CN102608013A - Method for measuring porosity in piping development process - Google Patents

Abstract

The invention discloses a method for measuring porosity in a piping development process. The porosity at a certain moment in the piping development process is determined by testing parameters such as initial porosity, volumetric strain and fine granule loss. By utilizing the method for measuring the porosity in the piping development process, the old problem that the soil mass porosity evolution process in the piping development process cannot be determined can be solved, and an important theoretical basis is provided for establishing a mathematical model for forecasting the piping occurrence and development process.

Description

A kind of method of measuring piping evolution mesoporosity rate

Technical field

The present invention relates to a kind of method of measuring piping evolution mesoporosity rate.

Background technology

Piping is the main dykes and dams seepage failure form of a kind of ten minutes, and its evolution relates to pore water seepage flow, movable fine grained corrodes numerous complicated mechanical behaviors such as migration, porous medium distortion, and is accompanied by the continuous variation of porosity.Confirm in the piping evolution that any time soil body porosity is accurately to predict the key of piping evolution, for comprehensive objective understanding piping mechanism, correctly predict that the piping evolution has important theoretical and practical significance.

Yet because the disguise of piping incidence and development process; About piping evolution mesoporosity rate Study of variation law report is not arranged at present; Porosity model commonly used all is not directed against the singularity of piping problem in the existing seepage stress Coupling Research; All do not consider the mass loss problem that movable fine grained runs off and causes in the piping evolution, therefore can not be used for the piping Study on Problems.

The inventor has submitted the patented claim of " a kind of seepage flow eroding stress coupling piping test unit " on August 23rd, 2011, application number is 201110242127.0.In this application, the inventor provides a kind of seepage flow eroding stress coupling piping test unit, and is as shown in Figure 1, comprises base 1, stephanoporate steel plate 11; Pressure chamber 2, sample 3, heat-shrink tube 4, block 5; Cobble filtering layer 6, top cover 7, axial pressure bar 8, axial pressure device 9; Rising pipe 10, photoelectric sensor 12, resistance strain gage 13, measuring cup 14.Arrange bakie in the base 1, pressure chamber 2 is arranged on base 1 top, and top cover 7 is arranged on the top of pressure chamber 2; One end of rising pipe 10 is connected with base 1 outlet at bottom, the other end extends into measuring cup 14; Sample 3 is arranged in pressure chamber 2 and is built on the base 1, arranges between sample 3 and the base 1 that stephanoporate steel plate 11, the outside of sample 3 closely wrap up heat-shrink tube 4, top layout block 5, fill cobble filtering layer 6 in the block 5; One end of axial pressure bar 8 passes top cover 7 and is connected with axial pressure device 9 with block 5 contacts, the other end; Photoelectric sensor 12 is arranged on the pipe shaft of rising pipe 10; Resistance strain gage 13 is arranged on the heat-shrink tube 4.The through-hole aperture of stephanoporate steel plate 11 is 0.075mm-5mm.The general through hole of 0.075mm diameter, 2mm diameter, 5mm diameter that adopts experimentizes.The permeate pressurization device is connected with block 5 through pipeline; The confined pressure pressurizer is connected with base 1 bottom through pipeline; And be communicated with pressure chamber 2; Displacement transducer is arranged in the top of axial pressure bar 8, and the strain data collector is connected with resistance strain gage 13, and pore water pressure sensor is connected with the stephanoporate steel plate 11 of base 1 top through pipeline.

This device can be considered the influence of pore water seepage flow-heterogeneous many coupling effects such as fine grained erosion migration-soil deformation to soil body piping evolution; The soil body that can tracking and monitoring be in the three dimension stress state; Under seepage effect, the dynamic changing process of indexs such as wherein movable fine particle content, porosity, perviousness, settling amount.But because the limitation of inventor's research, the inventor can accurately not grasp the method for measuring piping evolution mesoporosity rate, thereby has restricted going deep into the research of piping development mechanism.

Summary of the invention

Goal of the invention: the objective of the invention is to deficiency, on the basis that the inventor further studies, a kind of method of utilizing seepage flow eroding stress coupling piping test unit to measure piping evolution mesoporosity rate is provided to prior art.

