METHOD OF DESIGNING BOX-TYPE ENERGY-DISSIPATING SECTION OF BOX-TYPE ENERGY-DISSIPATING MUDFLOW DIVERSION FLUME, AND APPLICATION

Abstract

A method of designing a box-type energy-dissipating section of a box-type energy-dissipating mudflow diversion flume. Firstly, the longitudinal gradient J of the flume and the roughness coefficient n 0 of a fully-lined flume bottom (1) are determined. Then, the parameters of the box-type energy-dissipating section are set, and related parameters are substituted into a formula for calculation, so that the overall roughness coefficient n of the flume is obtained. Further, the flow velocity of the mudflow is calculated by means of the Manning formula. Finally, the flow velocity of the mudflow is compared with the non-scouring and non-silting velocity allowed by the flume, and the design value of the box-type energy-dissipating section is obtained through final optimization. The method factors in the longitudinal gradient J of the flume, the length L of the box-type energy-dissipating section, the width b of the box-type energy-dissipating section, and the average diameter D of filler stones. With the method, the overall roughness coefficient n of the flume under different design conditions can be determined reasonably, so as to further implement the optimized design of the box-type energy-dissipating section of the box-type energy-dissipating mudflow flume. Further provided is an application of the method of designing a box-type energy-dissipating section of a box-type energy-dissipating mudflow flume.

Claims

1-7. (canceled)

8. A method for designing an energy dissipation structure section of a drainage channel, wherein the drainage channel comprises a smooth channel, sidewalls, and the energy dissipation structure section; wherein the energy dissipation structure section comprises a transverse ground sill and a precast reinforced concrete energy dissipation box; wherein the energy dissipation structure section has a top surface that is open and the remaining five sides of the energy dissipation structure section are closed with stones; and wherein the height of filled stones in the box is 0.5 to 0.8 times the height of the energy dissipation structure section, the method comprising: step 1: determine a channel slope J of the drainage channel through a field survey and large-scale topographic map measurements; determining a construction material through a field survey and obtain the roughness coefficient n.sub.0 of the smooth channel; and determining an admissible velocity through a field investigation based on the characteristics of a debris flow source, particle gradation, and the construction materials; step 2: setting a length and a width of the energy dissipation structure section and a mean diameter of the filled stones according to a designed debris flow discharge and the channel slope J determined in step 1; step 3: determining the roughness coefficient n of the energy dissipation structure section using the following formula: $n=\left(0.0136.Math.\frac{\mathrm{bL}}{.Math..Math.D^2}.Math.J^{1.Math.\text{/}.Math.2}+1.1921\right).Math.n_0$ where nroughness coefficient of the energy dissipation structure section; n.sub.0roughness coefficient of the smooth channel determined in step 1; bwidth of the energy dissipation structure section determined in step 2; Llength of the energy dissipation structure section determined in step 2; Dmean diameter of the filled stones determined in step 2; Jslope of drainage channel determined in step 1; and Pi (approximately equal to 3.14); step 4: applying the parameters obtained in steps 1 through 3 into the Manning formula, wherein the debris flow velocity is obtained as follows: $V=\frac{1}{n}.Math.R^{2.Math.\text{/}.Math.3}.Math.J^{1.Math.\text{/}.Math.2}$ where V is the debris flow velocity, n is for the roughness coefficient of the energy dissipation structure section determined in step 3, R is the hydraulic radius, and J is the channel slope determined in step 1; step 5: comparing the debris flow velocity calculated in step 4 with the admissible velocity determined in step 1, wherein if the debris flow velocity obtained in step 4 is not within the range of the admissible velocities determined in step 1, reassigning the values of the parameters and repeat steps 2 to 5 until the debris flow velocity obtained in step 4 is within the range of admissible velocities determined in step 1; and wherein if the debris flow velocity obtained in step 4 is within the range of the admissible velocities determined in step 1, setting the length and the width of the energy dissipation structure section and the mean diameter of the filled stones determined in step 2 as design parameters of the energy dissipation structure section.

9. The method according to claim 8, wherein the ratio of the width of the energy dissipation structure section to the width of the drainage channel ranges from 0.5 to 1.0.

10. The method according to claim 8, wherein the ratio of the length of the energy dissipation structure section to the length of the drainage channel ranges from 0.10 to 0.25.

11. The method according to claim 8, wherein the ratio of the height of the filled stones in the energy dissipation structure to the height of the energy dissipation structure ranges from 0.5 to 0.8.

12. The method according to claim 8, wherein the debris flow depth upstream of the energy dissipation structure is equal to 1.0-4.0 times the mean diameter of the filled stones.

13. The method according to claim 8, wherein the channel slope ranges from 0.15 to 0.35.

14. The method according to claim 8, wherein the debris flow density ranges from 16 kN/m.sup.3 to 22 kN/m.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The features of the present invention, which is believed to be novel, are presented in detail in the appended claims. The organization and manner of operation of the invention, together with further objects and the associated advantages, may best be understood by referencing the following description and the accompanying drawings and figures:

[0025] FIG. 1 is a section view of a drainage channel with an energy dissipation structure; and

[0026] FIG. 2 is a perspective view of a drainage channel with an energy dissipation structure.

