Pdm RCC ICOLD B177-RCC dams preprint

INTRODUCTION

BULLETIN PURPOSE

The purpose of this Bulletin is to provide the general dam practitioner with a summary of contemporary typical and generally accepted practice in the use of roller compacted concrete construction for dams. This Bulletin therefore provides a comprehensive overview of the state of the art of the design and construction of RCC dams as of the current date of publication (2018).

THE KEY ADVANTAGE OF RCC DAMS

RCC DAM CONSTRUCTION

RCC DAM TYPES & APPLICATIONS

In addition, a number of variations on the RCC dam design and construction approach are being used internationally; some related to the local availability of certain material types, such as the. The establishment of an ICOLD Committee on Cemented Material (CMD) Dams in 2014 required a distinction to be made between CMD and RCC dams; the former was previously considered a variant of an RCC dam.

HISTORY OF DEVELOPMENT OF RCC DAMS

ADVANTAGES AND DISADVANTAGES OF RCC DAM CONSTRUCTION

The design and design development of an RCC dam and the optimization of the RCC mix can sometimes be more involved and time-consuming than is the case for a traditional (CVC), mass concrete dam. The design of an RCC dam is a process similar to that of a fill dam whereby materials are designed.

CURRENT RCC DESIGN CONCEPTS AND TYPES

TRENDS IN RCC TYPES

When non-cementitious fill materials are not available, a super retarded HCRCC will generally require a cementitious materials content exceeding 190 kg/m3. In the applicable content range of cementitious materials, it is generally not possible to rely on cement paste alone and accordingly, Total Paste is improved with non-cement fines to develop sufficiently impermeable RCC.

CONSTRUCTION CONSIDERATIONS

Success is increasingly being achieved using the previously less popular type of MCRCC with an impermeable RCC approach. Typically, this approach will be taken with a tighter treatment of the bed joints and possibly a bed mix in the upper "impervious" zone.

IMPROVED UNDERSTANDING OF THE EARLY BEHAVIOUR OF RCC

Sometimes this type of RCC will be zoned, creating only an upstream impervious zone, with the rest of the dam using more permeable MCRCC or even LCRCC. Notwithstanding the above, a range of useful solutions for RCC can be considered, and similar principles and approaches can now be applied to the mixed design and construction use of RCC with a significant range of cementitious content.

DESIGN OF RCC DAMS

BACKGROUND & Key Aspects
Early RCC Behaviour
Design considerations

General
Typical RCC strength characteristics
Bond between layers
Design for horizontal construction
Gravity dams
Arch dams (see Chapter 9)

Thermal considerations

General
Surface and Mass gradient effects
Thermal analysis and design
Temperature control measures
Contraction joints

Other considerations

Galleries
Spillways
Appurtenant structures and inserts
RCC Surfacing

Instrumentation

General
Appropriate instruments and instrumentation configurations
Instrument installation

References

The “zero stress” temperature is a function of the placement temperature, the total hydration temperature rise, and the stress relaxation creep. However, with very high (and wide) gravity dams it may prove necessary to provide a (longitudinal) shrinkage joint parallel to the dam axis up to a certain height above the foundation support.

MATERIALS

CEMENTITIOUS MATERIALS

General
Cement
Supplementary cementitious materials

AGGREGATES

General
Coarse aggregates
Fine aggregates
Overall grading

ADMIXTURES
REFERENCES

Ideally, the RCC inlet system of the main dam should be used for the construction of the FST. Excavation of fresh RCC (usually with a backhoe before the RCC has gained much strength).

SELECTION OF MIXTURE PROPORTIONS

RCC CONSISTENCY – LOADED VEBE TEST

TYPICAL MIXTURE PROPORTIONS

DEVELOPMENTS IN MIX DESIGN

GENERAL MIXTURE PROPORTIONING METHODOLOGY

OPTIMISATION OF THE AGGREGATE

Coarse aggregate
Fine aggregate
Overall gradation

RCD METHOD

MIXTURE PROPORTIONING FOR MEDIUM AND LOW-CEMENTITIOUS RCC (MCRCC &

General
Alternative approaches
Typical LCRCC mix characteristics and requirements

