Settlement reducing piles are a common solution used to mitigate the effects of differential settlement in constructions involving basement slabs and shaft slabs. These piles are specifically designed to reduce the amount of differential settlement that can occur in such structures.
The use of settlement reducing piles in piled shafts and basements has been thoroughly researched and various aspects of their design and implementation have been discussed. It is essential to understand the factors that influence the performance of these piles, such as soil conditions, pile spacing, and the number of piles required for effective settlement reduction.
Proper installation and testing of settlement reducing piles are crucial to ensure their effectiveness. The design process involves a detailed analysis of the soil and structural conditions to determine the required specifications for the piles. Once installed, the piles must be tested to ensure they are performing as intended.
Overall, settlement reducing piles play a critical role in mitigating the negative effects of differential settlement in basement and shaft slab constructions. Proper design, installation, and testing are necessary to ensure the effectiveness of these piles in reducing differential settlement.
Fig.1: Settlement Reducing Pile
Settlement Reducing Piles
What is settlement reducing pile in piled shafts and basements?
Pile reducing settlements is a technique utilized to address the issue of differential settlement of basement slabs and shafts. The name itself suggests that it involves reducing the number of piles in the foundation system. This method is implemented to ensure that the differential settlement of the structure is minimized, thereby preventing any damage that may result from uneven settling.
Fig.2: Use of Piles to Reduce Differential Settlements
Differential settlement can be prevented by using a combination of longer and stiffer piles at the center of a basement or shaft slab, and shorter and more flexible piles around the perimeter. The flexible piles are designed to yield under load, which helps to reduce differential settlement between the central region and the perimeter of the slab. As the outer columns yield, the load is distributed to the stiffer central piles through the slab.
There are other ways to configure piles in order to achieve the same goal of reducing differential settlement. For example, using piles of the same size can work as long as the distance between perimeter piles is increased and the load configuration allows for load redistribution. Another option is to change the geometry of the piles themselves. Soft-toe piles or short, expanded-base piles can be used for the perimeter, while long, straight-shafted piles can be used for the central region of the slab. Soft toes can be achieved by placing loose sand or soil at the base of the bore hole before pouring the concrete. Short, enlarged-base or soft-toe piles will settle more than long, straight-shafted piles for the same loading.
However, it’s important to ensure that the stability of the entire structure is not compromised by the use of settlement-reducing piles. To achieve this, the load should be shared between the raft and settlement-reducing piles. Settlement-reducing piles are said to be most effective when the underlying soil is both stiff and compressible.
Why is the purpose of a pile reducing settlements in piled shafts and basements?
Piles of the same length and diameter are often used to support basements and shafts slabs that carry uniform distributed loads. However, as the loading increases, the deflection of the slab takes on a dished shape, with central piles experiencing greater settlement than those located around the perimeter.
Initially, the slab would support most of the applied loads, but as the quantity of loads increases, the loads imposed on the piles progressively increase as well. The central pile settlement then affects the loads on piles at the center, leading to greater settlement in these areas. This eventually causes the applied load to be redistributed through the slab to stiffer piles located around the perimeter. As a result, greater loads are exerted on these perimeter piles, with around sixty percent of loads being supported by them, while nearly forty percent of the applied loads are carried by central piles.
Differential settlement, caused by this unequal distribution of loads, can be a serious problem that needs to be tackled properly. To address this issue, the use of settlement reducing piles is a suitable solution. This not only solves the problem of differential settlements but also results in a more economical construction.