Speaking of the difficulties in pile foundation construction, what are the current difficulties? What is the basic situation? Below is a summary of relevant content on the difficulties in pile foundation construction by the China editor. The basic situation is as follows:

In order to help enterprise personnel understand the difficulties in pile foundation construction, the editor of Construction Network has compiled relevant materials. The basic content is as follows:

With the increasingly widespread application of pile foundations, various quality problems have emerged during construction, such as necking, broken piles, displacement, inclined piles, and testing issues. We will analyze several points that are most easily overlooked in pile foundation construction.

Measurement and setting out

The main tasks of pile foundation construction measurement in building engineering are: first, accurately set out the pile positions of the building foundation on the ground of the proposed construction area according to design and construction requirements, providing markers for pile foundation construction as the basis for construction according to drawings and guiding construction; second, conduct pile foundation construction monitoring; third, after the completion of pile foundation construction, conduct as-built measurement of the pile foundation to provide pile foundation data for verifying construction quality and for above-ground building construction.

Theoretically, Article 5.1.3 of the Code for Acceptance of Construction Quality of Building Foundation Engineering (GB50202-2002) stipulates that the pile position deviation of driven (pressed) piles (precast concrete square piles, pretensioned prestressed pipe piles, steel piles) must comply with the regulations. For example, for piles with foundation beams, the allowable deviation along the centerline of the foundation beam is 150 mm, and the allowable deviation perpendicular to the centerline of the foundation beam is 100 mm. This article is a mandatory provision of engineering standards and must be strictly controlled. Article 5.4.5 of the code also lists pile position deviation as a main control item in the quality inspection standard for reinforced concrete precast piles, meaning that pile position deviation has veto power over pile foundation quality acceptance. If it exceeds the allowable deviation range, the construction quality is considered non-compliant. Measurement and setting out is the most common issue during pile foundation construction. Generally, if errors occur in measurement and setting out, the treatment methods are to enlarge the pile cap or add piles. However, this not only increases costs but also delays the construction period.

Groundwater issues

When the foundation depth is below the natural groundwater level, the problem of groundwater treatment is often encountered during foundation construction. In pile foundation engineering, groundwater has the greatest impact on the construction of manually excavated piles. There are many feasible methods for groundwater treatment. In terms of dewatering methods, they are generally divided into two categories: water-stop methods and drainage methods. The water-stop method is relatively costly and difficult to construct; wellpoint dewatering is simple and convenient to construct, and its operation technology is easy to master. It is an effective modern construction method and has been widely used.

When the groundwater level is not high, single-pile pumping can be carried out within the pile. When the groundwater level is high, simultaneous pumping from multiple piles can be used to lower the groundwater. If the designed pile depth is not large, wellpoint drainage can be considered around the site. During excavation of manually excavated piles, if fine sand or silty sand layers are encountered, combined with the action of groundwater, quicksand is easily formed, and in severe cases, well leakage occurs, causing quality and safety accidents.

In addition, the influence of groundwater is also a construction difficulty in permafrost foundations. We should adopt different construction methods according to different geological conditions. For example, in winter, we often use the freezing method construction technology. The freezing method uses artificial refrigeration to freeze water in the soil into ice to form a frozen soil curtain, using the artificial curtain structure to resist water and soil pressure and ensure smooth manual excavation. As a mature construction method, the freezing method construction technology has been widely used in urban construction internationally for over 100 years. China has also used the freezing method construction technology for more than 40 years, but mainly for coal mine shaft excavation. Practical experience in construction at home and abroad over the years has proven that the freezing method has the following characteristics: it can effectively isolate groundwater, and its impermeability is unmatched by any other method. The freezing method construction causes no pollution to the surrounding environment, no foreign matter enters the soil, and noise is low. After freezing is completed, the frozen soil wall melts without affecting the underground structures around the building. Freezing construction can be carried out in parallel with pile foundation construction or other processes, effectively shortening the construction period.