Construction of low pile cap with steel sheet pile cofferdam

Gui Xiaoming construction technology and method of steel sheet pile cofferdam.

There are two bridges on Jiefang Road Bridge and Gaocheng Road Bridge on the Huancheng Road in Lu'an City, Anhui Province. They both cross the Pi (he) Shi (he) Hang (Buhe) main canal. The bridges are designed as two-way four-lane, each bridge has two piers in the water, the water depth is 34m, designed as a low platform, the platform is about 1.5m below the soil surface. Geological data shows that 7m below the surface is dry hard plastic clay, bearing capacity = 280kPa, strong plasticity, no silt layer on the surface, the use of straw bag cofferdam is not easy to succeed. With the consent of the design unit, steel plate cofferdam is adopted.

1 Construction preparation (1) Establish a wharf, group transportation ships and elevated floating cranes In order to allow the steel plate to reach the insertion site smoothly, a 15mX15m wharf was erected on the riverside to facilitate the installation of the steel plate and launch a 80t The transport ship is responsible for the transportation of steel plates, and also assembled an elevated floating crane for lifting and pulling steel plates in the water.

Vibrating hammers are the key equipment for pulling steel plates. Special inspections must be carried out before pulling to ensure that the lines are smooth and function properly. The terminal voltage of the vibratory hammer should reach 380420V and the splint teeth should not wear too much.

①The steel plates of the same cofferdam can only use the same lock, calculate the number of steel plates used according to the design size to ensure that it is sufficient; ②Remove the steel plates with cracked, twisted, and deformed locks; Residual tumors left; ④ spread butter in the steel plate lock to reduce the friction between the locks during insertion and reduce the leakage of the steel plate cofferdam.

(4) Installation of steel plate guide device The shape of the bridge pier and abutment's low platform is mostly square, and sometimes it can be made into a circle. The size of the steel plate cofferdam can be around the circumference of the platform. Square cofferdam steel plate guide frame The square cofferdam steel plate is usually guided by a square shape. Eight positioning is made on the inside of the cofferdam, the corbel is welded, and then the guide frame is installed.

The square cofferdam steel sheet pile guide frame can be made into a round cofferdam in the absence of corners or in other special circumstances. For the guide frame, see 2 Inserting steel sheet piles. To ensure accurate insertion position, the first steel plate is inserted. The essential. Set a limit frame on the guide frame, the size of which is 1cm larger than each side of the steel plate. When the steel plate is inserted, the back of the steel plate is close to the guide frame, and the floating hook is slowly lowered while inserting. At this time, the instrument should be observed in two directions perpendicular to each other to ensure that the steel plate is inserted straight and straight. Then, based on the first steel plate, insert the steel plate symmetrically on both sides.

During the insertion process, there is soil squeeze on the lower end of the steel plate, the gap between the lock of the steel sheet pile and the lock is large, and the upper end will always be inclined away from the first steel plate. Therefore, every four or five steel plates must use vertical ball suspension wire, and the inclination of the steel plate should be controlled within 1%. Exceeding the limited inclination should be corrected. A piece of steel plate inserted). When the deviation of the steel plate is too much, the deviation can only be gradually reduced by multiple corrections. If the correction is difficult because the soil is too hard, the deviation can be corrected by using a four-wheel block.

②Strictly control the verticality when inserting, especially the first one; ③When inserting a steel plate on hard plastic clay, you can use ④When the steel plate is difficult to insert, you should stop to analyze the reason and check whether the lock is deformed. Whether it is deformed, there are no obstacles in the steel plate, etc., it must not be dry, and the steel plate is worn out; The steel plate falls due to the failure of the hydraulic pump; ⑦ The motor of the vibratory hammer is overloaded for a long time, which is easy to heat and burn, especially when pulling the steel plate pile on the hard plastic clay.

