Asymmetric debris flow drainage trough and design method and application thereof

Abstract

An asymmetric debris-flow discharge channel is provided. The debris-flow discharge channel has a main drainage channel for discharging a debris flow and an auxiliary channel provided outside of the main drainage channel. The side walls of the auxiliary channel are integrated with the side walls of the main drainage channel or provided outside of the side walls of the main drainage channel. The debris-flow discharge channel also has a break section integrated into a side wall of the auxiliary channel. The top width of the break section is equal to the top width of the auxiliary channel A method for designing and building the asymmetric debris-flow discharge channel is also provided, which provides a lower initial cost, higher safety performance, and a lower maintenance cost at the operating stage.

Claims

1. An asymmetric debris-flow discharge channel comprising: a main drainage channel for discharging a debris flow according to a predetermined standard, wherein the main drainage channel comprises side walls; an auxiliary channel provided outside of the main drainage channel, wherein the auxiliary channel comprises side walls that are integrated with the side walls of the main drainage channel or provided outside of the side walls of the main drainage channel, wherein the auxiliary channel has a top width defined by the side walls of the auxiliary channel; and a break section integrated into a side wall of the auxiliary channel, wherein the break section has a top width, wherein the top width of the break section is equal to the top width of the auxiliary channel; wherein the side walls of the auxiliary channel are made of a first building material and the break section is made of a second building material that is different from the first building material; wherein the break section has a first strength defined by the first building material and the side walls of the auxiliary channel has a second strength defined the second building material; and wherein the first strength is weaker than the second strength, such that when a load applied by the debris flow exceeds a predetermined value, the break section collapses and the sidewalls of the auxiliary channel maintains integral to allow a part of the debris flow to exit the auxiliary channel, the asymmetric debris-flow discharge channel further comprising a storage structure adjacent the break section for storing the part of the debris flow.

2. The asymmetric debris-flow discharge channel according to claim 1, wherein the break section has a cross section that is rectangular.

3. The asymmetric debris-flow discharge channel according to claim 1, wherein the auxiliary channel has a cross section that is trapezoidal or rectangular.

4. The asymmetric debris-flow discharge channel according to claim 1, wherein the side walls of the auxiliary channel is made of reinforced concrete or concrete.

5. The asymmetric debris-flow discharge channel according to claim 1, wherein the top width of the break section is in a range of 0.5 m to 1.5 m and the top width of the auxiliary channel is in a range of 0.5 m to 1.5 m.

6. The asymmetric debris-flow discharge channel according to claim 1, wherein the side walls of the main drainage channel are made of reinforced concrete or concrete and wherein the main drainage channel has a width in a range of 0.5 m to 1.5 m.

7. A method of building an asymmetric debris-flow discharge channel, the method comprising: step 1: determining a debris-flow density .sub.debris flow in the unit of kN/m.sup.3 through on-site survey and measuring, determining a debris-flow peak discharge Q.sub.total in the unit of m.sup.3/s by using a small-watershed hydrologic calculation method, determining a peak flood discharge by using the small-watershed hydrologic calculation method, and determining a critical debris flow peak discharge Q.sub.main river in the unit of m.sup.3/s based on the determined peak flood discharge, wherein the critical debris-flow peak discharge is the volume of a debris flow that causes blockage of a river when the debris flow is discharged into the river from the drainage channel; step 2: determining a building material of a break section of the asymmetric debris-flow discharge channel through on-site survey and measuring, determining a density of the break section .sub.break section in the unit of kN/m.sup.3 according to the determined building material, and determining a top width of the break section b.sub.0 in the unit of m and a height h.sub.2 of an auxiliary channel of the asymmetric debris-flow discharge channel in the unit of m through on-site survey and measuring; step 3: determining a debris-flow depth h.sub.debris-flow depth in the unit of m in the auxiliary channel using a method of cross-section superposition for calculating the discharge in a compound channel; step 4: determining a length L.sub.0 of the break section by using the following equation: $L_0=\frac{Q_{\mathrm{total}}-Q_{\mathrm{main}\mathrm{river}}}{\sqrt{2g}{h}_{\mathrm{debris}\text{-}\mathrm{flow}\mathrm{depth}}^{3\text{/}2}}$ wherein: L.sub.0=the length of the break section in the unit of m, Q.sub.total=the debris-flow peak discharge determined in step 1, Q.sub.main river=the critical debris-flow peak discharge determined in step 1, =a comprehensive coefficient ranging from 0.2 to 0.5, g=acceleration due to gravity, and h.sub.debris-flow depth=the debris-flow depth determined in step 3; and step 5: calculating a height h.sub.0 of the break section by using the following equation, under the condition that h.sub.0<h.sub.2: $h_{\mathrm{debris}\text{-}\mathrm{flow}\mathrm{depth}}<h_0<\frac{{}_{\mathrm{debris}\mathrm{flow}}{h}_{\mathrm{debris}\text{-}\mathrm{flow}\mathrm{depth}}^3}{3\left({}_{\mathrm{break}\mathrm{section}}{b}_0^2\right)}$ wherein: h.sub.0=the height of the break section in the unit of m, h.sub.debris-flow depth=the debris-flow depth determined in step 3, .sub.break section=the density of the break section determined in step 2, .sub.debris flow=the debris-flow density determined in step 1, and b.sub.0=the top width of the break section determined in step 2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic top view of the present invention in Embodiment 1;

