Reinforcement treatment of a teaching building foundation project?

The following is Zhongda Consulting to bring you about the reinforcement treatment of a teaching building foundation project for reference.

This paper first through the analysis of working conditions, quality accident cause investigation and analysis, the comparative analysis of several programs to determine the anchor static pile reinforcement program. Secondly, it discusses in detail the design and construction process of anchor static pile in this project, and finally summarizes the reinforcement results.

1 Project Overview

A teaching building in a region of South China is a pure frame structure without basement, the main body of six floors above ground, seven floors locally, the plane is "[" shape. The maximum size of the frame column network is 5000mm×9000mm, with internal corridors, covering an area of about 3000m2, with a floor area of about 13000m2, and a seismic intensity of 6 degrees. There is one expansion joint designed, in the middle of the longitudinal direction. ***Counting 92 columns.

This project belongs to the geological conditions are more complex, the building of the entire site after artificial backfill, backfill before the Gangchu washout, local reservoir, reservoir backfill before the unpumped, the designers according to the geological conditions, will be the foundation design is mainly a single-pile, single-column form of artificially dug pile foundation, the holding layer for the 5th fully weathered sandstone, 6 layers of strongly weathered sandstone. In addition to the expansion joints for 2 columns of a pile, the rest for each column of a pile, *** counting 88 manually dug hole piles, pile diameter of 900mm, 1000mm, 1200mm, 1500mm and so on 4 kinds of, the design bearing capacity of the largest up to 6800kN.

2 manually dug hole piles test results and treatment program

In the construction of manually dug hole piles due to a variety of reasons lead to Hole state is extremely bad, after dynamic small strain detection found: 65 piles of class Ⅰ, 7 piles of class Ⅱ, 15 piles of class Ⅲ, Ⅳ 5 piles. After analyzing the main causes of quality accidents: 1, the operator in the concrete configuration mixing arbitrarily, resulting in part of the concrete strength is insufficient; 2, the pile hole at the bottom of the water, slag is not cleaned up, resulting in the pile bearing capacity is insufficient; 3, the concrete pouring down the material does not use a chute or a string of measures, resulting in the free fall of the height of the norms beyond the requirements of the concrete has been segregated in the process of falling, the pile at the bottom of stone The mortar around the pile was seriously missing. This was also verified by core sampling. Add pile treatment to class Ⅳ piles, and take core samples of some Ⅱ and Ⅲ piles to verify; and carry out large strain test to get the approximate bearing capacity; after adding 9 manually bored piles to 5 Ⅳ piles, there are 6 Ⅲ piles in the small strain test; the approximate bearing capacity results of large strain test of some Ⅱ and Ⅲ piles are more than 40% of the approximate bearing capacity of Ⅱ piles compared with the design value. The approximate bearing capacity of Class Ⅲ piles is lower than the design value, and the largest difference is 1348kN. The following measures are taken for the above situation:

2.1 Continue to use manually dug hole piles with piles. After the previous lessons, there are the disadvantages of difficulty in hole formation, longer construction period and high cost;

2.2 Adopt hydrostatic pile plus pile. The equipment is bulky, occupies a large area, has high entry and exit fees, occupies a long period of time and costs a lot;

2.3 Grouting method of foundation soil reinforcement treatment. Because one of the main factors of the pile bearing capacity is not enough is the mud at the bottom of the pile, and the direction of the slurry flow is difficult to control, quality is not easy to guarantee, and occupy the construction period;

2.4 Anchor static pressure pile method. Using the existing pile first construction of the main body to 3 layers, and then pressure pile, the method of simple equipment, economic, reliable quality, does not occupy the construction period.

2.5According to the Technical Specification for Pile Foundation of Construction and the actual situation of the project, the Class III piles (*** counting 21 piles) are treated by static pressure anchor piles.

3 Laying pile design

3.1 Design bearing capacity of single pile: the design bearing capacity of each anchor static compression pile is 400kN, and the final pressure is 600kN.

