Description:DESCRIPTION:
Field of the invention:
[0001] The present disclosure generally relates to the technical field of soil nailing systems, and in specific relates a method based on coherent gravity approach mobilising sufficient pullout resistance and maintains minimum recommended factors of safety of against tension and pullout failures.
Background of the invention:
[0002] Deep excavations for high-rise buildings with basements need reliable support systems to prevent soil from collapsing. Soil nailing, with its simple installation, has become a popular choice for stabilizing vertical cuts. This technique involves inserting steel bars ("nails") in stages down the slope, creating a reinforced soil mass that improves soil's shear strength and restricts movement.
[0003] Driven nails are common for temporary excavations like cellars in multi-storey buildings. However, systems designed using the Gassler method often fail due to insufficient pullout resistance. Therefore, a more rational design method is needed for driven nail systems.
[0004] Driven nailing systems are a type of construction technology used to stabilize soil, by driving nails directly into them. Further, driven nailing systems can be used in a wide variety of applications and with different materials. Driven nailing is much faster and the process of driving nails creates minimal disturbance to the surrounding soil.
[0005] However, the potential failure zone for nailed walls is typically 0.3-0.4 times the wall height at the top. This means the tensile force distribution resembles that of a reinforced earth wall.
[0006] Further, the geometry of driven nailed systems designed by Gassler's method often doesn't provide enough pullout resistance. This means the nails don't anchor into the soil firmly enough to withstand the forces trying to pull them out (usually the weight of the soil pushing against the wall). Nails that are too widely spaced might not create a sufficiently dense reinforcing network within the soil. This leaves gaps where the soil can potentially bulge and push against the nails, putting extra strain on them. Different soil types offer varying levels of friction and adhesion, influencing nail performance.
[0007] If the pullout forces exceed the capacity of the nails, they can slip or even break, compromising the entire nailed wall system. This can lead to deformations, cracks, or even complete collapse of the wall, jeopardizing the safety of surrounding structures and personnel.
[0008] Therefore, there is a need for a method that ensured safety of nailed walls based on adequate pullout resistance in deep excavations accounting for specific soil properties, excavation depth, and surcharge loads.
Objectives of the invention:
[0009] The primary objective of the invention is to provide a method based on coherent gravity mobilises sufficient pullout resistance and maintains minimum recommended factor of safety of against tension and pullout failures.
[0010] The other objective of the invention is to provide a method for design of soil nailing systems in granular soils possessing required minimum cohesion.
[0011] Another objective of the invention is to provide a method that combines longer nails, optimized design approaches, and consideration of alternative techniques for ensuring stability and integrity of these crucial support systems for soil retention in excavations.
[0012] Yet another objective of the invention is to provide a method considering a two-wedge failure plane with the top most reinforcing layer critical for pullout failure to offer distinct advantages for designing safe and stable soil nail walls with driven nails.
[0013] The other objective of the invention is to provide a method that leverages a more realistic failure plane model to design safer and resource-efficient driven nail soil nail walls.
[0014] Further objective of the invention is to provide a method that provide a significant impact on the construction industry by promoting innovative and sustainable solutions for deep excavations.

