Dry method top feed vibroflotation(DMTFV) is the development and extension of the traditional top feed vibroflotation technology. In the process of vibroflotation construction, the traditional high pressure water is no longer used, but the high pressure air is applied instead to assist the penetration and stone column pile making.DMTFV does not need to consume a large amount of water resource, and at the same time does not produce a alrge amount of mud and sewage, so as to achieve the requirement of green construction.

It is also possible to use a small amount of water to facilitate the penetration of soil boring when the depth of boring is large or the strength of underlying soil layer is big. Because the amount of water required is small, the amount of water resource required is not too high and there is not enough mud to reach the ground.

In the projects requiring only dry method technology, DMTFV has the lower cost and higher efficiency compared with that of Bottom feed dry method vibroflotation.

2. Equipment need for DMTFV

1) Dry method vibroflot system (Dry method vibrator, extension tube, damper, hanging head, electric cabinet)

2) Circulating cooling system of vibrator motor

3) Air compressor (above 10m³）

4) Pump

5) Vibroflotation data recorder

6) Supporting machine ( Crane, loader)

3. DMTFV working methodology

1) Preparation for construction

(1) Feeding Material

It is advisable to adopt hard materials such as gravel, pebble,coarse sand and slag, mud content is less than 5% and appropriate gradation is suggested. The particle size range of material is generally 20mm-150mm.

(2) Main construction machines and tools

Dry method Vibroflot: Model selected according to the soil condition and design requirement

Lifting machine: Crawler crane or truck crane or movable pile frame, etc

Other auxiliary equipment: electrical cabinet, air compressor, high pressure pump, loader or small excavator, generator, data recorder etc

(3) Other preparations

Joint review of drawing, technical disclosure, site preparation (electricity, water,road and site formation), pile placement

2) Stone column construction

(1) Trail construction

Before the normal construction, the trail construction should be carried out to determine the construction parameters such as working electrical current, air pressure, vibration holding time and amount of filling.

(2) Construction process

A. Clean the site. Connect the power supply, water resource and measure the pile position

B. Machines are in the place and vibroflot is aligned with the pile point

C. Hole boring

a. Open the air compressor. When high pressure air spray from the outlet of vibrator, start the vibrator and begin the hole boring when vibrator operate normally. Slowly penetrate the vibroflot into the soil, until the design depth.

b. The vibroflot should be in a suspended state in the whole boring process.

c. The boring speed depend on the soil hardness and the type of vibroflot and the air pressure, etc., the maximum speed is generally controlled at no more than 2.0m/min. Commonly, water is not in need. In the case of penetration difficulties, the water pump can be opened and appropriate water pressure can be adjusted ( very low water pressure is in need, a small amount of water can significantly facilitate the penetration). The water pump can be closed to reduce the water consumption when the vibroflot penetrates smoothly.

D. Filling and compaction (pile making): Feed stone into the pore-hole, sink the vibroflot and compact the filling stone. When the electrical current increase to the specified value, lift the vibroflot to continue the next compaction segment. Generally, the length of compaction segment should be less than 50cm. There is no need to open the water pump if there is no difficulty in stone filling during the pile making process.

E. Compaction job should start from the bottom of the pore-hole and goes up segment by segment, and no leakage is allowed in the middle.

F. Continue the stone column making until achieve to the ground.

G. Finish this stone column making

4. DMTFV quality control

1) Quality control measures

According to the soil condition and the design requirements, the quality control factors in DMTFV mainly include:pile position deviation, construction depth, filling quantity and construction parameters,

(1) Deviation of pile position

In order to make the deviation of pile position meet the requirements of specification, the hole deviation should ne controlled when making holes.

(2) Pile length control

After the installation of vibroflot and the extension tube, the steel rules should be used to measure the vibroflot and the tube should be marked with a length of 0.5 meters, so that the operator can control the working depth.

(3) Filling quantity control

During the construction, it is necessary to accurately measure the filling loader and record the actual amount of filling at the same time.

2) Control of construction technical parameters

Construction technical parameters include working current, compaction segment length, air pressure and filling quantity.