(2) FIG. 2 is a schematic diagram of cross-section A-A in FIG. 1;

(3) FIG. 3 is a schematic diagram of cross-section B-B in FIG. 1;

(4) FIG. 4 is a schematic top view of the present invention in Embodiment 2;

(5) FIG. 5 is a schematic diagram of cross-section A-A in FIG. 4;

(6) FIG. 6 is a schematic diagram of cross-section B-B in FIG. 4;

(7) FIG. 7 is a schematic top view of the present invention in Embodiment 3;

(8) FIG. 8 is a schematic diagram of cross-section A-A in FIG. 7;

(9) FIG. 9 is a schematic diagram of cross-section B-B in FIG. 7;

(10) Labels in the figures are as follows:

(11) TABLE-US-00001 1 = main channel 2 = auxiliary channel 3 = main channel side walls 4 = auxiliary channel side walls 5 = break section B.sub.1 = width of the main channel B.sub.2 = width of the auxiliary channel h.sub.1 = height of the main channel h.sub.2 = height of the auxiliary channel H.sub.0 = height of the break section L.sub.0 = length of the break section b.sub.0 = top width of the break section b = top width of the auxiliary channel side wall h.sub.debris-flow depth = debris-flow depth in the auxiliary channel at the discharge design standard

DESCRIPTION OF THE EMBODIMENTS

Embodiment 1

(12) Embodiment 1 of the invented asymmetric debris-flow drainage channel is shown in FIGS. 1, 2, and 3. The area of the debris-flow drainage basin is 14 km.sup.2 and its mean longitudinal slope is 0.05. According to the distribution pattern of villages and towns on the debris-flow deposition fan, an asymmetric debris-flow drainage channel is proposed using the invention to discharge a debris flow triggered in the basin while protecting objects on each side of the channel with different design standards. Debris-flow mitigation can thus be conducted by means of asymmetric drainage engineering measures on the basis of fully utilizing the transport capacity of the main river downstream of the basin.

(13) According on the topographic conditions of the debris-flow deposition fan and the distribution of villages, towns, and farmlands upon it obtained from field surveys, the length of the drainage channel to be built is 480.0 m. This asymmetric debris-flow drainage channel consists of the main channel (1) to discharge the debris flow within the design standard, and the auxiliary channel (2) to discharge flow in excess of the design standard. The auxiliary channel side walls (4) are located outside of the main channel side walls (3). The height h.sub.1 and width B.sub.1 of the main channel are 2.5 m and 3.0 m, respectively. The side walls of the main channel are made of reinforced concrete with a thickness of 0.5 m. The height h.sub.2 and width B.sub.2 of the auxiliary channel are 2.5 m and 7.0 m, respectively. The break section (5) in the side wall of the auxiliary channel is designed to a lower protection standard. The break section (5) is rectangular in section, while that of the auxiliary channel (4) is trapezoidal. The top width, b.sub.0, of the break section (5) is 0.5 m, the same as the top width of the auxiliary channel (4), b. The side walls of the auxiliary channel (4) are made of reinforced concrete, while the break section (5) is constructed of M7.5 masonry.

