Effect Analysis of Supporting Structure and Surface Settlement on Deep Foundation Pit by Rainstorm: A Case Study in Zhengzhou
Abstract
:1. Introduction
2. Engineering Overview
2.1. Engineering Background
2.2. Risk Analysis of 20 July Heavy Rainstorm in Zhengzhou
2.3. Analysis of Monitoring Data
3. Establishment of the Numerical Model
3.1. Basic Assumptions of Model Establishment
- (1)
- The ground surface at the back of the supporting structure is horizontal and the strata are evenly distributed;
- (2)
- The soil is isotropic;
- (3)
- The reinforcement and concrete of the supporting structure are considered as a whole, and the bored pile is simplified as a 0.9m thick diaphragm wall for simulation according to the idea of the equal cross-sectional moment of inertia;
- (4)
- The supporting structure of the foundation pit is an ideal elastic body, and the leakage between retaining piles is not considered;
- (5)
- The foundation pit is divided into four times of excavation, the first excavation to the first strut 0.5 m, the second excavation to the second strut 0.5 m, the third excavation to the third strut 0.5 m, and the fourth excavation to the bottom of the pit.
3.2. Determination of Model Size and Parameters
3.3. Selection of Soil Constitutive
3.4. Analysis of the Simulation Results
4. Deformation and Stress Analysis of Foundation Pit before and after Rainfall
4.1. Deformation and Stress Characteristics of Foundation Pit Excavation
- (1)
- Area Ⅰ, In the Rankine active earth pressure zone, the soil displacement is mainly manifested as the squeezing into the pit and the soil subsidence;
- (2)
- Area Ⅱ, In the Rankine passive earth pressure zone, the soil displacement in this area mainly shows upward uplift due to the influence of excavation unloading and extrusion of the supporting structures on both sides.
4.2. Deformation and Stress Analysis of Foundation Pit after Rainfall
5. Analysis of Effect Factors of Rainfall on Foundation Pit
5.1. Effect of Soil Softening
5.2. Effect of Water Load
5.3. Effect of the Steel Strut Falls Off
5.4. Effect of Foundation Pit Backfill Water
5.5. Effect of Rising Water Tables
5.6. Analysis of Prevention and Control Measures
6. Conclusions
- (1)
- The results of simulating the rainfall effect on the deep foundation pit by the finite element software was good, the stress and strain states of the soil and supporting structure could be obtained in the simulation, while the results of the simulation were in good agreement with the monitoring data, which shows that the reliability of the numerical simulation and the calculation results can provide a reference for similar projects.
- (2)
- The 20 July heavy rainstorm in Zhengzhou city caused the typical foundation pit to undergo a signification change in the supporting structure and surface settlement. Under the failure of the first- and second-layer steel strut, the soil subsidence range had a signification increase. Under the failure of the third layer steel strut, the supporting effect of the supporting structure on the soil weakened, which led to the maximum bending moment and maximum displacement of the supporting structure to increase and move up in difference degrees.
- (3)
- The main factors affecting the deep foundation pit by heavy rain were the steel strut falling off and water filling in the whole pit, while the influence of the rise in the water tables, water load, and soil softening had a low effect. Among them, the backfill water increased the water pressure in the inner side of the supporting structure, which weakened the soil and the water pressure difference on both sides of the supporting structure. This weakened the deformation of the supporting structure and caused the steel strut to fall off; furthermore, the failure of the strut led to a greater deformation of the foundation pit.
- (4)
- When the foundation pit engineering suffers from a rainstorm, there is a positive significance in raising the retaining wall outside the foundation pit to prevent water accumulation. When the water accumulation is too deep, the retaining wall should be broken and guided recharge could weaken the deformation of the supporting structure, but the connection between the steel support and enclosing purlin should be strengthened in time before the recharge.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Monitoring Data | Maximum Deformation/mm | Deformation Rate mm/Day | Working Condition |
---|---|---|---|
July 18 | 10.15 | -- | Rainfall |
July 19 | 10.43 | 0.28 | Rainfall |
Heavy rain, site flooded, foundation pit recharge water | |||
July 23 | 16.73 | 2.10 | Hydrops dissipated |
July 24 | 16.80 | 0.07 | Hydrops dissipated |
July 25 | 17.36 | 0.56 | Hydrops dissipated |
July 26 | 17.20 | -0.16 | Hydrops dissipated |
July 27 | 17.94 | 0.74 | Foundation pit precipitation |
Strata | |||||
---|---|---|---|---|---|
Miscellaneous fill | 18.00 | 8.00 | 10.00 | 0.32 | 5.50 |
Clayey silt | 18.50 | 13.00 | 22.00 | 0.28 | 6.70 |
Silt | 19.00 | 3.00 | 28.00 | 0.23 | 11.00 |
Silty clay | 19.25 | 21.00 | 13.50 | 0.3 | 13.00 |
Silt | 19.50 | 3.00 | 30.00 | 0.23 | 20.00 |
Fine sand | 20.00 | 2.00 | 32.00 | 0.23 | 25.00 |
Silty clay | 20.50 | 31.50 | 15.60 | 0.28 | 18.00 |
Step | Time | Rain Progress |
---|---|---|
Step 1 | July 17 to 16:00 on 20 July | Soil softening |
Step 2 | 16:00 on 20 July to 20:00 on 20 July | Water load is generated on the surface |
Step 3 | 20:00 on 20 July to 04:00 on 21 July | Foundation pit recharge water |
Step 4 | 04:00 on 21 July to 04:30 on 21 July | Steel strut is shedding |
Step 5 | 04:30 on 21 July to 06:00 on 21 July | Fill the foundation pit with water |
Step 6 | 06:00 on 21 July to July 23 | The groundwater is rises and the water load dissipates |
Working Condition | Maximal Displacement/mm | Displacement of Pile Top/mm |
---|---|---|
Working condition 1 | 11.05 | 2.33 |
Working condition 2 | 11.30 | 2.93 |
Working condition 3 | 11.00 | 2.35 |
Working condition 4 | 11.21 | 2.46 |
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Wang, X.; Xiao, J.; Zhang, T.; Lin, Y. Effect Analysis of Supporting Structure and Surface Settlement on Deep Foundation Pit by Rainstorm: A Case Study in Zhengzhou. Water 2022, 14, 3654. https://doi.org/10.3390/w14223654
Wang X, Xiao J, Zhang T, Lin Y. Effect Analysis of Supporting Structure and Surface Settlement on Deep Foundation Pit by Rainstorm: A Case Study in Zhengzhou. Water. 2022; 14(22):3654. https://doi.org/10.3390/w14223654
Chicago/Turabian StyleWang, Xiaorui, Jianhang Xiao, Tao Zhang, and Yunhong Lin. 2022. "Effect Analysis of Supporting Structure and Surface Settlement on Deep Foundation Pit by Rainstorm: A Case Study in Zhengzhou" Water 14, no. 22: 3654. https://doi.org/10.3390/w14223654