Slope Stabilization using Drilled Shafts: Design and Long-Term Monitoring

Transcription

1 Slope Stabilization using Drilled Shafts: Design and Long-Term Monitoring Jamal Nusairat, Ph.D., P.E. E.L. Robinson Engineering of Ohio Co. & Izzaldin Almohd, Ph.D., P.E. Huesker Synthetic GmbH 8/4/2010

2 Presentation Outlines Introduction Geotechnical Analysis Structural Design Instrumentation & Long-Term Monitoring Summary and Conclusions

3 Introduction 1. Slope remediation using drilled shafts 2. Single row of drilled shafts Inexpensive Various techniques and equipments Has been successfully used Simple to design

4 Geotechnical Elements o Geometry o FS improvement o Shaft force o Soil Arching

5 Analysis Methodology Define Geometry Define Stratigraphy and Material Properties Initial Slope Stability Analysis (no stabilization) Determine the need and location of stabilization Elements Assume Shafts diameter, length, and spacing Verify/modify assumed shaft parameters Verify Shaft Structural adequacy (Lateral Analysis)

6 Stability Analysis: Limiting Equilibrium (Method of Slices) n i Potential Slip Surface Slice i + 1 Pile Slice i Slice i - 1 W??? Ni+1 S i+1/fs V i V Vi i-1 H i H i-1 W N i S i /FS V i-1 W V i-2 H i-2 S i-1 /FS N i-1

7 Arching Mechanism Liang and Zeng (2002) Soil Arching S Direction of Moving Soil S S Arching Load ODOT Research Report: Drilled Shaft Foundations for Noise Barrier Walls and Slope Stabilization (2002)

8 UA Slope Program to Design Landslides using Drilled Shafts

9 Initial Slope Stability

10 Slope Stability W/ Drilled Shafts

11

12

13 FS; S/D = 2 FS; S/D = 3 Shaft Force (Kip); S/D = 2 Shaft Force (Kip); S/D = Safety Factor Offset (ft) Shaft Force (Kip)

14 Lateral Analysis Results Assumed Shaft diameter, Reinforcement, and concrete strength. Defined loads from Slope Stability Analysis (UA Slope, FEM ) Run Lateral Analysis (L-Pile, COM624, FB-Multi Pier, FEM ) Results Deflection Moment Shear verify/modify section

15 Perform Lateral Analysis Verify assumed diameter, spacing, and length of shaft

16 Moment Shear

17 Structural Design of Drilled Shaft Net F Shaft Z Lateral Deflection P u 2F Net Shaft Z Slip Surface Design Shear = 1.69 V max Design Moment = 1.69 M max D

18 in D = 60 in 36#11 #6@12 in X X #6@12 in 3 in cover X - X #6@12 in

19 Field Instrumentation and Monitoring JEF WAS MRG HAM

20 Projects Design Summary Site D S/D Lp Lr Fshaft (ft) (ft/ft) (ft) (ft) (kips) # of Shafts Offset (ft) JEF WAS , MRG HAM

21 JEFF

22 Instrumentation Plans/Slope Section S.R. 152 Shaft # ft-diameter Drilled Shafts INC#3 PZ-2 PZ-1 40 ft Shaft #42 42 Drilled Shafts; S/D = 2 on centers The two instrumented drilled shafts (#20 & #21 PZ-3 Lateral Load Test Shafts Work Limits INC#4 250 ft Sliding Zone Limits PZ: Piezometers INC: Inclinometer Offset = 40 ft CL S. R ft 25 ft TOR Existing Slip Surface Water Table PZ-2 (22 ft) PZ-1 (20 ft) INC#3 PZ-3 (23 ft) 20 ft INC#4 A single row of 42 Drilled Shafts: (D = 3. 5 ft; S/D = 2 on centers) INC#1 & #2

23 Instrumentation/Shafts

24 JEF Shaft Properties D (ft) Reinforc. Moment capacity (k-f) Load kips #11 2, Max Deflection (in) Max. Deflection: LPILE Analysis Load : UA Slope Analysis

25 Drilled Shafts Deflection SH#20 SH#21

26 Moments in Shaft #20 and Shaft #21 Moment in SH#20 Moment in SH#21 Max. Moment Observed = 950 ft-kips Nominal Moment Capacity = 2,824 ft-kips A factor of 2.97

27 WAS

28 Shaft Properties D (ft) Reinforc. Moment capacity (k-f) Load kips #14 4, Max Deflection (in) Max. Deflection: LPILE Analysis Load : UA Slope Analysis

29 Up-Slope Soil Movement In-between Down-Slope

30 Drilled Shafts Deflection SH#53 SH#54

31 Moments in Shaft #20 and Shaft #21 Moment in SH#53 Moment in SH#54 Max. Moment Observed = 225 ft-kips Nominal Moment Capacity = 4,918 ft-kips The factor is very high

32 HAM

33 HAM

34 HAM

35 HAM

36 HAM

37 HAM

38 RI over Vermillion River

39 ERI over Vermillion River

40 RI over Vermillion River VERMILION PLAN RIVER 203' 254' 254' 230' 190' PIER 1 PIER 2 PIER 3 PIER 4 RIVER ELEVATION 60 Over

41 RI over Vermillion River

42 RI over Vermillion River 12'-0" DIAMETER DRILLED SHAFT 8 BARS 18-HP12x53 10-HP12x53 STEEL CASING INCLINOMETER TUBE (TYPICAL)

43 RI over Vermillion River

44 RI over Vermillion River

45 RI over Vermillion River

46 RI over Vermillion River

47 RI over Vermillion River

48 RI over Vermillion River 8 7 The number of tensioned anchors FEM Meas Deflection, in The deflection at the top of drilled shaft pier #2-1.2

49 RI over Vermillion River

50 RI over Vermillion River

51 RI over Vermillion River

52 CUY

53 CUY

54 CUY F.S.=1.1 F.S.=1.25

55 CUY

56 CUY

57 CUY

58

59 Summary and Conclusions The use of drilled shafts to stabilize slopes demonstrated to be an effective method The design process is an optimization of the drilled shaft size, spacing, location along the slip plane, and length The factor of safety was enhanced in all the cases The calculated shaft deflection is always more than the field measured deflection

60 Thank You QUESTIONS?