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  2. 2. Soil nail as stabilization measure for distressed slopes and for new very steep cut slopes has the distinct advantage of strengthening the slope without excessive earthworks to provide construction access and working space associated with commonly used retaining system such as reinforced concrete wall, reinforced soil wall, etc. In addition, due to its rather straightforward construction method and is relatively maintenance free.
  3. 3. Stabilization of existing retaining wall Tunnels excavations in unstable slopes Steep cutting stabilizations Stabilizing of over steep existing embankments Stabilization of highway and roadway cut slopes temporary excavation shoring Provide long term stability to existing concrete structures without demolition and rebuilding costs
  4. 4. Ground Condition a) Residual soil and weathered rocks b) Stiff cohesive soils such as clayey silts and other soils that is not prone to creep deformation. c) Dense sand and gravel with some cohesive properties. d) Ground conditions located above the ground water table (GWT). a) Soft to very soft fine- grained soils, Loose clean granular sand b) Soils with high groundwater, . c) Organic soils d) Highly fractured rocks with open joints or voids due to problem in grouting.
  5. 5. 3.1 Installation Methods a. Grouted Soil Nailing. b. Driven Nails c. Self drilling Soil Nail d. Jet Grouted Soil Nail e. Launched Soil Nail
  6. 6. 3.2 Basic Elements of a Soil-nailed System a) Steel bar- b) Centralizers- c) Grout e) Hex nut f) Temporary and Permanent Facing- g) Drainage System- d) Nail head-
  7. 7. 4 . advantage of soil nail It is suitable for cramped sites with difficult access. It can easily cope with site constraints and variations in ground conditions encountered during construction,. it causes less environmental impact. There could be time and cost savings . The failure mode of a soil-nailed system is likely to be ductile, thus providing warning signs before failure.
  8. 8. Disadvantages : 1. Nail encroachment to retained ground rendering unusable underground space, 2. Less suitable for course grained soil and soft clayey soil. 3. Lower mobilised nail strength at lower rows of nailing, 4. Suitable only for excavation above groundwater.
  9. 9. (a)The presence of utilities, underground structures (b)Permission has to be obtained from the owners of the adjacent land for the installation of soil nails beyond the lot boundary. (f)Long soil nails are difficult to install, and thus the soil nailing technique may not be appropriate for deep-seated landslides and large slopes.
  10. 10. (h)Because soil nails are not prestressed, mobilisation of soil-nail forces will be accompanied by ground deformation. The effects on nearby structures, facilities or services may have to be considered, particularly in the case of soil-nailed excavations.
  11. 11. 6 . PRINCIPLES OF A SOIL-NAILED SYSTEM 6.1 FUNDAMENTAL MECHANISM OF A SOIL-NAILED SYSTEM The effect of soil nailing is to improve the stability of slope or excavation through : Increasing the normal force on shear plane and hence increase the shear resistance along slip plane in friction soil. Reducing the driving force along slip plane both in friction and cohesive soil In soil nailing. Soil nail head and facing provides containment effect to limit the deformation near slope surface.
  12. 12. The internal stability of a soil- nailed system is usually assessed using a two-zone model, namely the active zone and the passive zone (or resistant zone). The active zone is the region in front of the potential failure surface, where it has a tendency to detach from the soil-nailed system. The passive zone is the region behind the potential failure surface, where it remains more or less intact. The soil nails act to tie the active zone to the passive zone.
  13. 13. These points must be noted for installation of soil nails 1. Soil Nails must penetrate beyond the slip plane into the passive zone typically for 4 to 5m. 2. The spacing of soil nails in horizontal or vertical direction must be related to strength of the soil 3. Soil nailing should start immediately after excavation. 4. Any delay in nailing may lead to collapse of soil slope
  14. 14. 7 . SITE INVESTIGATION AND TESTING which normally proceed in stages: (i) desk study, (ii) site reconnaissance, (iii) collection of field data including ground investigation and laboratory testing (iv) follow-up investigation and design review during construction
  16. 16. CONSTRUCTION Construction Sequence Excavate Initial Small Cut is excavated before the first row nail installation which is typically about 1to 2 m.The excavated face should be smooth so as to minimize shotcrete quantities. Drill Hole for Nail Holes are drilled at required location with suitable length and inclination. Install and Grout Nail With the help of centralizers, nails are properly placed (centered) in the drill holes.
