CN103322296A - Method for determining pipeline critical burial depth in debris flow areas - Google Patents

Abstract

The invention discloses a method for determining pipeline critical burial depth in debris flow areas. The method includes: for diluted debris flow, determining a forming initial flow velocity and a damaging initial flow velocity of an overlying soil armoring layer according to mutual effect between the diluted debris flow and pipeline overlying soil and critical hydraulic conditions of armoring layer forming and damaging, judging erosion modes of overlying soil according to scale and a flow velocity of the current debris flow, and calculating erosion depth of the pipeline overlying soil under the effect of the diluted debris flow; for viscose debris flow, judging erosion and deposition features of the debris flow according to relations between bed surface gradient and minimum slope required by debris flow movement, and calculating erosion depth, under erosion action, of the viscose debris flow if the bed surface gradient is larger than the minimum slope. The method has the advantages that erosion depth of the pipeline overlying soil under debris flows of different intensities is considered quantitatively, and technical guarantee is provided for scientific design and construction.

Description

Definite method of the critical buried depth of a kind of debris flow region pipeline

Technical field

The present invention relates to definite method of the critical buried depth of a kind of debris flow region oil and gas pipeline.

Background technique

Area on many mountains, because the alpine terrain complex geologic conditions, under the impact of ambient conditions, geological hazards in mountainous area take place frequently (such as debris flow), and oil, Long-distance Transmission Pipeline need to pass through this a large amount of class areas, will certainly cause a significant threat defeated passing through of oil-vapor pipe.

Present stage because people are not enough and lack corresponding engineering mitigation technology to the understanding of this special geology phenomenon of debris flow, cause most pipework in the crossing process of reality by virtue of experience the property judgement design and construct.Wherein relating to the most important parameter of pipe safety---the depth of burying, generally is to determine according to the facility of construction, does not consider scientifically and rationally the dynamical phase mutual effect (effect of especially corroding) of debris flow and pipeline.Such buried pipeline method and technology lack science and objectivity, and it is anti-risk, the ability of anti-disaster is very weak.

Summary of the invention

In order to overcome the above-mentioned shortcoming of prior art, the invention provides definite method of the critical buried depth of a kind of debris flow region pipeline, for diluted debris flow, according to the critical hydraulics that the interaction between the earthing and roughened layer on diluted debris flow and the pipeline form and destroy, determine the initial velocity U that upper earthing roughened layer forms _{* d35}Destroy critical incipient motion flow velocity U with roughened layer _{* dmax}, then according to the scale of working as time debris flow and the erosion pattern that flow velocity is judged upper earthing, and by corresponding calculation expression, provide under the diluted debris flow effect depth of erosion of earthing on the pipeline; For viscous mud-flow, the minimum gradient Relations Among required according to the bed surface gradient and mud-rock flow movement judged the erosion and deposition characteristic of debris flow.If the bed surface gradient can calculate viscous mud-flow depth of erosion under the corrosion function greater than the required minimum gradient of mud-rock flow movement.

The technical solution adopted for the present invention to solve the technical problems is: definite method of the critical buried depth of a kind of debris flow region pipeline comprises the steps:

Step 1, determine the fundamental type of debris flow:

According to the hydrometeorological data in locality and debris flow region prospecting guide, determine the type of debris flow:

(1) if soil body medium clay soil content＜3%, debris flow body viscosity＜0.3Pas, the volume concentration of the soil body＜50% in the debris flow, debris flow body unit weight＜1800kg/m ³And mudflow is 1200-1500kg/m ³Be turbulent motion; Deposit has obvious sorting, and soil body particle is thicker than the original soil body that debris flow occurs; Then be defined as diluted debris flow;

(2) if soil body medium clay soil content〉3%, debris flow body viscosity〉0.3Pas, the volume concentration of the soil body in the debris flow〉50%, debris flow body unit weight〉1800kg/m ³And mudflow〉1500kg/m ³Be whole laminar motion, a gust flow phenomenon is arranged; Remain with the original state soil block in the fluid; The deposit assortment; Then be defined as viscous mud-flow;

