Soil Nailing

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Introduction

Soil nailing was first implemented in 1972 for a railroad project near Versailles, France. It is a construction technique which reinforces unstable soil slopes such as excavations and retaining walls. This technique inserts slender elements, usually reinforced steel bar, into soil slope to provide passive loads to the ground. Different types of soil nailing includes grouted nail, driven nail, self-drilling soil nail, jet-grounted soil nail and launched soil nail.

Figure 1 Drill hollow bar bare epoxy coated galvanized

Favorable condition

In preliminary analysis, the site needs to match up a favorable condition for soil nailing, and both the advantage and disadvantage required to be considered for the site, otherwise another soil improve method would be used instead.

The suitable soil type to apply soil nailing is stiff to hard fine-grained soils, dense to very dense granular soils with apparent cohesion evenly weathered rock and glacial soil. The reason why these are the suitable types of soil is that during the construction, a one to two metres soil surface should be able to stand for a minimum 2 days after excavation. Therefore, soil nailing is not suitable for dry and cohesionless soils.
Another important condition requires to be made in preliminary analysis is the water level. Soil nailing better to be installed at a level above groundwater table. If not, engineers should check the overturning and sliding failure in design to make sure that the soil nailing structure can deal with the negative effects caused by water table. A high groundwater table can lead to trouble in drilling and excavation and corrosion of reinforced steel bar.

The advantages and disadvantages of soil nailing technique are always be...

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...ce between points changed. Inclinometer is installed behind the slope facing in horizontal distance, which is used for measuring the horizontal movement as well.
Drainage behaviour: Piezometre pipe need to install behind the face for monitoring any seepage effect on the nailing wall. In case there is some grout leakages within the wall will increase the permeability and ground water dam up, an unfavorable “wet” condition for nailing wall may cause failure. It is recommend measuring it every two wet season.
• Magnitude and position of maximum nail load: Strain gauges need to be attached to nail bar to measure the strain. Deformation or elongation of steel nail over time show that the loading exerts by soil may change. The excess loading which over the design loading capacity will make nail be weak and cause failure. It is important to check and monitor frequently.

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