Method for planning and designing debris flow drainage channels and applications thereof

Abstract

A method for planning and designing a debris flow drainage channel is provided. The position and total length of the drainage channel and a longitudinal slope of a gully bed of the drainage channel are determined. An inlet section, an outlet section and an acceleration section of the drainage channel are formed as fully lined channel type. After determining the length of the inlet section and the included angle between the side wall of the inlet section and the main channel, the length of the outlet section and the included angle between the side wall of the outlet section and the main channel, and the length of the acceleration section, the channel type and the length of the main channel section are also determined.

Claims

1. A method for constructing a debris flow drainage channel, wherein the debris flow drainage channel is divided into an inlet section, an acceleration section, a main channel section in which a debris flow flows in a balanced mode, and an outlet section along the flow direction of the debris flow, the method comprising: planning a position of the debris flow drainage channel and determining a total length (L) of the debris flow drainage channel based on a topographic condition of a debris flow accumulation fan, and determining a longitudinal slope of a gully bed of the debris flow drainage channel based on a principle in which cutting and filling are substantially balanced; forming the inlet section as a fully lined channel type, wherein the length (L.sub.1) of the inlet section and an included angle between a side wall of the inlet section and the main channel section are determined based on properties of the drained debris flow and the determined longitudinal slope of the gully bed of the debris flow drainage channel; forming the outlet section as a fully lined channel type, wherein the length (L.sub.4) of the outlet section and an included angle between a side wall of the outlet section and the main channel section are determined based on the properties of the drained debris flow and the determined longitudinal slope of the gully bed of the debris flow drainage channel; forming the acceleration section as a fully lined channel type, wherein the length (L.sub.2) of the acceleration section is determined based on a steady non-uniform channel gradually varied flow calculation model, wherein the length L.sub.2 is calculated based on the equation: L.sub.2=(E.sub.xE.sub.s)/(iJ), wherein E.sub.x refers to ever y of a downstream cross-section of the acceleration section; wherein E.sub.s refers to energy of an upstream cross-section of the acceleration section; wherein i refers to the determined longitudinal slope of the gully bed of the debris flow drainage channel; and wherein J refers to an average hydraulic gradient of a top surface of the debris flow at the acceleration section; determining a channel type of the main channel section based on the determined longitudinal slope of the gully bed of the debris flow drainage channel and longitudinal slope intervals of gully beds applicable to different channel types of debris flow drainage channels, and determining the length (L.sub.3=LL.sub.1L.sub.2L.sub.4) of the main channel section; and constructing the debris flow drainage channel based on the determined channel type of the main channel section and the determined length of the main channel section.

2. The method of claim 1, wherein a limited flow velocity of the debris flow drainage channel is determined based on material and structure of the debris flow drainage channel and wherein a designed flow velocity of the downstream cross-section of the acceleration section and a designed flow velocity of the main channel section are 0.8-1.0 times of the limited flow velocity.

3. The method of claim 1, wherein the channel type of the main channel section comprises at least one of a fully lined type, a symmetrical notched sill type, a staggered notched sill type, a transversely penetrated notched sill type and a box lined type.

4. The method of claim 3, wherein the longitudinal slope intervals of gully beds applicable to different channel types of debris flow drainage channels are as follows: 0.01-0.03 for a fully lined type, 0.03-0.08 for a symmetrical notched sill type, 0.08-0.12 for a staggered notched sill type, 0.12-0.20 for a transversely penetrated notched sill type and 0.20-0.40 for a box lined type.

5. The method of claim 1, wherein the length (L.sub.1) of the inlet section is 1.5-5.0 times of the width of the bottom of the debris flow drainage channel, and the included angle between the side wall of the inlet section and the main channel section is 10-30 degrees.

6. The method of claim 1, wherein the length (L.sub.4) of the outlet section is 1.0-3.0 times of the width of the bottom of the debris flow drainage channel, and the included angle between the side wall of the outlet section and the main channel section is 5-15 degrees.

7. The method of claim 1, wherein the total length (L) of the debris flow drainage channel is less than or equal to 300 m.

