FACTUAL REPORT CONSTRUCTION OF ANCHORS FOR WIND ... - … 13 - Part... · Tender (CEB) Name as per Geotechnical Report Name as per Tender (Vergnet) No. of Anchors per wind turbine

FFAACCTTUUAALL RREEPPOORRTT

CCOONNSSTTRRUUCCTTIIOONN OOFF AANNCCHHOORRSS FFOORR WWIINNDD TTUURRBBIINNEESS

AATT GGRREENNAADDEE,, RROODDRRIIGGUUEESS

PPHHAASSEE 22

Prepared for AJ Maurel Construction Ltée

Prepared by Water Research Co Limited

September 2010

OPG 0083 COL

Report on Anchors at Grenade Page 1 of 23

Revision Description Issued by Date

0 Issued for comments NC / ES 22nd September 2010

Produced Nazila Choolun

Signature

Date 22nd September 2010

Checked Emilio Saldivar

Signature

Date 22nd September 2010

OPG 0083 COL Report on Anchors at Grenade – Phase 2 Page 2 of 21

1 Introduction 3

1.1 Aims and Scope of the Report 3

1.2 Description of the Project and Site 3

1.3 Subsoil Conditions 4

2 Anchor works 5

2.1 General Description of Anchor Works 5

2.2 Health and Safety 6

2.3 Anchor Boring 6

2.4 Reinforcement and Grouting 11

2.5 Test Anchors 16

3 Closing remarks 17

4 References 18

5 Figures 19

Appendix A Layout of site and Location of Anchors

Appendix B Photographs of site works

Appendix C Photographs of Cuttings

Wind Turbine No. 3

Wind Turbine No. 3

Appendix D Anchor Records

Test Anchors

Wind Turbine No. 3

Wind Turbine No. 4

Contents


1 Introduction

1.1 Aims and Scope of the Report

In April 2010, Water Research Co Limited (Water Research) was appointed as subcontractor by AJ Maurel

Construction (Contractor) to carry out drilling and grouting of anchors for 2No. additional wind turbines at

Grenade, Rodrigues. Water Research’s scope of works comprised:

• Drilling and grouting of working and test anchors

• Control of the nature of the raised materials from the drilling

• Reporting on works

This Report presents the description of the work, including:

• General information for the site

• Factual description of fieldworks

• Records of raised materials, anchor drilling and grouting

1.2 Description of the Project and Site

The project comprised the construction of civil works for the installation of 2No. additional Wind Turbines, W3

and W4, in Rodrigues (Phase 2). Phase 1 of the Works was carried out in April/May 2009 and comprised of the

Construction of 2No. Wind Turbines (W1 and W2), an LV room and access roads within the windmill farm (Ref.

4).

The main contract was awarded to AJ Maurel Construction Ltee, who awarded the construction of the

restraining anchors for the wind turbines to Water Research. The wind turbines and associated equipment were

supplied by Vergnet S.A. The main elements of the wind turbines are a 55m tall tubular tower (mat) and 32m

diameter blades. The weight of the tower is 13.5tons and that of the nacelle (including all generative

components and the rotor) is 8.4tons.

The site is located on the north east coast of Rodrigues, at Grenade (Figures 1.1 to 1.3) on ground with an

average slope of 5% and elevations varying between 70m and 113m above mean sea level (amsl). The site is

covered by grass, cobbles and boulders and occasional trees and is bounded to the West by Montagne

Grenade and a valley, to the East by the un-developed land and Montagne au Sel, to the south by 2No. existing

Wind Turbines and the road to Pointe Coton and to the north by the sea. Access roads and power generating

facilities were built during Phase 1 of the works in April 2009.


1.3 Subsoil Conditions

The published geology of the site indicates the presence of ancient formations of tholeitic basalt (silica

oversaturated basalt) and olivine basalt (Ref. 1).

