A skyscraper rises from level ground, and its foundation is paramount. As a crucial part of civil engineering, the quality of pile foundation construction directly impacts the integrity of the entire building, highway, or railway embankment. Today, beyond fundamental construction techniques, it is essential to focus on integrating advanced technology into pile foundation engineering.
Information Technology Empowerment
Pile Foundation Information Construction Management System
The pile foundation management system is comprised of both web and mobile platforms. It streamlines construction planning, enabling engineers to proceed in an organized manner, guided by predefined plans and reference indicators. Intelligent sensing devices on site provide detailed records of each construction phase. The vast engineering data collected serves as a solid base for decision-making, allowing managers to monitor project progress comprehensively, make efficient choices, and pave the way for smart construction.
Pile Foundation Construction Management System
This intelligent system was developed to address the challenges of monitoring construction processes, especially in soft foundation treatment. It enhances process management by improving continuity, accuracy, and real-time supervision.
The system collects various raw data during construction, such as “high-precision pile position”, “verticality deviation”, “drilling depth”, “drilling rate”, and “drilling current”. After thorough processing, this information is displayed in real-time on industrial-grade vehicle terminals, helping operators achieve more precise construction and increasing the qualification rate of completed piles.
Resonance-Free Hydraulic Vibration Hammer
The Dutch ICE hydraulic vibration hammer offers safety, efficiency, low cost, and wide applicability. Additionally, its software and control systems are designed for user-friendliness: the electrical part uses CAN bus for intelligent control, human-machine interface display, fault code indication, automatic alarms, and multilingual options. Traditionally, selecting the right equipment in foundation construction is challenging because soil conditions vary. To address this, engineers have integrated complex calculations into the software. Customers simply enter geological and pile specifications, and the software automatically calculates resistance and amplitude for each stage of pile sinking, recommending the optimal model.
BIM + Cloud Platform
(1) Web Platform
After creating a lightweight BIM model for the pile foundation, the “seven steps” of pile quality control are integrated with the model to generate corresponding data forms. Quality management throughout the entire pile foundation process is tracked using the “BIM model + big data” approach. This data-driven method enhances quality management and sets the groundwork for standardized pile management. Through big data analysis on the web, once the seventh step—initial grouting—is completed, the pile is automatically marked green, indicating completion.
(2) Mobile App
The mobile app complements the web platform, offering similar features with greater convenience and efficiency. Its main function is to enable onsite managers to promptly access necessary data and initiate quality or safety improvement tasks in real time.
(3) Cloud Platform Testing and Optimization
Project management informatization requires collaboration among all parties. Throughout the development of the Hangshi Dayun platform, the Information Center team, including Zhang Chengtao and Chen Min, conducted extensive testing before each feature launch to ensure optimal performance. However, initial development and testing are only the beginning. Continuous optimization during use is crucial. As the “seven steps” of pile quality control were implemented via the cloud platform, both the EPC project department and the construction unit provided valuable feedback and suggestions. The Information Center responded effectively, further optimizing the product and advancing standardized management for pile foundation projects.
Key Construction Points
01
Bored Pile – Casing Embedding
Construction Steps
1. Drilling with Submersible Drilling Rig
A submersible drilling rig is a rotary machine with a waterproof motor and variable speed mechanism attached to a sealed drill bit. It is positioned with a pile frame and drill rod, then submerged in water or mud to drill. Mud is injected, and cut soil and slag are removed from the hole using positive or reverse circulation.
There are two types of slag discharge methods:
(1) Positive Circulation: The drill bit cuts the soil into slurry, which is pumped under high pressure to the drill bit and sprayed out, carrying the slurry upwards and discharged from the casing.
(2) Reverse Circulation: The sand and gravel pump is inserted with the main unit, and cuttings are pumped out directly with the mud.
2. Impact Drilling for Hole Formation
(1) The impact drill raises a heavy bit (impact hammer) by frame and winch, then releases it to cut and break the rock or soil into a hole.
(2) Impact drill bits come in cross-shaped, I-shaped, herringbone, etc., with cross-shaped being most common.
(3) Steel casing should be buried before drilling, and wall protection materials prepared.
(4) Once the rig is positioned, align the hammer with the casing center. Start with a short drop (0.4–0.8 m), using stones and mud for wall protection, until the casing sinks 3–4 m. Then increase drop (1.5–2.0 m) and switch to normal impact. Monitor mud density at all times.
(5) Regularly check the steel cable, machine tightness, and steering to prevent accidents.
Hole Cleaning
(1) Hole inspection uses detectors to check the position, diameter, depth, and condition. Cleaning removes sediment and floating soil from the bottom to reduce settlement and increase bearing capacity.
(2) For stable holes, an air suction mud machine with 0.5 MPa pressure can be used, flushing until clear water is seen.
(3) For less stable holes, use mud circulation or suction tube extraction. After cleaning, mud density should be between 1.15 and 1.25.
Concrete Pouring
(1) Pouring under mud wall protection is done in water or mud, known as underwater concrete pouring.
(2) Underwater concrete should be one grade stronger than the design strength and have good workability, with mix proportions determined by testing.
(3) The conduit method is commonly used for underwater pouring.
(4) First fill the conduit and funnel with concrete, making sure the conduit end is at least 0.8 m below the concrete surface. Then cut the wire holding the water stop, allowing the concrete to flow under its own weight.
