CN102230870B - Method for testing grading broken stone CBR numerical value - Google Patents

Abstract

The invention discloses a method for testing grading broken stone CBR numerical value. According to the invention, a physical model and a mechanical model are established for simulating the grading broken stone CBR test, the method comprises the following steps: testing basic parameters, simulating of a CBR testing model, test pieces, a load plate, a CBR pressure head and the like, endowing the physical model with micro mechanics parameters, simulating a loading process of CBR test, finishing an arrangement of the simulation result to obtain the relational curve of the pressure head penetration rate and the penetration force, and obtaining the penetration force corresponding to a penetration rate of 2.5 mm according to the relational curve of the penetration rate and the penetration force. According to the invention, the grading broken stone CBR value can be rapidly and accurately predicted by the method, and a change rule of grading broken stone stress-strain can be represented.

Description

A kind of graded broken stone CBR numerical experimentation method

Technical field

The invention belongs to the Transportation and Civil Engineering field, relate to a kind of graded broken stone CBR numerical experimentation method, described CBR is meant California bearing ratio.The present invention is based on PFC ^2DSoftware platform can be predicted graded broken stone CBR rule quickly and accurately, shortens research cycle, reduces graded broken stone research and optimization of material cost.

Background technology

Graded broken stone belongs to typical road basement material, adopts its intensity of CBR index evaluation usually and carries out the design of material composition.The ultimate principle and the step of graded broken stone CBR shop experiment method are following: (1) prepares test specimen by maximum dry density and optimum moisture content; (2) the load plate with certain mass places test specimen top and soaked by the regulation requirement; (3) test specimen after soaked is carried out penetration test; (4) arrangement is calculated the penetration test result and is obtained the CBR value.At present, do not see the report that graded broken stone CBR numerical experimentation method is arranged.

The applicant analyzes above-mentioned graded broken stone CBR shop experiment method; Have following defective: (1) has only through a large amount of CBR shop experiments of carrying out repeatedly; Just might deeply disclose gather materials, rule between aggregate grading and the graded broken stone CBR; And realize the optimal design of graded broken stone material, this cause the graded broken stone material design cycle long, cost is high; (2) inner material that is difficult to measure graded broken stone under the load action is migrated and the ess-strain characteristic.

Summary of the invention

Problem to above-mentioned prior art exists the purpose of this invention is to provide a kind of graded broken stone CBR numerical experimentation method.This method can be predicted graded broken stone CBR rule quickly and accurately.

For realizing above-mentioned task, the present invention takes following technical scheme to be achieved:

A kind of graded broken stone CBR numerical experimentation method is characterized in that, carries out according to following steps:

1) CONSTRUCTINT PHYSICAL MODELS

(1) simulation of CBR test specimen

1. the test of basic parameter:

Measure rubble density, confirm mineral aggregate gradation and maximum dry density thereof and optimum moisture content;

2. the simulation of die trial:

Utilize PFC ^2DBuilt-in command " wall " generates horizontal body of wall that vertical body of wall that two leaf length are H and a leaf length be D and forms semiclosed rectangle that opening makes progress with the simulation die trial;

3. the generation of graded broken stone:

Calculate the two-dimensional map area S that i kind specification is gathered materials according to rubble density, compactness, sample dimensions, mineral aggregate gradation and maximum dry density _i, see formula (1).Utilize PFC ^2DBuilt-in command " ball " generates particle in the simulation die trial, and makes it to meet the particle diameter requirement that i kind specification is gathered materials.When the total area that generates particle reaches S _iThe time, stop particle and generate;

$S_i=\frac{4\mathrm{dh}{\mathrm{KP}}_i}{{\mathrm{\ρ}}_i}{\mathrm{\ρ}}_{\max }---\left(1\right)$

In the formula: ρ _Max: maximum dry density, g/cm ³

D: test specimen diameter, cm;

H: test specimen height, cm;

K: compactness, %;

P _i: the grader retained percentage that i kind specification is gathered materials, %, i are the natural number greater than 0;

ρ _i: the density that i kind specification is gathered materials, g/cm ³, i is the natural number greater than 0;

Generate each specification aggregate particle as stated above successively;

4. the generation of imitation specimen:

Utilize PFC ^2DIt is the simulation pressing plate of D that built-in command " wall " generates length.Pressing plate promotes to simulate the aggregate particle in the die trial straight down with speed V, till the computing step number reaches n.N calculates by formula (2).