Step 2, the scour depth of calculating diluted debris flow and the depth of erosion of viscous mud-flow:

(1) scour depth of calculating diluted debris flow:

1) be calculated as follows roughened layer and form and destroy required critical hydraulics:

$U_{*d35}=1.34\sqrt{\frac{{\mathrm{\γ}}_S-{\mathrm{\γ}}_w}{{\mathrm{\γ}}_w}g{D}_{35}}{\left(\frac{h}{D_{35}}\right)}^{0.14}$

$U_{*d\max }=1.34\sqrt{\frac{{\mathrm{\γ}}_S-{\mathrm{\γ}}_w}{{\mathrm{\γ}}_w}g{D}_{\max }}{\left(\frac{h}{D_{\max }}\right)}^{0.14}$

In the formula: γ _SBe silt unit weight;

γ _wBe current unit weight;

G is gravity accleration;

H is that the mud of diluted debris flow is dark;

D ₃₅For cumulative percentage content on the Bed Particle grading curve is 35% corresponding particle diameter;

D _MaxBe the bed surface maximum particle diameter;

2) be calculated as follows drag velocity U _*:

In the formula, J is the gradient of debris flow gully;

3) to drag velocity U _*, maximum particle diameter when starting drag velocity U _{* dmax}, and starting drag velocity U _{* d35}Between size judge:

(I) works as U _*＜U _{* d35}The time, move for non-homogeneous sorting of bed material is defeated:

At first be calculated as follows the particle maximum particle diameter D that can start:

$D=\frac{U_{*}^{2.78}}{2.256h^{0.4}{\left(\frac{{\mathrm{\γ}}_S-{\mathrm{\γ}}_w}{{\mathrm{\γ}}_w}g\right)}^{1.4}}$

Then calculate diluted debris flow at U _*＜U _{* d35}Limiting scour h under the condition _Max:

$h_{\max }=E[1-\frac{(1-\mathrm{\χ})(1-{\mathrm{\η}}_1)}{(1-{\mathrm{\η}}_2)}]$

In the formula:

χ can be by the defeated shared ratio of bed material material of removing for what determine according to a component curve of bed material;

E is the thickness of bed surface active layer;

η ₁Porosity ratio for the bed surface active layer;

η ₂For fine grained is moved rear bed material porosity ratio by abundant failing;

(II) works as U _{* d35}≤ U _*≤ U _{* dmax}The time, will form firm roughened layer, d in the bed surface active layer ₃₅Following particle is moved by defeated, is calculated as follows diluted debris flow at U _{* d35}≤ U _*≤ U _{* dmax}Limiting scour h under the condition _Max:

$h_{\max }=E[1-\frac{(1-\mathrm{\χ})(1-{\mathrm{\η}}_1)}{(1-{\mathrm{\η}}_2)}],$ Wherein: χ=0.35;

(III) works as U _*U _{* dmax}The time, for ditch bed material moves defeated moving entirely, be calculated as follows the accumulation scour depth of a debris flow:

$h_{\max }=k\frac{\mathrm{\ρ}\·C}{B}\·{\∫}_0^{T}Q\left(t\right)\mathrm{dt}$

In the formula: k is coefficient of scouring;

ρ is the density of diluted debris flow;

The flow corresponding flow velocity that changes when C is the debris flow erosion bed surface;

B is the width of raceway groove;

Q (t) is the debris flow flow time-varying function of P for frequency;

T is a mudstone lasting time of flow;

(2) depth of erosion of calculating viscous mud-flow:

1) determines the required minimum gradient θ of viscous mud-flow motion according to following formula _m:

$\tan {\mathrm{\θ}}_m\≥\frac{({\mathrm{\γ}}_s-{\mathrm{\γ}}_w)\tan {\mathrm{\φ}}^{\′}}{{\mathrm{\γ}}_s}+\frac{{\mathrm{\τ}}_f}{C_{S1}{H}_c{\mathrm{\γ}}_s\cos {\mathrm{\θ}}_m}$

