Foundations have but one purpose: providing bearing capacity for the load of the structure. Calculating the bearing capacity, and right sizing the design is one of the main tasks of foundation design.

[Right sizing the length, diameter, and number of piles]. Shorter and fewer piles will minimize material cost and construction time.

In the city of Shanghai, a number of elevated highways have used steel pile foundations instead of in-situ bored pile foundations. As the steel pile foundation method is relatively new, scientific research projects have been carried out in recent years to better understand and optimize the method:

*  It has been shown that the bearing capacity of vibrated steel pile foundations improves over time. In many instances the soil will be more tightly packed after the soil has settled, the bearing capacity exceeds the original state of the soil prior to piling. There have been numerous studies carried out in Shanghai to establish the best practice for determining the settlement time, and the method has been included in the latest highway building standard DG/TJ 08-2160-2021 Technical Standard for Prefabricated Bridge.

*  The settling of the ground can be optimized through control of the frequency and moment of the vibro hammer bearing capacity. ICE has published a piling protocol to operate the vibratory hammer to achieve controlled pile driving results with high frequency variable moment vibratory hammers.

*  Studies have shown that adding elements to the pile to increase surface area, such as adding fins have shown no effect on bearing capacity. Installing cross plates inside the pile create a soil plug and stops the pile from penetrating the soil.

*  Shanghai Tongrenli  has patented a method “Steel pipe pile grouting device” for grouting piles from the inside to allow shorter pile lengths to attain the required bearing capacity. This is a promising technology as working this way further reduces the impact of the foundation on the environment, while reinforcing the benefits of the vibro driving (fast) and steel foundations (pile integrity is 100%).

In brief this is how the Tongrenli method works:

For grouting solutions the pile tip must enter a sand layer as this is where the grouting impact is most pronounced. In Shanghai this is the 7th soil layer. The patented technology (ZL 2022 2 0421736.6) prescribes running a grouting channel through the interior of the steel pile. The grout is injected at the tip of the pile where it increases soil cohesion, improving the strength of the soil and rapidly increasing the bearing capacity of the pile foundation.

Whether you are a foundation designer, city-leader, or construction company, we would love to hear from you so we can share our passion for steel foundations installed by resonance free vibratory hammers! Get in touch with us to have your questions answered.