particle sizes of the sample are respectively.
The second step is that: according to the particle breakage index BrDetermining the soil particle size coefficient nd
The initial and ultimate particle size grading of the subgrade filler is considered according to the talbot power function, as follows:
wherein D is the current particle diameter and DMIs the maximum particle size; p is the percentage of roadbed filling passing through the sieve pore; and n is a particle size coefficient.
In view of the larger randomness of the load bearing or water-soaking disintegration and crushing probability of the roadbed filling, the particle crushing index (B) is adoptedr) Determining the particle size coefficient n of the current grading curve by the equivalence principled. As shown in fig. 3, a particle test is performed on the soil sample sheared by the circulating triaxial test, an actual grading curve of the roadbed filler is drawn, and a particle grading crushing index B corresponding to the actual grading curve is calculated according to the formula (1)r. According to the equivalent principle of corresponding area of particle grading curve (namely B)r=Br' min), the equivalent talbot power function particle size coefficient n corresponding to the actual particle grading curvedCalculated as follows:
in the formula, S0For initial limit grading curve mappingThe area of (a) is,Suthe area corresponding to the initial limit grading curve,the initial particle size factor n of a typical road base filler0Taking 0.95-1.0, limit gradation nLThe value is 0.1 to 0.15.
The third step: determining shape parameters of soil arch (arch height and arch angle)
Under the action of high roadbed load or long-term train cyclic load, soil arch deformation or damage caused by soil particle crushing of a pile-supported roadbed often causes that the post-construction settlement of the pile-supported roadbed is increased or the bearing capacity of the pile-supported roadbed is reduced. In the actual engineering design and construction, the change of the soil arch state of the pile type roadbed is difficult to judge by naked eyes and difficult to directly measure. The invention determines the shape of the soil arch by considering the dynamic load of the train and the grading of filler particles, and comprises the following specific steps:
(1) determination of arching
The arching condition of the soil arch can be preliminarily judged according to the roadbed filling height: when H is less than or equal to 0.7(s-d), no arching occurs; a half-arch is formed when 0.7(s-d) < H <1.4 (s-d); when H is more than or equal to 1.4(s-d), a full arch is formed, wherein s is the distance between piles, d is the diameter of the piles, and H is the height of the roadbed. Under the condition of full arch formation, the base filler particle breakage probability caused by high roadbed load is higher, and the influence of particle grading characteristics on the shape of the soil arch is obvious. The invention mainly considers the shape change of the soil arch under the full arch condition.
(2) Determining the shape parameters of soil arch of roadbed fillers with different grain compositions
The physical significance of the arch height and the arch angle of the soil arch of the pile foundation is shown in figure 4. In the prior pile-supported roadbed design, the shape of a soil arch is assumed according to a single particle size, and the influence of the grading difference of roadbed filler particles on the height and the angle of the soil arch is not reflected. The invention combines the grading characteristics of the filler to determine the height of the soil arch and the size of the arch angle, and the arch height of any point between the piles is calculated according to the following formula:
in the formula, y is the height of a soil arch at any point between piles; x horizontal distance from any point between piles to the center of the pile; s and snThe distance between piles and the net distance between piles are respectively; h iscThe height of the soil arch at the middle point of the two piles is h in the prior designcAccording to the calculation of the pile spacing, H is calculated when the roadbed filling height H is more than or equal to s/2cS/2; when roadbed is filled with high H<s/2 is, hcH. Obviously, this method does not take into account differences in camber due to changes in grain composition. The method calculates h according to the following formulacTo compensate for the effect of filler particle composition differences on camber.
