Hydraulic vibrating hammer cooperating with rotary drilling machine for the whole pile casing method and the secant pile method.
Hydraulic vibrating hammers have been widely used in pile foundation construction, especially in the installation and extraction of steel sheet piles. In fact, another major application of hydraulic vibrating hammers is in pipe pile construction, especially for various types of steel pipe piles. These devices are often paired with rotary drilling machines to complete full casing construction and secant pile construction. In developed countries and some countries in the Middle East, slurry-supported bored piles are not allowed, thus requiring the use of full casing methods for most rotary drilling operations. With China's increasing emphasis on environmental protection and pile quality control, the full casing method is gaining more popularity, and hydraulic vibrating hammers are being used more frequently along with rotary drilling machines in pile foundation projects.
I. Bored Piles:
Piles in pile foundations are generally divided into bored piles and precast piles. Currently, bored piles account for approximately 70%-80% of the pile foundations in China, with a portion completed by rotary drilling machines and another portion by positive and reverse circulation drilling machines. In China, rotary drilling machines typically use slurry-supported methods for hole formation, but this practice is prohibited in developed countries, where full casing (also known as Benoto) methods are generally adopted.
II. Wall Protection Methods:
Rotary drilling machines generally use slurry to protect the wall during drilling, but it is necessary to install steel casing in the first few meters to ensure hole guidance and verticality. The main functions of the casing are: accurate positioning, drilling guidance, protecting the hole opening, preventing ground debris from falling into the hole, isolating the water outside the hole, maintaining slurry water level (pressure) to prevent collapse, controlling the pile top elevation, preventing sediment from flowing back during drilling, and maintaining the water level inside the hole higher than the construction water level to stabilize the wall. Depending on the length of the casing and geological conditions, there are several methods for installing and extracting the casing:
(A) Rotary Drill Power Head Self-Pressure Method
(B) Casing Driver Method
For steel casings exceeding 10m with strict verticality requirements, a casing driver connected to the rotary drilling machine is generally used for assistance. Generally, domestic rotary drilling machines rarely come equipped with casing drivers, while foreign brands such as Bauer, Soilmec, and Casagrande can be equipped with casing drivers upon request. Currently, domestic manufacturers like Sunward Intelligent and Jintai also offer rotary drilling machines with casing drivers. However, in hard geological conditions or when the casing diameter exceeds 2 meters, the casing driver may have difficulty functioning effectively. Additionally, due to the limited torque and pressure capacity of the casing driver itself (the drilling machine requires an additional 100 ton-meters of torque for every 10cm increase in hole diameter), it may have difficulty operating in extremely hard geological layers and extracting the casing.
(C) Excavator Hammer Method
(D) Vibrating Hammer and Pipe Jacking Machine Method:
When rotary drilling machines encounter muddy, sandy, high groundwater content, or karst geological conditions, they may adopt the full casing method for construction, also known as the Benoto method for bored piles.
Benoto Pile Construction Method, also known as the full casing method, utilizes a shaking device (or rotating device) to significantly reduce the frictional resistance between the steel casing and the soil layer. As the casing is shaken (or rotated), it is pressed into the soil while the grab bucket is used to excavate the soil until the casing reaches the bearing layer at the bottom of the pile. After excavation, the depth is measured and the bearing layer is confirmed. The loose soil at the bottom is then cleared. Once the hole is formed, the reinforcement cage is placed, and a tremie pipe is erected in the center of the hole. Finally, concrete is poured to form the pile. The Benoto method is essentially a grab bucket follow-pipe drilling method. The equipment used for this method is called a full casing drilling machine.
Introduction to the Method:
Due to its excellent environmental protection effects (low noise, minimal vibration, no slurry pollution or discharge), and civilized construction site, the Benoto pile method is widely adopted both domestically and internationally. In Hong Kong, this pile type accounts for approximately 45% of the market share. In Kunming, Wenzhou, and Beijing, over ten construction sites have successfully employed this pile type. Since 2001, in 13 subway stations in Shenzhen, Nanjing, Hangzhou, and Tianjin, the Benoto method using domestic full casing drilling machines has successfully replaced underground diaphragm walls, significantly reducing construction costs for project owners.