Wherein: φ ' is the coefficient of kinetic friction of debris flow movement of particles;

C _S1Grain volume fraction for debris flow;

H _cFor the mud of debris flow dark;

τ _fBe the viscous force of viscous mud-flow slurry at bed surface;

2) as bed surface gradient θ _bGreater than θ _mThe time, debris flow is to bed surface generation corrosion function; Be calculated as follows shear force τ this moment _s:

τ _s=C _S1H _c(γ _s-γ _w)cosθ _btanφ′+τ _y

Wherein: ${\mathrm{\τ}}_y=0.03e^{14.42C_{S1}}$

3) be calculated as follows bed surface soil shear strength τ:

τ=(C _S1H _c+C _S2H _ero)(γ _s-γ _w)cosθ _btanφ _s

Wherein: C _S2It is the grain volume fraction that corrodes soil layer;

H _EroTo corrode the thickness of the layer, i.e. depth of erosion;

φ _sIt is the angle of internal friction that corrodes soil layer;

4) be calculated as follows depth of erosion H _Ero:

$H_{\mathrm{ero}}=\frac{C_{S1}{H}_c({\mathrm{\γ}}_s-{\mathrm{\γ}}_w)\cos \mathrm{\θ}\tan {\mathrm{\φ}}^{\′}+{\mathrm{\τ}}_y}{C_{S2}({\mathrm{\γ}}_s-{\mathrm{\γ}}_w)\cos \mathrm{\θ}\tan {\mathrm{\φ}}_s}-\frac{C_{S1}}{C_{S2}}\·H_c$

Step 3, according to the result of calculation of step 2, determine the critical buried depth of pipeline:

For diluted debris flow, the critical buried depth of pipeline is at least greater than accumulation scour depth or limiting scour; For viscous mud-flow, the critical buried depth of pipeline is at least greater than depth of erosion.

Compared with prior art, good effect of the present invention is: the present invention is in conjunction with the concept of sediment movement mechanics, the first analysis of science and system the erosion problem of debris flow to earthing on the pipeline, the depth of erosion computational methods of debris flow to earthing on the pipeline have been proposed.The inventive method is not only from qualitative clear and definite erosion process and the mechanism of debris flow to surface soil layer, the more important thing is from having considered that quantitatively the mud-stone flow disaster of varying strength provides reliable technical support to the depth of erosion of earthing on the pipeline, for design and the construction of science.Use simultaneously the inventive method, can estimate that certain debris flow to the depth of erosion of earthing on certain built pipeline, in conjunction with the buried depth of this pipeline reality, can do further safety evaluation, it is with clearly defined objective, and is workable.Can greatly improve the Security of oil and gas pipeline operation, and reduce cost of disaster reduction, the data supporting of science is provided for passing through of debris flow region pipeline.

Embodiment

Definite method of the critical buried depth of a kind of debris flow region pipeline comprises the steps:

Step 1, determine the fundamental type of debris flow:

According to the hydrometeorological data in locality and debris flow region prospecting guide, can obtain the type of a certain larger debris flow of certain bar debris flow gully:

(1) if soil body medium clay soil content＜3%, debris flow body viscosity＜0.3Pas, the volume concentration C of the soil body in the debris flow _V＜50%, debris flow body unit weight＜1800kg/m ³(mudflow is 1200-1500kg/m ³); Be turbulent motion, without obvious battle array stream; Deposit has obvious sorting, and its soil body particle is thicker than the original soil body that debris flow occurs; Then be defined as diluted debris flow;

(2) if soil body medium clay soil content〉3%, debris flow body viscosity〉0.3Pas, the volume concentration C of the soil body in the debris flow _V50%, debris flow body unit weight〉1800kg/m ³(mudflow〉1500kg/m ³); Be whole laminar motion, a gust flow phenomenon is arranged; Remain with the original state soil block in the fluid; The deposit assortment; Then be defined as viscous mud-flow.