The site subsoil profile identified during the earlier geotechnical investigation consists of Topsoil (encountered

as soft dark brown gravely high plasticity clay), overlying Residual Soil and Completely Weathered Basalt (both

encountered as high plasticity clay of varying strength and reaching at least 7m in BH2 and BH4) and layers of

basalt rock of various grades of weathering as from 1.20m depth (BH2) and reaching up to the maximum drilled

depth of 15.0m. Highly to Moderately Weathered basalt was generally described as moderately strong to

moderately weak grey fine grained closely jointed vesicular basalt with rare amygdales. Depth at which this

stratum is encountered varies between 1.23m and 10.47m with thicknesses varying between 0.82m and 3.1m.

Moderately to Slightly Weathered basalt is generally described as moderately strong to strong grey fine grained

slightly vesicular basalt with rare amygdales. Depth at which this stratum is encountered varies between 1.20m

and 5.46m with thicknesses varying between 0.4m and 3.1m. In general the encountered rock is classified as of

weak to strong strength and poor to fair quality (Ref. 1).


2 Anchor works

2.1 General Description of Anchor Works

Anchorage works on site began on the 18th May 2010 and were completed on 7th June 2010. The Works

comprised the construction of 20No. working anchors and 1No. test anchor. The details of the anchors as given

in the Tender Document are reproduced in Table 2.1; the locations of the anchors are shown in Appendix A.

The photographs of the site works are shown in Appendix B.

Table 2.1 Summary of Anchor Details as per Tender Document

Name as per Tender (CEB)

Name as per Geotechnical Report

Name as per Tender (Vergnet)

No. of Anchors per wind turbine

Ø GEWI bar

Load Length for drilling

Angle of the

anchor

Right tower base slab

Base Anchors Ancrage d'embase (Ed

& Eg)

1No. @ 45° 40 mm 180 6m 45°

Left tower base slab

1No. @ 45° 40 mm 180 6m 45°

Holding side Retaining Anchor Ancrage de retenue (R)

1 No. @ 26° 63 mm 300 8m 26°

Right lateral side Lateral Anchors Ancrages latéraux (Ld

and Lg)

1 No. @ 26° 63 mm 300 8m 26°

Left lateral side 1 No. @ 26° 63 mm 300 8m 26°

Vertical lifting side M1

Manoeuvre Anchors

Ancrage de Manoeuvre

(M,Md & Mg)

1 No. vertical 63 mm 300 8m 0° (vertical)

Right tilted lifting side M2r

1 No. @ 40° 40 mm 350 7,9m 40°

Left tilted lifting side M2l

1 No. @ 40° 40 mm 350 7,9m 40°

Right anticyclonic support

Tower Anchors Ancrage securisation

cyclonique du mat (Bd)

1 No. @ 45° 25 mm 220 6m 45°

Left anticyclonic support

Ancrage securisation

cyclonique du mat (Bg)

1 No. @ 45° 25 mm 220 6m 45°

The drawings produced by Vergnet SA for the anchors were PL99072 MOE, DV911-8976BOR01and DV911-

8976BOR02.


2.2 Health and Safety

Health and safety management was strictly implemented on site. Use of Personal Protective Equipment (PPE)

such as safety helmets, safety footwear and high visibility clothing/jackets was implemented on site.

Housekeeping on site was maintained to the highest standard possible at all times. No major accidents

involving injury to personnel or damage to structures occurred. Progress meetings were held on site once a

week during the Works.

2.3 Anchor Boring

Prior to drilling, the positions of all anchors were checked by Water Research and the Main Contractor with

respect to reference points fixed on site by the latter and Vergnet SA. The Anchors were drilled in 200mm

diameter using a Rockgiant rig following down the hole hammer (DTH) technique (See Figure 2.1) as best

suitable under prevailing conditions; no steel casing was required on the upper section of the borehole. As per

Vegnet SA’s drawing PL99072MOE, the tolerance on the boring angles were ±3°. The angles of the anchors

were within this tolerance.

Figure 2.1 – Drilling Rig and DTH hammer

Records, including all details of the strata encountered, drilled lengths and grouting quantities, were set up for

each of the anchors and witnessed by the Main Contractor and the Client (CEB). The average boring times for


the anchors for each stratum, as requested by Vergnet SA, in the Phase 1 of the Works are also presented in

Table 2.2.

