rvm hydro electric project - cesnet 1 hydro electric power (pty) ltd/rvm... · rvm hydro electric...

Prepared by Hydro Tasmania South Africa (Pty) Ltd ‐ registration number: 2011/137429/07PO Box 50, Cape Town International Airport, Cape Town, 7525

RVM Hydro Electric Project Draft Construction Method Statement

7 May 2015

Entura in Australia is certified to the latest version of ISO9001, ISO14001, and OHSAS18001.

©Entura. All rights reserved.

Entura has prepared this document for the sole use of the client and for a specific purpose, as expressly stated in the document. Entura

undertakes no duty nor accepts any responsibility to any third party not being the intended recipient of this document. The information

contained in this document has been carefully compiled based on the client’s requirements and Entura’s experience, having regard to the

assumptions that Entura can reasonably be expected to make in accordance with sound professional principles. Entura may also have

relied on information provided by the client and/or other parties to prepare this document, some of which may not have been verified.

Subject to the above conditions, Entura recommends this document should only be transmitted, reproduced or disseminated in its

entirety.

RVM Hydro Electric Project ‐ Draft Construction Method Statement Revision No: 1.0 7 May 2015

i

Document information

Title RVM Hydro Electric Project

Draft Construction Method Statement

Client organisation RVM1 Hydro Electric Power (Pty) Ltd

Client contact Niel Theron

Document number

Project manager Nick West

Project reference E304773 ‐ P509337

Revision history

Revision 1.0

Revision description Draft for Information only

Prepared by Nicholas West

Reviewed by David Gerke

Approved by David Gerke

(name) (signature) (date)

Distributed to Niel Theron RVM1 Hydro Electric Power (Pty) Ltd

(name) (organisation) (date)


ii

This page is intentionally blank


1

1. General

1.1 Background

The purpose of this method statement is to outline the steps to be taken before, during and after construction of the RVM Hydro Electric Project to demonstrate compliance with:

likely Environmental Authorisation conditions,

likely Water Use Licence conditions,

the likely Construction Environmental Management Plan (CEMP)

It is also intended that this report satisfy the Department of Water and Sanitation (DWS), local authorities and surrounding property owners that on completion of the Project, there will be no potential short or long term environmental or physical scarring to the immediately adjacent to construction or operationally disturbed areas.

All the structures will be designed for a design life cycle of 40 years, however with appropriate remedial and maintenance actions taken as required, structures can be expected to perform as designed for over 100 years or more.

An overview of the arrangement is shown in Figures Figure 1.1 to Figure 1.4.

1.2 Site Establishment

The Contractor’s site office and construction camp locations are shown on in Figure 1.2. The construction camp is the staging area for the contractors and will contain such items as:

Concrete batch plant,

Equipment stores,

Fuel storage, and

Maintenance facilities.

1.3 Borrow Pits and Spoil Sites

Potential borrow pits are not considered to be necessary for this project since material won from headrace canal excavation and tunnel excavation is anticipated to be appropriate for use (once crushed) for a variety of purposes across the project. Spoil will be stockpiled in an area identified and assessed as part of the Environmental Impact Assessment (EIA) process (shown in Figure 1.4). Drainage around the spoil site will be designed according to the conditions of both the Environmental Authorisation and the Water Use Licence.


2

Figure 1.1: General layout of project infrastructure from diversion weir to tailrace outfall (CES, 2015, p 57)


3

Figure 1.2: Layout of weir and offtake structure (CES, 2015, p 58)


4

Figure 1.3: Layout of headpond, underground power chamber, tailrace tunnel and outfall (CES, 2015, p 59)


5

Figure 1.4: Position of the substation and proposed area for surplus spoil deposition (CES, 2015, p 60)


6

1.4 Crusher

A mobile crusher will be established on the site. The location is yet to be determined but it is likely to be near the spoil site.

The mobile crusher will be established to crush rock excavated from the headrace, penstock and access shafts and powerhouse cavern and tailrace. This material will be used as coarse aggregate for concrete, road construction and for erosion protection where required.

1.5 Pre‐Cast Yard

If required, a pre‐cast yard will be established in the vicinity of the construction camp.

1.6 Potable Water

The Contractor will ensure that potable water is supplied to and stored on site in adequate facilities.

1.7 Power

The temporary power to the site will be obtained from available local electricity infrastructure or, if not available by generator with appropriate fuel bunding.