Step 2, the scour depth of calculating diluted debris flow and the depth of erosion of viscous mud-flow:

(1) scour depth of calculating diluted debris flow:

Diluted debris flow refers to that to washing away for the first time of earthing on the raceway groove debris flow is to the ditch bed of the alligatoring defeated handling process of moving of piling up material not also.Can washing away for the first time in the process of diluted debris flow form stable roughened layer very large on the impact of diluted debris flow rate of sand transporting.The critical hydraulics that roughened layer forms roughly is equivalent to D ₃₅Starting conditions, also namely when bed surface silt nearly 65% is motionless particle, roughened layer is just accused formation, the hydrodynamic condition of this moment is designated as U _D35The critical hydraulics that roughened layer destroys should be equivalent to the starting conditions of the largest particles under the alligatoring grating condition, and the hydrodynamic condition of this moment is designated as U _Dmax

1) is calculated as follows roughened layer and forms and destroy required critical hydraulics (the drag velocity U that the Bed Particle starting is required _{* d35}And the required drag velocity U of maximum particle diameter starting _{* dmax}):

$U_{*d35}=1.34\sqrt{\frac{{\mathrm{\γ}}_S-{\mathrm{\γ}}_w}{{\mathrm{\γ}}_w}g{D}_{35}}{\left(\frac{h}{D_{35}}\right)}^{0.14}$

$U_{*d\max }=1.34\sqrt{\frac{{\mathrm{\γ}}_S-{\mathrm{\γ}}_w}{{\mathrm{\γ}}_w}g{D}_{\max }}{\left(\frac{h}{D_{\max }}\right)}^{0.14}$

In the formula: U _{* d35}Be starting drag velocity (m/s);

γ _SBe silt unit weight (N/m ³), generally get 26000N/m ³

γ _wBe current unit weight (N/m ³), generally get 9800N/m ³

G is gravity accleration (9.81m/s ²);

H is the mud dark (m) of diluted debris flow;

D ₃₅For cumulative percentage content on the Bed Particle grading curve is 35% corresponding particle diameter (m);

D _MaxBe bed surface maximum particle diameter (m);

U _{* dmax}Drag velocity when starting for maximum particle diameter.

2) be calculated as follows drag velocity U _*:

In the formula, J is the gradient of debris flow gully;

The parameters such as the mud of above-mentioned debris flow is dark, the gradient of flow velocity, grading curve, debris flow gully and debris flow endurance all can obtain according to record and the debris flow region prospecting guide of historical data.

3) to drag velocity U _*, maximum particle diameter when starting drag velocity U _{* dmax}, and starting drag velocity U _{* d35}Between size judge:

(I) works as U _*＜U _{* d35}The time, move for non-homogeneous sorting of bed material is defeated:

At first according to the critical incipient motion velocity formula of viscosity non-uniform granular:

$U_{*}=1.34\sqrt{\frac{{\mathrm{\γ}}_S-{\mathrm{\γ}}_w}{{\mathrm{\γ}}_w}\mathrm{gD}}{\left(\frac{h}{D}\right)}^{0.14}$

The particle maximum particle diameter D that inverse can start:

$D=\frac{U_{*}^{2.78}}{2.256h^{0.4}{\left(\frac{{\mathrm{\γ}}_S-{\mathrm{\γ}}_w}{{\mathrm{\γ}}_w}g\right)}^{1.4}}$

Then calculate diluted debris flow at U _*＜U _{* d35}Limiting scour h under the condition _Max:

$h_{\max }=E[1-\frac{(1-\mathrm{\χ})(1-{\mathrm{\η}}_1)}{(1-{\mathrm{\η}}_2)}]$

In the formula: χ can be by the defeated shared ratio of bed material material of removing for what determine according to a component curve of bed material;

E is the thickness (m) of bed surface active layer, and in the Practical Calculation, its value is generally 1.5 times of bed material maximum particle diameter;

η ₁Porosity ratio for the bed surface active layer;

η ₂For fine grained is moved rear bed material porosity ratio by abundant failing;

(II) works as U _{* d35}≤ U _*≤ U _{* dmax}The time, will form firm roughened layer, d in the bed surface active layer ₃₅Following particle is moved by defeated:

