What is the HUW Method

The HUW method (Chinese: 型钢钢板连续墙, English: H steel U steel continuous wall) is a new technique that can replace Larsen steel sheet piles, SMW piles, bored piles, and other foundation pit support methods. It is a steel wall formed by driving H-beams with interlocks and U-shaped steel sheet piles with interlocks through a positioning frame and connecting them into an integrated wall.

In recent years, through extensive practical construction in land and deep-water deep foundation pit support projects, and in various deep foundation pit support projects such as building foundations, underpasses, utility tunnels, high-speed railways, and bridges, the HUW method has fully demonstrated its excellent characteristics: safety, environmental friendliness, energy saving, high efficiency, and high water tightness.‍

Method Overview

1. Background Technology

With the rapid development of the national economy and the rapid growth of construction engineering, foundation pit support works in foundation and foundation engineering are the first to bear the brunt. At present, commonly used foundation pit support methods mainly include diaphragm walls, column-type bored piles, SMW method, Larsen steel sheet piles, cement-soil mixing piles, and reinforced concrete sheet piles. Most of these methods require large amounts of cement during operation or generate large amounts of mud during construction, causing great impact on the environment and consuming large amounts of resources. In response to this situation, through extensive basic engineering practice, and in view of the advantages and disadvantages of foundation support structure engineering technologies such as the SMW method, bored piles, steel sheet piles, and diaphragm walls, combined with the advantages of some advanced foreign foundation support structure engineering, our company has researched and invented a steel H-beam and U-shaped steel sheet continuous wall.

2. Technical Features

This technology is safe, clean, energy-saving, low-carbon, and environmentally friendly, with recyclable resources and controllable pollution emissions. The scheme is economical and reliable, and it is a green foundation pit support technology featuring high efficiency, energy saving, environmental protection, and sustainable development. Through extensive scientific verification, this technology can completely replace the above traditional support structure methods, with advantages such as short construction period, low construction cost, small environmental impact, and good safety performance.

3. Efficiency Features

Compared with column-type bored piles, this technology saves more than 20% in construction cost and more than 50% in construction period.

4. Flexibility

For general geological conditions, the HUW method can be designed for excavation depths up to 13 meters. If an ultra-deep foundation pit is required, 350*350 H-beams can be inserted between the U-shaped plates, and the designed excavation depth can reach 20 meters.

Design Diagrams

Parameters and Application Scope

For soft soil and general non-hard soil layers, combined with a corresponding support system, the foundation pit excavation depth is greater than 8.0 meters. The construction site occupies a small area, making it suitable for narrow site construction. Due to the large stiffness of H-shaped piles, the deformation of the foundation pit is smaller than that of general steel sheet piles. There is no spoil or mud pollution, and all materials can be recycled. The cost is close to that of the SMW method, and under certain conditions, costs can be saved.

Comparison of Support Schemes

Construction Process and Key Points

1. Process Flow of Steel H-beam and U-shaped Steel Sheet Continuous Wall (On Land)

Survey and setting out, leveling the site, placing the positioning frame for the steel H-beam and U-shaped steel sheet continuous wall + adjusting the level → inserting H-shaped steel plates and U-shaped steel plates → adjusting and fixing → driving U-shaped steel plates and H-beams to the predetermined height → after one group is driven, lifting the positioning frame to proceed to the next section → driving the first section of U-shaped steel plates and H-beams to the design elevation - thus completing the driving of the steel H-beam and U-shaped steel sheet continuous wall - excavation (meeting support construction requirements) → support construction → excavation to the base slab → pouring the base slab structure to the surface - backfilling and removing supports - extracting the piles

2. The steel sheet continuous wall can be constructed not only on land but also on water.

Water construction sequence:

(1) Drive guide piles. Use positioning equipment to control the position of the guide piles. The allowable deviation of the guide piles is within ±2 cm. During driving, the penetration rate is mainly controlled to ensure the force on the guide piles.

(2) Install the positioning frame. Lift the positioning frame into the 4 guide piles, and make the positioning pile fixer at one end clamp onto the already driven steel sheet pile (except for the first time). Use the suspension device to adjust the plane position of the guide frame and the verticality of the guide piles. Finally, tighten the fixing device, and the installation of the positioning frame is completed.

(3) Insert and drive the pile body with a vibratory hammer. Sequentially insert and drive the H-beams and steel sheet piles to the predetermined height above the positioning frame. After one group is driven, lift and remove the positioning frame to proceed to the next section, and re-drive the steel sheet piles and H-beams to the design height.

3. Construction Method:

(1) Survey and positioning, place the positioning frame for the steel H-beam and U-shaped steel sheet continuous wall;

(2) Use a crane to lift the pile body into the guide frame;

(3) Adjust the fixing device on the positioning frame to fix the pile body;

(4) Use a crane to lift the vibratory hammer and clamp the pile body;

(5) Start the hydraulic clamp switch of the vibratory hammer, clamp the pile body, and make fine adjustments to the pile position;

(6) After confirming that the pile position error is within the allowable range, start the vibratory hammer and use a gradual acceleration method to sequentially sink the piles to the predetermined height above the positioning frame;

(7) After one group of pile bodies is driven, lift and remove the positioning pile guide frame to proceed to the next section, and then re-drive the previous group of pile bodies to the design height.

4. Verticality Control of the Steel H-beam and U-shaped Steel Sheet Continuous Wall

When placing the positioning frame, use two sets of levels on the diagonal corners of the positioning frame and hydraulic jacks to keep the positioning frame horizontal and vertical, with the error controlled within 3 mm. After adjusting the positioning frame, fix it. Lift the H-beam into the positioning frame, adjust the fixing device in the positioning frame, and maintain the verticality of the H-shaped steel plate.

Advantages

1. Cost Saving

Compared with traditional foundation pit support methods such as steel sheet piles, SMW method, and bored piles in deep-water foundation pits, this process can save 5% to 20% in cost.

2. Shortened Construction Period

The HUW method uses a fully automatic leveling positioning guide frame. Piles are first fed and then driven by a vibratory hammer, so the daily construction progress can be ensured at more than 20 linear meters. Compared with the SMW method and bored piles, the construction period can be shortened by more than 30 days.

3. Convenient Material Sourcing

Since the materials used in the HUW method have relatively simple structures, mainly domestic steel such as H-beams, 14mm coiled plates, 60*10 seamless steel pipes, and Φ28 round pipes can be processed and used, so material sourcing is very convenient.

Material picture‍

Construction Photos

Driving H-shaped piles in the guide frame

H-shaped piles driven to the predetermined position

Construction site

Pile sealing completed

Excavation and installation of steel supports

Effect after support excavation

Pile extraction operation

Water construction site

Utility tunnel construction example

Summary