DIAMOND MINE PROJECT

SPECIAL SUPPORT PROJECT - DIAMOND MINE - KIMBERLITE - SOUTH AFRICA

It was decided to test the V-seal product at at a diamond mine in Kimberley on 1020 level development at T1, T2, T3 and T4 access tunnels, the tunnels will be developed from the rim tunnel situated in the competent country rock advancing through the Schist zone into the Kimberlite. This report focuses on the overall performance of V-seal and the rock mass responds after V-Seal has been applied as a rock support liner.

OBSERVATIONS:

T2 was visited on the 10th of September 2021 and the access tunnel was in the transition zone between the Schist and the Kimberlite, 8mm of V-Seal was applied and the primary support was installed. The Schist contact plane from country rock is still intact with no displacement or signs of weathering.

No welded mesh was installed for 10.0m in the T2 access tunnel to allow the rock mass to respond to any deformation or weathering.

The integrity of the rock mass was observed to be enhanced to a uniformed profile after the 8mm V-Seal has been applied sealing all blasting fractures and geological discontinuity that can promote deformation or unravelling of the tunnel profile.

A blast on test was also done on the V-seal that was applied on the Schist transition zone to see the reaction of the bonding on contact and how the product reacts to blasting.

The bonding contact of the V-seal was still intact, and signs of bond separation could be observed along the blasted area. The V-seal sheared during the blasting which emphasizes the strength of the cohesive mechanism design in V-seal.

T2 access tunnel intersected Kimberlite and V-seal was applied to the Kimberlite rock type, I visited the area on the 29th of September 2021 to assess the V-seal performance and Kimberlite responds after the application.

V-seal was applied up to the face of T2 access tunnel as seen in figure 8 below, no dump weathering or deformation was observed on the V-seal after the V-seal has bonded and dried after the shift.

Access tunnel, V-Seal, Primary Support Tendon

Access tunnel T2 with 8mm of V-Seal & Primary Support Tendon.

Sidewalls of T2 access tunnel displaying an even placement of V-Seal onto the tunnel profile.

CONCLUSION:

An additional method of determining the support requirements for tunnels underground is by means of evaluating the Rockwall Condition Factor (RCF). This method is based on the quality assessment of the rock mass as well as stress levels to which the excavation is subjected.

In evaluating the proposed development, the σ1 critical criterion is widely used and is based on a critical stress value. Should this critical value be exceeded, the sustainability of the excavation cannot be guaranteed, and the support installation will be significant. In evaluating the stability of access tunnels, the Rockwall Condition Factor (RCF) is commonly used (Jager and Ryder, 1999).

(RCF) = ((3 x Sigma 1) – Sigma 3) / F*UCS))

Where:

Sigma 1 = major principal stress vector,
Sigma 3 = minor principal stress vector,
Factor = Down grading the rock strength usually for weak rock and for Schist which is the weakest rock type I used 0.9 factor and 0.5 for the Kimberlite due to the high weathering status of the rock type.
UCS = Uniaxial Compressive Strength (Peak strength in uniaxial direction)

ROCK TYPES

Granitic Gnessis

Foliated Granitic Gnesiss

Granite

RANGE OF UCS

(MPa)

MEAN UCS

(MPa)

101 - 320

245

Kimberlite Breccia

75 - 149

107

Kimberlite

116 - 151

128

Dolerite Dyke

202 - 248

231

Schist

25 - 67

UCS values taken from JPE Hamman (2008 Geotechnical Assessment OA Kimberlite Pipe)

The stress state is governed by the depth of mining and the development is done on 1020 meters below surface Sigma 1 can be calculated as: Depth below surface X Density X Gravity = Stress (MPa). Sigma 3 is equal to the Sigma 1 due to the K-ratio is 1 this means that the Horizontal stress field and the Vertica stress field is equal.

Sigma 1 = 1020m x 2.8 t/m³ X 9.81 m/s

Sigma 1 = 28.02 MPa

Thus – RCF for Schist ((3 X 28.02 MPa) – 28.02 MPa) / 0.9 x 42 MPa (Schist)) = 1.48

RCF for Kimberlite ((3 X 28.02MPa) – 28.02 MPa) / 0.5 x 128 MPa (Kimberlite)) = 0.9

RCF < 0.7 good ground conditions prevail with minimum support (Table 4)
0.7 > RCF < 1.4 average conditions prevail with typical support systems (Table 5)
RCF > 1.4 poor ground conditions prevail with special support requirements (Table 6)

Case

Primary Support

(typical requirements)

Secondary Support

(typical requirements)

Static Stress Conditions

'Spot' support where necessary (friction bolt, split sets, rock studs, etc.)

'Spot' support where necessary (friction bolts, split sets, rock studs, etc.)

Stress Changes Anticipated

'Spot' support where necessary (friction bolt, split sets, rock studs, etc.)