CHEMICAL ADMIXTURES

Consistency
Cementitious paste vs. void ratio of compacted fine aggregate
Volume of cementitious paste and volume of total paste
Setting time
Density

AIR-ENTRAINED RCC

FULL-SCALE TRIAL

MIXTURE PROPORTIONS OF GROUT FOR GEVR/GERCC AND BEDDING MIXES

MIXTURE PROPORTIONS FOR RCC ARCH DAMS

CONSTRUCTION

GENERAL

RCC Construction Requirements
RCC Placement Rates

FULL-SCALE TRIALS

AGGREGATE PRODUCTION AND STOCKPILING

Aggregate production
Aggregate stockpiling and storage

PRODUCTION OF RCC

General
Mixers
Silage of cementitious materials

COOLING AND HEATING TECHNIQUES

Pre-cooling methods
Post-cooling methods
Pre-heating methods
Post-heating methods

TRANSPORTATION

Trucks to point of placement ("total truck")
Conveyor with trucks on the surface of the dam
All-conveyor system
Combination of trucks, conveyors and telescopic conveyor
Vacuum chutes and pipes
Other methods

OVERALL PLACING METHODS

Horizontal placement
Slope-layer placement
Split-level placement
Block placement
Non-continuous horizontal layer placement

SPREADING AND COMPACTION

Start of placement: levelling concrete
Interface concrete
Spreading
Layer thickness
Compaction

JOINTS BETWEEN RCC LAYERS

Transverse "vertical" construction joint in a layer
Longitudinal "vertical" construction joint in a layer

CONTRACTION JOINTS AND WATERSTOPS

Forms of contraction joint
Grouting of contraction joints
Waterstops, drains and surface joint inducing systems

FORMING THE FACES OF RCC DAMS

CVC
GERCC
GEVR
IVRCC
Formwork
Pre-cast concrete panels or segments
Slip-forming of facing elements
External membrane
Pre-cast concrete blocks
Unformed downstream face
Pressure maintenance edge slope compaction
Other methods
Forming the spillways of RCC dams

GALLERIES

CURING AND PROTECTION OF RCC

Curing of the RCC surface and dam faces
Protection under rainy conditions
Protection in hot weather conditions
Protection in cold weather conditions

GENERAL

QUARRY

PLANT AND EQUIPMENT

General
Aggregate plant
Concrete batch plant
Conveyors and intermediate holding hoppers
Placement equipment

MATERIALS TESTING

FRESH RCC TESTING

HARDENED RCC TESTING

FULL-SCALE TRIAL

ACCELERATED CONCRETE CURING

INSPECTION AND TESTING DURING PLACEMENT

CONTROL OF FRESH CONCRETE

General
Layer Joints and Setting Times
Temperature

CONTROL OF HARDENED CONCRETE

TRAINING

PERFORMANCE

Layer JOINT performance – bond and impermeability

Requirements for layer joint integrity and impermeability
RCC layer surface conditions
Layer joint performance objectives

In RCC dams that are placed continuously from one abutment to another, the entire layer surface is exposed to ambient weather conditions. In modern construction of RCC dams, the use of mixtures that delay setting is common, the setting time is measured and the maturation of the layer surface is closely monitored. For large RCC dams it is even possible to have all three conditions develop on the same layer surface at one time or another, depending on the mixture curing time and placement sequence.

The next requirement to achieve monolithic performance is the surface preparation method for each layer's surface condition.

Layer JOINT Strength performance

Evaluation of layer joint integrity through drilled coring
Direct tensile strength
Shear strength performance of parent RCC and layer joints
Effect of compaction on strength properties

The direct tensile strength of RCC layer connections is usually compared to compressive strength or direct tensile strength of the original (unbonded) RCC. Tests on LCRCC mixtures (loaded VeBe time ~ 45 sec or higher) showed that both the percentage of bonded layer joints and the direct tensile strength of cold joints were significantly improved by the use of a bottom concrete or mortar. Long-term shear properties of parent RCC and two types of layer joints with HCRCC mixture and without soil mixtures.

Direct shear properties of bonded layer joints for HCRCC with Loaded VeBe times of 15 to 20 sec. and LCRCC with Loaded USA.