When H is more than or equal to s/2,
when H is present<At the time of s/2, the ratio,
as shown in fig. 4, the distance soil arch springing sb=0.15snWithin this range, the camber varies substantially linearly. Camber angle alphahCalculated according to the following formula:
arch height range h of arch linear variationbIs calculated according to the following formula
(3) Determining the shape parameters of the soil arch under the action of train load
The subgrade bed range (0.7 m of graded broken stone and 2.3m of subgrade filler of A, B groups) which is 3m (meters) below the top surface of the subgrade is higher in rigidity, and the dynamic stress generated by train load is quickly attenuated by 60 percent. The residual 40 percent of dynamic stress is attenuated along the depth direction of the roadbed from the depth of 3m below the roadbed surface to the plane of the pile topOften slowly. The dynamic stress acting 3m below the top surface of the roadbed is about 0.4 time of the dynamic load of the train. The dynamic stress is within the range of less than 3m of the top surface of the roadbed according to the diffusion angle alphahAnd the diffusion is carried out along the depth direction of the roadbed, as shown in figure 4. The dynamic stress acting on the pile top at the bottom surface of the roadbed and the soil surface between the piles is calculated according to the following formula:
dmp=d+2(H-3)/tanαh (7-3)
dms=sn-2(H-3)/tanαh (7-4)
in the formula, PdpAnd PdsRespectively the dynamic stress, kPa (kilopascal), acting on the pile top and the top of the soil between the piles at the bottom surface of the roadbed; pdThe dynamic stress acting on the top surface of the roadbed is kPa; a. thempAnd AmsRespectively the dynamic stress diffusion area m of the piles at the depth of 3m below the roadbed surface2(square meter); a. thebpAnd AbsRespectively the dynamic stress diffusion area m between piles at the bottom of the roadbed2;dmpAnd dmsThe diameters of dynamic stress diffusion m of piles and between piles at the position 3m below a roadbed surface are respectively.
The deformation of the soil arch generated when the dynamic load of the train is transmitted to the bottom surface of the roadbed is calculated according to the following formulacd:
When H is more than or equal to s/2,
when H is present<At the time of s/2, the ratio,
in the formula, ndThe size coefficient of the road base filler particles in the operation period can be obtained by opening a soil sample after being sheared by a circulating dynamic triaxial testObtaining a particle spreading test; psi is the deformation coefficient of the soil arch,gamma is the subgrade filler severity.
In the operation period, the size of the soil arch angle considering the dynamic load effect of the train and the crushing of filler particles can be determined according to the following formula:
in the formula, alphahdThe arch angle of the soil arch formed after the filler particles are crushed under the action of the dynamic load of the train.
The fourth step: determining pile-soil stress ratio of pile bearing roadbed according to soil arch shape parameters
In most cases, the pile-supported subgrade forms a relatively stable soil arch under the action of the compaction of the subgrade due to the dead weight load in the filling period and the placing period. The design and related calculation of the pile type roadbed are carried out on the basis of the existing design specifications. However, the attenuation amplitude of the dynamic load of the train in the roadbed range above the pile top and the soil between the piles is obviously different, so that the soil arch is deformed, soil body particles at the bottom of the superposed roadbed are broken, and the deformation degree of the soil arch is aggravated and even the damage is caused. The invention considers the change of the contact force chain of the soil arch caused by the broken particles of the roadbed filling material under the long-term running condition of the train. And re-determining the shape of the soil arch, and calculating the pile-soil stress ratio of the pile-supported roadbed. The method can solve the problems of pile body working efficiency reduction caused by filler particle crushing, pile bearing type roadbed design defects such as high estimation of geogrid (geogrid gravel layer) tension and the like, and also provides a new method for evaluating the service performance of the pile bearing type roadbed.
According to the change of the grain composition and the change of the arch shape of the pile-supported roadbed soil caused by the load of the train, as shown in fig. 5, the average soil stress acting on the pile top and the soil surface between the piles is considered according to a circular table to calculate the pile soil stress, and the pile soil stress is calculated according to the following formula:
dtp=d+2H/tanαhd (10-3)
dts=s-2H/tanαhd (10-4)
wherein eta is the stress ratio of the pile soil,gamma is the roadbed filling weight, KN/m3(kilonewtons per cubic meter); dtpAnd dtsRespectively the stress diffusion diameter m between piles and piles at the bottom of the roadbed; ppAnd PsRespectively the top surface stress of the pile top and the top surface stress between the piles.