1.8 Sewerage

The Contractor will ensure that adequate facilities are available for the workforce in the form of chemical toilets or via conservancy tank.

The disposal of waste will be undertaken with the approval of the local authority.

1.9 Batching Plant

A concrete batching plant will be established on site to produce all the concrete required for construction of Project infrastructure. This will require local water and power.

Aggregate stockpiling as well as cement storage is required and will be located within the construction camp.

1.10 Equipment

A comprehensive inventory of the construction equipment to be used on site will be prepared at a later stage and prior to site establishment.

Refuelling and maintenance facilities will be located in the construction camp shown in Figure 1.2 and will have appropriate spill management systems in place.

1.11 Access Control Edge Protection of Animals and Humans

As the design develops, the access control measures for animals and humans will be developed in conjunction with the EIA & WULA requirements.


7

1.12 Initial Investigations

Detailed topographical survey has been performed, which will be used as the design develops.

Geotechnical investigations are planned to be undertaken that will allow the design to develop and to provide more detailed information on the foundations and suitability of the in‐situ materials as construction materials. These invasive investigations will include activities such as:

Excavation of test pits,

Drilling, and

Seismic tests.

These investigations have the potential to cause disruption in the local area and any investigations will be adopted in accordance with with the EIA & WULA requirements and in conjunction with the relevant authorities.

1.13 Experience of Contractor, Staff and Senior Management

Construction of the RVM Hydro Electric Project is scheduled to begin in early to mid 2017. At this stage it is envisaged that the majority of parties involved with the construction of the Neusberg Hydro Electric Project, which is began operation in January 2015, will remain involved for the RVM Hydro Electric Project. Experience at Neusberg will give all parties a comprehensive understanding of the issues likely to be faced at RVM.

One major component of the works not present at the Neusberg Hydro Electric Project is tunnelling. An experienced contractor will be engaged to undertake the Tunnelling Works. This contractor will be a sub‐contractor to the Civil Works Contractor and will be made aware of the requirement of the CEMP and the likely repercussions associated with a breach.

2. Weir

A coffer dam is required to create a “water‐free” environment in which to construct the weir. It is envisaged that the cofferdam will be constructed in 2 stages (half of the river width each stage) to ensure existing flows can pass unimpeded during construction of the weir. The cofferdam will not be watertight, which will mean that continual pumping of seepage water will be required. Seepage water could be contaminated with suspended fines and sediment from the foundations or coffer dam and as such, will be treated to remove excess sediment and then discharged on the downstream side of the coffer dam into the main river channel.

As the invert of the river will be sloping and uneven, it is envisioned that “heavy duty” sand bags filled with a sand/cement mixture will be placed on the rock bed. The bags will be profiled to create a top surface on which to build the coffer dam walls. The fill material will set when in contact with the water to produce a solid and robust stable foundation.

The walls will be created by dry stacking a system of keyed pre‐cast blocks that can be tied together with chains or cable to counter the infill surcharge. As blocks are laid and tied together, layers of infill material, rock and finer material, will be placed with the block walls forming an almost impermeable wall that will allow for dewatering on the offtake side.


8

The weir will be constructed in two stages –the left and right stages. The cofferdam will need to be removed from one site and replaced on the other side to allow construction of the weir in dry conditions.

The coffer dam wall must be removed on completion of construction of the offtake structure. As such, the proposed design will allow for the removal of the fill material followed by removal of the blocks and lastly, the foundation bags, this process will minimise any contamination into the existing watercourse.

The coffer dam will be constructed during the low flow summer season to ensure that this is constructed when water levels are at their lowest.

This system is being proposed as it will be the least intrusive in terms of environmental impact. Mass fill operations will result in silt and suspended materials impacting significantly on water quality in the river downstream of the works.

3. Offtake Structure

The inlet structure will be a cast in‐situ reinforced concrete structure located on the right abutment of the weir. The structure will house trashracks, stoplogs and gates. This structure will be the primary mechanism for stopping flow in the headrace.

The river bed at the offtake structure will be excavated to a depth that allows efficient conveyance of water into the headrace. The floor of the excavation will require blinding before the reinforced concrete slab is cast. The walls will be cast hard onto the rock face with an internal shutter. The superstructure will be cast with shutters on both faces.

The structure will have slots for stoplogs and gates cast in.

