How to calculate riprap slope protection in municipal engineering
Underwater riprap revetment construction scheme 2009-04- 19 22:48 1. Underwater topographic survey before riprap.
Before construction and throwing, the underwater topographic survey shall be reported to the supervision engineer for approval.
2, the construction area (grid) division
The key of underwater riprap construction is to reasonably divide the construction community (grid). According to our company's experience in underwater riprap construction for many years and the specific situation of our company's riprap ship at present, the construction community (grid) can be divided into standard grids of 10m (vertical flow direction) ×20m (downstream direction), and each standard grid can be divided into upper and lower areas for riprap. The throwing area with width less than 10m can be divided into small areas with fixed width for construction. According to the thickness of each riprap area in the design drawing and the underwater topographic survey results before riprap, the riprap quantity of each grid is calculated, and the construction document bitmap is compiled.
3, measurement and lofting
Because the riprap construction position is located in the water, it is impossible to establish the construction position in the water, so it is necessary to set up signs corresponding to the construction position on the shore to determine the construction position.
(1) measuring and setting-out method
A. On the shore near the dumping area, according to the control points provided by the construction unit, a point is laid out on the shore by the method of forward intersection or rear intersection, and the construction baseline is released from this point.
B) Establish a positive baseline (parallel to the length direction of the throwing area) or an oblique baseline (not parallel to the length direction of the throwing area) according to the known points in the measurement.
C, according to the length of each construction plot on the baseline, divide and release each baseline pile.
D the piles (directional piles) of each section shall be laid from the baseline piles, and the directional piles shall be perpendicular to the length direction of the throwing area.
(2) Technical requirements for survey and lofting
A. Baseline piles and directional piles released by survey and lofting shall have good visibility with positioning ships.
B. infrared rangefinder is used for measurement.
C, taking the measuring point as the control point, releasing the baseline pile and the directional pile by the polar coordinate method, and the distance error between the piles is less than 5 mm ..
4. Ship positioning
(1) Selection of positioning vessel
This project plans to invest 1450 ton steel positioning ship, which is in good condition and equipped with professional operators.
(2) Positioning
Selection of anchor and cable
In order to accurately and firmly position the positioning ship, we must first choose the appropriate anchorage and anchor cable.
A. Anchor selection: 1000kg anchor is selected for the upstream anchor, 600kg anchor for the downstream anchor and 400kg anchor for the head anchor.
B. Anchor cable
The two upstream cables and two downstream cables shall be anchored cables with diameters larger than φ 2 1.5, and the specifications of the two plug cables shall not be less than φ 16.5.
(3) Positioning the anchor sequence and anchor position of the ship
A. anchoring sequence
Outer upstream anchor (territorial sea anchor)-inner upstream anchor-outer anchor-inner head anchor-inner downstream anchor-outer downstream anchor. It should be noted that the upstream and downstream anchors should be opened to facilitate the positioning of the ship to move inside and outside.
B. Determination of offset (drift)
In the process of throwing stones at the bottom of the river, stones move downstream due to the action of water flow, so the impact distance of stones should be calculated before throwing, so as to calculate the moving distance of stones under the action of water flow and ensure the accuracy of throwing position. The empirical formula of riprap offset is: S=0.8VoJ/W 1/6.
S offset (m)
VO-water surface velocity (m/s), and the water surface velocity at the throwing point is measured by a speedometer.
H—— water depth (m), and the water depth of the throwing point is measured by the sounder.
W is the weight of the stone (kg), which can be calculated according to the representative weight of the stone in construction.
C. anchor positioning of positioning ship
After the positioning ship is anchored, it can be positioned. Firstly, move the positioning ship to the section to be thrown, measure the velocity and water depth, and calculate the offset (drift distance). The distance from the offset to the blank area of the stone bow is the advance of the positioning ship, and the theodolite is used for accurate positioning. So that the position of the stone anchored on the downstream side of the positioning boat corresponds to the position to be thrown after entering the water.
5. Stone inspection, measurement and gear shifting of stone ship
Selection of riprap boat: 40t barge is adopted, and a standard ship type is established during construction. Communities are divided according to the standard ship type, and a riprap boat is selected according to the standard ship type, specifically, the length from the bow to the cargo hold is 20m, 3.5m, the cargo hold 10m and the rear hold is 6.5m. ..
(1) stone quality control and quantity determination
A. Stone control
Underwater riprap should ensure the quality of stone, and the supply of stone should be inspected to ensure that it meets the design and specification requirements, and can only be selected after being confirmed by the supervisor to be qualified. Put an end to wind fossils, hydrolysis, gravel and so on.
Qualified stone.