Table 2.2 Summary of boring time as per strata

Strata Boring Time / metre

Max Min Average

Clay with boulders 19min27 45s 3min20

CWB to HWB 4min 1min39 2min44

HWB 3min25 1min 1min39

HWB to MWB 10min37 45s 2min12

MWB 7min09 1min 2min19

MWB to SWB 6min34 1min16 2min54

SWB 19min18 1min10 5min39

Some of the drilled lengths of the anchors were increased to cater for the variations in soil strata encountered

with respect to the design profile. The adjusted lengths of the anchors are presented in Table 2.3.

Table 2.3 Adjusted Drilled Lengths of Anchors

Name of Anchor Wind Turbine No. 3 Wind Turbine No. 4

Drilled Length as

per Tender (m)

Actual Drilled Length (m)

Drilled Length as per Tender

(m)

Actual Drilled Length (m)

Right tower base slab 6.0 9.0 6.0 7.5

Left tower base slab 6.0 9.0 6.0 7.0

Holding side 8.0 9.5 8.0 9.5

Right lateral side 8.0 11.0 8.0 8.5

Left lateral side 8.0 9.0 8.0 9.5

Vertical lifting side M1 8.0 11.0 8.0 9.5


Name of Anchor Wind Turbine No. 3 Wind Turbine No. 4

Right tilted lifting side M2r 7.9 11.0 7.9 11.5

Left tilted lifting side M2l 7.9 9.5 7.9 10.3

Right anticyclonic support 6.0 9.5 6.0 7.0

Left anticyclonic support 6.0 9.0 6.0 6.5

Total drilled length (m) 71.8 97.5 71.8 86.8

For the DTH technique, flushing air (compressed air) carries the cuttings from the bottom of the hole to the

surface. When drilling anchors in close proximity (e.g. Manoeuvre and Tower Base Anchors) the previously

drilled holes were covered during the drilling of the adjacent anchors and flushed with air at the end of drilling of

the group. Whenever the anchor hole was grouted on the following day, the hole was flushed again to remove

any spoil that might have fallen in. Following heavy rain on 29th May 2010, the manoeuvre anchors on W4 were

filled with mud. The depth of the mud at the bottom of the anchor hole was measured and since it was thicker

than 1.5m, the drilling hammer was re-introduced into the hole and the mud was removed and the depth of the

hole readjusted to the lengths previously drilled (as shown in Table 2.3 above).

Samples of the cuttings were collected and the material was logged by an engineer as per BS 5930 - Code of

practice for site investigations. Note that the description is based on fragments resulting from the DTH works

and thus it is approximate. The encountered strata are summarised in Tables 2.4 and 2.5 below. Photographs

of the collected samples are presented in Appendix C.


Table 2.4 Summary of strata encountered Wind Turbine 3

Strata Ld Lg R Bg Bd Ed Eg M1 M2g M2d

Clay with boulders 0.0 – 1.0 0.0 - 3.0 0.0 – 4.0 0.0 – 2.0 0.0 – 2.0 0.0 – 3.0 0.0 – 1.5

2.0 – 2.5 0.0 – 1.0 0.0 – 2.0

CWB to HWB 3.0 – 4.0 6.0 – 7.5 6.0 – 7.0

HWB 4.0 – 6.0 7.0 – 8.0

5.0 – 6.0 8.0 – 9.0 8.0 – 9.0 5.0 – 6.0 7.0 – 8.0

2.0 – 3.0 7.0 – 8.0

3.0 – 3.5 5.0 – 7.0

9.0 – 10.0

HWB to MWB 6.0 – 7.0 8.0 – 11.0 8.0 – 8.5 5.0 – 7.0

8.0 – 9.0 4.0 – 5.0 5.0 – 9.0 2.0 – 4.0 6.0 – 7.0 3.5 – 5.0 3.0 – 5.0 3.5 – 5.0

7.0 – 8.0

MWB 3.0 – 4.0 5.0 – 6.0

3.0 – 5.0 (with clay)

2.0 – 5.0 4.0 – 8.0 (with clay)

3.0 – 6.0 (with clay)