$n=\frac{L}{{\mathrm{Vd}}_t}=\frac{H-h}{{\mathrm{Vd}}_t}---\left(2\right)$

In the formula: n: computing step number, step;

L: simulation pressing plate displacement, cm;

V: simulation pressing plate translational speed, cm/s;

d _t: time step, s/step;

H: die trial height, cm;

H: test specimen height, cm.

(2) simulation of CBR pressure head and load plate

1. the simulation of pressure head:

Utilize PFC ^2DBuilt-in command " wall " generates horizontal body of wall that vertical body of wall that two leaf length do not limit and a leaf length be 5cm and forms semiclosed rectangle that opening the makes progress pressure head with simulation CBR numerical experimentation;

2. the simulation of load plate:

Utilize PFC ^2DIt is the load plate of the horizontal wall n-body simulation n CBR numerical experimentation of l that built-in command " wall " generates two leaf length, and l calculates by formula (3):

$l=\frac{D-5}{2}---\left(3\right)$

In the formula: D: die trial internal diameter, cm.

2) structure of mechanical model

1. choosing of contact model:

Adopt Hertz model and gliding model to describe the graininess architectural feature and the nonlinear mechanics characteristic of graded broken stone.Wherein, the Hertz model is through Poisson ratio v, shear modulus G definition, and gliding model is through the coefficientoffriction definition;

2. the input of micro mechanics parameter:

Utilize PFC ^2DBuilt-in command " prop " is given the graded broken stone physical model with the micro mechanics parameter, comprises Poisson ratio v, shear modulus G, coefficientoffriction.

The micro mechanics parameter can be obtained through graded broken stone CBR laboratory test results inverse.

3) simulation of CBR test loading procedure and result's arrangement

1. the simulation of CBR test loading procedure:

The simulation pressure head is pressed in the graded broken stone imitation specimen with constant speed, write down the displacement and the contact force of simulation pressure head in going on foot when each calculates, and arrangement obtains the relation curve of pressure head penetrating power～injection amount;

2. result's arrangement:

Pairing penetrating power when from penetrating power～injection discharge curve, reading the injection amount and being 2.5mm calculates graded broken stone CBR value by formula (4).

$\mathrm{CBR}=\frac{p_{2.5}}{7000}\×100---\left(4\right)$

In the formula: p _2.5: pairing penetrating power when pressure head injection amount is 2.5mm, KPa;

The present invention has the following advantages:

(1) can predict graded broken stone CBR value quickly and accurately, and optimize graded broken stone and form;

(2) graded broken stone ess-strain characteristic, further investigation graded broken stone Mechanical Characters of Composite Ground and failure mechanism can omnidistancely be described;

(3) can realize the research that some are difficult to carry out owing to the restriction of factors such as funds, time.

Description of drawings

Fig. 1 is the synoptic diagram of graded broken stone CBR numerical experimentation simulation die trial;

Fig. 2 is the synoptic diagram that graded broken stone CBR numerical experimentation is gathered materials and generated;

Fig. 3 is the synoptic diagram of graded broken stone CBR numerical experimentation simulation compacting process; Be 0step from left to right successively, 10000step, 20000step, 30000step.

Fig. 4 is the synoptic diagram of graded broken stone CBR numerical experimentation simulation pressure head and simulation load plate;

Fig. 5 is the synoptic diagram of graded broken stone CBR numerical experimentation loading procedure;

Fig. 6 is the penetrating power～injection discharge curve (A grating) of graded broken stone CBR numerical experimentation;

Fig. 7 is the penetrating power～injection discharge curve (B grating) of graded broken stone CBR numerical experimentation;

Fig. 8 is the penetrating power～injection discharge curve (C grating) of graded broken stone CBR numerical experimentation;

Fig. 9 is the penetrating power～injection discharge curve (D grating) of graded broken stone CBR numerical experimentation;

Below in conjunction with accompanying drawing and embodiment the present invention is done further detailed description.

Embodiment

According to technical scheme of the present invention, present embodiment provides a kind of graded broken stone CBR numerical experimentation method, is example with lake, safe and comfortable sea limestone gravel, and rubble density measurement result sees table 1, and the micro mechanics parameter is seen table 2.