8. A method of applying the method of claim 1, wherein the method of claim 1 is used for constructing a debris flow drainage channel with a total length of less than or equal to 300 m and the upstream part of the inlet section of the debris flow drainage channel is provided with a check dam used with the constructed drainage channel.

9. A method of applying the method of claim 1 when a length of a debris flow accumulation fan is greater than 300 m, wherein: the method of claim 1 is used to construct at least two debris flow drainage channels that are independent and connected in tandem; and the upstream part of the inlet section of the upstream-most drainage channel is provided with a check dam used with the drainage channel.

10. The method of claim 9, wherein a transition zone is arranged between two adjacent upstream and downstream drainage channels, for accommodating the afflux of a debris flow in a tributary ditch on the surface of the debris flow accumulation fan or leading out part of the debris flow to prevent depositing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a plane layout schematic diagram of a debris flow drainage channel constructed according to the method for planning and designing debris flow drainage channels described by the invention.

(2) FIG. 2 is a plane layout schematic diagram of a debris flow drainage channel constructed according to the method for planning and designing debris flow drainage channels described by the invention when the length of the debris flow accumulation fan is greater than 300 m and a transition zone accommodates the afflux of a debris flow in a tributary ditch.

(3) FIG. 3 is a plane layout schematic diagram of a debris flow drainage channel constructed according to the method for planning and designing debris flow drainage channels described by the invention when the length of the debris flow accumulation fan is greater than 300 m and a transition zone directs part of the debris flow outward to prevent depositing.

(4) The labels in the figures are as follows:

(5) TABLE-US-00001 1 inlet section 2 acceleration section 3 main channel section 4 outlet section 5 transition zone a: included angle between side wall of inlet section and main channel : included angle between side wall of outlet section and main channel L total length L.sub.1 length of inlet section L.sub.2 length of acceleration section L.sub.3 length of main channel section L.sub.4 length of outlet section

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) The following section further describes the preferential embodiments of the invention with reference to the accompanying drawings.

Embodiment 1

(7) As shown in FIG. 1, the debris flow gully contains a viscous debris flow, the drainage area is 5.4 km.sup.2, and the length of the accumulation fan is 260 m. To control debris flow disasters, a prevention and control scheme based on constructing a check dam group in the drainage basin and constructing a drainage channel on the accumulation fan is planned. The drainage channel is divided into a big-end-up bell-mouthed inlet section 1, an acceleration section 2, a main channel section 3 in which the debris flow flows in a balanced mode, and a big-end-down bell-mouthed outlet section 4 along the flow direction of the debris flow; the drainage channel is constructed of concrete materials. Therefore, the limited flow velocity of the drainage channel is determined to be 8.0 m/s. A method for planning and designing the above drainage channel comprises the following steps.

(8) (1) According to the topographic condition of the debris flow accumulation fan, plan the drainage channel at the mid position of the deposited fan and arrange a check dam to regulate debris flow movement at the upstream part of inlet section 1 of the drainage channel. The total length L of the to-be-constructed drainage channel is 250 m according to the length of the deposited fan; the longitudinal slope of the gully bed of the drainage channel is 0.15 according to the principle that cut and fill are basically balanced; and the width of the bottom of the drainage channel is 4.0 m if the designed drain flow of the drainage channel is 400 m.sup.3/s;

(9) (2) The channel type of inlet section 1 is determined to be a fully lined channel type. Under the condition that the debris flow is a viscous debris flow according to drainage design standards and that the longitudinal slope of the gully bed of the drainage channel determined in step 1 is 0.15, the length L.sub.1 of the inlet section is 5.0 times as large as the width of the bottom of the drainage channel, i.e., L.sub.1=5.04.0=20.0 m, and the included angle between the side wall of the inlet section 1 and the main channel is 10 degrees;

(10) (3) The channel type of outlet section 4 is determined to be a fully lined channel type. Under the condition that the debris flow is a viscous debris flow according to drainage design standards and that the longitudinal slope of the gully bed of the drainage channel determined in step 1 is 0.15, the length L.sub.4 of the outlet section is 3.0 times as large as the width of the bottom of the drainage channel, i.e., L.sub.4=3.04.0=12.0 m, and the included angle between the side wall of the outlet section 4 and the main channel is 5 degrees;

