Knowledge fragments: construction of dynamic compaction, cost analysis of dynamic compaction works


Release Date:

2020-08-31

The dynamic compaction method is the super-force compaction method, also known as the driving force sand method. It is the application of large, medium and small chain-rail ramming machines to continuously raise 8-40 tons of heavy hammer type to a high place (6-40 meters), so that it can fall casually, giving the foundation damage and vibration, thus improving the tensile strength of the foundation and reducing its compressibility.

1, defined

(1) The dynamic compaction method is the super-force compaction method, also known as the driving force sand method. It is the application of large, medium and small chain-rail ramming machines to continuously raise 8-40 tons of heavy hammer type to a high place (6-40 meters), so that it can fall casually, giving the foundation damage and vibration, thus improving the tensile strength of the foundation and reducing its compressibility.

(2) Tamping energy: the product of hammer weight and falling distance is called tamping energy.

2. Main purpose

Dynamic compaction method can be used to deal with gravel soil, sand soil, low saturation gravel soil and cohesive soil, collapsible, collapsible and plain fill foundation.

3. Effect of dynamic compaction method

(1) Improve the tensile strength of the foundation;(2) Reduce the compressibility of the foundation soil;(3) Improve the professional ability of the foundation soil to resist gasification;(4) Eliminate the collapsibility of the foundation soil.

4. Classification of dynamic compaction method

According to the tamping area, it is divided into two types: point tamping and full tamping.

(1) Point tamping: For foundation reinforcement, the deep level is shallow (within 3M) and is an independent foundation method, only point tamping can be selected.

(2) full tamping: for the foundation reinforcement is relatively deep (above 3M), and for the continuous foundation, point tamping should be selected first, and then full tamping should be performed.

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Construction of dynamic compaction foundation

1. Construction process

(1) Make site preparations before construction, including: finding out the hidden objects in the lower range and adopting certain reasonable countermeasures to properly handle them; Selecting seismic shock absorption or other preventive measures; If the temperature in the interior of the site is high or there is water storage, the preventive measures of drop and sewage pipeline shall be selected.

(2) Eliminate and level the site (try to keep it level);

(3) Lay hard cushion to support lifting equipment;

(4) mark the location of the ramming point and measure the design elevation of the site;

(5) The hoisting machinery shall be timely to bias the rammer to the ramming point, and the elevation of the hammer top before ramming shall be measured;

(6) Lift the rammer to the ordered height, open the unhooking machinery and equipment, learn to give up the hook after the rammer is erected casually, and measure the design elevation of the top of the hammer again. If the bottom of the pit is found to be inclined, it should be leveled;

(7) Continuously step 6, according to the number of tamping and control standards specified in the scheme design, carry out the tamping of a tamping point;

(8) Change the tamping points, continue steps 5-7, and carry out tamping of all tamping points once;

(9) Use excavators to smooth the ramming pit and measure the design elevation of the site;

(10) After the specified time interval, carry out all tamping according to the above steps, and then use low mechanical energy to fully tamper the surface soil of the site, and measure the design elevation after tamping.

 

2. Ramming development and number of blows

Ramming shall be carried out according to the characteristics of foundation soil, generally 2-5 times, the first 2-3 times shall be "point ramming" and the second time shall be "full ramming" (I .e. hammering and printing shall be connected with each other's steel bars). The loose topsoil layer in the middle of the short ramming point shall be reinforced by engineering. For inhalable particulate soil with poor water absorption, tamping shall be carried out to improve.

3. Reasonable layout of ramming points

 

 

3. Construction equipment for dynamic compaction foundation

Important construction machines have auxiliary industrial equipment such as lifting equipment, hook machinery and equipment, rammers and excavators, and compaction machinery.

3.1. Crane tools

Chain rail hoisting machinery or other special hoisting equipment with professional capacity of hoisting equipment above 15t should be selected, but the requirements of net lifting weight and lifting height of rammer should be considered as far as possible, and devices should be set to prevent the boom from tilting backward during ramming.

3.2, hook

It is required to have sufficient tensile strength, and the hook will not slide when lifting. The hook is flexible and can keep the rammer landing smoothly. In addition, the hook is convenient, fast and fast.

3.3. Rammer

The hammer weight of dynamic compaction foundation can be 10~40t, and the bottom method should adopt ring or combined figure. The raw material of the rammer is preferably stainless steel casting. If the specification limits, the carbon steel plate shell can be filled with concrete. The bottom of the rammer should be symmetrically set with a number of φ250~300mm and the wall of the whole line through the exhaust air outlet, in order to facilitate the rammer to touch the ground when the pit bottom steam quickly discharged to reduce the adsorption of the pit bottom when the hammer. The hammer bottom area should be established according to the characteristics of the soil. For sandy soil and sand gravel backfilling, the bottom area of 2~1m2 is more appropriate. For general cohesive soil, 3~1m2 is recommended. For silt sand, 4~6 ㎡ is recommended.

3.4, auxiliary industrial equipment

Excavators, small road rollers, rammers, etc. are used for ramming money, leveling and compaction after ramming, and leveling of sand and gravel, and filling of roadbeds.

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Overview of dynamic compaction foundation

1. Advantages: The mechanical energy of one-time tamping is large, and the foundation can be reinforced in many aspects according to the control of tamping point, density and tamping method. After reinforcement by dynamic compaction foundation engineering, uneven foundation settlement can be eliminated. The mechanical energy of one-time tamping on the construction site is easy to control, so that a foundation with uniform compactness can be obtained.

 

2. Disadvantages: At present, there is no sound basic knowledge and scheme design calculation method; Mechanical equipment and equipment characteristics are required for reinforcement in many aspects. Vibration and noise are large, urban and rural population are heavily polluted areas, and building structures are not suitable for heavy pollution areas.

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