Inside, the structure will have a slab cast and frame constructed to accommodate a gantry and hoists for stoplogs and gates. The structure will have a steel roof.

The hydromechanical equipment will be fitted once the concrete has reached the required strength.

4. Headrace

The headrace is a covered conduit that conveys water from the intake structure to the headpond, by utilising a covered conduit it does not create a visual issue and allows animals to traverse safely during operation. A trench will be excavated along the route and spoil will be stockpiled. Excavation will be done by mechanical means as far as possible but it is considered that significant amounts of controlled blasting may be required due to the presence of hard rock close to the surface.

Once the excavation has reached the design profile, the floor will be treated with a blinding layer of concrete followed by a reinforced concrete floor for the headrace conduit. Inverted box culverts will be cast on top of the floor to form two parallel culverts. Once the culverts are cost, the trench will be backfilled with selected material and the surface will be rehabilitated.


9

Where the headrace canal intersects existing drainage lines, additional compaction of backfill will be required to ensure water flowing in the drainage lines can pass over the headrace without infiltrating into the disturbed ground.

Construction will be staged so that the length of open trench is minimised for safety reasons, although construction activities are likely to be continuous.

5. Headpond

The headpond is a small reservoir that regulates flow into the penstock. The headpond is formed by an earth and rockfill embankment with a small spillway on the left abutment.

Topsoil within the headpond will be stripped and stockpiled for use elsewhere on the project. Once stripping is complete the foundations of the headpond will be inspected and any locations of potential excessive leakage areas will be grouted to prevent this leakage.

A cut‐off trench will be constructed along the alignment of the embankment. This trench helps to seal the interface between the foundations and the embankment. A geosynthetic liner will be placed over the foundation and the graded embankment fill be placed on top. Geofabric filters will prevent seepage and loss of material through the embankment.

In the centre of the embankment, a concrete intake structure will be constructed that houses a hilltop valve that closes to prevent flow into the powerhouse. This intake structure and valve are the interface between the headpond and the penstock. The intake structure will be constructed out of reinforced concrete, which will encase the hilltop valve.

The spillway on the left abutment of the headpond embankment will be a wide open channel that follows the natural contours. Erosion protection downstream of the spillway will be in the form of rip‐rap, depending on the erodability of the surface material.

Depending on the outcomes of sediment studies, a sediment settling basin may be required at the headpond. This will be a reinforced concrete structure located within the headpond. Discharge of slurry from the settling basin will be piped through the powerhouse and discharged into the tailrace.

6. Tunnelling (Penstock/Access Shafts, Powerhouse Cavern and Tailrace)

The underground works are likely to be the first to start construction. It will be performed using the drill and blast method.

The underground works include the:

Access and penstock shafts,

Powerhouse cavern, and

Tailrace.


10

Ground support requirements for the underground works will be determined based on the outcomes of geotechnical investigations and will be refined once excavation has been carried out.

The powerhouse cavern and tailrace will be lined with cast in situ concrete with a floated floor.

The items listed below will be elaborated on as the design develops:

6.1 Excavation of topsoil and overburden

Loose material will be removed by excavator and trucks.

6.2 Tunnelling

The Tunnelling Contractor, once engaged, will provide a method statement on tunnelling prior to the commencement of construction. This method statement will cover the following items.

Temporary works

Preliminary works

Drilling

Blasting

Barring down

Mucking out

Ground support

Tunnel lining

Rehabilitation

6.3 Stabilisation of topsoil and overburden on exposed slopes

Suitably sized rip‐rap from the rock excavation will be used to stabilise exposed slopes.

6.4 Headrace tunnel lining

6.4.1 Overbreak/underbreak

Where gross overbreak is experienced, this will be filled with shotcrete filler.

Where there is underbreak, further blasting will be undertaken or hand or small mechanical rock breaking equipment will be used to achieve the required design profile.

6.4.2 Floor

The headrace tunnel floor will receive a blinding layer to achieve level control.

The tunnel floor will then be cast. The floor will have thickened edges to support the wall lining.


11

Based on modelling outcomes and expected sediment loads a rock trap may be required near the downstream end of the tunnel.

6.4.3 Walls and crown

If required, lining of the walls and crown will be done with cast in‐situ concrete. The lining will be cast hard against the excavated rock face with an internal shutter. The wall thickness will be confirmed once rock conditions and design calculations have been confirmed.