Figure 7.5 shows an 11.3 m long core (the length of the core barrel) – one of several extracted from the Yeywa dam in Myanmar

Performance of crack inducing systems
Performance of contraction joint/waterstop systems
Performance of post-construction, grouted contraction joints
Performance of post-construction crack repairs

Causing contraction joints with a vibrating plate up to 2/3 of the layer depth was effective. At the Shah wa Arus Dam in Afghanistan (Sayed Karim Qarlog, 2015), cracks developed between induced shrinkage joints and propagated through the upstream side of the dam to the gallery. The goal of the post-construction grouting program was rated as satisfactory with a 95% reduction in seepage, according to the owner, the US Army Corps of Engineers (Drahushak-Crow & Dolen, 1988).

In addition, a sprayed membrane was applied to the upstream side of the dam over the other cracks.

Figure 7.17 shows a crack wandering around the waterstop due to poor support details for the wasterstop and misalignment of the flexible plastic sheet

Performance of dam facing systems

Formed CVC facing
Grout-Enriched RCC (GERCC) and Grout-Enriched Vibrated RCC (GEVR) facing
Performance of impermeable PVC membranes
Performance of spray-on membranes

A critical aspect for satisfactory GERCC and GEVR performance is the size of the internal vibrators. The Galesville dam used a spray-on coal tar-based elastomeric membrane shortly after the RCC dam was completed. It is noted that there were no induced contraction joints in either of the two dams.

The capacity of the dam, in terms of seepage through the upstream wall of the dam, is quite satisfactory so far (less than 10 l/s) (Pietrangeli, 2017).

Durability Performance of RCC

Performance in freeze-thaw environments
Abrasion and erosion resistance / performance
Deleterious chemical reactions

The key to the successful implementation of this system is the preparation of the upstream RCC surface, including carefully removing, by pressure washing or sanding, all traces of dirt and loose material and applying an epoxy-cementitous layer. primer on the RCC surface. The reservoir level reached approximately 90% of maximum head at the end of the 2016 rainy season. Due to the emergency nature of the project and the short expected life (5 to 10 years) of the structure, the dam was constructed using locally available and potentially reactive aggregates and high alkali cement.

As expected, alkali-aggregate reaction was found in RCC within approx. 5 years after construction.

Performance of RCC dams under Extreme loading conditions

Performance under seismic loadings
Performance of RCC spillways
Performance under geological non-conformities

The 132 m long three-center RCC arch dam was completed in 2003 in Sichuan Province, China, and is located 32 km from the epicenter of the Wenchuan Fault, which was the site of an M 8.0 earthquake in May 2008. With a reservoir almost The dam structure was full at the time and was completely undamaged by the event, although the joint and discharge galleries were flooded due to a rockfall blocking the outlets and causing one of the spillway portals to light was damaged. Although very few concrete dams have failed worldwide, foundation problems and associated stability issues are the leading cause of the failures that have occurred.

Water pressure from the impoundment caused seepage, causing progressive erosion of the weathered material until insufficient stability remained and failure of the rock mass occurred.

Examples of some of the important RCC arch dams completed in China up to 2017 are listed in Table 9.1. The hinge joint structure was developed during the design of the Shimenzi RCC arch dam (Liu, Li & Xie, 2002). All RCC arch dams have incorporated flush in the cementitious materials, with percentages up to 65%, depending on the qualities of cement and fly ash available.

Experience to date has shown that most induced joints in an RCC arch dam will no longer be open after initial grouting.

OTHER USES FOR RCC IN DAM CONSTRUCTION

OVERTOPPING PROTECTION

General

Many early uses of RCC, specifically in the United States, were rehabilitation projects, specifically overtopping protection for dams. ICOLD Bulletin 126 (ICOLD/CIGB 2003) provided appropriate design guidance for RCC overstepping protection which is still valid. Contraction Joints - joints are typically not required in assault protection schemes, but may be preferred to prevent uncontrolled cracking.

Visual impacts – many projects have covered the RCC on top of the protection layer with a layer of soil with seeded grasses to give a positive aesthetic appearance to the project, which must be maintained to prohibit large bushes or tree growth, as shown in Figure 8.2 (BEFORE) and 8.3 (AFTER).