Summary of the invention:
[0015] The present disclosure proposes a method for designing a driven soil nailing system in granular soil. The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview. It is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
[0016] In order to overcome the deficiencies of the prior art, the present disclosure is to solve the technical problem to provide a method based on coherent gravity approach mobilises sufficient pullout resistance and maintains minimum recommended factor of safety of against tension and pullout failures.
[0017] According to an aspect, the invention provides a method for designing a soil nailing system in granular soil. First, the soil properties of the granular soil, including unit weight, cohesion, and angle of interfacial friction for proposed depth of excavation are determined. Next, an induced tensile force (T) in each nail level is calculated or estimated.
[0018] Next, a pullout resistance force (F) for each nail level is calculated or estimated using standard equation. Next, a nail length (Le) each nail is selected based on the minimum recommended safety factor against pullout failure.
[0019] Later, a soil nail wall is designed based on proposed nail diameter and nail spacing with the calculated nail length ensuring a minimum recommended safety factor against tension failure.
[0020] In specific, the method for designing soil nail walls in granular soils with a minimum cohesion of 7 kN/m². The induced tensile force (T) is calculated or estimated based on effect of soil cohesion. The length of nail is obtained is at least 1.33H in granular soil (c=10kN/m2, f=31°, ?=20kN/m3 with driven nails of dia.20mm at 0.5m c/c spacing in horizontal and vertical directions).
[0021] Further, objects and advantages of the present invention will be apparent from a study of the following portion of the specification, the claims, and the attached drawings.
Detailed description of drawings:
[0022] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, explain the principles of the invention.
[0023] FIG. 1 illustrates a block diagram of a method for designing a soil nailing system in granular soil, in accordance to an exemplary embodiment of the invention.
Detailed invention disclosure:
[0024] Various embodiments of the present invention will be described in reference to the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps.
[0025] The present disclosure has been made with a view towards solving the problem with the prior art described above, and it is an object of the present invention to provide a method based on coherent gravity mobilises sufficient pullout resistance and maintains minimum recommended factor of safety of against tension and pullout failures.
[0026] According to an exemplary embodiment of the invention, FIG. 1 refers to a block diagram 100 of a method for designing a soil nailing system in granular soil. At step 102, the soil properties of the granular soil, including unit weight, cohesion, and angle of interfacial friction for design of nailing system for proposed depth of excavation are determined.
[0027] In specific, coherent gravity method used to verify the internal stability of reinforced earth wall in cohesionless soils. The proposed method considers a two-wedge failure plane in which the maximum tensile force falls within the range of 0.3H at the top, it can be used to design soil nail walls with driven nails.
[0028] At step 104, induced tensile force (T) in each nail level is calculated or estimated. In specific, the induced tensile force (T) is calculated or estimated using equation (1). The calculation of induced tensile force (T) further considers surcharge load.

where, K is a lateral earth pressure coefficient, svj is the vertical stress at each nail level, Sv and Sh are the vertical and horizontal spacing of nails, respectively and c is the soil cohesion.

where, Tf is ultimate tensile strength of nail.
[0029] At step 106, a pullout resistance force (F) for each nail level is calculated or estimated using a standard equations (3) and (4).


where, d is diameter of bar, Le is length of the nail beyond failure zone.
[0030] At step 106, anchorage length (Le) of each nail is selected based on the minimum recommended safety factor against pullout failure.

[0031] In specific, equation (5) defines the minimum required anchorage length (Le) of a nail based on its pullout resistance. Where Le Represents the length of the nail embedded in the soil beyond the failure zone. T Denotes induced tensile force of the nail, calculated using the provided equation (1). ? is unit weight of the soil, hj is depth of the nail, d is diameter of the nail, and tand is tangent of the interfacial friction angle of the soil. Further, a safety factor of 2 applied to the pullout resistance equation.
[0032] In another embodiment, the length of the nail needs to be long enough to ensure its pullout resistance can safely withstand the forces acting on it, with a built-in margin of safety (represented by the factor of 2). In simpler terms, a longer nail provides more surface area for gripping the soil, making it harder to pull out and leading to a more stable soil nailing system.
[0033] At step 108, a soil nail wall is designed using a calculated nail spacing, the calculated nail length, and a nail diameter, ensuring a minimum recommended safety factor against tension failure. Further, this method adopts minimum factors of safety for design of soil nailed walls for temporary excavations in static condition against tension and pull-out failures as 1.8 and 2 respectively (FHWA 2003).
[0034] According to another exemplary embodiment of the invention, a study is conducted at a construction site with an excavation depth of 4.5m and a surcharge of 24kN/m2. Soil at the construction site is classified as clayey sand with pebbles possessing unit weight of 20kN/m3, cohesion of 10kN/m2 and angle of internal friction of 31°.
[0035] For instance, engineering properties of soil are presented in table 1.
[0036] Table 1:
Property Value
Specific gravity 2.67
Grain size distribution
Gravel (%) 18
Sand (%) 58
Fines (%) 24
Plasticity Characteristics
Liquid Limit 30
Plastic Limit 19
Plasticity Index Ip 11
IS Classification SC
Effective Shear Parameters
Cohesion(kN/m2) 10
Angle of Internal Friction 31°