Fully grouted tendons/ friction bolts >1.5m in length installed on a basic 2m pattern.

Support resistance:

30-50kN/m2. Welded mesh (sidewall only)

Seismic Activity Anticipated

Friction bolts or tendons > 1.2m in length, installed as close to the face as possible, on a basic 2m or 1.5m pattern.

Support resistance: 30-50kN/m2

Fully grouted (pref. yield) tendons/ friction bolts >1.5m in length installed on a basic 2m pattern.

Support resistance:

50kN/m2. Welded mesh (hanging wall & sidewalls)

Righthand sidewall of T2 access tunnel.

Hanging wall of T2 access tunnel after blasting on the V-Seal.

Little area of Kimberlite was left to demonstrate that V-Seal bonds to Kimberlite.

T2 access tunnel supported with V-Seal up to the face.

Table 4: Support recommendations for good ground conditions. (By Ryder JA & Jager AJ)

Case

Primary Support

(typical requirements)

Secondary Support

(typical requirements)

Static Stress Conditions

Friction bolts or tendons > 1.5m in length, installed as close to the face as possible, on a basic 2m or 1.5m pattern.

Support resistance: 30-50kN/m2

Welded mesh integrated with primary support tendons/ friction bolts.

Stress Changes Anticipated

Fully grouted tendons or steel ropes > 1.8m in length, installed as close to the face as possible, on a basic 2m or 1.5m pattern.

Support resistance: 40-60kN/m2

Welded mesh integrated with primary support tendons/ friction bolts.

Seismic Activity Anticipated

Fully grouted (pref. yield) tendons or steel ropes > 1.8m in length, installed as close to the face as possible, on a 1.5m or double 2m pattern.

Support resistance: 80-100kN/m2

Welded mesh integrated with primary support tendons/ friction bolts, plus optional shotcrete.

Table 5: Support recommendations for average ground conditions. (By Ryder JA & Jager AJ)

Case

Primary Support

(typical requirements)

Secondary Support

(typical requirements)

Static Stress Conditions

If necessary, shotcrete to face, then fully grouted tendons/ friction bolts or steel ropes, length > 1.8m on a basic 1.5m pattern, as close to the face as possible. Support resistance: 80-110 kN/m2

Support resistance:

80-110kN/m2

Stress Changes Anticipated

If necessary, shotcrete to face, then fully grouted steel ropes or yielding tendons/ friction bolts, length > 1.8m on a basic 1m or double 2m pattern, as close to the face as possible. Support resistance: 120-230 kN/m2

Welded mesh integrated with primary support tendons/ friction bolts. Add integral shotcrete in long-life tunnels. If necessary, additional hanging wall support comprising grouted steel ropes.

Seismic Activity Anticipated

If necessary, shotcrete to face, then fully grouted steel ropes or yielding tendons/ friction bolts, length > 2.3m on a basic 1m pattern, as close to the face as possible. Support resistance: 80-100 kN/m2

Welded mesh integrated with primary support tendons/ friction bolts. Add integral shotcrete in long-life tunnels. If necessary, additional hanging wall support comprising grouted steel ropes.

Table 6: Support recommendations for poor ground conditions. (By Ryder JA & Jager AJ)

The V-seal support capability was tested in a key block test whereby the CSIR with the certificate reference T27063 certified that 8mm of V-seal generated 88Kn/m² during the key block testing. (Figure 1 & 2)

The required support resistance based in the code of practice is calculated on the span and the fall out thickness history of this diamond mine, taking the findings of the RCF calculations into consideration of 1.48 for the Schist area the V-seal is more than capable to support the weak rock types integrated with the primary support system.

Looking at the underground test done at the diamond mine the V-seal Product that was applied in July 2021 the bonding of the V-seal has not deteriorate with the underground conditions taken all the environmental constrains into consideration. The Product improves the overall profile of the excavation.

The application of the V-seal product is easy and low labour intensive. In some mines we have phoned and asked for their testimony on the product and all feedback from them was positive.

16mm of V-seal was applied in area with an average RCF and it replaced the welded mesh and the mine reduced there support cost on steel dramatically.

From a sound Geotechnical perspective, I would recommend and motivate the V-seal product as a Rock Support liner to improve the Health and Safety of the workforce and the stability of our mine.

RECOMMENDATIONS:

Apply 8mm of V-Seal up to the face in all access tunnels that is mined in Schist and Kimberlite zones on diamond mine operations.

The K1 support standard will be amended to K1V that includes the V-seal product to be maintained up to the advancing face before the installation of the primary support system.

K1V Support standard will be amended for ring tunnels only in the SLC mining areas as this reduces the secondary support in the ring tunnels.

V-Seal must be applied after the cleaning cycle up to the face covering the entire face of all access tunnels developed in the Schist and Kimberlite zones.