[0027] Labels in the figures are as follows: [0028] 1 Baseplate of the smooth drainage channel [0029] 2 Ground sill [0030] 3 Energy dissipation structure [0031] J Slope of the drainage channel [0032] L Length of the energy dissipation structure section [0033] b Width of the energy dissipation structure section [0034] B Width of the drainage channel [0035] h Debris flow depth

DETAILED DESCRIPTIONS OF THE ILLUSTRATED EMBODIMENTS

Embodiment 1

[0036] In this section, please refer to the drawings presented in FIGS. 1 and 2. A debris flow drainage basin is located at the left bank of the Mianyuan River, and the area of this drainage basin is 1.36 km.sup.2. The main gully length is 2590 m. The elevation of the drainage basin ranges from 810 to 1987 m, representing a relative elevation difference of 1177 m. The area of slopes greater than or equal to 25 is approximately 1.16 km.sup.2 in this drainage basin. Steep slopes with large longitudinal gradients are predominant in this drainage basin. This characteristic favors the concentration of precipitation processes and makes the basin prone to debris flow initiation. Before the devastating Wenchuan earthquake, no debris flow disaster had occurred in this gully in the past 100 years. However, the Wenchuan earthquake triggered numerous landslides and avalanches upstream of this drainage basin, and the total volume of transported material was approximately 8010.sup.4 m.sup.3.

[0037] To protect local highways, infrastructure, lives and properties, debris flow hazard mitigation projects were conducted in the gully. A debris flow drainage channel is necessary for a debris flow to bypass a highway. A drainage channel includes a smooth channel, sidewalls, and an energy dissipation structure section. The energy dissipation structure is located between the two adjacent ground sills.

[0038] The method of designing the energy dissipation structure section is as follows based on the steps presented in the Summary of the Invention section.

[0039] Step 1: In this case, based on a field survey, it is determined that J=0.35, the debris flow density is 22 kN/m.sup.3, the length of the drainage channel is 105 m, the width of the drainage channel is B=6.0 m and the height of the sidewall is 3.5 m. The construction material was determined through a field survey, and a roughness coefficient of n.sub.0=0.02 was obtained for the smooth channel. Additionally, based on a field survey, it is determined that the permissible debris flow velocity must be smaller than 8 m/s and larger than 2.7 m/s to eliminate scour and deposition on the baseplate.

[0040] Step 2: The length and width of the energy dissipation structure section are b=3.0 m and L=15 m, respectively, and the mean diameter of the filled stones is D=0.4 m based on the designed debris flow discharge and the channel slope J=0.35 determined in Step 1.

[0041] Step 3: The roughness coefficient of the energy dissipation structure section was determined using the following formula:

[00003]$n=\left(0.0136.Math.\frac{\mathrm{bL}}{.Math..Math.D^2}.Math.J^{1.Math.\text{/}.Math.2}+1.1921\right).Math.n_0=\left(0.0136.Math.\frac{315}{3.14{0.4}^2}.Math.{0.35}^{1.Math.\text{/}.Math.2}+1.1921\right)0.02=0.038$ [0042] where [0043] nroughness coefficient of the energy dissipation structure section; [0044] n.sub.0roughness coefficient of the smooth channel determined in Step 1; [0045] bwidth of the energy dissipation structure section (unit: m) determined in Step 2; [0046] Llength of the energy dissipation structure section (unit: m) determined in Step 2; [0047] Dmean diameter of the filled stones (unit: m) determined in Step 2; [0048] Jslope of the drainage channel determined in Step 1; and [0049] Pi (approximately equal to 3.14).

[0050] Step 4: Applying the parameters obtained in Step 1 to 3 into the Manning formula, wherein h=4D=1.6 m. Thus, the debris flow velocity (unit: m/s) can be obtained as follows:

[00004]$V=\frac{1}{n}.Math.R^{2.Math.\text{/}.Math.3}.Math.J^{1.Math.\text{/}.Math.2}=\frac{1}{n}.Math.{\left(\frac{\mathrm{Bh}}{B+2.Math.h}\right)}^{2.Math.\text{/}.Math.3}.Math.J^{1.Math.\text{/}.Math.2}=\frac{1}{0.038}.Math.{\left(\frac{6\mathrm{.6}}{6+21.6}\right)}^{2.Math.\text{/}.Math.3}{0.35}^{1.Math.\text{/}.Math.2}=12.67.Math..Math.m.Math.\text{/}.Math.s$

[0051] where V is the debris flow velocity (unit: m/s), n is the roughness coefficient of the energy dissipation structure section determined in Step 3, R is the hydraulic radius (unit: m), and J is the channel slope determined in Step 1.

[0052] Step 5: Comparing the debris flow velocity calculated in Step 4 with the admissible velocity determined in Step 1, the debris flow velocity obtained in Step 4 is not within the range of admissible velocities determined in Step 1 (12.67 m/s>8.0 m/s). Therefore, the values of the parameters are re-determined, and Steps 2 to 5 are repeated.