3.2 Number of piles: the number of compression piles under the bearing platform of each column foundation is symmetrically 4 piles, but taking into account the existence of solitary stone in part of the soil layer, the construction of the bearing platform under each column is therefore reserved in 8 directions during construction of 8 pressure pile holes. At the same time, HRB335 φ25 rebar was pre-buried as anchors. Final arrangement of pressure pile holes and anchors. The other 4 reserved pressure pile holes are distributed in 4 corners.

3.3 Pile body design, using 200mm×200mm section, each section of the pile is 2m long, using C25 concrete, the main bar is equipped with HRB335, 4φ14. sulfur cement is used to connect the pile.

4 Pressure pile equipment

Pressure pile equipment site assembly design. Lattice type steel strut plus I-beam beam.

5Construction

5.1Preparation

a, prefabrication of pile sections at precast component factory;

b, cleaning of working surface for pressure pile holes and anchor construction;

C, installation of pressure pile equipment.

5.2 Pressure pile

Basic process of construction is: transportation→pile driving machine in position→pile lifting→pile pressing→pile jointing (sulphur cement)→pressing pile (until the pressing force reaches the design requirement)→dismantling pressure pile equipment after completion of pressure pile→pile driving machine in position to start the construction of the second pile (until the construction is completed in full)→sealing pile.

Pressing pile should pay attention to:

a. Pressing pile frame should be kept vertical, the nuts or anchors of anchoring bolts should be tightened evenly, and the loose nuts should be tightened at any time during the pile pressing process;

b. Pile section in position should be kept vertical, so that the axes of the jacks, pile sections and pile holes can coincide, and the pressurizing should not be eccentrically:

C. The whole pile should be pressed to the design elevation in one go. d. Pressure pile construction shall be carried out symmetrically, but should not be pressurized by several pile presses at the same time on an independent foundation:

e. When connecting piles with sulphur cement, make the upper and lower piles' anchorage bars coincide with the anchorage holes. When jointing piles, make the upper and lower pile faces fully bonded and aligned to prevent misalignment of pile faces.

f. The final pressure is judged by the method that the pressure must reach the design requirement of 600kN, and the pile tip should reach the depth of not less than 500mm of the designed holding layer, and the pressure should be maintained for 10min when the pressure reaches 600kN as a way to improve the friction force of the pile tip and the compensation for the embedding depth of the pile tip.

5.3 Pile Sealing

After the pile tip reaches the compression force and design holding layer depth, the jack can be unloaded, the compression pile frame can be removed, the anchor cross reinforcement can be welded, the debris, water and slurry can be removed from the hole of the compression pile, and the surface of the top side of the pile can be chiseled and brushed clean, and then the concrete interfacial agent is applied, and then the micro-expansion early-strengthening C30 concrete can be poured.

6 Analysis of foundation reinforcement results

The reinforcement design and study of this teaching building project has been completed, and the project was also put into use in 2006. No anomalies were observed.

7 Conclusion

The following lessons have been drawn from the reinforcement design and study of the project:

7.1 The choice of reinforcement program must pay attention to the combination of the requirements of the work schedule, and strive for good economic efficiency, construction simplicity and so on.

7.2 For there has been a mature theory, there is a standard construction process of technology, according to the actual situation of the project to make some adjustments, can not be copied. For example, this project is the foundation reinforcement of the new construction, the pressure pile hole is reserved when doing bearing platform, and considering the complex geological conditions, 8 holes are left. The anchors were also pre-buried when the bearing platform was made.

7.3 Reasonable determination of reinforcement standards, mastering the scale of reinforcement

In the reinforcement project, the height of the reinforcement standard is subject to the constraints of a variety of factors, such as the owner's knowledge and understanding, the level of design, the technical strength of the construction team, the amount of reinforcement costs, the length of the construction period, and the limitations of the use of the function, and so on. This also brings us some difficulties in the design of this reinforcement project. Our reference standard is mainly the Technical Specification for Foundation Reinforcement of Existing Buildings (JGJ123-2000).

7.4 Quality supervision and testing is an important link that should be strengthened in the reinforcement technology. In this project, the main control in the reinforcement work is the verticality of compression pile and the size of compression pile force. There is no monitoring work for the settlement after the reinforcement construction, whether there is rebound and so on. However, there were accidents of excessive settlement and pile rebound in similar reinforcement works, which should be noticed in the reinforcement work.

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