Table 1 rubble density

Aggregate size (mm)	19～31.5	9.5～19	4.75～9.5	≤4.75
					Apparent density (g/cm 3)	2.712	2.709	2.692	2.681

Table 2 micro mechanics parameter

Poisson ratio	Modulus of shearing (GPa)	Friction factor
			0.25	8.0	0.35

Table 3 mineral aggregate gradation

Be that example explains that the implementation step of graded broken stone CBR numerical experimentation method is with grating A in the table 3 down:

1) CONSTRUCTINT PHYSICAL MODELS

(1) simulation of CBR test specimen

1. the simulation of die trial:

Utilize PFC ^2DBuilt-in command " wall " generates horizontal body of wall that vertical body of wall that two leaf length are 15cm and a leaf length be 15.2cm and forms semiclosed rectangle that opening makes progress with the simulation die trial, sees Fig. 1;

2. the generation of graded broken stone:

Prepare Φ 15.2cm * h12cm test specimen by 98% compactness, then the graded broken stone generative process of gathering materials is following:

Calculate the two-dimensional map area that 19～31.5mm gathers materials:

Utilize PFC ^2DBuilt-in command " ball " generates the particle of diameter between 19～31.5mm constantly, when its total area reaches 324.3cm ²The time, stop particle and generate; Calculate the two-dimensional map area that 9.5～19mm gathers materials:

Utilize PFC ^2DBuilt-in command " ball " generates the particle of diameter between 9.5～19mm constantly, when its total area reaches 108.2m ²The time, stop particle and generate; Calculate the two-dimensional map area that 4.75～9.5mm gathers materials:

Utilize PFC ^2DBuilt-in command " ball " generates the particle of diameter between 4.75～9.5mm constantly, when its total area reaches 108.9cm ²The time, stop particle and generate; Calculate the two-dimensional map area that 2.36～4.75mm gathers materials:

Utilize PFC ^2DBuilt-in command " ball " generates the particle of diameter between 2.36～4.75mm constantly, when its total area reaches 38.6cm ²The time, stop particle and generate; Calculate the two-dimensional map area that 0.6～2.36mm gathers materials:

Utilize PFC ^2DBuilt-in command " ball " generates the particle of diameter between 0.6～2.36mm constantly, when its total area reaches 57.9cm ²The time, stop particle and generate, thereby Fig. 2 is seen in the generation of completion graded broken stone.

3. the generation of imitation specimen:

Confirm that body of wall speed is 0.1cm/s, the step is 0.001 during calculating, and then computing step number is:

So utilize PFC ^2DBuilt-in command " wall " generate a leaf length be the horizontal body of wall of 12cm with the simulation pressing plate, and make its speed promote to simulate the aggregate particle in the die trial straight down with 0.1cm/s, reach till 30000 until the computing step number, see Fig. 3.

(2) simulation of CBR pressure head and load plate

1. the simulation of pressure head:

Utilize PFC ^2DIt is that the horizontal body of wall of 5cm is formed semiclosed rectangle that opening the makes progress pressure head with simulation CBR numerical experimentation that built-in command " wall " generates two vertical bodies of wall and a leaf length, sees Fig. 4.

2. the simulation of load plate:

Utilize PFC ^2DBuilt-in command " wall " generates the load plate of two horizontal bodies of wall with simulation CBR numerical experimentation, sees Fig. 4.Body of wall length is:

2) structure of mechanical model

Utilize PFC ^2DBuilt-in command " prop " is given the graded broken stone physical model with micro mechanics parameter in the table 2, generates mechanical model.

3) simulation of CBR test loading procedure and result's arrangement

1. the simulation of CBR test loading procedure:

Speed with 1mm/min promotes to simulate the pressure head (see figure 5) straight down, and writes down displacement and the contact force that goes on foot interior simulation pressure head when each calculates;

2. result's arrangement:

Draw the relation curve (see figure 6) of pressure head penetrating power～injection amount, and pairing penetrating power when therefrom obtaining the injection amount and being 2.5mm, can calculate the graded broken stone CBR value of grating A: $\mathrm{CBR}=\frac{p_{2.5}}{7000}\×100=\frac{45000}{7000}\×100=643\%.$

According to above-mentioned steps, can obtain the graded broken stone CBR analog result of grating B in the table 3, grating C and grating D successively, see Fig. 7～Fig. 9 and table 4.

Table 4 numerical simulation result and measured result contrast

Can be found out that by table 4 the graded broken stone CBR measured result of different gradation and the relative error of analog result all are lower than 7%, average relative error is merely 4.49%; In addition, the numerical simulation process time spent less than 5 minutes of one group of grating.Proof the present invention can predict graded broken stone CBR rule quickly and accurately.