DAM STABILIZATION

General
Representative projects

An important consideration of using RCC to stabilize existing concrete structures is the development of a composite dam structure where the original concrete and the new RCC function as a monolithic structure under static and dynamic conditions. In some cases, the toe excavation will need to go deeper than the original dam to reach a given rock quality target - the safety of such excavation must be proven before excavation to avoid a weakened condition temporary (minimum) of the original. the structure. Existing drainage will need to be addressed to maintain or improve downspouts that relieve uplift pressures on the original and new structures.

Carefully match strength and modulus values to the original concrete and new RCC materials – care must be taken with RCC which can take one to two years to reach ultimate strength properties.

EROSION PROTECTION

General
Representative project

In 1998, the Big Dalton Dam (Glendora, CA, USA) was reconstructed to address seismic stability problems with a lightweight multi-tube dam ("Eastwood" type). Although the Big Dalton Dam is sufficiently stable with seismic forces in the upstream-to-downstream direction, it has shown inadequate levels of stability for soil movement in the direction of the dam axis. RCC fill of Big Dalton Dam (Glendora, California, USA) (Photo: Los Angeles County, Department of Public Works, USA).

RCC used as erosion resistant lining of still basin at Platanovryssi Dam (Greece) (Photo: Malcolm Dunstan & Associates, UK).

FOUNDATION REPLACEMENT

General

The design required excavating part of the weathered surfaces and replacing them with large concrete ones. The design optimized the lateral behavior of the dam during an earthquake by reducing the differential movement between the monolithic sections. Foundation molding blocks increase and restore the structural and topographical integrity of the "saddle" in the foundation. The RCC foundation of the structure provides structural support and erosion resistance against flows from the valves and adjacent.

The extensive repair work following the Oroville Dam spillway incident in 2017 (ICOLD, 2018) provides another example of the use of RCC for replacing missing or eroded foundations.

COFFERDAMS

General

The expectation for a temporary RCC box dam is that the downstream construction site can quickly recover from an overburden event to resume construction with as little delay as possible. RCC cofferdam at Three Gorges Dam (circa 2006, China) (Photo: China Three Gorges Company, China). The concept of integrating an RCC cofferdam into a finite RCC dam was first developed at Beni Haroun Dam (Algeria) in 1999 and was also used for Yeywa Dam (Myanmar) in 2006.

As shown in Figure 8.11 for the Beni Haroun project, the intention is to construct an RCC cofferdam as the upstream.

RAISING CONCRETE DAMS

General

The tests aimed to determine the quality (deterioration due to aging effects), strength, Young's modulus, thermal properties and temperature of the existing dam. The other critical factor was to design the RCC so that its ultimate compressive strength and modulus would be close to the existing embankment concrete. A more detailed discussion of the RCC mix design program was presented by Zhou et al (2009).

As shown in Figure 8.15, the dam includes a wall at the upper part of the embankment.

CONCLUSIONS

RCC ARCH DAMS

INTRODUCTION
DESIGN OF RCC ARCH DAMS

Introduction
RCC arch dams in China
Layout
Arch geometry and cross section
Short structural joint
Hinge joint
Arch dams
Arch-gravity dams and curved gravity dams
Arch and arch-gravity dams using low stress-relaxation creep RCC

RCC MATERIALS & MIXES FOR ARCH DAMS

General
RCC arch dams in China
Arch dams outside China

THERMAL STRESS ANALYSIS
THERMAL CONTROL

General
Pre-cooling
Post-cooling
Joint forming systems
Groutable transverse contraction joint
Joint grouting
Special materials

INSTRUMENTATION
PERFORMANCE

Construction
In operation

REFERENCES

Although the RCC arch dams built in China to date generally exhibit relatively simple geometry, many of the structures have a low base thickness/height (W/H) ratio and more recent dams have been built with double curvature (Wang, 2007). RCC installation rates for arch dams are generally lower than for gravity dams due to several of the above issues; And. The contraction joint system is installed together with/as part of the transverse joint induction system; And.

Structural analysis demonstrates that high tensile stresses often develop in RCC arch dams at the upstream face against the abutments and in the lower portions of the crown at the downstream face as the arches bend under load.