Introduction

PAPER ON

The theme

Advancement In Geotechnical Engg

Technique for slope stabilizationSOIL NAIL

&

ROOT TECHNOLOGYFOR

QUANTUM09 IN

RAJARAMBAPU INSTITUTE OF TECH.

FROMDept. of Civil Engineering

K.I.T.s COLLEGE OF ENGG.

--PRESENTED BY--

Abhinandan C. Batkadli Vinayak B. Patil.

B.E. CIVIL

B.E. CIVIL

abhinandan_batkadli@rediffmail.com vbpatil_9999@rediffmail.com 99 75 50 90 36 96 65 72 68 27 CONTENTS

Sr. No.NamePage No

1.Introduction.3

2.The fact.3

3.Terminology.4

4.The

SNART

Technology5

5.The SNART Design.8

6.The construction.9

7.SNART Feasibility.9

8.SNART Economics.10

9.SNART Features.10

10.Conclusion.11

11.References.11

Introduction : Definition of ground stabilization

The ground improvement technique/stabilization in broad sense, incorporate the various methods of employed for modifying the properties of soil to improve its engineering performance. Stabilization is being used for a variety of engineering works the most common application being in the construction of roads and airfields pavements, where main objective is to increase the strength and stability to of the soil.

Along with that the strength and stability of the soil on steep slop is also important, since the failure of soil on slope may lead to considerable loss of life and property. It is therefore essential to study the stabilization of soil on steep slope.

So here in this paper we introduced one modern technique of stabilization of soil on steep slope, which is SOIL NAILING AND ROOT TECHNOLOGY.

The fact : In many cases, a soil slope, which is over steepened and unstable, can be stabilized in expensively by simply regarding the slope to less than the angle of repose, whether by cutting or filling or by both however there are many site constraints preventing such a simple solution. Examples are the river at the toe, environmental permitting requirement, impossible access to the toe, building and infrastructure at the crest, or the trees on the slope that must not be disturbed.

Unfortunately the next simplest solution is a retaining wall either at the top or bottom, which is often the most costly, especially when considering soaring for installation and crane access. In addition, retaining wall construction can be disruptive to the environment and to the neighboring.

As an alternative to conventional retaining wall system mechanically stabilized earth is often considered. It is very economical consisting simply of fabric other reinforcing sandwich within the slope. It is best suitable for new construction, so that the reinforcing layers can be incorporated with the construction. It is not so simple and economical if it means digging up an existing slope already unstable, give the necessary soaring and disruption. MSE system effectively provide internal stability to a construction earth embackment founded on competent foundation soil, but tend to fail short where weak foundation soil lead to stability ensure in terms of global stability, of compound failure modes. Terminology.

The concept, which is introduced in this paper, is Soil Nail And Root Technology.

To understand this its important to have knowledge of some definitions.

1) Soil Nailing

Soil nailing is a technique in which soil slope, excavation or retaining walls are reinforced by the insertion of relatively slander elements normally steel reinforcing bar. The bar bars are usually installed into predrilled holes and grouted simultaneously they are usually installed intentioned at a slight downward inclination. A rigid or flexible facing or isolated soil nails head may be used at the surface, soil nailing is how a well-established technique around the world.

2) Shortcrete

Shortcrete is a mortar or concrete conveyed through a hose and pneumatically projected at high velocity on to a surface. There are two distinct process of shortcrete application, dry and wet process.

3) The SNART nails

On the basis of many engineering analysis many installation trials and stabilizing several sites it was found that slope typically requires 30 to 50 mm diameter steel nails on a grid spacing of 1 to 2 m. the length of nail increases with slope height, level of water table and target safety factor.

# SOIL NAIL AND ROOT TECHNOLOGY# The SNART system was developed specially for slopes that cannot be stabilized by simply flattening them or draining them, whether due to access restriction or environmental issues. SNART is an economical design built alternate to retaining walls and mechanically stabilized earth in fact it has proven in most cases to be the lowest cost solution for the most unstable slopes up to 45 degrees.