7.0 – 8.0 8.7 – 10.0

6.0 – 7.0

MWB to SWB 1.0 – 3.0 4.0 – 5.0 1.0 – 2.0 8.0 – 8.7

SWB 6.0 – 8.0 8.5 – 9.0

0.0 – 1.0 2.0 – 3.0 7.0 – 8.0

7.5 – 9.5 1.5 – 2.0 (boulder) 2.5 – 3.5

10.0 – 11.0

1.0 – 2.0 (boulder?) 5.0 – 6.0 8.0 – 9.5

2.0 – 3.0 8.0 – 9.0

10.0 – 11.0


Table 2.5 Summary of strata encountered Wind Turbine 4

Strata Ld Lg R Bg Bd Ed Eg M1 M2g M2d

Clay with boulders 0.0 – 1.0 0.0 – 2.0 0.0 – 1.0 0.0 – 2.0 0.0 – 3.0 0.0 – 1.0 0.0 – 2.0 0.0 – 2.0 0.0 – 2.0 0.0 – 4.0

CWB to HWB 2.0 – 3.0 2.0 – 3.0 4.0 – 5.0

HWB 6.5 – 7.0 4.0 – 4.5 2.0 – 3.0 6.0 – 7.0 8.0 – 9.5

4.0 – 5.0 5.0 – 6.0 2.0 – 4.0

2.0 – 6.0 5.0 – 7.0 8.0 – 9.0

11.0 – 11.5

HWB to MWB 3.0 – 4.0 9.0 – 9.5 1.0 – 2.0

5.0 – 6.0 6.0 – 6.5 5.0 – 7.5 6.0 – 7.0 4.0 – 6.0

9.0 – 9.5 6.0 – 7.0 9.0 – 10.0

4.0 – 5.0

MWB 7.0 – 8.0 3.0 – 4.0 4.0 – 5.0 3.0 – 4.0 6.0 – 7.0 7.0 – 8.0 7.0 – 8.0 9.0 – 11.0

MWB to SWB 8.0 – 8.5 4.5 – 5.0 7.0 – 8.0 2.0 – 4.0 5.0 – 6.0 3.0 – 4.0

SWB 1.0 – 2.0 (boulder?) 4.0 – 6.5

5.0 – 9.0 3.0 – 4.0 4.0 – 6.0 6.0 – 7.0 1.0 – 3.0 2.0 – 5.0

7.0 – 9.0 8.0 – 9.0

10.0 – 10.3


The soil profile identified through the anchor drilling is characterised by the following strata, in order of vertical

sequence: Clay with boulders up to a maximum of 4.0m depth and alternating layers of weathered basalt

reaching to the maximum drilled depths. Shallow bedrock (Moderately to Slightly Weathered Basalts) was

encountered on the Retaining Anchor on Wind Turbine No. 3 and on the anti-cyclonic support Anchors and

Base Anchors on Wind Turbine No. 4 as from as from the surface and reaching up to a depth of 5.0m.

The above profile identified during the drilling is consistent with the design profile determined during the

geotechnical investigation. As mentioned above, the anchor lengths were increased whenever variations to the

design profile were encountered.

2.4 Reinforcement and Grouting

Previous to grouting, the 3m/5m long anchor rods were assembled through the coupling sleeve screw and

spacers were placed every metre, fastened with steel wire along the anchor rod as mentioned in the technical

specifications of the tender document (Figure 2.2). The anchor reinforcement was designed by Vergnet SA.

The typical Anchor reinforcement consisted of GEWI bar in diameters as shown in Table 2.1; as per the product

guide (Ref. 2) of the GEWI High Yield Thread bar.

Figure 2.2-GEWI Reinforcement Bar with spacers at 1m intervals


On average, 2No. anchors were drilled and subsequently grouted per day. The three anchors in the manoeuvre

support were drilled and then the anchor eyes were placed at the top of the GEWI bars after which the tool kit

was mounted in the anchor eyes (Figure 2.3). The anchors were grouted after positioning and checking of the

anchors’ alignment and angles.