3 When closing, start to measure and calculate the straight-line distance at the bottom of the steel plate, then calculate the number of steel plates according to the width of the steel plate, and then determine how to insert the steel plate next (whether to add the steel plate or the steel plate to insert) When playing, the arc is outward).

① In order to facilitate the closing, the two pieces at the closing should be one high and one low. For the round shape, the situation of "upper small and lower large" (the bottom is squeezed by the bottom and the upper end is free) often occurs. Take the four pulley block and pull it to both sides until the distance between the tops of the two sides is equal to the width of the steel plate. When it is close to parallel, insert the close and hit the design elevation.

②The square cofferdam has 4 faces, and each steel plate after finishing should be perpendicular to the normal and tangent direction of the guide frame, and the closing should be selected near the corner (generally 4 ~ 5 pieces away from the corner). Adjust the distance from the guide frame to the adjacent side of the closed side. In order to prevent the two pieces at the closing place from being in a plane, be sure to adjust the angle direction so that the lock on one side and the lock on the opposite steel plate are as parallel as possible.

4 In addition to considering the stress, the setting of the internal support should also consider that it does not hinder the formwork of the pier. The internal support is set from top to bottom. While pumping, it is installed at the same time. The number of supports is determined according to the calculation of water pressure and earth pressure. Pumps for drainage in the cofferdam, the displacement of the pump should be greater than 1.5 to 20 times the amount of water seepage in the cofferdam (1 to 2 sets are reserved after pumping). When pumping water, obvious leakage can be found. The sawdust can be placed outside the leaking cofferdam. As the water flows from the outside to the inside, the sawdust flows into the gap of the steel plate, which plays a role of plugging. It can also be used in the cofferdam. Insert the dried kelp or cotton yarn into the gap of the steel plate with a scraper on the inside.

In 2002, the cause of the large rail gap of the first line and its prevention measures Xu Yaping, Tang Wenlong, Zhang Zhiqiang.

1Problem raised The rail joint is the weak link of the railroad track. The large rail joint is one of the main reasons for the joint defects and the joint damage. It is also one of the factors that cause the joint bolt to break and the splint to break, which affects the driving safety.

At present, there are two types of standard rails laid on ordinary lines in China: 12.5m and 25m, most of which are 25m steel rails. According to "The iron joints all use 18. Large rail joints that are larger than the structural rail joints, when the train passes, they will add the wrong height of the joint, forming an excitation source to cause vibration, and the inertial force generated by the vibration forms a huge additional dynamic load, causing The violent impact of the wheel rail, the impact load can sometimes reach 3-4 times the static wheel load. Over time, joint flashes, flaking pieces, splint bending, low joints, saddle wear and other diseases will form. This article discusses the causes and prevention measures of 50m / m and 60kgm 25m standard rails.

2 The reason for the large rail gap 21 The reason for the temperature limit of the laying construction, and the rail gap is not adjusted within the rail temperature limit.

(2) When laying or replacing rails or adjusting rail joints, the size of rail joints is not set according to the fifth section of "Railway Line Maintenance Rules". Before piling and pulling, water is poured into the cofferdam, the inner support is removed from the bottom up, and the first floor is removed. Support, pour water into the first floor, and open the vibratory hammer when pulling the pile. After the side soil is loosened, the floating crane hooks at the slowest speed. Observe the draft of the floating crane and gradually increase the lifting speed.

If the draught of the floating crane is too deep, stop lifting and try to loosen the soil on the side of the pile before pulling it out.

6 The steel sheet pile construction process flow is summarized above. The steel sheet construction process flow is as follows: assembling the transport ship> construction preparation * assembly floating floating steel sheet pile finishing and steel sheet pile inspection. Maintenance and positioning positioning * Welded corbel installation guide frame production guide frame insertion steel plate measurement, deviation correction adjustment close production internal support installation internal support platform construction Bu pumping excavation foundation removal internal support pull one> steel plate cleaning steel plate cofferdam construction process flow ( Responsible editor Bai Minhua)