Abstract
A model test system for vertical bearing characteristics of the jacked piles in saturated soil foundations under excavation has been introduced. The system device comprises a soil pressure loading system, a model pile loading system, a soil vacuum saturation system, a model box, a model pile, and a control and data acquisition system. The soil vacuum saturation system designed for the model box of this test device can ensure that the saturated soil in the model box can reach a higher degree of saturation. Loading and unloading were conducted on the soil sample in the model box through the soil pressure loading system to simulate the soil excavation so that the soil sample and that in the field have the same stress state and history. The soil consolidation pressure, pile jacking pressure, pile tip force, soil consolidation settlement, and pile displacement at the top were collected and monitored in real time through the control and data acquisition system. This device is used to conduct an experimental study on the bearing characteristics of the jacked piles in saturated silt foundations under excavation. The results indicate that the static load test increases the residual pressure on the tip of the jacked pile while also increasing soil stiffness at pile tip and ultimate tip resistance, thereby increasing the pile top stiffness and ultimate load-carrying capacity. However, when the jacked pile is left undisturbed for the same time, the static load test on the jacked pile does not affect the pile skin friction resistance. There is a better linear relationship between the pile skin friction resistance and the undrained shear strength of the soil under the corresponding stress path during the static load test of the normally consolidated soil and the jacked pile after overburden pressure unloading. There is a good linear relationship between the ultimate resistance and the undrained shear strength of the soil under the corresponding stress path in pile sinking, normally consolidated soil, and during the static load test on jacked pile after unloading.
Highlights
IntroductionIn the construction of underground engineering structures or substructures of high-rise buildings, pile foundation is often set first. en, the foundation pit (soil around the pile) is excavated, and the elevation is designed. e construction is carried out upward successively (the engineering piles are gradually loaded with the construction of buildings). e excavation unloading of soil around the pile will have a greater influence on the foundation pile at the pit bottom [1,2,3,4]
In the construction of underground engineering structures or substructures of high-rise buildings, pile foundation is often set first. en, the foundation pit is excavated, and the elevation is designed. e construction is carried out upward successively. e excavation unloading of soil around the pile will have a greater influence on the foundation pile at the pit bottom [1,2,3,4]
(4) After the first static loading test was performed on the model pile and the model pile was left undisturbed for two days, the overburden pressure of the soil sample was unloaded to the target value through the software control system. e change of the residual pressure on the pile tip was monitored to ensure that the residual pressure on the pile tip was stabilized before the overburden pressure of the soil was unloaded
Summary
In the construction of underground engineering structures or substructures of high-rise buildings, pile foundation is often set first. en, the foundation pit (soil around the pile) is excavated, and the elevation is designed. e construction is carried out upward successively (the engineering piles are gradually loaded with the construction of buildings). e excavation unloading of soil around the pile will have a greater influence on the foundation pile at the pit bottom [1,2,3,4]. Chen et al [9] simulated the soil excavation around piles by heaped loading and unloading of soil and conducted a model test study on the vertical compressive bearing characteristics of a single pile. The experimental studies on the vertical bearing characteristics of jacked piles under the excavation unloading of soils are sparse. 2. Description of the Test System e model test system for studying the vertical bearing characteristics of jacked piles under excavation includes a vertical soil pressure loading system, model pile loading system, soil vacuum saturation system, model box, model pile, and control and data acquisition system. E pile sinking test and vertical bearing characteristic test can be carried out on the jacked pile under different working conditions by applying different stress paths to the soil in the model box. (4) e test system is controlled by software and operated automatically, which has higher accuracy and can perform data feedback and data storage in realtime
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