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Construction and monitoring of bolt

A, bolt construction points: 1, drilling, 2, set up reinforcement or steel strand bundle, 3, grouting, 4, prestress tension; Two, bolt monitoring:

A,anchorThe main points of construction

1, drilling,

(1) Mark the holes according to the design before drilling. Drill hole depth should exceed design bolt length0.3m~0.5m.

(2)anchorThe hole distance error in the horizontal direction is not greater than 50mm, the hole distance error in the vertical direction is not greater than 100mm. Hole bottom deflection size, not greater than the length 3%, the drilling direction can be controlled by drilling inclinometer.

If the soil layer is easy to collapse, you can drill with wall protection casing, not mud wall protection, drilling in the rock layer can use auger, percussion drilling into holes.

2, set up steel bar or steel strand bundle

The tie rod can be made of steel bar or steel strand, when the grade andⅢDouble-sided lap welding should be used for the joint length of grade rebar, and the weld length should not be less than 8d (d Is the diameter of steel bar). Rod lengthening or rod body and screw welding must be used according to the design requirements of the welding rod, the finished rolled thread steel bar can be connected with the shape of the sleeve.

3, the grouting

The strength grade of grouting material is C32.5 Above ordinary Portland cement, water cement ratio 0.40.45. If mortar is used, the mix ratio is 1:11:2, the sand is not greater than 2mm, the mortar is only grouting once.

The primary grouting pipe should be put into the borehole together with the bolt, and the distance between the end of the grouting pipe and the bottom of the hole should be 500mm1000mm, the grouting hole and end of the secondary high-pressure grouting pipe should be sealed to ensure that the grout does not enter the secondary high-pressure grouting pipe during primary grouting.

The strength of the secondary high pressure grouting should be up to that of the cement stone formed by the primary grouting 5.0MPa The secondary grouting pressure should be controlled in 2.5MPa4.0MPa The grouting amount can be determined according to the grouting process and the volume of the anchor solid, which should not be less than one grouting amount.

4, prestressed tension

The bolts shall be of solid anchor and outer anchor head strength 15.0MPa The tension lock is carried out root by root, and the tension load is the designed load 1.051.1 Stable times, 510min After that, back to lock load lock.

Anchor curing generally achieves cement mortar strength 70%Value, can be carried out prestressed tension.

(1) In order to avoid stress loss of adjacent bolts during tension, it can be adopted"Jump a method"The isolation 1 la1Methods.

(2) Before formal tension, the design tension should be taken 10%~20%, and pretension the bolt 12 Times, make each part close contact, produce the initial cut.

(3)Formal tension should be loaded in stages, each stage after loading dead load 3min Record the elongation value. Tension to design load (not exceeding axial force)The dead load 10minNo more changes can be locked.

(4) lock the prestress to design the shaft tension 75%It is advisable.


With the excavation of earthwork of foundation pit, the stress condition of anchor rod is changing constantly, so it is necessary to monitor the change of prestress of anchor rod in major foundation pit engineering.

Monitoring bolts should be representative and the number of monitoring bolts should not be less than engineering bolts 2%, and should not be less than 3 The root.

anchorThe monitoring time is generally no less than 6 Months after tensioning locked initially 10d It should be measured daily. 11d30devery 3d Measure once, and then every 10d Measurement once, when necessary (such as excavation, rainfall, lower row bolt tension, sudden signs, etc.) should be encrypted monitoring times.

The monitoring results should be fed back to the relevant units in time. If necessary, repeated tension, appropriate relaxation or increase the number of bolts can be adopted to ensure the safety of the foundation pit.

In addition to conventional material inspection, slurry strength inspection and bolt acceptance test should also be carried out in the quality inspection of laying rod.

Slurry strength test block number per 30 There is no less than one group of bolts, and the number of test blocks in each group is 6 Block.

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