(14) The design procedure of this asymmetric debris-flow drainage channel is as follows:

(15) Step 1: Through field surveys, the debris-flow density .sub.d is determined to be 17 kN/m.sup.3. According to the small-watershed hydrologic calculation method, the total peak discharge of the debris flow Q.sub.total under the design standard for a 5% frequency is 480 m.sup.3/s. The peak flood discharge of the main river under the design standard can also be determined using the same method. According to the peak flood discharge of the main river under the design standard, the critical peak debris-flow discharge Q.sub.main river of the drainage channel that will block the main river is determined to be 300 m.sup.3/s.

(16) Step 2: Based on the actual site conditions, the material of the break section (5) is selected to be M7.5 masonry with a density of 22 kN/m.sup.3 and a top width b.sub.0 of 0.5 m. The height of the auxiliary channel h.sub.2 is 2.5 m.

(17) Step 3: According to the method of cross-section superposition for calculating the discharge in a compound channel, the debris-flow depth in the auxiliary channel h.sub.debris-flow depth=1.5 m when the debris flow reaches the main river under the design standard.

(18) Step 4: When the debris-flow peak discharge exceeds the maximum allowable peak discharge (Q.sub.total) of the entire drainage channel, the break section (5) of the auxiliary channel side wall (4) automatically breaks and the debris flow in excess of the design standard is then discharged directly onto the side with the lower design protection standard. The length of the break section (5) L.sub.0 can be determined by:

(19) $L_0=\frac{Q_{\mathrm{total}}-Q_{\mathrm{main}\mathrm{river}}}{\sqrt{2g}{h}_{\mathrm{debris}\text{-}\mathrm{flow}\mathrm{depth}}^{3\text{/}2}}=\frac{480-300}{0.4\sqrt{29.81}{1.5}^{3\text{/}2}}=55.3m$

(20) The safety factor of the break section (5) be 1.1, so the L.sub.0 in the final engineering design should be rounded up to 61.0 m.

(21) Step 5: When the debris-flow depth in the auxiliary channel (2) reaches the design value (h.sub.debris-flow depth), break section (5) automatically breaks. The required height h.sub.0 of the break section (5) can be determined by:

(22) $h_{\mathrm{debris}\mathrm{flow}\mathrm{depth}}<h_0<\frac{{}_d{h}_{\mathrm{debris}\mathrm{flow}\mathrm{depth}}^3}{3\left({}_{\mathrm{outburst}}{b}_0^2\right)}$$1.5m<h_0<\frac{17{1.5}^3}{3\left(22{0.5}^2\right)}=3.5m$

(23) Considering that the required height h.sub.0 of the break section (5) must be smaller than that of the auxiliary channel (2), h.sub.2, namely, 1.5 m<h.sub.0<2.5 m, the height of the break section (5) is set to 2.0 m in the final engineering design.

Embodiment 2

(24) Embodiment 2 of the invented asymmetric debris-flow drainage channel is shown in FIGS. 4, 5, and 6. The area of the debris-flow gully is 24 km.sup.2, and its mean longitudinal slope is 0.20. According to the distribution pattern of villages and towns on the debris-flow deposition fan, an asymmetric debris-flow drainage channel is proposed using the invention in to discharge a debris flow triggered in the basin while protecting objects on each side of the channel with different design standards. Debris-flow mitigation can be conducted by means of asymmetric drainage engineering measures on the basis of fully utilizing the transport capacity of the main river downstream of the basin.