(11) (4) The channel type of acceleration section 2 is determined to be a fully lined channel type. According to field investigation, the flow velocity v.sub.1 of the debris flow at the upstream cross-section of the acceleration section 2 is 2.3 m/s, and the sludge-level depth h.sub.1 of the debris flow at the upstream cross-section of the acceleration section 2 is 4.35 m, i.e., h.sub.1=designed drain flow/(width of bottom of drainage channelv.sub.1)=40.0/(4.02.3)=4.35 m. The designed flow velocity of the debris flow at the downstream cross-section of acceleration section 2 is 1.0 times as large as the limited flow velocity, i.e., v.sub.2=8.0 m/s, and the sludge-level depth h.sub.2 of the debris flow at the downstream cross-section of the acceleration section 2 is 1.25 m, i.e., h.sub.2=designed drain flow/(width of bottom of drainage channelv.sub.2)=40.0/(4.08.0)=1.25 m. Substituting the parameters above into a steady non-uniform channel gradually varied flow calculation model to conduct iterative calculation results in a length L.sub.2 of the acceleration section 2 of 10.9 m.

(12) (5) According to the longitudinal slope (0.15) of the gully bed of the drainage channel determined in step 1 and the optimal longitudinal slope intervals of the gully beds applicable to different channel types of drainage channels, the channel type of main channel section 3 is a transversely penetrated notched sill type, and the length L.sub.3 of the main channel section 3 is 207.1 m, i.e., L.sub.3=LL.sub.1L.sub.2L.sub.4=207.1 m.

Embodiment 2

(13) As shown in FIG. 1 and FIG. 2, the flow in the debris flow gully is a dilute debris flow, the drainage area is 8.6 km.sup.2, and the length of the accumulation fan is 500 m. To control debris flow disasters, a prevention and control scheme based on constructing a check dam group in the drainage basin and a drainage channel on the deposited fan is planned. Because the length of the debris flow-deposited fan is greater than 300 m, the proposed drainage channel includes two relatively independent debris flow drainage channels (i.e., an upper drainage channel and a lower drainage channel), which are connected in an end-to-end mode from upstream to downstream. Transition zone 5 is arranged between the upper and lower drainage channels, its along-the-flow direction of the debris flow is 20 m, and it is used to accommodate the afflux of the debris flow in a tributary ditch on the surface of the fan.

(14) The upper drainage channel is divided into a big-end-up bell-mouthed inlet section 1, an acceleration section 2, a main channel section 3 in which the debris flow flows in a balanced mode, and a big-end-down bell-mouthed outlet section 4 along the flow direction of the debris flow. The upper drainage channel is constructed of reinforced concrete; therefore, the limited flow velocity of the drainage channel is determined to be 8.0 m/s. The method for planning and designing the upper drainage channel comprises the following steps.

(15) (1) According to the topographic condition of the debris flow accumulation fan, the upper drainage channel is planned at the upper position of the accumulation fan, and a check dam is arranged to regulate debris flow movement at the upstream part of inlet section 1 of the upper drainage channel. The total length L of the proposed upper drainage channel is 300 m; according to the principle that cut and fill are basically balanced, the longitudinal slope of the gully bed of the upper drainage channel is 0.22; and the width of the bottom of the upper drainage channel is 5.0 m if the designed drain flow of the upper drainage channel is 64.0 m.sup.3/s;

(16) (2) The channel type of inlet section 1 is determined to be a fully lined channel type. Under the conditions that the debris flow is a dilute debris flow according to drainage design standards and that the longitudinal slope of the gully bed of the drainage channel determined in step 1 is 0.22, the length L.sub.1 of the inlet section is 1.5 times as large as the width of the bottom of the drainage channel, i.e., L.sub.1=1.505.0=7.5 m, and the included angle between the side wall of inlet section 1 and the main channel is 30 degrees.

