Effect of Solidified Depth on the Vertical Compressive Bearing Characteristics of the Soil Continuously Solidified Pile Group Foundation

Abstract

To meet the ultra-high bearing capacity design requirements of pile foundations under geological conditions without a good holding layer, we invented a new type of group pile foundation with the soil continuously solidified between piles (hereinafter referred to as the SCS group pile foundation). Considering the solidified depth as a key influencing factor, the vertical ultimate compressive bearing capacity, load transfer law, and damage pattern of the soil around the continuously solidified group pile foundation were investigated using an indoor half-model test. The results revealed that the setting of the continuously solidified part has a significant effect on its compressive bearing characteristics. The ultimate compressive bearing capacity of the SCS group pile foundation was increased by four to nine times compared with the traditional group pile foundation. When the pile spacing is 4–6D (D = pile diameter), designing a continuously solidified depth greater than 14D is recommended. Except for the solidified depths of 2D and 18D, the lateral resistances of the other model piles first increase and then decrease with increasing depth. The maximum values were located at the continuously solidified part and were obviously larger than those of the other pile sections. The maximum pile lateral frictional resistance was provided at the maximum depth of the continuously solidified part. After setting up the continuously solidified part, none of the bearing capacity of the pile ends exceeded 5%. The bearing capacity of the SCS group pile foundation was mainly shared by the continuously solidified part and the pile lateral frictional resistance. For the same pile spacing, the high strain damage zone of the soil at the bottom of the continuously solidified 2D–14D foundation was “abacus bead”; when the burial depth of the continuously solidified part reached 18D, the foundation soil exhibited “inverted bowl” damage.

Model Test Study on the Vertical Uplift Bearing Characteristics of Soil Continuous Solidified Pile Group Foundations

“…According to the research of the "Technical Code for Building Pile Foundation" (JGJ94-2008) [42] and Sun et al [30], the theoretical formula of the ultimate uplift bearing capacity of the new pile type is derived as follows:…”

“…According to the research of Song, Sun et al [30][31][32][33], this study used a half-model test and the sand rain method [34,35] to control the falling sand height to 120 cm (approximately 0.95 in density) to establish the model foundation.…”

“…The completed model pile is shown in Figure 2. The test device includes a load sensor, displacement sensor, data acquisition instrument, and strain gauges [30,32,33], as shown in Figure 3.…”

“…Such studies are based on the concept of soil reinforcement between piles and propose a new type of pile group foundation with the soil continuously solidified between piles (hereinafter referred to as the SCS pile group foundation) [29,30]. The continuously solidified member (CSM) is used to strengthen the soil layer between piles through foundation treatment methods such as MJS construction method, forming a continuous high-strength entity in the horizontal direction.…”