6.4.4 Survey

Survey is a key aspect of tunnel construction. Prior to each blast, the excavated profile will be surveyed against the required design profile.

Geological conditions will be mapped prior to lining of the tunnel.

7. Penstock

The penstock is likely to be steel pipes welded together to convey water from the headpond to the powerhouse. A manifold in the powerhouse will distribute flow to each turbine.

The penstocks will be large diameter (up to 3.5m) so the pipe lengths will be very heavy. It is likely that pipes will be shipped as two semicircular sections and welded together on site. This will be a complex operation since one half of the pipe will have to be lowered into the shaft and attached to the walls of the shaft. The second half of the pipe will then have to be lowered into position, welded and fixed to the wall as well. This will require a crane to be located on site.

8. Powerhouse

The powerhouse is the structure that will house the turbines and generators, with a range of mechanical and electrical equipment to service these main items. In this case, the powerhouse is located in a cavern underground. It is expected that this cavern will be in the order of 45m long x 30m wide x 20m high. The depth of the powerhouse (approximately 120 m below the surface) is determined by the water level required for flow to freely discharge from the tailrace. These dimensions will be confirmed during the detailed design stage.

The transformer yard will have a transformer catch pit being a reinforced concrete slab as a floor with upstand walls. Each transformer will be seated on a mass concrete plinth. The entire yard will either near the surface or within the powerhouse, but will be set below ground level to reduce visual intrusion.

8.1 Construction

The floor of the excavation will have a mass concrete blinding layer to create a surface as close as possible to the underside of floor slab level. The floor slab will be a reinforced cast in‐situ slab. Concrete will be lowered into the powerhouse cavern then pumped to cast slab and wall concrete. The concrete will be manufactured at the site batching plant.


12

The concrete mix design will be designed for strength, watertightness and have a longevity span of a minimum of 40 years. This might require the introduction of additives into the concrete mix.

Concrete cube tests for this and all the other structures will be regularly tested to ensure they are consistent with strength and quality requirements.

The turbines are fixed to the concrete floor slab as well as the downstream wall where the openings to the draft tubes have been formed.

Access into the powerhouse will be via the access shaft lifts or steel staircases.

8.2 Installation

Many of the mechanical items required for placement in the powerhouse are very heavy. These items will be lowered into the powerhouse by crane. Once inside the powerhouse, a gantry crane will be used to move equipment about. The gantry crane must be installed first.

9. Access Roads

Access roads, both temporary and permanent will be required and will be designed for all weather access during construction and operational phases.

9.1 Haul Roads

Temporary haul roads will be required for the full length of the construction process, between various site locations. This road will be a basecourse finish and be reinstated once construction has been finalised.

9.2 Permanent Roads

A permanent road will be required to the Power Station. This will also have a basecourse finish and be designed to specific levels and falls required by the detailed design. The design life of the roads will be consistent with the Project requirements and will need to be maintained during the construction and operational phases.

Where haul roads and new roads cross existing roads, the existing roads will be overlaid with a minimum of 150mm basecourse.

Culverts will be placed at necessary locations along all roads to prevent erosion of road materials.

10. Flood Protection

Structures will, in general be located outside the 1:100 AEP flood line. Where structures lie within the 1:100 AEP flood line they will be appropriately designed/protected to withstand flood events.

The offtake structure will have waterproof level above the 1:1000 AEP flood line.


13

11. Conclusion

During the construction phase of this Project, the most important consideration for the Civil Works Contractor is to adhere to the conditions of various authorisations. The significant issues to be addressed are;

The pre‐construction survey will document in detail the condition prior to construction of the infrastructure.

The safety of humans and animals is a priority and all necessary measures will be put in place to ensure this.

Blasting will be undertaken in accordance with accepted practices. This will mean that these operations will pose no risk to the existing infrastructure.

Site Management in all aspects will be carefully monitored to ensure that the site boundaries are respected.

Waste Management will be well controlled to ensure no contamination.

Lastly, the environment will be returned to an acceptable condition which will allow for rejuvenation of flora to natural pre‐existing state.

12. References

EOH Coastal & Environmental Services (CES), 2015, Environmental Impact Assessment Report, April


14

This page is intentionally blank.

rvm hydro electric project - cesnet 1 hydro electric power (pty) ltd/rvm... · rvm hydro electric...

Documents