The Concept : SNART is a modern system suitable for stabilizing soil on slope and landslides; here steel nails are inserted very rapidly in to a slope by percussion, vibration or screw method. Grid spacing is typically 0.8 to 1.5 m., nails are installed perpendicular to and through the failure planes (or potential failure planes) and as such as designed bending and shear (rather than tension) using geotechnical engineering principles. Potential failure surface less than 2m deep normally require nail to be wider near the top and is typically achieved with steel plates fastened at the nail heads. An effective and aesthetic facing to prevent soil loss between the nails can be designed plant roots.

Explanation: Give the above there is need for a solution that stabilizes the over steepened slope economically. Such a system should be ideally meet the following criteria (a) A design basis using engineering analysis (b) Installation without affecting traffic on embankment (c) installation in areas with difficult access (d) be a similar cost to conventional slope fattening or widening (e) Have minimum impact on environmental (f) be aesthetically pleasing and

(g) Have the ability to be monitor for performance.

The new system has been developed that will meat these criteria. It combines two proven technology, namely soil nailing (traditionally installed with a shortcrete facing on almost vertical cut slopes) and a biotechnical facing (traditionally used to stabilize slopes against erosion.)

Traditional soil nail consist of steel bars inserted generally perpendicular to the slopes usually by drilling and grouting method. The surface is covered with steel mesh and shortcrete is then applied to complete the stabilized cut. To meet the criteria for fill slope new installation method had to be developed that avoided costly drilling and grouting and permit installation without requiring equipment at the top of the embankment. This involves field installation trials to develop. Further more the facing while still stabilization the shallow soil between the nails. This requires large scale testing to establish analytical method for shallow failure modes of soil slippage around nails.

The Technology : The fundamental concept of SNART consist of reinforcing the soil using passive closely spaced bars together with an engineered sacrificial facing comprising plant root reinforcement. Designs are site specific and often required geotechnical data to optimize the design with SNART nails are steel bars 30 to 50 mm in diameter with lengths of 2m to 15m and an design with an allowance for corrosion over there design life. Nails are typically spaced at 1 to 2 m , extending above 1m into stable material. This system requires small movement within the slope in order for the required resistance to be mobilized. A typical system is illustrated in previous figure. Soil nail technology is well developed for vertical slopes for temporary excavation including design methods. A shortcrete or precast concrete facing deal with shallow slip of near surface soil, while deeper potential slip failures are stabilized with the lateral resistance of the nails across the slip planes. Fill slope on the other hand, are flatter and do not require high strength facing such a shortcrete. Furthermore, in many instances a shortcrete facing is not suitable where frost action is a long-term consideration.

Full scale model studies at lab have shown that a nail head details is required to stabilize the slope against the failure, more where by shallow consideration less soil could flow around the embedded nail (see figure bellow) New analytical method therefore had to be develop to deal with this. As a result various types of nail heads were investigated for working in association with a shallow root system over the slope surface. The optimum head was found to be a 200 X 200 mm shere plate welded near the top of the nail and oriented parallel to slope (see figure bellow). This was developed to achieve the minimum of 5 km resistance per nail.

Another way to embackment slopes are different than steep cut slope is the need to maintain the stable shoulder. This is particularly important for railway embackment whether the narrow shoulder provides lateral support that integrate with SNART, including epoxy stabilization, precast tied and inclined concrete retainer and inclined retainer strip (see above figure.)

A biotechnical facing is an integral part of the system. This incorporate a layer of sacrificial roots that impact on effective cohesion to soil properties. Furthermore, the facing keeps the near surface soil moist, imparting, a small additional cohesion which is known to extend deeper than the roots themselves. The facing is engineered with respect to root depth depending on the site specification condition.

Developing economical installation methods that do not affect train or highway traffic is an important hurdle in unlocking the power of this technology. To that end methods are developed for installation the nails with equipment that could access the steep slope (as steep

as 45 degrees) and using percussion, vibratory and rotary methods. This eliminate the traditional high drilling and grouting cost with providing number of rapid and economical installation methods that could be subjected to fit sit specific soil condition. The ability to monitor the installation resistance of the nail also provided to be a valuable tool, to identify localized variations in a stratigrafy, allowing field adjustment during installation to optimize the design.