Figure 2.3 – Preparing the Manoeuvre Anchor for grouting

Grouting proceeded as follows:

All grout surfaces were cleaned of oil, grease and other foreign matter. The colonial mixer (1500

revolutions per minute) did not contain free water.

Full quantity of water was place into the mixer (corresponding ratio to cement weight) and run the

mixer up to full speed.

Cement was slowly poured into the mixer.


At the end of the mixing, the grout wa injected under gravity from the bottom of the borehole by means

of a tremie pipe. Grouting with the end of the tremie pipe placed at the bottom of the hole enables any

trapped water to come up to the surface and flow out.

Grouting lasted an average of 45min with an average oversupply ratio (grout placed: theoretical volume needed)

varying between 0.8 (undersupply) and 1.5 (oversupply) (Table 2.6) .

Figure 2.4 – Grouting Mixer


Table 2.6 Summary of Grouting

Anchor Name Drilled Length

(m)

Ø GEWI bar (mm)

volume of bar (m3)

Volume of hole (m3)

Volume of hole (m3)

Volume Theory (L) Grout details

Volume of grout placed

(m3)

Oversupply (Ratio)

Wind turbine No. 3

Right tower base slab, Ed

9.0 40 0.011 0.442 0.430 430 12 bags 490 1.1

Left tower base slab, Eg

9.0 40 0.011 0.442 0.430 430 12 bags 490 1.1

Holding side, R 9.0 63 0.028 0.442 0.414 414 12 bags 490 1.2

Right lateral side, Ld

11.0 63 0.034 0.540 0.506 506 14 bags 572 1.1

Left lateral side, Lg

9.0 63 0.028 0.442 0.414 414 10 bags 359 0.9

Vertical lifting side M1 11.0 63 0.034 0.540 0.506 506 12 bags 490 1.0

Right tilted lifting side

M2r 11.0 40 0.014 0.540 0.526 526 11 bags 449 0.9

Left tilted lifting side

M2l 9.5 40 0.012 0.466 0.454 454 12 bags 490 1.1

Right anticyclonic support, Bd

9.0 25 0.004 0.442 0.437 437 16 bags +

20litres 674 1.5

Left anticyclonic support, Bg

9.5 25 0.005 0.466 0.462 462 11 bags 449 1.0


Anchor Name Drilled Length

(m) Ø GEWI bar

(mm) volume of bar (m3)

Volume of hole (m3)

Volume of hole (m3)

Volume Theory (L) Grout details

Volume of grout placed

(m3) Oversupply

(Ratio)

Wind turbine No. 4

Right tower base slab

7.5 40 0.009 0.236 0.226 226 8 bags 327 1.4

Left tower base slab

7 40 0.009 0.220 0.211 211

6 bags -

20litres (3 litres

used for test

cube)

242 1.1

Holding side 9.5 63 0.030 0.466 0.437 437 12 bags -

20litres 470 1.1

Right lateral side

8.5 63 0.026 0.267 0.241 241 8 bags +

40litres 367 1.5

Left lateral side

9.5 63 0.030 0.298 0.269 269 8 bags +

20litres 347 1.3

Vertical lifting side M1

9.5 63 0.030 0.466 0.437 437 12 bags 490 1.1

Right tilted lifting side

M2r

11.5 40 0.014 0.565 0.550 550 13 bags 531 1.0

Left tilted lifting side

M2l

10.3 40 0.013 0.506 0.493 493 11 bags 449 0.9

Right anticyclonic

support

7 25 0.003 0.344 0.340 340 6 bags +

20litres 265 0.8

Left anticyclonic

support

6.5 25 0.003 0.319 0.316 316 7 bags 286 0.9


Like in the construction of Phase 1 (Ref. 4), a 0.5 W/C ratio grout mix was used for the project. Cement on site

was supplied by the Main Contractor. Cubes from grout mixes were taken and handled by the Main Contractor

for compression strength testing.

In accordance with the requirements of the Technical Specifications Water Research provided a daily record of

drilling and grouting operations. This information includes:

1. Location, number, diameter, angle and depth of the anchor holes drilled.

2. Details of grout, volumes of grout injected, quantities of any other material injected and injecting times.

3. Times of sampling and location where samples were taken.

4. Remarks on grouting incidents, delays, surface leaks, interconnections, refusals and any other factors,

which might influence the effectiveness of the grouting.

