Irrigation and Drainage Engineering

(A) water source engineering

1. Water source engineering program

From the water resources storage situation in the project area and the local planting and irrigation habits, the water supply for farmland in the project area is mainly solved by the works of mountain ponds and cisterns, etc. The project area is planned to build 27 new cisterns, of which 23 cisterns with a volume of 100 cubic meters are mainly used for irrigation.

2. Cistern design

The project area plans to build 27 new cisterns, of which 23 cisterns with a volume of 100 cubic meters are mainly used for irrigation; 4 cisterns with a volume of 200 cubic meters are mainly used for water storage. Most of the cisterns mainly rely on natural precipitation water storage, a small part of the cistern from the project area outside the creek water, the following only 100 cubic meters of cisterns as an example to illustrate the design.

According to the Technical Specification for Rainwater Storage and Utilization Project (SL267-2001), Technical Specification for Comprehensive Management of Soil and Water Conservation (GBT16453-2008), Technical Specification for Slope to Staircase Project Construction in Sichuan Province, and Technical Specification for Water-saving Irrigation (SL207-98), and in conjunction with the project area, the project area will be designed as an example of a 100-meter cistern. 98), combined with the actual situation of the project area, intercepting slope runoff, natural water storage, according to p = 80% guarantee rate, five-stage building design, the catchment area is determined according to the following formula:

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System: w -- annual water supply,

The annual water supply,

The annual water supply is calculated as follows. cubic meters;

Si - the catchment area of the ith material, square meters;

pp - the annual rainfall when the guarantee rate is p, millimeters (p = 80%, pp = 1,356 mm);

Ki -- annual catchment efficiency of the ith material (0.45);

n -- number of material types.

Cistern volume formula:

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In the formula: V - water storage volume, cubic meters;

w - annual water supply, cubic meters;

α -- reservoir project evaporation, seepage loss coefficient, take 0.05 ~ 0.1, this time take 0.1;

k -- volume coefficient, semi-arid areas, drinking water for humans and animals project to take 0.8 ~ 0.9, irrigation water supply project can be taken as 0.6 ~ 0.9; humid, semi-arid areas, water supply project can be taken as 0.6 to 0.9; humid, semi-humid areas can take 0.24 to 0.4, this time to take 0.3. Pools over the value of 0.3 meters.

Based on the above formula, the cistern diameter design for 7.5 meters, 2.7 meters deep, the effective volume of 100 cubic meters of circular cistern catchment area of 491.64 square meters.

Also according to the above formula for the volume of 200 cubic meters of cistern, the catchment area of 983.28 cubic meters, designed diameter of 8 meters, 4.3 meters deep.

Based on the results of the above calculations, select the catchment relatively concentrated place to arrange the cistern, avoid filling or landslide-prone areas, and configure the diversion channel, drainage ditch, sand cesspit.

According to the requirements of agricultural production and cistern function settings, the cistern is built on the slope with a good confluence surface. The cistern adopts a circular structure with a volume of 100 cubic meters, a diameter of 7.5 meters and a height of 2.7 meters. The wall of the pool is made of standard bricks with M10 cement mortar, and the bottom of the pool is cast in place with C20 concrete. Arrangement of brick protective fence panels on the top of the pool, and set up warning signs, in the pool side of the arrangement of diversion channel and sand cesspool, used to gather the slope confluence and sedimentation of sand, diversion channel and drainage ditch total length of 50 meters, the bottom of the channel with C20 cast-in-place concrete, the two sides of the wall with the slurry of standard bricks, the inner wall and the bottom of the pool with the M10 cement mortar plastering; sedimentation of cesspool with a capacity of 1.0 cubic meters, with the M10 cement mortar with the standard bricks,*** the construction of diversion channel 1.35 kilometers long (the area is hilly, in the design of the catchment area of the cistern using the hillside one-sided catchment, the diversion channel can meet the 491.64 square meters of water storage area), the construction of sand cesspools 27 ports. In the pool below the arrangement of drainage ditch, used to drain storm water.

(2) Irrigation canal

According to the "Land Development and Consolidation Project Planning and Design Specification" (TD/T1012-2000), the irrigation method adopts surface irrigation, and if the arid area or water-scarce area is mainly planted with dry crops, the irrigation design guarantee rate is taken as 50% to 75%. According to the actual situation of the project area and the practical experience of local water conservancy construction, it is determined that the irrigation design guarantee rate is 75%.

