Abstract: Shuibuya CFRD is presently the highest of its kind in the world, its design, theoretical analysis and experiment researches are very important with higher difficulty which formed the key technical issues of Shuibuya CFRD. This paper dealt with the site compression test, design as well as requirement of construction process of Shuibuya CFRD. Through site compression test, defined the calculation parameters. Theoretically, the dam body stress/strain and deformation condition after impounding was calculation by the use of Tsinghua University's K-G model. This pointed out the technical difficulties and related technical solution of Shuibuya CFRD and submitted the related control requirement on construction process.

Key words: CFRD, Model, Stress, Deformation, Construction process, Compression test

2.1 Introduction to Tsinghua University's K-G model

Theoretically, Tsinghua University's K-G model was used for the 3D non-linear FEA of Shuibuya CFRD. This model is a kind of non-linear model through years of research and development based on large-scale 3-axis test on rockfill material. This model is suitable for various kind of complex stress route in earth-rock fill dam which can reflect to various kind of deformation properties on earth body, such as elastic-, non-linearity, deformation dependence on strength and shear-shrunk etc. It is with better suitability compared with Ducan's E-B model. The model is less in parameter and each of the parameter is clear in physical meaning. Together with the special developed increment regression method for the model related deformation parameters, basically similar parameters can be obtained by the regression from single loading test curve in different stress path. This has showed that the parameter of this model is not impacted by different stress path, and is with good regression performance. Hence, a long-term not solved difficulty in civil research is solved in this model. This model also provided a special developed matrix method used for finite element analysis and created a favorable condition for engineering data calculation.

2.2.1 Dam body deformation

After the dam storage, the horizontal displacement (along flow direction) is divided by the cross-section of dam axis, the displacement of upstream side dips toward upstream with maximum value at 0.006m, the displacement of downstream side dips toward downstream with maximum value at 0.38m.

The maximum settlement is appeared at the two third dam height position of the cross-section of dam axis, the value is 1.36m after the dam storage. In view of the percentage of dam settlement in dam height during storage period, the prototype observation value of constructed Areia is 2.4%, Achikaya is 0.55%, Khao Laem is 0.92%. According to China's 3D calculation, Tianshengqiao is 0.82%, Hongjiadu is 0.46%, and Shuibuya is 0.6%. The result is within the same level compared with the settlement value of these constructed higher than 100m CFRDs both in China and abroad and the dam deformation is concord to the rule. Meanwhile, it also indicated that the designed dry density of 2.15 t/m³ is suitable.

2.2.2 Dam body stress

After the dam storage, the maximum value of large main stress is 4.07 Mpa, and the maximum value of small main stress is 1.33 Mpa, the ratio of the large main stress to the weight of related earth pole is about 0.8. Through the analysis on isogram of the large main stress and small main stress, the result showed that both the limit are at the middle with a little bit to upstream of the dam bottom. This is concord with the stress distribution rule of constructed projects.

2.2.3 Slab displacement and stress

The slab displacement and stress situation is the core issue of 3D non-linear finite element analysis. In view of the vertical slab displacement, the maximum displacement is at the slab center, the slab shaped as a curve surface under the hydraulic pressure. The changing grad of displacement and the isogram is large and dense at the edge, small and sparse at center. This situation is fully concord to the intuitively judgement made from physics conception. The maximum value of slab deflection is 0.60m at about one third of the dam height of the middle riverbed cross-section. The vector direction is toward slab downstream. This showed that the slab is compressive, and the deformation is mainly controlled by rockfill settlement and water load. The slab deflection at both banks is gradually reduced and the vector direction is gradually moving to the upstream which shows that the slab is changing from compressive to tensile gradually. This is concord to the general stress distribution of slab. Compared with constructed projects, the slab deflection of Hongjiadu is 0.45m, Tianshengqiao 0.70m, and Shuibuya is 0.60m. This value is not big related to a 233m high, 403m long slab.

Slab stress analysis showed that the maximum compressive stress at slope direction is 8.8 Mpa appeared at about one third of the dam height of the valley center with a little bit to right bank, and the maximum tensile stress is 7.0 Mpa appeared at about one second of the dam height of the left bank steep slope and the right bank abrupt changing point with deep fovea. The riverbed bottom and both river banks are small in tensile stress, the value is about 2.0 Mpa. The maximum compressive stress at dam axis direction is 11.9 Mpa appeared at two third of the dam height of the riverbed with a little bit to right bank, and the maximum tensile stress is 4.0 Mpa appeared at the both abutments.