2.5 Test Anchor

The test anchor was constructed near BH 1 and the Medium Voltage MV control room and the details are as

follows:

Name: Test Anchor No. 1

Ø anchor GEWI Bar (mm): 40

Theoretical Drilled Length (m): 8

Drilled Length (m): 12

Angle of the Anchor: 0° (Vertical)

1No. Test Anchor was drilled in view of carrying out on-site testing (pull out test). The testing will be handled by

the Main Contractor. The summary of the drilling and grouting of the Test Anchor is presented below in Table

2.7.

Table 2.7 Summary Test Anchor No. 1

Clay HWB H/MWB MWB M to SWB

Theoretical Grout Volume

(L)

Actual Grout placed (L)

Oversupply Ratio

0.0-2.0 3.0-4.0 7.0-9.0

2.0-3.0 4.0-5.0 9.0-12.0

5.0-6.0 6.0-7.0 574 594 1.0


3 Closing remarks

The Report presents factual information from Anchor Drilling and Grouting Works carried out at Grenade,

Rodrigues from 18th May 2010 to 7th June 2010. The Works comprised the construction of 20No. working

anchors of diameter 200mm. The Works also included the construction of 1No. 200mm diameter Test Anchor

for pull out testing.

The site is located on the north east coast of Rodrigues, at Grenade on ground with an average slope of 5% and

elevations varying between 70m and 113m above mean sea level (amsl). The site is covered by grass, cobbles

and boulders and occasional trees. The site is bounded to the West by Montagne Grenade and a valley, to the

East by the un-developed land and Montagne au Sel, to the south by 2No. existing Wind Turbines and the road

to Pointe Coton and to the north by the sea. Access roads and power generating facilities were already built (as

phase 1 of the Works carried out in April 2009) at the time of the anchor construction works.

The soil profile at the site up to the bored depths is characterised by the following strata, these are in order of

vertical sequence, where present: Clay with boulders up to a maximum of 4.0m depth and alternating layers of

weathered basalt reaching to the maximum drilled depths. Shallow bedrock (Moderately to Slightly Weathered

Basalts) was encountered on the Retaining Anchor on Wind Turbine No. 3 and on the anti-cyclonic support

Anchors and Base Anchors on Wind Turbine No. 4 as from as from the surface and reaching up to a depth of

5.0m.

Some of the drilled lengths of the anchors were increased to cater for the variations in soil strata encountered

with respect to the design profile. The adjusted lengths of the anchors are presented in the Report. The detailed

construction records has been compiled and annexed to the Report. The drilling and concreting were witnessed

by the Client (CEB) and the Main Contractor Colas (Mauritius) and the Anchor Records have been duly signed.

Health and safety was strictly implemented on site. Water Research made use of Personal Protective

Equipment (PPE) such as safety helmets, safety footwear and high visibility clothing/jackets on site.

Housekeeping on site was maintained to the highest standard possible at all times. No major accidents

involving injury to personnel or damage to structures occurred.

We trust that the information contained in this report is satisfactory. Should you have any questions, please do

not hesitate to contact this office.


4 References

1. Saldivar, E., Choolun, N. (2008), Report on Subsoil Investigation for windmills at Grenade, Rodrigues.

2. Dywidag Systems International, Gewi Threadbar System Brochure,

3. British Standards (1999), BS 5930, Code of practice for site investigations.

4. Saldivar, E., Choolun, N. (2009), Factual Report for Construction of Anchors For Wind Turbines At

Grenade, Rodrigues.


5 Figures

Figure 1.1 General location of the site

Site


Figure 1.2 Location of the site

SITE


Figure 1.3 Aerial view of the site

Documents

FACTUAL REPORT CONSTRUCTION OF ANCHORS FOR WIND ... - … 13 - Part... · Tender (CEB) Name as per Geotechnical Report Name as per Tender (Vergnet) No. of Anchors per wind turbine