(17) (3) The channel type of outlet section 4 is determined to be a fully lined channel type. Under the condition that the debris flow is a dilute debris flow according to drainage design standards and that the longitudinal slope of the gully bed of the drainage channel determined in step 1 is 0.22, the length L.sub.4 of the outlet section is 1.0 times as large as the width of the bottom of the drainage channel, i.e., L.sub.4=1.05.0=5.0 m, and the included angle between the side wall of outlet section 4 and the main channel is 15 degrees.

(18) (4) The channel type of acceleration section 2 is determined to be a fully lined channel type. According to a steady non-uniform channel gradually varied flow calculation model, iterative calculations determine that the length L.sub.2 of the acceleration section 2 is 6.1 m.

(19) (5) According to the longitudinal slope (0.22) of the gully bed of the drainage channel determined in step (1) and optimal longitudinal slope intervals of gully beds applicable to different channel types of drainage channels, the channel type of the main channel section 3 is a box lined type, and the length L.sub.3 of the main channel section 3 is 281.4 m, i.e., L.sub.3=LL.sub.1L.sub.2L.sub.4=3007 0.56.15.0=281.4 m.

(20) The lower drainage channel is divided into a big-end-up bell-mouthed inlet section 1, an acceleration section 2, a main channel section 3 in which the debris flow flows in a balanced mode, and a big-end-down bell-mouthed outlet section 4 along the flow direction of the debris flow. The lower drainage channel is constructed of cement-rubble material; therefore, the limited flow velocity of the drainage channel is determined to be 6.0 m/s. The method for planning and designing the lower drainage channel comprises the following steps.

(21) (1) According to the topographic condition of a debris flow-deposited fan, the lower drainage channel is planned for the lower position of the deposited fan. The total length L of the to-be-constructed lower drainage channel is 180 m, and according to the principle that cut and fill are basically balanced, the longitudinal slope of the gully bed of the lower drainage channel is 0.07. Because the afflux of the debris flow in a tributary ditch on the surface of the fan is 13.0 m.sup.3/s and the designed drain flow of the lower drainage channel is 77.0 m.sup.3/s, the width of the bottom of the lower drainage channel is 6.0 m.

(22) (2) The channel type of inlet section 1 is determined to be a fully lined channel type. Under the condition that the debris flow is a dilute debris flow according to drainage design standards and that the longitudinal slope of the gully bed of the drainage channel determined in step 1 is 0.07, the length L.sub.1 of inlet section 1 is 2.0 times as large as the width of the bottom of the drainage channel, i.e., L.sub.1=2.06.0=12.0 m, and the included angle between the side wall of inlet section 1 and the main channel is 30 degrees.

(23) (3) The channel type of outlet section 4 is determined to be a fully lined channel type. Under the condition that the debris flow is a dilute debris flow according to drainage design standards and that the longitudinal slope of the gully bed of the drainage channel determined in step 1 is 0.07, the length L.sub.4 of the outlet section is 1.5 times as large as the width of the bottom of the drainage channel, i.e., L.sub.4=1.56.0=9.0 m, and the included angle between the side wall of outlet section 4 and the main channel is 15 degrees.

(24) (4) The channel type of acceleration section 2 is determined to be a fully lined channel type. According to a steady non-uniform channel gradually varied flow calculation model, iterative calculations determine that the length L.sub.2 of the acceleration section 2 is 4.3 m.

(25) (5) According to the longitudinal slope (0.07) of the gully bed of the drainage channel determined in step 1 and the optimal longitudinal slope intervals of gully beds applicable to different channel types of drainage channels, the channel type of the main channel section 3 is a symmetrical notched sill type, and the length L.sub.3 of main channel section 3 is 154.7 m, i.e., L.sub.3=LL.sub.1L.sub.2L.sub.4=18012.04.39.0=154.7 m.

Embodiment 3

(26) As shown in FIG. 1 and FIG. 3, the details identical to embodiment 2 are not repeated. Embodiments 3 and 2 differ as follows: transition zone 5 is used to lead out part of a debris flow to stop depositing, and a filed for stopping depositing is provided at the left side of the transition zone that faces the lower drainage channel.