【Excerpts】How to deal with broken piles in grouted piles?

Common treatment methods for broken piles

1、In-situ re-piling.

     For the broken pile found in time during construction and ultrasonic detection, use a thorough cleanup and re-cast a new pile in-situ to achieve a more thorough treatment. This method is effective, difficult, long-period and expensive, and can be used according to the importance of the project, geological conditions, the number of defects and other factors.

2、Join the pile.

       To ensure the quality of the project, stop the pouring of concrete and pull out the conduit in advance. Determine the pile connection program, first, sound survey of the pile to determine the site of good concrete; second, according to the geological information provided by the design to determine the well point precipitation-excavation-20# plain concrete for retaining wall, retaining wall reinforced with reinforcing hoops. Third, digging to the qualified number of the use of manual chiseling, concrete pouring according to the concrete construction method of the dug-out method.

3、Pile core drilling method.

      This method is easier said than done, that is, while precipitation, the use of wind picks in the center of the defective pile cut a well of 80 cm in diameter, the depth of at least more than the defective parts, and then closed to clean the sediment, placing the reinforcement cage, with dug concrete construction method of pouring expanded concrete. This method day progress slowly, if encounter individual pile water treatment is not good, can not be lowered, it is more difficult, resulting in quality, schedule and economic significant losses.

4、Supplemental delivery combined method.

When the pile is driven into the pile using the section connection, sinker by sinker, poor connection of the pile may occur to connect the node off, at this time can be used to send a complementary combination method. First of all, the pile with doubt replay, make it sink, the loose joint and then tighten, so that it has a certain vertical bearing capacity; secondly, the appropriate fill some full-length complete pile, on the one hand, to make up for the lack of vertical bearing capacity of the whole foundation, on the other hand, fill the whole pile can withstand the earthquake load.

5、Deflection method.

Pile tilt, but not fracture, and the pile length is short, or due to the excavation of the pit caused by the pile tilt, but not fracture, can be used after the local excavation with a jack correction reset method to deal with.

6、Expanded bearing method.

     Due to the following three reasons, the original pile bearing platform plane size can not meet the requirements of the structure or foundation bearing capacity requirements, and the need to expand the area of the pile bearing platform.

     (1) The pile position deviation is large. The original design of the bearing plane size can not meet the structural requirements of the specification, available to expand the bearing method.

     (2) Consider the joint action of pile and soil. When the single pile bearing capacity does not meet the design requirements, it is necessary to expand the bearing platform and consider the pile and natural foundation to share the load of the upper structure.

     (3) Uneven quality of pile foundation, to prevent uneven settlement of independent bearing, or to improve the seismic capacity, can be used to connect the independent pile bearing into a block, improve the integrity of the foundation, or set up seismic ground beam.

Preventive measures for broken piles

      1、 the pile cross-sectional tensile strength of the test, to ensure the quality and amount of material to ensure the design strength of the cross-section

     (1) Because not all the bridge design by special design units. Especially local road projects in the middle and small bridges, in the design process rarely consider or even do not consider the harmful effect of frost swelling force on the pile body, which requires the design must ensure the pile strength.

     (2) The amount of concrete per m3 is generally not less than 350kg, and the actual scale of the ratio should generally exceed the design scale by 10% to 15%. (3) for the steel used, before use must do mechanical properties experiments, strict quality control, the quality of substandard steel is strictly prohibited to use, for the welding process of steel, the need for welding rod level, must adhere to the standard, according to the specification to implement.

     2、strict construction organization and design, before construction, all the equipment and tools to fill the hole are ready to ensure the continuity of concrete construction, as short as possible to shorten the pouring time

    (1) the decomposition length of the conduit should be easy to disassemble and transport, and less than the lifting height of the conduit lifting equipment, the middle section is generally about 2m, the lower end can be lengthened to 4 ~ 6m. conduit wall smooth, straight, no local convexity, each section of the inner diameter should be the same size, deviation of not more than ± 2mm, should be strictly controlled dial the conduit, demolition of the conduit time, demolition of the conduit time should not be greater than 15min, can be shortened as much as possible Time, once the filling begins, never stop in the middle.

    (2) in order to ensure the fluidity of concrete, strict control of the degree of collapse, should be guaranteed between 18 ~ 22cm, the aggregate as far as possible to use pebbles suitable particle size of 0.5 ~ 3.0cm, so that the maximum particle size is not greater than 4.0cm, concrete initial setting time of not earlier than 5h, if necessary, need to add some admixtures to extend the initial setting time.

    (3) the conduit in the concrete should generally be less than 2m, at least should not be less than lm, the maximum should not exceed 6m, buried too deep will be detrimental to the lifting of the conduit, but also to the concrete in the conduit to increase the resistance of the decline, pulling the guide too violently easy to pull the conduit off, in addition, will also make the conduit in the concrete buried too small, easy to make the mud gushing into the bottom mouth.

     3、 to prevent the conduit or the bottom of the mouth into the water, strengthen the water barrier facilities

    (1) conduit in the concrete before filling should be necessary watertight pressure test and joint tensile test, strictly check whether the joint is tight, whether the weld is broken, timely and early repair.

    (2) The amount of the first batch of concrete should be calculated. Both to meet the sufficient burial depth, but also to fill the conduit, in order to ensure the continuity of concrete construction.

    4、Prevent collapsing hole

    In the construction, there should be a person responsible for observing the construction water level, observing whether the water seeps around the shoring, in the construction of bored piles in water, due to the river flood, pay attention to measuring the river water level, if the water level difference is found to be reduced, measures should be taken in time to ensure the height of the head in the hole, be careful not to let the hole vibrate too much and try to reduce the weight near the hole.

     5、Surplus pouring and pile jointing

     In order to ensure the quality of the top of the pile, the design elevation of the top of the pile should be filled with a certain height, generally 0.5 ~ 1m, after the initial final condensation before digging out. However, more than 30cm should be retained to be cut out before pile receiving or bearing construction. When receiving the pile, the excess concrete will be removed and then rinsed with clean water before receiving the pile.

Summary

      The consequences of bridge foundation bored pile quality accidents are quite serious, so the construction unit should strengthen the management in the construction process and adopt a scientific construction plan and a practical backup plan. Only by strictly following the specifications and procedures and strengthening supervision and testing can quality accidents be avoided or reduced to a minimum.

      For the pile foundations that have problems, broken piles to find the causes of accurate analysis, should have detailed and accurate site information, timely organization of expert consultation, the development of safe, reliable and economic treatment program.

      The pile breakage factor can be prevented by strictly controlling the feed of steel materials, strict welding process requirements and construction in strict accordance with scientific operation procedures.

——Source: Building Industry Software

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