Claims (1)

1. a graded broken stone CBR numerical experimentation method is characterized in that, carries out according to following steps:

1) CONSTRUCTINT PHYSICAL MODELS

(1) simulation of CBR test specimen

1. the test of basic parameter:

Measure rubble density, confirm mineral aggregate gradation and maximum dry density thereof and optimum moisture content;

2. the simulation of die trial:

Utilize PFC ^2DBuilt-in command " wall " generates horizontal body of wall that vertical body of wall that two leaf length are H and a leaf length be D and forms semiclosed rectangle that opening makes progress with the simulation die trial;

3. the generation of graded broken stone:

Calculate the two-dimensional map area S that i kind specification is gathered materials according to rubble density, compactness, sample dimensions, mineral aggregate gradation and maximum dry density by formula (1) _i

Utilize PFC ^2DBuilt-in command " ball " generates particle in the simulation die trial, and makes it to meet the particle diameter requirement that i kind specification is gathered materials, when the total area that generates particle reaches S _iThe time, stop particle and generate;

$S_i=\frac{4\mathrm{dhK}{P}_i}{{\mathrm{\ρ}}_i}{\mathrm{\ρ}}_{\max }---\left(1\right)$

In the formula: ρ _Max: maximum dry density, g/cm ³

D: test specimen diameter, cm;

H: test specimen height, cm;

K: compactness, %;

P _i: the grader retained percentage that i kind specification is gathered materials, %, i are the natural number greater than 0;

ρ _i: the density that i kind specification is gathered materials, g/cm ³, i is the natural number greater than 0;

Generate each specification aggregate particle as stated above successively;

4. the generation of imitation specimen:

Utilize PFC ^2DIt is the simulation pressing plate of D that built-in command " wall " generates length, and pressing plate promotes to simulate the aggregate particle in the die trial straight down with speed V, till the computing step number reaches n;

N presses following formula (2) and calculates:

$n=\frac{L}{{\mathrm{Vd}}_t}=\frac{H-h}{{\mathrm{Vd}}_t}---\left(2\right)$

In the formula: n: computing step number, step;

L: simulation pressing plate displacement, cm;

V: simulation pressing plate translational speed (cm/s);

d _t: time step, s/step;

H: die trial height, cm;

H: test specimen height, cm;

(2) simulation of CBR pressure head and load plate

1. the simulation of pressure head:

Utilize PFC ^2DBuilt-in command " wall " generates horizontal body of wall that vertical body of wall that two leaf length do not limit and a leaf length be 5cm and forms semiclosed rectangle that opening the makes progress pressure head with simulation CBR numerical experimentation;

2. the simulation of load plate:

Utilize PFC ^2DIt is the load plate of the horizontal wall n-body simulation n CBR numerical experimentation of l that built-in command " wall " generates two leaf length;

L presses following formula (3) and calculates:

$l=\frac{D-5}{2}---\left(3\right)$

In the formula: D: die trial internal diameter, cm;

2) structure of mechanical model

1. choosing of contact model:

Adopt Hertz model and gliding model to describe the graininess architectural feature and the nonlinear mechanics characteristic of graded broken stone; Wherein, the Hertz model is through Poisson ratio ν, shear modulus G definition, and gliding model is through the coefficientoffriction definition;

2. the input of micro mechanics parameter:

Utilize PFC ^2DBuilt-in command " prop " is given the graded broken stone physical model with the micro mechanics parameter, comprises Poisson ratio ν, shear modulus G, coefficientoffriction;

The micro mechanics parameter is obtained through graded broken stone CBR laboratory test results inverse;

3) simulation of CBR test loading procedure and result's arrangement

1. the simulation of CBR test loading procedure:

The simulation pressure head is pressed in the graded broken stone imitation specimen with constant speed, write down the displacement and the contact force of simulation pressure head in going on foot when each calculates, and arrangement obtains simulating the relation curve of the penetrating power ~ injection amount of pressure head;

2. result's arrangement:

Pairing penetrating power when from penetrating power ~ injection discharge curve, reading the injection amount and being 2.5mm, calculate graded broken stone CBR value by formula (4):

$\mathrm{CBR}=\frac{{\mathrm{\ρ}}_{2.5}}{7000}\×100---\left(4\right)$

In the formula: p _2.5: pairing penetrating power when simulation pressure head injection amount is 2.5mm, KPa.

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