Technical scheme: the method for mensuration piping evolution of the present invention mesoporosity rate, the seepage flow eroding stress coupling piping test unit that utilizes the inventor to invent carries out, and mainly comprises the steps:

(1) according to the initial porosity φ that dry density and saturated water requirement confirm to fill sample that fills of sample ₀Confirm the bulk strain of specimen test initial time

Be 0; Confirmed test initial time stream of fine particles vector

Be 0;

(2) at 0～t ₀Period, the settling amount of monitoring through displacement transducer obtains axial strain ε divided by specimen height ₁Hoop strain ε is obtained in resistance strain gage collection through sticking on the sample middle part ₂According to bulk strain ε in the triaxial test _v, axial strain ε ₁And hoop strain ε ₂Relation:

Confirm t ₀The bulk strain of sample constantly

(3) at 0～t ₀Period, gather t ₀Stream of fine particles vector constantly

(4), calculate 0～t according to following formula ₀T in period ₀Porosity constantly

In the formula, ρ ^SRThe density of expression soil particle.

(6) at t ₀～t ₁Period, the settling amount of monitoring through displacement transducer obtains axial strain ε divided by specimen height ₁Hoop strain ε is obtained in resistance strain gage collection through sticking on the sample middle part ₂According to bulk strain ε in the triaxial test _v, axial strain ε ₁And hoop strain ε ₂Relation:

Confirm t ₁The bulk strain of sample constantly

(7) at t ₀～t ₁Period, test t ₁Stream of fine particles vector constantly

(8), calculate t according to following formula ₀～t ₁T in period ₁Porosity constantly

Beneficial effect: the method for mensuration piping evolution provided by the invention mesoporosity rate can solve the old problem that soil body porosity evolution process can't be confirmed in the piping evolution; Help deepening deep understanding, will important theoretical foundation be provided for setting up forecast piping incidence and development process mathematical model to the piping development mechanism.

Description of drawings

Fig. 1 is the structural representation of seepage flow eroding stress coupling piping test unit.

1 is base among the figure, the 11st, and stephanoporate steel plate, the 2nd, pressure chamber, the 3rd, sample, the 4th, heat-shrink tube; The 5th, block, the 6th, cobble filtering layer, the 7th, top cover, the 8th, axial pressure bar, the 9th, axial pressure device; The 10th, rising pipe, the 12nd, photoelectric sensor, the 13rd, resistance strain gage, the 14th, measuring cup.

Embodiment

Be elaborated in the face of technical scheme of the present invention down, but protection scope of the present invention is not limited to said embodiment.

Embodiment: the present invention utilizes seepage flow eroding stress coupling piping test unit as shown in Figure 1, measures the porosity of the soil body in the piping evolution.

The method of testing of seepage flow eroding stress coupling piping test unit, step is following:

(1) preparation, installation sample.At first, based on dry density and water content requirement, utilize special split cavity to prepare sample, the sample outer surface adopts heat-shrink tube closely to wrap up.Secondly, (stephanoporate steel plate is mainly used in the crude fines, and this test supposes that movable fine grain particle diameter is less than 2mm on base, to place the stephanoporate steel plate of aperture 2mm; Promptly in the test; Only particle diameter can flow out sample less than the fine grained of 2mm), sample is fixed on the instrument base tighten the screws.At last, in sample top cover upper cap, attention will remain sample and be in vertical state, and unlikely generation eccentric compression when guaranteeing that the later stage is born axle pressure influences test result.

(2) adhering resistance strain sheets.In order to monitor the hoop strain of sample, so the bulk strain of sample in definite piping evolution, on same circumference, 4 resistance strain gages evenly being sticked on the heat-shrink tube near the sample centre position, each foil gauge angle differs 90 degree.In the process of the test, collect the strain value of 4 resistance strain gages, replace the hoop strain value of number mean value as sample.

