Local Stability of End-suspended Piles in Ultra-deep Foundation Pits

doi:10.11988/ckyyb.20240025

Abstract

Abstract:

At present, the reserved rock shoulder width of end-suspended piles and the embedded depth of support piles in foundation pits are mostly determined from the impact on internal forces and deformations of the upper support structure. This approach often overlooks the local stability issues near the bottom of the support structure. Based on the ultra-deep shaft project of the Pearl River Delta Water Resources Allocation Project, we identified three potential failure modes for end-suspended pile foundation pits with inclined structural planes or fractured rock masses. We employed the limit equilibrium method to calculate the stability safety factor and analyze the impact of various parameters on the safety factor under different failure modes, such as rock layer burial depth, mechanical properties of structural planes, rock shoulder width, and rock shoulder depth. Our findings reveal that the inclination angle of outward-dipping structural planes and the mechanical properties of structural planes or rock masses significantly affect the stability safety factor. This study offers valuable insights for similar projects.

Key words: deep foundation pit, vertical shaft, end-suspended pile, structural plane, limit equilibrium method, safety factor

CLC Number:

TU470地基和基础的理论和计算

SUN Chang-li, CHEN Fu-qiang, LI Zhi-ling, JIA Kai. Local Stability of End-suspended Piles in Ultra-deep Foundation Pits[J]. Journal of Yangtze River Scientific Research Institute, 2024, 41(10): 133-139.

Figures/Tables 15

Fig.1 Schematic diagram of sliding failure along the underlying bedrock structural plane

Fig.2 Schematic diagram of sliding failure along the structural surface of the wall bottom

Fig.3 Schematic diagram of sliding failure along the arc sliding surface of the wall bottom

Fig.4 Profile of typical vertical shaft

Table 1 Mechanical parameters of structural planes in moderately weathered rock masses

序号	岩体	天然重度/ (kN·m^-3)	黏聚力/ kPa	摩擦角 φ/(°)
1	泥岩	25.4	20	14
2	泥质粉砂岩	25.6	50	19
3	砂岩、砾岩	26.0	80	24
4	片麻岩、花岗岩	26.8	200	35

Table 2 Calculation results of local stability of end-suspended piles

序号	岩体	稳定安全系数
序号	岩体	沿下卧基岩滑动K₁	沿墙底结构面滑动K₂	沿墙底圆弧滑动K₃
1	泥岩	1.015	1.019	0.817
2	泥质粉砂岩	1.591	1.501	1.182
3	砂岩、砾岩	2.145	2.006	1.382
4	片麻岩、花岗岩	3.795	3.475	1.587

Fig.5 Horizontal displacement of support structure versus depth

Fig.6 Vertical displacement of support structure against time

Fig.7 Relationship between stability factor of safety and upper overburden thickness L1

Fig.8 Relationship between stability factor of safety and structural plane inclination β

Fig.9 Relationship between stability factor of safety and internal friction angle φ of structural plane

Fig.10 Relationship between stability factor of safety and rock shoulder width b of failure mode 2

Fig.11 Relationship between stability factor of safety and embedment depth H of failure mode 2

Fig.12 Relationship between stability factor of safety and rock shoulder width b of failure mode 3

Fig.13 Relationship between stability factor of safety and embedment depth H of failure mode 3

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