2016年09月21日

Soil nail system


Soil nail system , an ideal anchor system for underground construction, is an environmental
solution for metro tunnel projects. Especially in weak conditions, soil nail has better
reinforcement effect over other anchoring systems. Soil nail system can change themechanical property of surrounding rocks, enhance self-supporting capacity, reduce
deformation of surrounding rocks and then keep tunnel’s stability.
The soil nail system was ideal for top down construction in this project because they
provide a permanent, safe and economic reinforcement of slopes without the requirement for
additional support. The soil nail system installed featured galvanized protection, which
provides comprehensive corrosion protection for soil nailing applications. This application
of soil nail system had great benefits, not only economic ally, but also technically.
Sinorock have the qualifications and experience in the concept of soil nailing , which briefly is to reinforce and strengthen existing ground by installing closely spaced grouted steel bars, called ”nails,” into a slope or excavation as construction proceeds from the ”top down.”
This soil nailing process creates a reinforced section that is itself stable and able to retain the ground behind it. Soil nailing works in tension, bending and shear. Generally, the soil nails significantly increase the apparent cohesion of the soil through their ability to carry tensile loads. A construction facing is also usually required, and is typically shotcrete reinforced by welded wire mesh. This technique is also be used in rock, to anchor structures against the floatation reaction due to ground water.
We have used a variety of different equipment to carry out the process. We have used the Wimmer Rock drill with the most effective results due to the versatility of the Unit. The Wimmer Rock drill is machine mounted on a 30 ton excavator and can Drill and install at any angle,through any material, from any position.  

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2016年09月13日

Typical soil nailed wall

Many citizens have a false sense of security about the soil-nailed wall , believing that the wall was designed to hold back the bluff or to somehow “anchor” the bluff to more stable ground.

The general purpose of the soil nailed wall is to prevent rainwater and surface drainage from washing over the side and eroding the face of the loess bluff. It does not address the seepage of water into the flat surface of the bluff top itself.

The function of the spear-like SOIL NAILS that were sunk into the face of the bluff is to anchor the wall to the side of the bluff. Therefore, it is the bluff that holds up the soil nail wall, not vice versa.

The soil nails in the Natchez Bluff range in length from 20 to 40 to 160 feet.

In a typical soil nailed wall, the average distance between nails (viewed from the top down) is normally 1 nail per five feet.
However, because of the unique and unstable loess soil conditions, the frequency of nails at Clifton Avenue Wall in Natchez (Phase I of the Stabilization Project) was 1 nail per 8 inches when viewed from the top of the wall. (550 soil nails per 450 linear feet). (Source: Innovative Stabilization of Loess Bluff along Mississippi River. D’Appolonia.)

(Click for larger view)
Unlike the diagram above, large sections of the soil-nailed wall at Natchez only cover the top of the 200-ft Bluff. They do not reach the ground. Basically, they hang on the side of the bluff.

The wall does not protect the lower section of the bluff or address the “toe” of the bluff, where mudflow occurs.
It will not stop a problem that originates more than 30 or 40 feet back from the bluff’s edge, which is where most MAJOR collapses originate.
Finally, the Historic Natchez Bluff Stabilization Project was the first time soil nails have been used in the United States in windblown LOESS soils. It is not proven to be a permanent solution.  

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2016年09月06日

Self drilling soil nail

The construction industry has developed self drilling soil nail systems (or pressure injected bored, IBO) that combine both drilling, placing and grouting in a single operation as a solution to speed up construction. While the soil nail system is extensively used for temporary applications, nevertheless, some concerns, particularly about corrosion, has limited the use of this technology as a permanent system in North America. This study presents several issues related to self drilling soil nail systems, the results of a field investigation and a summary of the research project.
Self drilling soil nail system manufactured by sinorock factory consisting of the drill bit attached to the hollow grouted bar, which is encased by the spreading column, is lowered into the hole. The spreading apparatus is attached and centered in contact with the surface.
It is used in applications with rock at the surface, without coring requirements, its installation is greatly simplified.
The soil nail system is rotated using the hole drilling power unit, opening the drill bit into the load bearing media, in a predetermined controlled manner. This places the drill bit conically into the rock, which effectively utilizes the maximum strength of the load bearing
rock via the Anchoring System. The spreading column is removed allowing the system to be immediately tested and placed into its designed use. If required, the system may be post-tensioned in order to meet current seismic loading safety measures.
  

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2016年09月02日

Soil nail strengthening work


For all soil nail strengthening works, the primary objective is to improve the safety factor to the design requirement. Slope stability program by either limit equilibrium method or strength reduction method in finite element analysis will normally be used to assess the original safety factor and the improvement after strengthening. The extent of such stability assessment shall be carried out, at least, at areas where there is impact to human being if slope instability occurs. If there is any surcharge loading, it should be considered in the stability assessment. Both global stability and local stability shall be carried out for the concerned slope.
The use of soil nail anchors works best in soils that are sandy but with sufficient clay to allow unsupported cuts of up to 7 feet to stand temporarily. This system is not advisable to use next to buildings. Their strength is derived from the fact that the wall displaces slightly and the steel tendons stress and induce increased shear strength to the soil.

The soil nails are typically closely spaced and a 4″ thick shotcrete facing is applied to the earth face after the nails are drilled. One of the advantages of soil nails is that only a small percentage (5-10%) of the nails are tested which reduces the cycle time between rows.

This method can result in cost-effective top-down construction.
http://www.comunicati.net/comunicati/istituzioni/comuni/basilicata/403919.html  

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