  17. 17. Place Drainage System To control seepage Place construction facing temproray( install bearing plates Steel and securing nut are placed at each nail head) . Repeat Process to final grade . Place final facing For long term stability reason and durability reason, a CIP concrete facing is used. Precast concrete can also be used as final facing for soil nail
  18. 18. . DESIGN OF A SOIL-NAILED SYSTEM .3.Engineering programs used in designing soil nailing .2 Design method steps 1DESIGN CONSIDERATION S Stability . Service ability Durability . Economi c Consider ations. Environme ntal Considerati ons.
  19. 19. 1. SNAIL-plus computer program 2. GOLDNAIL computer program 3. Geo-Studio computer program
  20. 20. .DESIGN CONSIDERATIONS. stabilit y Durability Economic Considerations. Environmental Considerations. Serviceability
  21. 21. Design external failure mode. internal failure mode facing failure mode Dependence on the (FHWA,2003) in the design. global failure sliding failure bearing failure Pullout Failure Tensile Failure of Nail Headed Stud Tensile Failure Punching Failure Flexure Failure
  22. 22. 1-external failure mode External failure modes refer to the development of potential failure surfaces passing through or behind the soil nails .For external failure modes, the soil nail wall mass is generally treated as a block.  global failure mode  sliding failure mode  bearing failure mode
  23. 23. a- Global Stability This failure is induced in the soil, the nail and the injection material because the fixed wall does not bear the impeded loads and this type of failure depends on both the tensile strength and the length of the nail and also on the amount of bonding between the soil and the nail.
  24. 24. It is the failure that occurs in the soil, the nail, or the substance used in the injection due to the intolerance of the imposed loads and depends on the tensile strength, the length of the nail and the bonding material, as shown in the figure 2- Internal Failure modes
  25. 25. a-Pullout Failure It is the failure that occurs along the line of contact between the nail and the substance used in the injection, and usually results from insufficient strength of the substance used in injection or that the length of the nail is not sufficient. several factors control it:  location of the failure surface depended on soil type  Drill diameter and method of fixing nails  Friction surface area.
  26. 26. b-Tensile Failure of Nail It is the failure that occurs due to insufficient tensile strength in the material used for the nail. Where the tensile force is generated in the nail fixed in the soil in the passive area and extends to the nail head
  27. 27. (a) Failure of Ground around Soil Nails (b) Soil-nail Head Bearing Failure (c) Local Failure between Soil Nails (d) Tensile Failure of Soil Nails (e) Pullout Failure at (f) Bending or Shear Ground-grout Interface Failure of Soil Nails (or Grout-reinforcement Interface) (g) Structural Failure and Connection Failure of Soil-nail Head (h) Structural Failure and Connection Failure of Facing Figure 8.2 Potential Internal Failure Modes of a Soil-nailed System
  28. 28. 3- Facing Failure The most common and likely failure forms of a facing are when the thickness of the concrete used is low or the amount of reinforcement used on the facing is small. The most common types of failure are • Due to the high curvature of the face, whether permanent or temporary • It occurs around the head of the nail whether permanent or temporary • As a
  29. 29. Steps to design an earthen wall installed using nails with depend on FHWA,2003
  30. 30. 1.Soil wall height obtained from field (H) = 7m 2.Density of the soil obtained from the field Ճm= 18 KNm3 3.Soil cohesion and angle of friction obtained from the field = 42 , 25 4. SH & SV Between the soil nails Within the range specified in the approved standard SH * SV <= 4 m2. SV = 1.25m SH = 1.25m