Although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (4)
1. A method of obtaining pile-bearing subgrade pile-soil stress ratio under particle crushing conditions, the method comprising:
determination of the particle breakage index Br;
According to the particle breakage index BrDetermining the soil particle size coefficient nd;
According to the soil body particle size coefficient ndDetermining the arch height h of the soil archcAnd arch angle alphah;
According to the arch height h of the soil archcAnd arch angle alphahDetermining the pile-soil stress ratio eta of the pile bearing roadbed;
wherein,
determining the particle breakage indicator from:
the area difference corresponding to the current particle grading curve and the initial particle grading curve, and the area difference corresponding to the limit particle grading curve and the initial particle grading curve;
determining the particle breakage indicator B according to the following formular:
In the formula:
F0(D) is an initial particle grading curve expressed in terms of particle mass;
Fc(D) is a current particle grading curve expressed in terms of particle mass;
Fu(D) is a limit particle grading curve expressed in terms of particle mass;
S0,Scand SuAreas corresponding to the initial, current and limit particle grading curves, respectively;
△Sc0the area difference corresponding to the current particle grading curve and the initial particle grading curve is obtained;
△Su0the area difference corresponding to the limit particle grading curve and the initial particle grading curve is obtained;
d is the particle diameter;
Dmis the minimum particle size of the sample;
DMthe maximum particle size of the sample;
according to the particle breakage index BrDetermining the soil particle size coefficient ndThe method specifically comprises the following steps:
in the formula:
S0is the area corresponding to the initial grading curve,
Suthe area corresponding to the limiting grading curve,
d is the particle diameter;
Dmis the minimum particle size of the sample;
DMis the maximum particle size of the sample;
initial particle size coefficient n of roadbed filling0Taking 0.95-1.0, limit gradation nLThe value is 0.1 to 0.15.
2. The method of claim 1, the arch angle α being determined according to the following formulah:
In the formula:
s and snThe distance between piles and the net distance between piles are respectively;
ndthe soil particle size coefficient is obtained;
hcis the arch height of the soil arch, wherein:
when H is more than or equal to s/2,
when H is present<At the time of s/2, the ratio,
h is the height of the roadbed;
psi is the deformation coefficient of the soil arch,
gamma is the subgrade filler severity;
Pdpthe dynamic stress acting on the pile top at the bottom surface of the roadbed.
3. The method of claim 2, determining the pile-soil stress ratio η according to the formula:
wherein,
in the formula:
d is the pile diameter;
h is the height of the roadbed;
Pdpand PdsRespectively acting on the dynamic stress of the pile top at the bottom surface of the roadbed and the dynamic stress of the top of soil between the piles;
gamma is the subgrade filler severity;
dtpthe stress diffusion diameter of the pile at the bottom surface of the roadbed; dtp=d+2H/tanαh;
dtsThe diameter of stress diffusion between piles at the bottom of the roadbed; dts=s-2H/tanαh;
snIs the clear distance between the piles;
and s is the pile spacing.
4. A method according to claim 3, determining the dynamic stress P acting on the pile top at the subgrade bottom surface according to the following formula respectivelydpAnd dynamic stress P of top of soil between pilesds:
In the formula:
Pddynamic stress acting on the top surface of the roadbed;
Ampand AmsRespectively the dynamic stress diffusion areas of piles at the depth of 3m below the roadbed surface and among the piles;
Abpand AbsRespectively the dynamic stress diffusion areas of the bottom surface of the roadbed between the piles;
dmpand dmsThe diameters of dynamic stress diffusion between piles and piles at the position 3m below a roadbed surface are respectively.
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