(1) section form selection. After the site investigation, the local irrigation bucket customarily used trapezoidal stone canals, considering the convenience of construction, while combining the design of the study and the views of the local people, after the selection, the new section of agricultural canals designed for trapezoidal stone canals, the project area needs to be remediated agricultural canals are also considered according to the trapezoidal stone canals.

(2) Cross-section design. The water flow in the irrigation channel can be considered to be open channel uniform flow, according to the open channel uniform flow formula to project the channel cross section. Irrigation canal water flow is controlled at 0.3 to 0.5 m3/sec; according to the "Irrigation and Drainage Engineering Design Code", the irrigation canal water flow velocity should be less than the permissible non-flushing flow velocity of impermeable lined channels 2 m/sec, and also to meet the requirements of the flow velocity of small-scale irrigation canals of not less than 0.3 to 0.4 m/sec.

Calculation of the over-water flow rate using the nullah uniform flow formula:

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In the formula: Q - design flow rate, m3/sec;

A - over-water cross-section area, square meters;

R - hydraulic radius (m), R = A/x, x for the wet week;

i - specific drop at the bottom of the canal, the specific layout combined with the topography;

C Xie Cai coefficient, using the formula for calculation, where n is the ditch bed roughness, slurry stone to take 0.020, concrete channel to take 0.014 ~ 0.017.

Channel bottom specific drop can be calculated in accordance with the following formula:

V = n-1-R2/3-i1/2(10-14)

Trapezoidal cross-section of the hydraulic element Calculated using the following formula:

A = (b + m - h)h (10-15)

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The formula: x - wetted circumference, meters; b - - bottom width, meters; m - side slope coefficient; h - water depth, meters.

Table 10-9 Table of hydraulic elements of irrigation canals

The hydraulic elements of irrigation canals planned for the project area are shown in Table 10-9, in accordance with the requirements of the hydraulically optimal cross-section, for the 30-centimetre wide canals planned for the project area, with a depth of water of 25 centimetres, and an over-height design calculated by 1.30-1.50 times the flow rate, with the channel cross-section designed to be 30 centimetres by 30 centimetres, and the slope ratio designed to be 1: 0.2. Design flow rate of 0.06>0.04, to meet the requirements.

(3) longitudinal section design. In order to ensure that the irrigation area controlled by the channel can be self-flowing irrigation, all levels of channels at the point of diversion have sufficient water level elevation. The water level control elevation of the diversion point, is based on the ground elevation of the irrigated land plus the channel along the head loss and canal water through a variety of hydraulic structures of the local head loss, the formula is:

B points = A0 + h + ∑ l-i + ∑ Φ (10-18)

Symbol: B points - indicates that The control water level required by the diversion;

A0 - the elevation of the ground reference point within the irrigation range of the channel, meters;

h - the height difference between the selected reference point and the water surface of the last fixed channel at that place, take 0.1 meters;

< p>l--length of each level of channel;

i--ratio drop of each level of channel;

Φ--head loss of water flow through the canal building.

According to the formula (10-18) check all kinds of channel longitudinal section meet the requirements.

(4) channel lining form. Channel lining form in the water conservancy project occupies a very important position, it determines the project investment, efficiency, time and management costs.

Channel lining form of choice should generally take into account the following principles: ① design should strive to be economically rational, technically feasible; ② project construction does not affect normal irrigation, construction convenience, quality control feasible; ③ operation and management is convenient, the use of a long period of time; ④ as far as possible to use local materials.

According to the natural and geographical conditions of the project area, combined with the current local channel lining commonly used form, the planning and design of the channel using slurry pebble lining.

Slurry pebble lining (concrete base plate) main advantages are: ① slurry pebble lining channel frost and impact resistance, good stability, durability; ② slurry pebble construction is simple, easy to control the quality; ③ lining pebbles can be locally sourced, inexpensive; ④ the lining program for the local form of commonly used.

Based on the needs of the project area, the need to improve the irrigation canal 990.00 meters, the new irrigation canal 562.00 meters.

(C) Interceptor Ditch

The interceptor ditch of the project is mainly arranged at the bottom of slopes with large differences in altitude to protect farmland, villages, towns and other facilities from flooding. Four interceptor ditches are planned for remediation in the project area, with a length of 950 meters***. The cross section of the interceptor ditch should be calculated according to the catchment area of the area and the maximum rainfall of the area in 3 hours or 6 hours, when the drainage plot has a small rainfall catchment area and there is no obvious creek or gully, the slope catchment method can be used to calculate the design flood, because the seismic area is mostly a mountainous area, a simplified method of calculating the flood flow rate can be used:

Using the formula (7-1) to the formula (7-4) to calculate the flow rate, such as flow rate not to cause Scour or siltation, then check whether the section can achieve the design requirements of the water transfer capacity. If the flow rate is big or small, should change the section specifications, separate calculations, until the calculated flow rate and ditch design flow can be consistent. If the interceptor ditch is longer, due to the ditch section to take on different water, accordingly can take a different water cross section.

