Adaptation of TGS HY700 Steel Tube to Rock Reinforcement & Roof/Rib Supporting

❑ Overview of TGS HY700 Steel Tube T.G.S PIPE developed extremely high strength tube using Posco's newly developed Ti(Titanium) added low

alloyed HR coil. Its mechanical properties @ coil status are like below. T/S : over 750 MPa, Y/P : over 650 MPa, E/L : over 20% TS to YP raio : 87% ○ Product Feature

① ERW based cold-hardened steel tube Since ERW process is a cold-metalworking, hardness is increased after pipemaking process. (T/S increases

about 5% and also TS to YP ratio increases). So, after tube making process T/S will be around 900MPa and Y/P 750MPa at the minimum.

② High machinability Adding on to the increased hardness, what should be focused on is Elongation. Although this material is very

high strength steel, elongation is over 15%. It means that this material keeps machinability in the high extent of hardness.

❑ Basic Understanding of Rock Reinforcement, Roof/Rib Supporting and Rock Bolt ○ Rock Reinforcement For rocks with widespread fractures caused by blasting in tunneling process, individual blocks may fall out and as

a result slope failure may occur. Rock reinforcement (e.g rock dowels, rock bolts or rock anchors) is installed to bolt through the discontinuities in rock to enhance the rock to behave as a single unit. With the bolting across block interfaces, the stress would be altered within the rock mass. Since bars or tubes used for rock reinforcement are inserted perpendicularly into the tunnel arch, its surface is usually threaded for intensifying adhesion. (see fig 1.)

<<Fig 1. Mechanism of rock reinforcement>>

○ Roof / Rib Proofing This technique is aimed at limiting the decompression in the crown immediately ahead of the face. Steel pipes

are drilled from the periphery of the crown in the direction of tunneling. After drilling, the holes are filled with grout. Roof/Rib proofing technique is classified into two types by pipes’ size and distance between them. ① Forepoling Comparatively small diameter pipes are used and distance is short ② Forepiling (Roof pipe umbrella) Comparatively large diameter pipes are used and distance is long

Since tubes are installed into the direction of tunneling, tubes’ surface is not usually threaded. (see Fig 2.)

○ Rock Bolt Rock bolt is a long anchor bolt, for stabilizing rock excavations, which may be used in tunnels or rock cuts. It

transfers load from the unstable exterior, to the confined (and much stronger) interior of the rock mass. It is a kind of material used for rock reinforcement. It is classified into 3 types by using mortal or not and the rod type (bar or hollow bar, see table 1).

<<Fig 2. Mechanism of Roof/Rib Supporting>>

<<Table 1. Rock Bolt Type and Usage>>

❑ Calculation of Weight-Lightening by TGS HY700 Steel Tube (Example) ① As mentioned at the first page of this article, TGS HY700’s mechanical properties are like below Min T/S 900 MPa, Min Y/P 750 MPa

② From the viewpoint of R38N, weight-lightening effect using TGS HY700 is like below

(Cross Sectional Area will be described as CSA) 1) Yield Load Static Case - 400,000N (Ultimate Yield Load) = 750 (YP of TGS HY700) x New CSA ∴ New CSA = 533.3 mm2 - Weight Lightening Effect = (As-Is CSA – New CSA) / As-Is CSA = (770 – 533.3) / 770 = 30.7%

2) Tensile Load Static Case - 500,000N (Ultimate Load) = 900 (YP of TGS HY700) x New CSA ∴ New CSA = 555.6 mm2 - Weight Lightening Effect = (As-Is CSA – New CSA) / As-Is CSA = (770 – 555.6) / 770 = 27.8%

※ Since form-rolling process executed for threading the pipe is also the cold metal-working, cold-hardening and related weight-lightening effect will be improved.

❑ Real World Application of TGS HY700 Steel Tube

○ Customer : KFC (Japanese no.1 ground controlling technology specialist) ○ Applied Product : Tubes for fore-poling ○ Analysis of Weight Reduction Effect

KFC designed cross sectional area of new product keeping ultimate load at the same level with as-was product. As a result, they reduced weight 16.4%. At the same time their new product improved in Tensile Load by 18%, Yield Load by 54%. (See the comparison table below)

<<Table 2. Self Drilling Anchor Technical Data of Maker A>>

<<Comparison Table>>

❑ Benefit of TGS HY700 Steel Tube Reduction of Manufacturing Cost

Material cost for manufacturing pipe-based ground controlling material such as Self-Drilling Anchor, tubes for roof proofing, etc. can be reduced by weight reduction.

Improvement of Final Product

Since YP to TS ratio of TGS HY700 is very high, if the final product is designed keeping ultimate load at the same level with as-is product, yield load will be improved significantly.

Saving of Trucking Cost

Trucking cost to construction site can be reduced by increasing loadable pieces per truck and at the same time, decreasing numbers of trucking

As-Was As-Is

Pipe Dimension (mm) ∮ 27.2 x t 5.0 ∮ 27.2 x t 4.0

Cross Sectional Area (mm2) 349 292

Tensile Strength (N/mm2) 630 900

Yield Strength (N/mm2) 410 750

Tensile Load (KN) 220 260

Yield Load (KN) 143 220