The SNART design : Traditional soil nail design based on tension capacity, is not readily applied to fattern the slope. SNART nails instead relay on the resistance of the soil as it bears against the side of nail immediately bellow and above the potential shear plane. The nail is selected for adequate shere and bending resistance. The nail stiffness will control the length of the available soil resistance along the nail as well as the deformation requires to mobilize the resistance.

The slope is analysed with limit equilibrium methods based on site-specific soil parameters slope geometry, external load such as earthquake and water table level where minimum information is available, conservation assumption can be applied. The design is then based on the desired level of risk (through target safety) using limit equilibrium, methods for circular translation and wedge type failure. A soil resistant function with depth is developed for the nails using FHWA and LPILE methods, which can also be derived from an in situ bar resistance test. Adjustment are made for strain softening soil, where required. Resistance data is applied to the stability analysis to find the optimum nail diameter, length and spacing. Finally check are made for over stressed zone in the slope and for deformation. The latter are typically less than 20 mm diameter near the surface and much less with depth

The Construction : The soil nail were installed using small equipment working on the slope (see figure bellow) this spider like equipment has four legs (two of which have wheels) and an excavator arm, and can work on slopes up to 45 degrees. Percussion hammer was mounted on arm. Minor grade adjustment were made where steep scraps remained 38 cm diameter steel bar were inserted in 5 m length using percussion method. Lap slices with weld were used. The nail heads were designed to terminate just bellows the slope surface.

During the work, a sliding pipe underground detector system was installed. A SPUP is simply a plastic casing installed vertically into ground at the crest. A short piece of pipe sliding inside the casing is designed to jam within the casing if its curvature exceeds. The maximum deformation allowance selected. The pipe is left on the end of string at the bottom of the casing.

Pulling the pipe up a few time per day will warm the screw if unsafe movement has occurred.

SNART Feasibility : SNART feasible for most soils, having been used successfully for sand, silt and clay soil. However it dose not stop erosion at the toe as a result of waves and currents. Furthermore it may not be more economical than mechanically stabilized earth where the slope has yet to be constructed. Finally, it cannot be applied easily to slopes steeper than 50 degrees, or soil containing boulders.

SNART economics

The economics of SNART consist of construction coasting for slope flattering, widening solution versus soil nailing. The cost of SNART is similar to that of traditional bank widening and slope flattering, although the SNART had the advantages of retaining no environmental approval and no need to relocate poles and signals.

Typical costs excluding mobilization are in the range of $15 to $50 (US) per square meter of slope face. A typical slope in granular soil utilizes 3m long nails with heads on a 1.2m grid an including a biotechnical facing, the cost is $23 per square meter of slope traced. For a case of deeper slip planes, in cohesion material-utilizing nails typically 6m to 8m long nails with heads on a 1.2m grid and a biotechnical facing, the cost is $40 per meter square.

The SNART Features : Fast and safe installation using light equipments.

Engineered for site-specific soil and ground water condition.

A very feasible system accommodates a wide range of design criteria.

A green solution, leaving no evidence of the system after installation.

Existing vegetation can be preserved.

No excavation or soil deposition required.

No construction impact on nearby road or railways.

Available as design build solution.

Proven performance on sand.

Surgically applied only to affected area.

Custom design to fit budget and degree of risk.

A 100 years design life.

Virtually no maintenance.

Very low cost.

Conclusion : An innovative soil nail system and root technology system has proven to be a cost effective alternative to retaining wall and mechanically stabilized earth walls over the past five years the system has developed with new analytical technique, light installation equipment, rapid placing technique, special nail heads and biotechnical facing.

The soil nail and root technology system borrows from and integrates three proven technologies: soil nail walls, shallow biotechnical stabilization and laterally loaded piles.

References : 1) www .dstgroups.com 2) An innovative slope stabilization system: SNART

-- Mike Fabius.

-- Goard Maki.

-- Scott Tozer.

3) Steep nailed Embackment Technology.

2 SNART case studies.

-- Scott Tozer.

-- Mike Fabius.

4) SNART

-- A Technical Overview

-- DST groups.

5) DSI LANG GEOTECH, LLC.

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