Calculation showed that the maximum slab compressive stress is far below the allowed compressive stress of concrete. And the maximum tensile stress at the abrupt changing point of both banks is beyond the allowed tensile stress of concrete but proper engineering measures can be taken to improve the local slab stress condition.

2.2.4 Displacement of permetric joint and vertical joint

The deformation on the three directions of permetric joint are below 4.0cm, the deformation requirement of water-stop structure of permetric joint can be satisfied.

Shuibuya CFRD is presently the highest if its kind in the world, the dam engineering is in a certain difficulty. From the dam body settlement, the face deflection, the permetric joint deformation, the slab water-stop system, the slab reinforcing to the instrumentation and observation data analysis in safety monitoring are with high difficulty, especially for these issues, such as slab stress and reinforcing of high CFRD, dam body creep, permetric structure joint and water-stop design as well as the difference control on temporary dam filling section during the flood season in construction period.

• Theoretically, Tsinghua University's K-G and Ducan's E-B model was used for the 3D non-linear finite element analysis.
• In reference to the successful experiences on these CFRDs, such as Tianshengqiao in China and Xingo, Areia, Segredo, Aguamilpa etc in abroad, and according to the results both in experiment and theoretical research, the design of dam zoning, slab reinforcing and jointing, permetric joint, water-stop system and safety monitoring was carried out seriously.
• In the aspect of slab anti-cracking, the research on concrete additive, site and in-door test of mix design have gained breaking progress. Meanwhile, further knowledge also gained on the improvement of slab reinforcing.
• Through site compression test, strictly submit the compression standard on rockfill, high attention was given to the elevation difference of the temporary cross-section during the flood season in construction period with related requirement on construction process.
• In the aspect of safety monitoring, based on the successful experience on Tianshengqiao CFRD, the equipment selection and arrangement for the safety monitoring of Shuibuya CFRD was further improved. In pointing to the dam body deformation, slab and permetric joint deformation, force condition of slab reinforcing bar as well as the seepage flow, well organize the observation and data analysis, so that to ensure the successful construction of Shuibuya CFRD.

The quarry excavation of Shuibuya CFRD adopts deep-hole micro-differential rundle blasting method, excavator together with self-unload truck to dam.

Dam foundation adopts micro-differential rundle blasting method, slope excavation adopts pre-splitting or smooth-surface blasting with one time of micro-differential rundle blasting at the bottom protection layer.

The construction of filter material includes filling, slope adjustment, slope compression and slope protection etc. Adopts self-unload truck backward feed in, bulldozer or loader for placement with layer thickness of 0.40m, and compressed by 11~ 13 t vibration roller for 4~ 8 passes. The corners and edges will be compacted by flat-plate vibrator. The slope adjustment will be carried out by laser guided backacter every about 5m lift and compacted by flat-plate vibrator. In every about 15m lift, slope compression will be carried out by 12.5 t slope compressor and the slope will be protected by emulsifying asphaltum sand.

Transition material and filter material will be lifted at the same time with layer thickness of 0.60~ 0.80m and compacted by 16~ 18 t vibration roller 6~ 8 passes.

The construction of rockfill adopts self-unload truck forward feed in and leveled by bulldozer. Layer thickness 0.8~ 1.0m, compacted by 16~ 18 t vibration roller 6~ 8 passes and add water by compartment or through dam surface.

Plinth concrete is transported by concrete mixing truck, poured in by sliding-chute, concrete pump and cranes with load tank and placed by railed slide-form and routine form-plate with the sequence of riverbed first, then both banks.

The slab concrete adopts jump placement with well temperature control. The concrete is transported by concrete mixing truck, poured in by sliding-chute, and placed by slide-form without rail.

Despite there is no constructed CFRD higher than 200m in the world presently, the current site compression test and in-door test, theoretical researches and engineering experience can fully meet the requirement of the key technical issues of Shuibuya CFRD. It is believed that the world dam construction technology on CFRD will be greatly improved by the further researches on key CFRD technologies and the construction practice in Shuibuya Project.

References:

1. Dai Feng, Zhu Jiaqi, Liu Luping, Study on CFRD Rockfill Material Properties, People's Changjiang, 1998.29(8).
2. Changjiang Water Resource Commission, Feasibility Study Report of Qingjiang Shuibuya Water Conservancy Project, 1998.10
3. Gao Lianshi, Wang Zhaohua, Zhaoyong etc, 3D Stress/Strain Analysis of Shuibuya CFRD. 1998.12