If ditch bed solid matter is fully washed away, just roughened layer can form and not be destroyed d gradually ₃₅Following particle is moved by defeated.After bed surface is by abundant alligatoring, debris flow will sharply descend to the scour rate of bed surface, at this moment scour rate and time-independent.Therefore, under this dynamic condition, bed scour rate over time rule is complicated, if but from the bed surface structure, the limit of Calculation of Debris Flow is rushed the degree of depth will make problem greatly simplify.This situation essence is a kind of special case of condition (I), is equivalent to limiting scour h _MaxGetting χ=0.35 in the formula gets final product.

(III) works as U _*U _{* dmax}The time, for ditch bed material moves defeated moving entirely:

This moment, the dynamic condition of debris flow was enough to defeated all bed material particles that moves, and this also is the comparatively general flushing mode of nature (the minority megalith can't be failed and remove outward).At this moment, debris flow is closely related to scour rate and the flushing time of ditch bed.Changes in flow rate in debris flow process will make it on the basis of previous flow or wash away aggravation, or wash away and reduce even deposit.The accumulation scour depth of a debris flow is shown below:

$h_{\max }=k\frac{\mathrm{\ρ}\·C}{B}\·{\∫}_0^{T}Q\left(t\right)\mathrm{dt}$

In the formula: k is coefficient of scouring;

ρ is the density (kg/m of diluted debris flow ³);

The flow corresponding flow velocity (m/s) that changes when C is the debris flow erosion bed surface;

B is the width of raceway groove;

Q (t) is the debris flow flow time-varying function (m of P for frequency ³/ t);

T is a mudstone lasting time of flow.

This shows, the process of washing away of debris flow and the unit weight of debris flow self, flow velocity and flow are relevant.And can ask for by following formula of reduction calculating for the accumulative total of the debris flow in small watershed scour depth: $h_{\max }=0.264k\frac{T_{\mathrm{\ρ}}\·Q_{\max }^2}{B^{2}h}$

Wherein the k span is 1.6 * 10 ^-6～7.3 * 10 ^-6,

Q _MaxIt is maximum flood peak (can obtain according to local hydrological data);

H is that debris flow mud is dark.

(2) depth of erosion of calculating viscous mud-flow:

The motion of debris flow at first needs to judge the flowability of debris flow on the impact of bed surface, be motion or alluvial.The required minimum gradient θ of this native power class mud-rock flow movement of viscous mud-flow _MFor

$\tan {\mathrm{\θ}}_m\≥\frac{({\mathrm{\γ}}_s-{\mathrm{\γ}}_w)\tan {\mathrm{\φ}}^{\′}}{{\mathrm{\γ}}_s}+\frac{{\mathrm{\τ}}_f}{C_{S1}{H}_c{\mathrm{\γ}}_s\cos {\mathrm{\θ}}_m}$

Wherein: φ ' is the coefficient of kinetic friction (gravel soil is generally got 25 °-35 °) of debris flow movement of particles;

C _S1Grain volume fraction for debris flow;

H _cMud dark (m) for debris flow;

τ _fBe the viscous force of viscous mud-flow slurry at bed surface

As bed surface gradient θ _bGreater than θ _MThe time, debris flow is to bed surface generation corrosion function; The shear force of this moment is:

τ _s=C _S1H _c(γ _s-γ _w)cosθ _btanφ′+τ _y

Wherein: ${\mathrm{\τ}}_y=0.03e^{14.42C_{S1}}$

The bed surface soil shear strength is:

τ=(C _S1H _c+C _S2H _ero)(γ _s-γ _w)cosθ _btanφ _s

Wherein: C _S2It is the grain volume fraction that corrodes soil layer;

H _EroTo corrode the thickness of the layer, i.e. depth of erosion;

φ _sIt is the angle of internal friction that corrodes soil layer.