B. Determination of quantity
After the stone ship arrives at the designated place, the qualified stone shall be measured in the presence of the supervision engineer of the supervision unit. Measure the length of the stone twice, the width four times and the height eight times. Take the average value to calculate the quantity, and appoint someone to count the quantity according to the void ratio and stone quality. During the construction, the supervision engineer and the quality inspector of the project department randomly select the ship for weighing, determine the coefficient according to the weighing results, and eliminate the virtual tonnage, subject to the quantity approved by the supervision.
C. the riprap boat is put into gear and riprap.
After the positioning of the positioning ship is completed, the stone ship can be hung on the lower side of the positioning ship for construction. According to the principle of uniform throwing, the positions of stone carriers should be staggered to ensure uniform throwing.
According to the determined standard ship type and effective riprap width, the half area 10m× 10m grid of the standard riprap grid is divided into eight strip areas (i.e. four ship positions) with length 10m and width 1.25m for riprap, and each ship position is staggered1.
In the standard grid, the riprap of the rock loader should be distributed from both sides of the ship, and in the fixed-width community of the non-standard grid, the riprap should be distributed from one side of the ship, so that the blocks will fall into the designated area after entering the water, thus achieving the goal of uniform riprap.
Step 6 throw by hand
After the stone ship enters the gear and hangs firmly, it will start to organize personnel to throw it, and the cable can not be separated from the gear until all the ships have been thrown. The archivists timely and accurately put the input quantity on the archives bitmap, so that the actual input quantity of each grid is controlled within the range of 95%~ 105% of the design quantity, and the actual input quantity of the unit project is controlled within the range of 100%~ 103% of the design quantity.
7. Complete underwater topographic survey
After the underwater riprap project is completed, our unit will assign a special person to cooperate with the surveyors entrusted by the owner to conduct underwater topographic survey on the riprap area and some adjacent waters by using the GPS system, draw an underwater topographic map with the scale of 1: 2000, and compare the underwater topographic maps before and after riprap to determine the riprap results.
The thickness measured at fixed points should be controlled at 70%~ 130%. If the thickness is less than 70%, it is necessary to throw stones. If it exceeds 130%, it is necessary to arrange divers to bury the slope underwater.
8, construction technical requirements
( 1)
Strictly control the length of each construction section: during the construction period, due to the influence of monsoon, in order to ensure the accuracy of riprap gondola and reduce the influence of wind and water flow, if the water flow direction is consistent with the design riprap direction and the flow speed is not high, the unit riprap length is 80m per day; if the angle between the water flow direction and the design riprap direction is large or the water flow is disordered, the unit riprap length is 40~60m.
(2) According to the field investigation and design drawings, the riprap width and water flow in the construction area of this bid section, in order to ensure the riprap accuracy and uniformity, during positioning, a positioning boat is arranged upstream and downstream of the construction unit, so that the upstream and downstream of the rock loader are fixed and will not swing when put into series, which ensures the riprap requirements of the design drawings. (Downstream, the upper winch of the positioning ship is used to tighten and fix the stone loading ship. The upstream and downstream positioning methods are the same.
A. Selection of stone carrier: 40t stone carrier shall be selected in strict accordance with the standard ship type during construction to ensure the uniformity and thickness of riprap.
B establish a perfect positioning system, complete the layout of permanent control traverse, pile number and fixed observation section pile in the presence of supervision engineer, and mark each section pile with a small red flag to ensure that the positioning does not deviate.
C. During construction, follow the construction sequence of "upstream first, downstream later, deep flood first, and nearshore later", and then uniformly throw them in turn.
D, before the formal riprap, riprap test is carried out, and the relationship between impact distance and water depth, flow velocity and block diameter is obtained through the test.
E. The positioning ship shall timely adjust its position according to the current velocity and water level, and frequently measure parameters such as current velocity, flow direction and water depth, and calculate and adjust the riprap falling distance.
F. After throwing the first unit, the throwing results should be analyzed, so as to timely adjust the slicing grid throwing scheme and the positioning position of water operation.
G. Dry riprap: During the construction near the toe groove of the slope protection, when the local ship cannot riprap due to the water level, it must be hoisted by hand on the shore, and riprap (dry riprap) must be hoisted on the shore, so as to ensure the connection between toe protection project and slope protection and the stability of the sill.
H. In order to ensure the safety and smoothness of the Yangtze River waterway during the construction period, take the initiative to contact the shipping management department, obey the unified command and dispatch, and set up obvious navigation marks and surface buoys to show the scope of riprap operation area and the waterway of construction ships and ships sailing on the Yangtze River.
9, riprap construction quality control
(1) material quality control
The construction materials for riprap construction are relatively simple, mainly stones and stones.