(25) According to the topographic conditions of the debris-flow deposition fan and the distribution of villages, towns, and farmlands upon it obtained from field surveys, the length of drainage channel to be built is 980.0 m. This asymmetric debris-flow drainage channel consists of the main channel (1) to discharge the debris flow within the design standard and the auxiliary channel (2) to discharge flow in excess of the design standard. The auxiliary channel side walls (4) are located outside of the main channel side walls (3). The height h.sub.1 and width B.sub.1 of the main channel are 5.0 m and 8.0 m, respectively. The side walls of the main channel are made of reinforced concrete with a thickness of 1.0 m. The height h.sub.2 and width B.sub.2 of the auxiliary channel are 3.5 m and 16.0 m, respectively. The break section (5) in the side wall of the auxiliary channel is designed to a lower protection standard. The break section (5) is rectangular in section, while the auxiliary channel (4) section is trapezoidal. The top width, b.sub.0, of the break section (5) is 1.0 m, the same as the top width of the auxiliary channel (4), b. The side walls of the auxiliary channel (4) are made of reinforced concrete while the break section (5) is constructed of gabions, which are rock-filled stone cages.

(26) The design procedure of this asymmetric debris-flow drainage channel is as follows:

(27) Step 1: Through field surveys, the debris-flow density .sub.d is determined to be 21 kN/m.sup.3. According to the small-watershed hydrologic calculation method, the total peak discharge of the debris flow Q.sub.total under the design standard for a 2% frequency is 1245 m.sup.3/s. The peak flood discharge of the main river under the design standard can also be determined using the same method. According to the peak flood discharge of the main river under the design standard, the critical peak debris-flow discharge Q.sub.main river of the drainage channel that will block the main river is determined to be 834 m.sup.3/s.

(28) Step 2: Based on the actual site conditions, the material of the break section (5) is selected to be gabions with a density of 20 kN/m.sup.3 and a top width b.sub.0 of 1.0 m. The height of auxiliary channel h.sub.2 is 3.5 m.

(29) Step 3: According to the method of cross-section superposition for calculating the discharge in a compound channel, the debris-flow depth in the auxiliary channel h.sub.debris-flow depth=2.0 m when the debris flow reaches the main river under the design standard.

(30) Step 4: When the debris-flow peak discharge exceeds the maximum allowable peak discharge (Q.sub.total) of the entire drainage channel, the break section (5) of the auxiliary channel side wall (4) automatically breaks and the debris flow in excess of the design standard is then discharged directly to the side with the lower design standard. The length of the break section (5) L.sub.0 can be determined by:

(31) $L_0=\frac{Q_{\mathrm{total}}-Q_{\mathrm{main}\mathrm{river}}}{\sqrt{2g}{h}_{\mathrm{debris}\mathrm{flow}\mathrm{depth}}^{3\text{/}2}}=\frac{1245-834}{0.2\sqrt{29.81}{2.0}^{3\text{/}2}}=164.0m$

(32) The safety factor of the break section (5) must be 1.1, so the L.sub.0 in the final engineering design should be rounded to 180.0 m.

(33) Step 5: When the debris-flow depth in the auxiliary channel reaches the design value (that is h.sub.debris-flow depth), the break section (5) automatically breaks. The height h.sub.0 of the break section (5) can be determined by:

(34) $h_{\mathrm{debris}\mathrm{flow}\mathrm{depth}}<h_0<\frac{{}_d{h}_{\mathrm{debris}\mathrm{flow}\mathrm{depth}}^3}{3\left({}_{\mathrm{outburst}}{b}_0^2\right)}$$2.0m<h_0<\frac{21{2.0}^3}{3\left(20{1.0}^2\right)}=2.8m$

(35) Considering that the required height h.sub.0 of the break section (5) must be smaller than that of the auxiliary channel (2), h.sub.2, namely, 2.0 m<h.sub.0<2.8 m, the height of the break section 5 is set to 2.2 m in the final engineering design.

Embodiment 3

(36) Embodiment 3 of the invented asymmetric debris-flow drainage channel is shown in FIGS. 7, 8, and 9. The area of the debris-flow drainage basin is 16 km.sup.2 and its mean longitudinal slope is 0.30. According to the distribution pattern of villages and towns on the debris-flow deposition fan, an asymmetric debris-flow drainage channel is proposed using the invention to discharge a debris flow triggered in the basin while protecting objects on each side of the channel with different design standards. Debris-flow mitigation can be conducted by means of asymmetric drainage engineering measures on the basis of fully utilizing the transport capacity of the main river downstream of the basin.