Condition according to the limit equilibrium of bed surface damage of soil body:

τ _s+τ _f=τ

Can be in the hope of depth of erosion

$H_{\mathrm{ero}}=\frac{C_{S1}{H}_c({\mathrm{\γ}}_s-{\mathrm{\γ}}_w)\cos \mathrm{\θ}\tan {\mathrm{\φ}}^{\′}+{\mathrm{\τ}}_y}{C_{S2}({\mathrm{\γ}}_s-{\mathrm{\γ}}_w)\cos \mathrm{\θ}\tan {\mathrm{\φ}}_s}-\frac{C_{S1}}{C_{S2}}\·H_c$

Step 3, according to the result of calculation of step 2, determine the critical buried depth of pipeline:

For diluted debris flow, the critical buried depth of pipeline is at least greater than accumulation scour depth or limiting scour h _MaxFor viscous mud-flow, the critical buried depth of pipeline is at least greater than depth of erosion H _Ero

Claims (3)

1. definite method of the critical buried depth of debris flow region pipeline is characterized in that: comprise the steps:

Step 1, determine the fundamental type of debris flow:

According to the hydrometeorological data in locality and debris flow region prospecting guide, determine the type of debris flow:

(1) if soil body medium clay soil content＜3%, debris flow body viscosity＜0.3Pas, the volume concentration of the soil body＜50% in the debris flow, debris flow body unit weight＜1800kg/m ³And mudflow is 1200-1500kg/m ³Be turbulent motion; Deposit has obvious sorting, and soil body particle is thicker than the original soil body that debris flow occurs; Then be defined as diluted debris flow;

(2) if soil body medium clay soil content〉3%, debris flow body viscosity〉0.3Pas, the volume concentration of the soil body in the debris flow〉50%, debris flow body unit weight〉1800kg/m ³And mudflow〉1500kg/m ³Be whole laminar motion, a gust flow phenomenon is arranged; Remain with the original state soil block in the fluid; The deposit assortment; Then be defined as viscous mud-flow;

Step 2, the scour depth of calculating diluted debris flow and the depth of erosion of viscous mud-flow:

(1) scour depth of calculating diluted debris flow:

1) be calculated as follows roughened layer and form and destroy required critical hydraulics:

$U_{*d35}=1.34\sqrt{\frac{{\mathrm{\γ}}_S-{\mathrm{\γ}}_w}{{\mathrm{\γ}}_w}g{D}_{35}}{\left(\frac{h}{D_{35}}\right)}^{0.14}$

$U_{*d\max }=1.34\sqrt{\frac{{\mathrm{\γ}}_S-{\mathrm{\γ}}_w}{{\mathrm{\γ}}_w}g{D}_{\max }}{\left(\frac{h}{D_{\max }}\right)}^{0.14}$

In the formula: γ _SBe silt unit weight;

γ _wBe current unit weight;

G is gravity accleration;

H is that the mud of diluted debris flow is dark;

D ₃₅For cumulative percentage content on the Bed Particle grading curve is 35% corresponding particle diameter;

D _MaxBe the bed surface maximum particle diameter;

2) be calculated as follows drag velocity U _*:

In the formula, J is the gradient of debris flow gully;

3) to drag velocity U _*, maximum particle diameter when starting drag velocity U _{* dmax}, and starting drag velocity U _{* d35}Between size judge:

(I) works as U _*＜U _{* d35}The time, move for non-homogeneous sorting of bed material is defeated:

At first be calculated as follows the particle maximum particle diameter D that can start:

$D=\frac{U_{*}^{2.78}}{2.256h^{0.4}{\left(\frac{{\mathrm{\γ}}_S-{\mathrm{\γ}}_w}{{\mathrm{\γ}}_w}g\right)}^{1.4}}$

Then calculate diluted debris flow at U _*＜U _{* d35}Limiting scour h under the condition _Max:

$h_{\max }=E[1-\frac{(1-\mathrm{\χ})(1-{\mathrm{\η}}_1)}{(1-{\mathrm{\η}}_2)}]$

In the formula:

χ can be by the defeated shared ratio of bed material material of removing for what determine according to a component curve of bed material;

E is the thickness of bed surface active layer;