Advantages of the Method:
Compared to slurry-supported drilling, impact drilling, and other large-diameter bored pile construction methods, the full casing method has the following advantages in hole formation and pile construction:
A. Excellent environmental protection: Low noise, minimal vibration; no slurry use,
Construction Equipment
For pile construction with full casing, the general approach can be to utilize the pile casing driving machine (also known as auger pile driver) and vibratory hammer in combination with rotary drilling machines. Below, we will focus on introducing the pile casing driving machine and the vibratory hammer equipment.
- Pile Casing Driving Machine, also known as Full-casing Drilling Machine or Benoit Drilling Machine
This equipment was originally developed and manufactured by the French company Benoit in the early 1950s. Later, Japan, Germany, the UK, Italy, and other countries introduced and developed it. By December 1997, Japan had produced 770 rocking-type full-casing drilling machines and 433 full-rotation type full-casing drilling machines. According to a survey conducted by the Japan Infrastructure Association in 1993 on 101,000 cast-in-place piles by 31 construction companies, the full-casing method accounted for 26%. Currently in Hong Kong, various foundation construction companies have owned no less than 300 full-casing drilling machines, and the market share of pile formation is approximately 45%. China began to introduce this equipment in the 1970s, and in the mid-1990s, a pile foundation company in Kunming first developed the MZ series of rocking-type full-casing drilling machines, also known as pile grinding machines. Later, the Institute of Exploration Technology, Chinese Academy of Geological Sciences, Beijing Sanyi, and other companies began to develop pile casing driving machines. However, due to the high price of this equipment, it has not been widely used in mainland China.
Prospect:
China began to introduce rocking-type full-casing drilling machines in the 1970s, but due to their high price, construction companies seldom adopted them. However, for the special geology of karst landforms in southwest China and the pile foundation construction in vast coastal cities in southern China, this method is indeed required to complete high-quality bored piles. In addition, with the further development of pile foundation equipment and construction methods, China's requirements for construction safety, environmental protection, and quality are getting higher and higher, and the full-casing method will have a good development trend.
- Stratigraphic Adaptability and Characteristics of Vibratory Hammer for Installing Casing
Stratigraphic Adaptability:
For muddy clay prone to shrinkage, loose miscellaneous fill strata prone to collapse, sand layers, and severely permeable strata, long casings or full casings must be used for wall protection. Generally, a vibratory hammer is used to install the casing.
Construction Steps for Installing Casing with Vibratory Hammer: Use a truck crane or crawler crane to suspend the electric or hydraulic vibratory hammer holding the casing. Through high-frequency vibration, the soil around the casing is liquefied, and under the action of the gravity of the casing, the casing is inserted into the soil layer.
Vibratory Hammer Equipment: Vibratory hammer equipment has been widely popularized in China. In Hong Kong and Taiwan, hydraulic vibratory hammers have been widely used due to their light weight, low noise, high exciting force, low vibration, and no need for electricity. In mainland China, due to the lack of mandatory construction standards from design institutes and cost considerations from construction enterprises, hydraulic vibratory hammers have not been well promoted, and electric hammers are used more often. For shorter casings, excavator hammers can be used directly for driving and extracting (the casing generally cannot exceed 10 meters). For casings over 10 meters or hard geological strata, crawler cranes need to be used to suspend the vibratory hammer for construction.
Advantages of This Method:
A. Equipment: The hydraulic vibratory hammer equipment is relatively flexible in application. In addition to being suspended for construction by crawler cranes or truck cranes, it can also be installed on the slide rails of rotary drilling machines, three-point pile drivers, and other equipment to ensure the verticality during construction.
B. Fast installation and extraction of casings, enabling dry hole forming or reducing slurry costs by using natural water during hole formation. However, attention should be paid to adjusting the verticality of the casing during the initial installation.
C. Low construction cost: The hydraulic vibratory hammer equipment is relatively lightweight and can be matched with smaller crawler cranes. If matched with crawler cranes for construction, there is no need to modify the rotary drilling machine or rely on its hydraulic power (the pile casing driving machine needs to be installed on the rotary drilling machine and requires the hydraulic power of the rotary drilling machine).
D. Extremely fast construction speed and strong geological adaptability.
E. Strong pile extraction capability.
Generally speaking, for pile casings with a length