02
Immersed Tube Bored Pile
1. Pile Driving Method
Immersed piles are installed by sinking a reinforced concrete pile tip (or steel shoe) or steel pipe with a flap-type shoe into the soil using a hammer or vibrator. After forming the pile hole, the reinforcement cage is inserted, concrete poured, and the casing removed. The vibration during pipe extraction compacts the concrete, forming the cast-in-place pile.
2. Classification of Piles
Hammers are used for sinking and extracting pipes—these are hammer-driven piles. Vibration is used for vibrating immersed tube piles.
3. Sequence of Pore Formation
During construction, compaction and vibration affect the soil. The sequence of drilling should be planned based on site conditions:
– Drill at intervals of one or two pile positions.
– For industrialized construction, form adjacent pile holes before or after the concrete sets.
– For piers with more than 5 piles, drill the middle pile first, then the outer ones.
4. Construction Techniques
To improve pile quality and bearing capacity, techniques include single extraction, compound extraction, and flip insertion.
– Single Extraction: Vibrate for 5–10 seconds for each 0.5–1.0 m lift, then repeat until fully extracted.
– Compound Extraction: Perform two consecutive single extractions in the same hole, or locally as needed. Ensure pipe axes align, and complete before the concrete sets.
– Flip Insertion: For every 0.5 m lift, insert pipe 0.3 m down, repeating until removed.
1. Hammer-Driven Cast-in-Place Pile
(1) Place a washer at the pile tip-pipe interface to prevent water ingress and serve as a buffer. Start with a low hammer, check alignment, then proceed.
(2) Before extraction, hammer or vibrate the casing to confirm concrete flow.
(3) Fill pile pipe with concrete as much as possible, pull out evenly, keep continuous hammering, and control speed (not more than 1 m/min in soil, 0.8 m/min at soil boundaries).
(4) Do not interrupt pouring or tapping until the pipe is extracted to the pile top elevation. Keep the concrete inside slightly above the ground until fully extracted.
(5) For piles spaced less than 2 m or five times the pipe diameter, use jumping construction. The middle pile can be driven only after adjacent concrete reaches 50% strength.
2. Vibration Immersed Tube Cast-in-Place Pile
(1) Uses vibrators or impact tubes for installation.
(2) The process: position driver, sink pipe, load material, extract pipe.
(3) Common defects and solutions:
Necking
– Necking is when the pile diameter is smaller than design.
– In silt or soft soil, compressed wall pressure can create necking during extraction.
– Extracting too quickly, insufficient concrete, or poor mix can also cause necking.
– Solution: Maintain concrete surface above ground, control concrete slump to 50–70 mm, use repeated extraction, and strictly control extraction speed.
Broken Pile
– Broken pile refers to partial breakage or lack of concrete in the pile.
– Can result from piles being too close, and adjacent piles are not fully cured.
– Solution: Keep center-to-center distance at least 4 times the pile diameter. Determine sequence and route to minimize impact on uncured piles. Use jumping method or wait until concrete reaches 60% strength before proceeding.
Suspended Pile
– Suspended pile occurs when concrete at the pile bottom is isolated or soft, not fully embedded in the soil.
– Causes include high groundwater pressure, damaged pile tip, large valve gap, or improper extraction.
– Solution: Use slow, dense extraction at the start, partially flip and insert the pile tip, then proceed normally. Use high-performance lining materials at the interface to prevent water and mud infiltration.
Excessive Concrete Usage
If concrete consumption is more than double the normal amount, there may be cavities at the hole bottom or soil disturbance in saturated silt. Before construction, investigate site geology thoroughly. For saturated silt, drive test piles first. If overuse is detected, consult the design unit and consider alternative pile types.
Quality Inspection
1. Static Load Test Method
The static load test is regarded as the most direct and reliable method for evaluating the vertical bearing capacity of foundation piles. It is simple, safe, and reliable. However, sometimes inspectors might overlook the benchmark piles, leading to insufficient pile depth or displacement during testing.
2. Core Drilling Method
Also known as the pile core testing method, this approach is scientific and practical, and is widely used for detecting cast-in-place piles. It determines pile length, concrete strength, and sediment thickness at the pile bottom, as well as identifying rock and soil properties at the pile tip.
3. Low Strain Method
The low strain method (or reflection wave method) uses a hammer or force rod to strike the pile top, generating a stress wave that travels down the pile. Sensors detect reflections to analyze pile integrity and locate defects. Key points:
– Test 3–4 points for piles with 120 cm diameter or more.
– Hammering point should be 20–30 cm from the sensor.
– Use proper bonding agents (paraffin, butter, putty) to ensure dry pile heads.
– Take at least 10 readings per pile and confirm waveform consistency.
4. High Strain Method
The high strain method applies dynamic loads to assess pile bearing capacity. Based on one-dimensional rod wave theory, it is widely used in China and abroad. It helps determine if the pile meets vertical bearing requirements and can supplement low strain tests to identify and evaluate defects.
5. Acoustic Transmission Method
This method embeds two or more acoustic tubes in the pile to transmit and receive sound waves, making it an important tool for integrity testing of cast-in-place piles. It is widely used in civil, water conservancy, power, industrial, and railway construction. Compared to other methods, it offers comprehensive and detailed detection with minimal limitations, although wave diffusion and reflection can affect results.
Source: Architectural Technology Magazine
Must log in before commenting!
Sign Up