[0037] For instance, one of the four excavated faces of the site supported by installing driven nails designed based on Gassler’s method has experienced failure. The causes of failure have been investigated and new design details obtained from formulated methodology are compared with the conventional design details. Both the design details are presented in table 2.
[0038] Table 2:
Parameter Gassler’s Method Proposed Method
Height of wall or depth of excavation H (m) 4.5 4.5
Length of Nails L (m) 2.7 6
Inclination of end of nails 0 0
Grade of steel (Mpa) 500 500
Diameter of nail (mm) 16 20
Vertical spacing (m) 1 0.5
Horizontal spacing (m) 1 0.5
Pull out resistance (kN) 3.6 17.4
Max. Tensile force(kN) 9.7 8.25
Tensile strength (kN) 100 157

[0039] In one embodiment, the Gassler's charts only provide for a nail length to wall height ratio of 0.6. This leads to shorter nails, which don't mobilise sufficient pullout resistance as recommended by FHWA. So, longer nails are needed than Gassler's method suggests to make sure the nails don't pull out, with a minimum safety factor of 2. The proposed method exhibits that nails should be 1.33 times the wall height, compared to the usual 0.6 times the wall height. Walls built with nails designed using the proposed method are stable and don't fall apart easily. This proves that the proposed method is safe for designing driven nails in granular soils.
[0040] Numerous advantages of the present disclosure may be apparent from the discussion above. In accordance with the present disclosure, a method is disclosed based on coherent gravity approach mobilises sufficient pullout resistance and maintains minimum recommended factor of safety of against tension and pullout failures.
[0041] The proposed method ensured safety of nailed walls based on adequate pullout resistance in deep excavations. The proposed method is provided for design of soil nailing systems in granular soils possessing required minimum cohesion. The proposed method combines longer nails, optimized design approaches, and consideration of alternative techniques for ensuring stability and integrity of these crucial support systems for soil retention in excavations. The proposed method considers a two-wedge failure plane with the top most reinforcing layer critical for pullout failure to offer distinct advantages for designing safe and stable soil nail walls with driven nails. The proposed method leverages a more realistic failure plane model to design safer, and resource-efficient driven nail soil nail walls. The proposed method provides a significant impact on the construction industry by promoting innovative and sustainable solutions for deep excavations.
[0042] It will readily be apparent that numerous modifications and alterations can be made to the processes described in the foregoing examples without departing from the principles underlying the invention, and all such modifications and alterations are intended to be embraced by this application.

, C , Claims:CLAIMS:
I / We Claim:
1. A method for designing a soil nailing system in granular soil, comprising:
determining of soil properties of the granular soil, including unit weight, cohesion and angle of interfacial friction;
estimating induced tensile forces (T) in nails at different levels;
estimating pullout resistance forces (F) for nails at different levels;
selecting an anchorage length (Le) of each nail based on the minimum recommended safety factor against pullout failure; and
designing a soil nail wall based on proposed nail diameter and nail spacing with the estimated nail length and ensuring a minimum recommended safety factor against tension failure.
2. The method for designing a soil nailing system in granular soil as claimed in claim 1, wherein the method for designing soil nail walls in granular soils with a minimum cohesion of 7 kN/m².
3. The method for designing a soil nailing system in granular soil as claimed in claim 1, wherein the induced tensile force (T) is calculated or estimated based on effect of soil cohesion.
4. The method for designing a soil nailing system in granular soil as claimed in claim 1, wherein the length of nail is obtained is at least 1.33H, wherein c is at least 10kN/m2, f is at least 31°, ? is at least 20kN/m3 with driven nails of diameter is 20mm at 0.5m c/c spacing in horizontal and vertical directions.