Passive soil nailing technique has gained popularity for temporary and permanent slope strengthening

14/lug/2016 11:50:03 sinorocksoilnailing Contatta l'autore

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Passive soil nailing technique has gained popularity for temporary and permanent slope

strengthening works at both in-situ cut slopes of virtually any formations and also man-made filled slopes in Malaysia. However, there are still many misconception and myth in the design and construction of soil nails. Various design and construction practices have been adopted in the local industry of soil nailing works

Soil nailing technique has been applied to civil engineering

project at Mexico City back to 1960s and

has gained popularity in Europe since 1970. During

the development of soil nailing technique, cementitious

grouted drilled nail, post-grouted driven

nail, percussion-driven nail, jet nail, and etc have

been devised and improved.

Hereafter, the advantages and disadvantages of soil

nailing are briefly discussed.

Advantages :

1. Allow in-situ strengthening on existing slope

surface with minimum excavation and backfilling,

particularly very suitable for uphill

widening, thus environmental friendly,

2. Allow excellent working space in front of the

excavation face,

3. Sub-vertical cut surface reducing loss of

space,

4. Avoid unnecessary temporary works,

5. Only requires light machinery and equipment,

6. Flexible at constraint site and excavation

shape,

7. Can be used for strengthening of either natural

slope, natural or man-made cut slopes,

8. Robust and higher system redundancy,

9. Thinner facing requirement.

Disadvantages :

1. Nail encroachment to retained ground rendering

unusable underground space,

2. Generally larger lateral soil strain during removal

of lateral support and ground surface

cracking may appear,

3. Tendency of high ground loss due to drilling

technique, particularly at course grained soil,

4. Less suitable for course grained soil and soft

clayey soil, which have short self support

time, and soils prone to creeping,

5. Lower mobilised nail strength at lower rows

of nailing,

6. Suitable only for excavation above groundwater.

3.0 SUITABILITY OF SOIL NAILING WITH

RESPECT TO SOIL TYPES

As soil nail construction requires temporary stability

in both the staged excavation and also the drilledhole

stability, any soils with sufficient temporary

self-support of about 2m sub-vertical height for

minimum of 1 to 2 days and hole stability for minimum

four hours are considered suitable ground for

soil nailing.

With the above criteria, the following soil types

would be suitable for soil nailing:

i. Stiff fine/cohesive soils

ii. Cemented granular soils

iii. Well graded granular soils with sufficient

apparent cohesion of minimum 5kPa as

maintained by capillary suction with appropriate

moisture content

 

v. Most residual soils and weathered rock

mass without adverse geological settings

(such as weak day-lighting discontinuities,

highly fractured rock mass, etc) exposed

during the staged excavation

v. Ground profile above groundwater level

Soil nailing can still be considered suitable for

certain soil types or ground conditions if proper

drilling equipment and flushing agent are carefully

selected.

The major impacts to soil nailing works in the

unsuitable ground conditions are mostly :

i. Loss of grout though the fractured rock

mass, open joints and cavities

ii. Collapse of drilled-hole

iii. Poor nail-to-soil interface resistance due

to disturbance of drilled-hole

iv. Localized face stability

4.0 DESIGN OF SOIL NAILING

The following documents have been widely referred

by designers in designing the soil nailing strengthening

works.

a. BS8006:1995 Code of practice for

Strengthened/reinforcement soils and other

fills

b. Federal Highway Administration (FHWA)

: Manual for Design & Construction

Monitoring of Soil Nail Walls

c. BS8081:1989 Code of practice for Ground

Anchorage

http://plaza.rakuten.co.jp/sinorocksoilnail/diary/201607140000/
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