Treatment and suggestions of the hottest accident

2022-08-15
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According to the geological characteristics of Chongqing and my practical experience in the field in recent 20 years, it is believed that the main causes of pile foundation quality accidents are as follows

1. The measurement and setting out are wrong, causing the dislocation of the whole building or excessive deviation of pile position

2. The bearing capacity of single pile cannot meet the design requirements

3. Pile completion interruption accident. If the hole of bored cast-in-place pile collapses, the drill is stuck

4. The quality of cast-in-place piles, including excessive sediment, concrete segregation, mud inclusion in the pile body, concrete strength not meeting the design requirements, serious dislocation and deformation of reinforcement, etc

5. Pile breaking. The pouring concrete construction quality is out of control, and the pile breaking accident occurs

6. The pile position deviation during pile foundation acceptance is too large

7. The elevation of cast-in-place pile top is insufficient. There are three common ones: first, the construction control is not strict, and the concrete pouring is stopped when the design elevation is not reached; On the other hand, although the elevation reaches the design value, the pile top elevation is insufficient after chiseling because the concrete laitance layer on the pile top is thick

after the pile foundation accident, if it is not handled in time, the result will leave hidden dangers to the project. In order to prevent the occurrence of similar problems, I summarize some experience in dealing with the accidents of bored pile foundation over the years for the reference of colleagues

I. General procedures for accident analysis and treatment of bored pile foundation

II. General principles of pile foundation treatment

(I) conditions that should be met before treatment

1. The nature and scope of the accident are clear

2. The purpose should be clear and there should be a predetermined treatment plan

3. The participants basically agreed and determined the treatment plan

4. Signature of the designer

(II) basic conditions that should be met for accident treatment

1. The accident treatment scheme is required to be safe, reliable, economical and reasonable, with short construction period and reliable method

2. Preventive and improvement measures should be put forward for the part not under construction to prevent the recurrence of accidents

(III) the accident should be handled in time to prevent hidden dangers

1. After the pile is drilled, the depth of the pile hole embedded in the bearing layer, rock strength, sediment thickness, verticality of the pile hole and other data must meet the design requirements. As long as there is one item that does not meet the design requirements, it should be analyzed and solved in time. After the construction unit representative signs and approves, the concrete can be poured and the drilling rig can be moved to prevent unnecessary waste caused by the requirements of rechecking later

2. Before the excavation of foundation piles, the pile forming records and pile test data must be comprehensively checked. If there are controversial problems in quality, opinions must be given; The soil can be excavated only after the foundation pile is excavated, so as to prevent unnecessary trouble caused by treatment after the foundation pile is excavated

(IV) the impact of accident handling on the quality of completed projects and the way of subsequent projects should be considered. Will the adjacent piles with low concrete strength be damaged if pile mending is adopted in the accident treatment

(V) choose the best treatment scheme. There are many methods to deal with pile foundation accidents, but the schemes should be compared technically and economically, and the schemes that are safe, reliable, economical, reasonable and convenient for construction should be selected

III. common treatment methods for pile foundation accidents

common methods include pile connection, pile reinforcement, reinforcement, expansion of bearing platform (beam), change of construction method, modification of design scheme, etc. The following introduces the application of several methods in combination with the causes of the accident

(I) pile extension method

as the elevation of the pile top after the pile is insufficient, it is necessary to use a constant speed tensile testing machine. The pile extension method is often used, and there are two methods

1. Excavate and connect the pile, dig out the pile head, Chisel out the concrete laitance and loose layer, Chisel out the reinforcement, arrange and wash it, lengthen it with reinforcement, and then pour concrete to the design elevation

2. This method can be used when it is difficult to remove the poured concrete after the concrete stop accident in the embedded pile extension

(II) pile filling method

before the construction of pile cap (beam), if the distance between bored piles is too large to bear the upper load, piles can be added between piles

(III) drilling reinforcement method

this method is suitable for accidents such as serious honeycomb, segregation, looseness, insufficient strength and principal of the foundation concrete, and excessive thickness of sediment at the pile bottom. High pressure grouting method is commonly used to deal with such accidents, but this method is generally not suitable for standards, and it is extremely urgent to adopt

1. High pressure grouting reinforcement

(1) when there is local segregation in the concrete of the pile body and honeycomb, the drill can be used to drill to the next time of the pile diameter under the quality defect for high-pressure grouting after cleaning

(2) when the principal is insufficient, use a drill to drill to the design bearing layer elevation; Grouting reinforcement shall be carried out for the part with insufficient pile length

(IV) expanding the bearing platform beam method

1. The pile position deviation is too large, and the original design bearing platform (beam) section width cannot meet the specification requirements. At this time, expanding the bearing platform (beam) is used to deal with it

2. Considering the interaction on the pile, when the bearing capacity of a single pile cannot meet the design requirements, the method of expanding the bearing platform (beam) and considering the pile and natural foundation to jointly group the superstructure load can be used. It should be noted that while expanding the section width of the bearing platform (beam), the reinforcement of the bearing platform (beam) should be appropriately increased

(V) change the construction method

some pile foundation accidents are caused by the wrong construction sequence or improper method and technology. On the one hand, appropriate remedial measures should be taken for the accident pile; On the other hand, we should change the wrong construction methods to prevent accidents. There are two common methods

1. Change the pile forming construction sequence

if the pile layout is too dense for construction, the interval pile forming method can be used

2. Change the pile forming method

if there is large groundwater in the hole forming pile, the pile forming method in the casing shall be adopted

(VI) modify the design

1. Change the pile type

when the geological data is inconsistent with the actual situation, resulting in pile foundation accidents, the method of changing the pile type can be used. If it is difficult to cast water-free, acid and other mixture piles, precast piles can be used

2. Change the pile position

if the cast-in-place pile is abandoned or meets the obstacle of underground pipeline, the pile position can be changed for treatment. For example, in the 8 # and 9 # houses of Daqing Village drilling base in dashiba, Jiangbei District, there are 420 natural gas pipelines that are processed about 5m underground. It also has the functions of automatic algorithm generation and automatic experiment report; It greatly facilitates the debugging and system redevelopment ability

3. Superstructure unloading

some major pile foundation accidents are difficult to deal with, and the cost is huge. Only by reducing the number of building floors or replacing the original design materials with light materials, can we reduce the load of the superstructure

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