The use of nullah uniform flow to determine the section of the interceptor ditch, the interceptor ditch flow direction according to the location of the longitudinal drainage ditch to determine the conditions allow the best is the section of two-way water flow, in order to alleviate the phenomenon of interceptor ditch Yongshui occurred, at the same time can be appropriately reduced interceptor ditch cross-section. The longitudinal ratio of intercepting ditch is mainly determined according to the topography, and at the same time try to reduce the amount of earth and stone excavation, generally controlled in 1/800 ~ 1/1500. intercepting ditch using slurry masonry, stone material especially sufficient areas can be slurry masonry, the thickness of ditch wall is not less than 30 centimeters, the bottom of the ditch using slurry masonry or slurry masonry bar stone (bar stone placed horizontally), such as the lack of stone area can be used with C20 concrete, but the construction of the best! Set up lateral ditch marks to reduce the flow rate, both sides of the bottom plate should be beyond the outer wall of the ditch wall 10 to 20 centimeters to meet its service life.

The planned interceptor ditch is designed in trapezoidal shape, because the project area is more sufficient stone, take the slurry block masonry, no washout flow rate checking table take 3.0 m/s, no silt flow rate checking table take 0.4 m/s, the roughness checking table take 0.025, the longitudinal ratio drop is designed as 1/1000. according to the Ganxi Hydrological Station Chenjaba Hydrological Observation Point on September 23rd, 2008, the whole day rainfall was 255.5 mm, 1 hour rainfall amounted to 10.64mm, the rainfall is 10.64mm, the rainfall is 10.64mm, the rainfall is 10.64mm. The 1-hour rainfall amounted to 10.64 millimeters, and from the site observation, the estimation concluded that the catchment area of the slope surface of group 2 and group 3 in Dazhu Village was less than 1.0 square kilometers, which was calculated according to 1.0 square kilometers. After repeated calculations, the bottom width of 180 centimeters, both sides of the wall height of 200 centimeters, wall thickness of 50 centimeters, slope ratio according to 1: 0.3 design, the bottom and both sides of the wall are used slurry masonry block stone, of which the design of the super-high 70 centimeters. Overwater cross-section area of 2.847 square meters, the design depth of 1.3 meters, calculated interceptor ditch flow rate of 0.945 m / s, to meet the requirements of the flow rate does not wash and does not silt, and its cross-section design is reasonable. By the side of the hillside set 180 cm long, 10 cm thick C15 concrete overflow surface, the other side of the production road.

(4)Drainage ditch

According to the layout of the project, the drainage ditch is basically arranged vertically with the contour line, and is mainly used for discharging excess water. The project area needs to improve 7 drainage ditches, with a total length of 2162 meters. Drainage ditch cross-section design for trapezoidal, the bottom width of 180 centimeters, both sides of the wall height of 200 centimeters, slope ratio according to the design of 1: 0.3, the bottom and both sides of the wall are using slurry masonry stone repair, its water depth of 100 centimeters, the design of 100 centimeters of super-high.

(E) Culvert and bridge

The project planning and design of the culvert and bridge is mainly arranged in the ditch and production road junction, which is convenient for the local farmers to walk and cultivate. Culvert bridge in this project area **** 7, including remediation of production road and ditch intersection more, there are 6 need to set up culvert bridge, culvert bridge width is designed for 1 meter, spanning 2 kinds of specifications, including a span of 200 centimeters; a span of 400 centimeters, according to the width of the ditch to choose the appropriate span. At the bottom of the culvert bridge, one C20 concrete foundation is placed on each side, with the foundation size of 50 cm × 30 cm × 100 cm, and C20 concrete columns are placed on the foundation, with the concrete column size of 30 cm × 150 cm × 100 cm, and two precast concrete slabs are placed side by side on the top of the concrete columns, with the specifications of each precast concrete slab being 50 cm wide and 12 cm thick, with the length and the two spanning diameter specifications correspond to 200 cm and 400 cm, respectively.