[0053] In the second calculation process, the length of the energy dissipation structure is L=20 m; the width of the energy dissipation structure is b=4 m; and the mean diameter of the filled stones is D=0.4 min. Additionally, the calculated roughness coefficient of the energy dissipation structure section is n=0.049, and the designed debris flow depth is h=4D=1.6 m. The calculated debris flow velocity is 10.12 m/s, which is larger than 8 m/s and is not within the range of admissible velocities determined in Step 1. Therefore, the values of the parameters are re-assigned, and Steps 2 to 5 are repeated.

[0054] In the third calculation process, the length of the energy dissipation structure is L=25 m; the width of the energy dissipation structure is b=6 m; and the mean diameter of the filled stones is D=0.3 m. Additionally, the calculated roughness coefficient of the energy dissipation structure section is n=0.109, and the designed debris flow depth is h=4D=1.2 m. The obtained debris flow velocity is 4.89 m/s, which is within the range of admissible velocities determined in Step 1. Therefore, the design parameters of the energy dissipation structure section can be established as L=25 m, b=6 m, and D=0.3 m.

Embodiment 2

[0055] In this section, please refer to the drawings presented in FIGS. 1 and 2. A debris flow drainage basin is located at the left bank of the Mianyuan River, and the area of this drainage basin is 7.81 km.sup.2. The main gully length is 3250 m. The elevation of the drainage basin ranges from 883 to 2402 m, representing a relative elevation difference of 1519 m. After the Wenchuan earthquake, numerous large-scale debris flows were triggered by rainfall in this gully, and these flows are dangerous to local residents.

[0056] To protect local highways, infrastructure, lives and properties, debris flow hazard mitigation projects were conducted in the gully. A debris flow drainage channel is necessary for a debris flow to bypass a highway. A drainage channel includes a smooth channel, sidewalls, and an energy dissipation structure section. The energy dissipation structure is located between the two adjacent ground sills.

[0057] The method of designing the energy dissipation structure section is as follows based on the steps presented in the Summary of the Invention section.

[0058] Step 1: In this case, J=0.15, the debris flow density is 16 kN/m.sup.3, the length of the drainage channel is 150 m, the width of the drainage channel is B=8.0 m and the height of the sidewall is 4 m. Based on the channel material, the roughness coefficient of the smooth channel is n.sub.0=0.02, and the permissible debris flow velocity must smaller than 8 m/s and larger than 2.7 m/s to prevent scour and silt deposition on the baseplate.

[0059] Step 2: The length and width of the energy dissipation structure section are b=8.0 m and L=30 m, respectively. Additionally, the mean diameter of the filled stones is D=0.4 m based on the designed debris flow discharge and the channel slope J=0.15 in Step 1.

[0060] Step 3: The roughness coefficient of the energy dissipation structure section was determined using the following formula:

[00005]$n=\left(0.0136.Math.\frac{\mathrm{bL}}{.Math..Math.D^2}.Math.J^{1.Math.\text{/}.Math.2}+1.1921\right).Math.n_0=\left(0.0136.Math.\frac{830}{3.14{0.4}^2}.Math.{0.15}^{1.Math.\text{/}.Math.2}+1.1921\right)0.02=0.074$ [0061] where [0062] nroughness coefficient of the energy dissipation structure section; [0063] n.sub.0roughness coefficient of the smooth channel determined in Step 1; [0064] bwidth of the energy dissipation structure section (unit: m) determined in Step 2; [0065] Llength of the energy dissipation structure section (unit: m) determined in Step 2; [0066] Dmean diameter of the filled stones (unit: m) determined in Step 2; [0067] Jslope of the drainage channel determined in Step 1; and [0068] Pi (approximately equal to 3.14).

[0069] Step 4: Applying the parameters obtained in Steps 1 through 3 into the Manning formula, h=1D=0.4 m. Thus, the debris flow velocity (unit: m/s) can be determined as follows:

[00006]$V=\frac{1}{n}.Math.R^{2.Math.\text{/}.Math.3}.Math.J^{1.Math.\text{/}.Math.2}=\frac{1}{n}.Math.{\left(\frac{\mathrm{Bh}}{B+2.Math.h}\right)}^{2.Math.\text{/}.Math.3}.Math.J^{1.Math.\text{/}.Math.2}=\frac{1}{0.074}.Math.{\left(\frac{80.4}{8+20.4}\right)}^{2.Math.\text{/}.Math.3}{0.15}^{1.Math.\text{/}.Math.2}=5.06.Math..Math.m.Math.\text{/}.Math.s$

[0070] where V is the debris flow velocity (unit: m/s), n is the roughness coefficient of the energy dissipation structure section determined in Step 3, R is the hydraulic radius (unit: m), and J is the channel slope determined in Step 1.

[0071] Step 5: Comparing the debris flow velocity calculated in Step 4 to the admissible velocity determined in Step 1, the obtained debris flow velocity is within the range of admissible velocities determined in Step 1 (8.0 m/s>5.06 m/s>2.7 m/s); thus, the design parameters of the energy dissipation structure section can be established as L=30 m, b=8 m, and D=0.4 m.