(3) apply confined pressure.At first, confined pressure chamber water-filling.Sealing is noted in the setting pressure chamber.Open the air release at top, pressure chamber, begin slowly to add water, treat that water all is full of the pressure chamber and when air release overflows, tightens air release, closes water intaking valve to the pressure chamber.Secondly, installation shaft is to pressure rod, the adjustment (adjusting) lever balance.Installation shaft guarantees that to pressure rod the axial pressure bar just in time places in the groove at block top, and fastening nut guarantees closely contact, and displacement transducer is positioned over nut top, keeps closely contact, and the adjustment hammer makes lever be in the equilibrium position.At last, open the confined pressure operation valve and begin to apply confined pressure, open draining valve simultaneously, sample begins consolidation process, and current get into measuring cup through rising pipe.

(4) apply axle pressure.According to the discharging consolidation process of sample, start the axial pressure device, apply axle pressure.Add counterweight, lever becomes imbalance by balance, and the spin balancing regulating device becomes balance up to lever by imbalance again.In the loading procedure, adopt classification to apply, monitor the settling amount of sample in consolidation process closely through displacement transducer, apply first class pressure after, when the sample settling amount no longer changes, begin to apply next stage pressure, until the xial feed that is loaded into requirement.After treating the sample settlement stability, keep confined pressure and axle pressure constant, in order to simulate the residing three dimension stress state of the original state soil body in the actual engineering.

(5) apply seepage pressure.Open the seepage pressure operation valve, start the permeate pressurization device, the beginning classification applies seepage pressure, and infiltration water stream gets into sample through water inlet pipe, and through rising pipe, gets into measuring cup.In this process, monitor following data closely: (a) sample flow～infiltration gradient relation; (b) turbidity of photoelectric sensor monitoring～infiltration gradient relation, the critical infiltration gradient when beginning to start in order to pass judgment on movable fine grained; (c) stream of fine particles vector～time relationship; (d) sample sedimentation～time relationship, sample hoop strain～time relationship, sample sedimentation～infiltration gradient relation, sample hoop strain～infiltration gradient relation.

Above-mentioned seepage flow eroding stress coupling piping test unit is applied in the inventive method, and concrete theoretical derivation process is following:

The general soil body is by three phase compositions, i.e. soil skeleton phase, movable fine grained phase, water.For the heterogeneous fluid system, the mass-conservation equation of α phase:

In the formula, ρ ^αBe the branch density of α phase, v ^αBe the true velocity of α phase, t is the time,

For producing the mass rate of α phase.The branch rate of change of the density of first expression in left side α phase; The clean accumulation of second expression α in cell cube dV, the right item

is in unit volume dV because the mass rate of the α phase that erosion action produces.The physical significance of formula (1) is: the mass rate of the quality rate of growth of α phase and generation α phase in α clean accumulation mass rate sum mutually equals dV in the dV.

In the formula, dm ^αBe the quality of α phase, ρ ^SRThe density of expression soil particle, n ^αVolume fraction for the α phase.With formula (2) substitution formula (1), obtain:

For the soil skeleton phase, its mass-conservation equation is:

In the formula, n ^sBe the volume fraction of soil skeleton phase,

φ is a porosity, v ^sMovement velocity for soil skeleton.Produce the mass rate of soil skeleton phase in

expression dV; Negative sign representes that soil skeleton receives water erosion to produce movable fine grained phase, mass loss mutually.Therefore, formula (4) can be reduced to:

Further formula (5) is launched, obtained

In the formula, the 1st of left end is the local derivative item of field, reflected a non-stationarity that changes; The 2nd is the space derivative item of field, and essence is the convective term that causes because of the solid skeletal displacement, has reflected a heterogeneity that changes.In solid mechanics small deformation theory, can ignore; The 3rd is the caused variation item of solid skeletal distortion, utilizes the relation of speed and displacement:

By the small deformation geometric relationship,

In the formula, ε _vBe bulk strain, u (u _x, u _y, u _z) be the soil skeleton motion vector.With formula (7)～(8) substitution formula (6), obtain:

At t ₀～t ₁In period, the following formula integration is obtained:

In the formula:

Be respectively t ₀, t ₁Porosity constantly,

Be respectively t ₀, t ₁Bulk strain constantly,

Be respectively t ₀, t ₁Stream of fine particles vector constantly.