(F) Ferry Trough

The ferry troughs planned and designed for the project are basically arranged at the intersection of the irrigation canal and the drainage ditch, and are placed on top of the drainage ditch to ensure the flow of the irrigation canal, and to avoid being blocked by the drainage ditch. Project area *** planning 5 ferry, because the width of the drainage ditch is different, the ferry is also designed accordingly spanning 400 cm and spanning 200 cm two specifications, of which spanning 400 cm of 4, spanning 200 cm of 1, a total length of 18 meters. The design of this ferry is rectangular, the bottom section is 12 cm × 80 cm of reinforced concrete precast panels, the two sides of the wall with mortar masonry standard bricks, one side of the wall section is 30 cm × 24 cm.

(VII) Culverts

The project area is designed for 23 new culverts, of which 10 spanning 400 centimeters, with a design clear height of 300 centimeters and a culvert deck width of 500 centimeters,*** a span; 7 spanning 200 centimeters, with a design clear height of 150 centimeters and a culvert deck width of 500 centimeters,*** a span; 6 spanning 300 centimeters, with a design clear height of 200 cm, culvert deck width 500 cm, *** one span. The bridge foundations are made of C20 cast-in-place concrete, the abutments are made of C20 cast-in-place concrete, and the bridge decks are made of C25 reinforced concrete precast panels.

Culvert bridge body of the foundation under the first 20 cm thick gravel bedding, and then cast-in-place concrete strip foundation, the foundation should be at least 1 meter below the ground or the riverbed buried depth. Foundation bearing capacity characteristic value?αk should be not less than 200 kPa.

The bearing capacity of the bridge cover is calculated as follows.

1. Parameter setting

Culvert bridge deck slab, concrete strength grade C25 (?cd = 11.9 Newton/mm2, ?td = 1.27 Newton/mm2), longitudinal stress reinforcement with HRB335 (Ф), the rest of the steel reinforcement with HPB235 (Ф). The standard value of bridge deck live load is considered according to the fourth grade highway, two lanes load, uniform live load (crowd load) take qk = 3.0 kilonewtons/m2, span centralized live load Pk = 130 kilonewtons (automobile load, according to the fourth grade highway considerations).

2. precast reinforced concrete panel calculation

Each panel is 1.0 meters wide, 26 centimeters thick, calculated length l0 = 400 centimeters. The mortar capacity is 20.0 kN/m3; the concrete capacity is 25.0 kN/m3.

(1) Load calculation.

a. Calculation of permanent load

Railing post 0.2 × 0.2 × 25 = 1.0 kN/m

Railing 0.1 × 0.1 × 25 = 0.25 kN/m

Handrail 0.2 × 0.15 × 25 = 0.75 kN/m

Concrete panel 0.26 × 25 × 1.0 = 6.5 kN/m

Cement mortar surface 0.02×20×1.0 = 0.4 kN/m

Total: gk = 8.9 kN/m

b. Calculation of variable load

Uniform load qk = 3.0×2.0 = 6.0 kN/m

Concentration of load in the span Qk = 130 kN×1/2 = 65 kN

c. Design value of load

Design value of uniform load q = 1.2 × 8.9 + 1.4 × 6.0 = 19.08 kN/m

Design value of centralized load Q = 1.4 × 65 kN = 91 kN/m

(2) Internal force calculation.

Calculation of mid-span bending moment according to simply supported plate:

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(3) Calculation of bending capacity of positive section.

h0 = h-40 = 260-40 = 220 mm

From M ≤ ξ(1-0.5ξ)

Solved by: ξ = 0.257 < ξb = 0.55;

From As = = 2246.00 mm2

>>＞ρminbh0 = max(0.002, 45?t/?y) × 1000 × 260 = 520 sq. mm;

Take 12Ф20 (As = 3768 sq. mm) (double reinforcement).

(4)Calculation of shear capacity of inclined section.

Optional Ф8@200 hoop, shear bearing capacity is calculated as follows:

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=0.7×1.27×1000×220+1.25×210××220=216.4 kN＞V=83.06 kN, meet the requirements.

The same can be calculated for precast reinforced concrete panels for 200 cm span and 300 cm span culverts.

(viii)RPVC pipeline

The RPVC pipeline for the planning and design is taken from the creek outside the project area, and is mainly used for irrigation and local residents' production and domestic water. The project's RPVC pipeline *** 2 kinds of pipe diameter were Ф125 and Ф50, pipe diameter Ф125 RPVC pipeline is mainly used to take water from the creek to the cistern, pipe diameter Ф50 RPVC pipeline is mainly used for connecting the cistern. RPVC pipeline buried depth of 80 centimeters, the slope ratio of the excavation line is 1: 0.2. Due to the pipeline pipe diameter relative to the depth of the smaller, the area of backfill earth excavation with the earth. The same.