(37) According to the topographic conditions of debris-flow deposition fan and the distribution of villages, towns, and farmlands upon it obtained from field surveys, the length of the drainage channel to be built is 580.0 m. This asymmetric debris-flow drainage channel consists of the main channel (1) to discharge the debris flow within the design standard, and the auxiliary channel (2) to discharge flow in excess of the design standard. The auxiliary channel side walls (4) are located outside of the main channel side walls (3). The height h.sub.1 and width B.sub.1 of the main channel are 1.0 m and 8.0 m, respectively. The side walls of the main channel are made of high-grade C30 concrete with a thickness of 1.5 m. The height h.sub.2 and width B.sub.2 of the auxiliary channel are 6.0 m and 8.0 m, respectively. The break section (5) in the side wall of the auxiliary channel is designed to a lower protection standard. The break section (5) is rectangular in section, as is the auxiliary channel (4). The top width, b.sub.0, of the break section (5) is 0.5 m, which is the same as the top width of the auxiliary channel (4), b. The side walls of the auxiliary channel (4) are made of high-grade C30 concrete, while the break section (5) is constructed of low-grade C20 concrete.

(38) The design procedure of this asymmetric debris-flow drainage channel is as follows:

(39) Step 1: Through field surveys, the debris-flow density .sub.d is determined to be 15 kN/m.sup.3. According to the small-watershed hydrologic calculation method, the total peak discharge of the debris flow Q.sub.total under the design standard for a 2% frequency is 975 m.sup.3/s. The peak flood discharge of the main river under the design standard can also be determined using the same method. According to the peak flood discharge of the main river under the design standard, the critical peak debris-flow discharge Q.sub.main river of the drainage channel that will block the main river is determined to be 360 m.sup.3/s.

(40) Step 2: Based on the site actual conditions, the material of the break section (5) is selected to be C20 concrete with a density of 23 kN/m.sup.3 and a top width b.sub.0 of 1.5 m. The height of the auxiliary channel h.sub.2 is 6.0 m.

(41) Step 3: According to the method of cross-section superposition for calculating the discharge in a compound channel, the debris-flow depth in the auxiliary channel h.sub.debris-flow depth=4.5 m when the debris flow reaches the main river under the design standard.

(42) Step 4: When the debris-flow peak discharge exceeds the maximum allowable peak discharge (Q.sub.total) of the entire drainage channel, the break section (5) of the auxiliary channel side wall (4) automatically breaks and the debris flow in excess of the design standard is then be discharged directly onto the side with the lower design protection standard. The length L.sub.0 of the break section (5) can be determined by:

(43) $L_0=\frac{Q_{\mathrm{total}}-Q_{\mathrm{main}\mathrm{river}}}{\sqrt{2g}{h}_{\mathrm{debris}\mathrm{flow}\mathrm{depth}}^{3\text{/}2}}=\frac{975-360}{0.5\sqrt{29.81}{4.5}^{3\text{/}2}}=29.1m$

(44) The safety factor of the break section (5) must be 1.1, so the L.sub.0 in the final engineering design should be rounded up to 32.0 m.

(45) Step 5: When the debris-flow depth in the auxiliary channel (2) reaches the design value (h.sub.debris-flow depth), the break section (5) automatically breaks. The required height h.sub.0 of the break section (5) can be determined by:

(46) $h_{\mathrm{debris}\mathrm{flow}\mathrm{depth}}<h_0<\frac{{}_d{h}_{\mathrm{debris}\mathrm{flow}\mathrm{depth}}^3}{3\left({}_{\mathrm{outburst}}{b}_0^2\right)}$$4.5m<h_0<\frac{15{4.5}^3}{3\left(23{1.5}^2\right)}=8.8m$

(47) Considering that the height h.sub.0 of the break section (5) must be smaller than that of the auxiliary channel (2), h.sub.2, namely, 4.5 m<h.sub.0<6.0 m, the height of the break section (5) is set to 5.0 m in the final engineering design.