Thereby utilize above-mentioned seepage flow eroding stress coupling piping test unit to measure the method for the porosity in the piping evolution, comprise the steps:

(1) according to the initial porosity φ that dry density and saturated water requirement confirm to fill sample that fills of sample ₀Confirm the bulk strain of specimen test initial time

Be 0; Confirmed test initial time stream of fine particles vector Be 0;

(2) at 0～t ₀Period, the settling amount of monitoring through displacement transducer obtains axial strain ε divided by specimen height ₁Hoop strain ε is obtained in resistance strain gage collection through sticking on the sample middle part ₂According to bulk strain ε in the triaxial test _v, axial strain ε ₁And hoop strain ε ₂Relation:

Confirm t ₀The bulk strain of sample constantly

(3) at 0～t ₀Period, gather t ₀Moment stream of fine particles vector

(4), calculate 0～t according to following formula ₀T in period ₀Porosity constantly

In the formula, ρ ^SRThe density of expression soil particle.

(6) at t ₀～t ₁Period, the settling amount of monitoring through displacement transducer obtains axial strain ε divided by specimen height ₁Hoop strain ε is obtained in resistance strain gage collection through sticking on the sample middle part ₂According to bulk strain ε in the triaxial test _v, axial strain ε ₁And hoop strain ε ₂Relation:

Confirm t ₁The bulk strain of sample constantly

(7) at t ₀～t ₁Period, test t ₁Moment stream of fine particles vector

(8), calculate t according to following formula ₀～t ₁T in period ₁Porosity constantly

In the formula, ρ ^SRThe density of expression soil particle.

As stated, although represented and explained the present invention that with reference to specific preferred embodiment it shall not be construed as the restriction to the present invention self.Under the spirit and scope of the present invention prerequisite that does not break away from the accompanying claims definition, can make various variations in form with on the details to it.

Claims (1)

1. a method of measuring piping evolution mesoporosity rate is characterized in that comprising the steps:

(1) according to the initial porosity φ that dry density and saturated water requirement confirm to fill sample that fills of sample ₀Confirm the bulk strain of specimen test initial time

Be 0; The stream of fine particles vector of confirmed test initial time

Be 0;

(2) at 0～t ₀Period, the settling amount of monitoring through displacement transducer obtains axial strain ε divided by specimen height ₁Hoop strain ε is obtained in resistance strain gage collection through sticking on the sample middle part ₂According to bulk strain ε in the triaxial test _v, axial strain ε ₁And hoop strain ε ₂Relation: ε _v=ε ₁+ 2 ε ₂, confirm t ₀The bulk strain of sample constantly

(3) at 0～t ₀Period, gather t ₀Moment stream of fine particles vector

(4), calculate 0～t according to following formula ₀T in period ₀Porosity constantly

${\mathrm{\φ}}_{t_0}=\frac{1}{1+({\mathrm{\ϵ}}_{v_{t_0}}-{\mathrm{\ϵ}}_{v_0})}({\mathrm{\φ}}_0+({\mathrm{\ϵ}}_{v_{t_0}}-{\mathrm{\ϵ}}_{v_0})+\frac{m_{t_0}^s-m_0^s}{{\mathrm{\ρ}}^{\mathrm{sR}}})$

In the formula, ρ ^SRThe density of expression soil particle;

(5) at t ₀～t ₁Period, the settling amount of monitoring through displacement transducer obtains axial strain ε divided by specimen height ₁Hoop strain ε is obtained in resistance strain gage collection through sticking on the sample middle part ₂According to bulk strain ε in the triaxial test _v, axial strain ε ₁And hoop strain ε ₂Relation: ε _v=ε ₁+ 2 ε ₂, confirm t ₁The bulk strain of sample constantly

(6) at t ₀～t ₁Period, test t ₁Moment stream of fine particles vector

(7), calculate t according to following formula ₀～t ₁T in period ₁Porosity constantly

${\mathrm{\φ}}_{t_1}=\frac{1}{1+({\mathrm{\ϵ}}_{v_{t_1}}-{\mathrm{\ϵ}}_{v_0})}({\mathrm{\φ}}_{t_0}+({\mathrm{\ϵ}}_{v_{t_1}}-{\mathrm{\ϵ}}_{{v_t}_0})+\frac{m_{t_1}^s-m_{t_0}^s}{{\mathrm{\ρ}}^{\mathrm{sR}}})$

In the formula, ρ ^SRThe density of expression soil particle.

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