  31. 31. 5.Calculate the area of influencen= 1.25*1.25 = 1.56 m2 <= 4 (FHWA) 6.Soil Nail pattern on Wall Face, and it turned out square 7.Soil Nail Inclination(i) = 15 8. Angle of face batter α= 0 9. back slope angle β=0 10.Nail length (L1 = 0.7-1.2H). FHWA L= 0.7 * 7 = 4.9 m
  32. 32. The length of the nail in the lower rows should not be less than 0.5 H Nails of irregular length should be used when layers of soil are of different conditions. When using different lengths of nails, the length of the nails in the upper rows should be longer than the length of the nails in the lower rows in order to reduce
  33. 33. 11.Select the Drillhole Diameter which ranges between (100-200) OR (100-300) .(FHWA) Assume DDH=150mm 12. Determine the values of safety factors and failure patterns = 2 from table 13. The ultimate bond strength ( qu) = 50 kpa from table 14. The allowable bond strength qa = 25 kpa F.SP : pullout Resistance
  34. 34. 15. (Normalized Bond Strength) μ μ= (qa . DDH)/( γm . SH . SV) = 0.133 16. .The Normalized cohesion c* c*=c/γ . H =0.33 17.Find a value (L/H) from the value μ = 1.15 from fig Angle of face batter α= 0 back slope angle β=0
  35. 35. 25
  36. 36. 19.Find DDH & (C1L) correction factor=
  37. 37. 20.Find Soil Cohesion correction C2L=0.85 21. Find (FSG) Global factor of Safety C3L=0.52 X 1.35+0.30= 1.00 ≥ 0.85
  38. 38. 22. Find Length of Soil Nail 23. Correction ( t max-s ) for drill diameter • C1F=1.47 • Soil Cohesion : C2F= -4.0 X C* + 1.09 ≥ 0.85 C2F= -4.0 X 0.33 + 1.09 = -0.23 < 0.85 Use C2F= 0.85 t max-s = C1F X C2F X t max-s t max-s = 1.47 X 0.85 X 0.22 = 0.27
  39. 39. 24. The maximum design nail force: Tmax-s=γ . H . Sv .SH . t max-s Tmax-s=18 X 7 X 1.25 X 1.25 X 0.27= 53.15 KN 25. F.ST=1.8  The nail tensile capacity RT RT= F.ST * T max-s =1.8 X 53.15=95.67 KN  The necessary nail bar cross-sectional area (AT): AT=(T max-s X F.ST)/fy = RT/ fy AT =53.15 X 1.8/517 = 0.185m2=185mm2 Fy=517 MPa 26. Facing Design:T0 = T max-s[0.6+0.2(Sv -1)] T0 =53.15[0.6+0.2(1.25-1)]= 34.55 KN
  40. 40. Sliding Stability failure
  41. 41. 28. Bearing failure
  42. 42. Discuss the results From FHWA the minimum F.SG = 1.35 Through the study of multiple cases of (i , SH=SV , ϕ) i = 10 , 15 , 20 SH=SV = 1 , 1.25 Φ = 25
  43. 43. Recommendations are for reference only : • See the design method in FHWA,2003 Extensively It includes a comprehensive design method for soil nailig , • British Standard BS 8006:1995 code of practice for strengthened reinforcement soils and other fills. • British Standard BS 8081:1989 code of parametric for ground Anchorage. • https://gnpgroup.com.my/wp- content/uploads/2017/03/2006_06.pdf • ‫رساله‬ ‫الطالبه‬ ‫محمد‬ ‫جيهان‬ ‫الحيالي‬ , ‫خليل‬ ‫احمد‬ ‫امينه‬ ‫الست‬ ‫اشراف‬ , ‫الموصل‬ ‫جامعه‬ , 2020
  44. 44. summary a soil nailing is one of the recent in situ techniques used for soil improvement and in stabilizing slopes .my search include applications ( Stabilization of highway and roadway embankments and cut slopes Tunnel portals in unstable and steep stratified slopes). We also covered fundamentals of a soil-nailed system ( installation methods .Basic Elements of a Soil-nailed System ) We mentioned a advantages of soil nail and limitations of The soil nailing technique and study . then studied site investigation and testing Which includes buildability , durability of soil nails and Soil aggressivity and we studied design of soil nailed Which includes tow methods Which manual depends on fhwa and Engineering programs used in designing soil nailing (snail -plus computer program goldnail computer program geo studio computer program) monitoring and maintenance finally we studied construction and
  45. 45. thank you for your listening