η ₁Porosity ratio for the bed surface active layer;

η ₂For fine grained is moved rear bed material porosity ratio by abundant failing;

(II) works as U _{* d35}≤ U _*≤ U _{* dmax}The time, will form firm roughened layer, d in the bed surface active layer ₃₅Following particle is moved by defeated, is calculated as follows diluted debris flow at U _{* d35}≤ U _*≤ U _{* dmax}Limiting scour h under the condition _Max:

$h_{\max }=E[1-\frac{(1-\mathrm{\χ})(1-{\mathrm{\η}}_1)}{(1-{\mathrm{\η}}_2)}],$ Wherein: χ=0.35;

(III) works as U _*U _{* dmax}The time, for ditch bed material moves defeated moving entirely, be calculated as follows the accumulation scour depth of a debris flow:

$h_{\max }=k\frac{\mathrm{\ρ}\·C}{B}\·{\∫}_0^{T}Q\left(t\right)\mathrm{dt}$

In the formula: k is coefficient of scouring;

ρ is the density of diluted debris flow;

The flow corresponding flow velocity that changes when C is the debris flow erosion bed surface;

B is the width of raceway groove;

Q (t) is the debris flow flow time-varying function of P for frequency;

T is a mudstone lasting time of flow;

(2) depth of erosion of calculating viscous mud-flow:

1) determines the required minimum gradient θ of viscous mud-flow motion according to following formula _m:

$\tan {\mathrm{\θ}}_m\≥\frac{({\mathrm{\γ}}_s-{\mathrm{\γ}}_w)\tan {\mathrm{\φ}}^{\′}}{{\mathrm{\γ}}_s}+\frac{{\mathrm{\τ}}_f}{C_{S1}{H}_c{\mathrm{\γ}}_s\cos {\mathrm{\θ}}_m}$

Wherein: φ ' is the coefficient of kinetic friction of debris flow movement of particles;

C _S1Grain volume fraction for debris flow;

H _cFor the mud of debris flow dark;

τ _fBe the viscous force of viscous mud-flow slurry at bed surface;

2) as bed surface gradient θ _bGreater than θ _mThe time, debris flow is to bed surface generation corrosion function; Be calculated as follows shear force τ this moment _s:

τ _s=C _S1H _c(γ _s-γ _w)cosθ _btanφ′+τ _y

Wherein: ${\mathrm{\τ}}_y=0.03e^{14.42C_{S1}}$

3) be calculated as follows bed surface soil shear strength τ:

τ=(C _S1H _c+C _S2H _ero)(γ _s-γ _w)cosθ _btanφ _s

Wherein: C _S2It is the grain volume fraction that corrodes soil layer;

H _EroTo corrode the thickness of the layer, i.e. depth of erosion;

φ _sIt is the angle of internal friction that corrodes soil layer;

4) be calculated as follows depth of erosion H _Ero:

$H_{\mathrm{ero}}=\frac{C_{S1}{H}_c({\mathrm{\γ}}_s-{\mathrm{\γ}}_w)\cos \mathrm{\θ}\tan {\mathrm{\φ}}^{\′}+{\mathrm{\τ}}_y}{C_{S2}({\mathrm{\γ}}_s-{\mathrm{\γ}}_w)\cos \mathrm{\θ}\tan {\mathrm{\φ}}_s}-\frac{C_{S1}}{C_{S2}}\·H_c$

Step 3, according to the result of calculation of step 2, determine the critical buried depth of pipeline:

For diluted debris flow, the critical buried depth of pipeline is at least greater than accumulation scour depth or limiting scour; For viscous mud-flow, the critical buried depth of pipeline is at least greater than depth of erosion.

2. definite method of the critical buried depth of a kind of debris flow region pipeline according to claim 1 is characterized in that: silt unit weight γ _SGet 26000N/m ³Current unit weight γ _wGet 9800N/m ³

3. definite method of the critical buried depth of a kind of debris flow region pipeline according to claim 1, it is characterized in that: E is 1.5 times of bed material maximum particle diameter.