Keywords

1 Introduction

The deformation is accompanied by the whole life cycle of the dam. The earth-rock dam will be settled and displaced due to its weight, initial impoundment and other reasons. During stable operation, the settlement caused by the dead weight will gradually decrease, and the change of external load caused by the change of water level is the main reason for the deformation of the dam [4]. Deformation is a macroscopic effect size that can directly reflect the safe operation performance of dam [2]. Long-term deformation monitoring is an important task to the safe operation of a reservoir [1]. Therefore, reliable and efficient safety monitoring of dam becomes more and more important, and accurate prediction of dam deformation development is an important part of the whole monitoring process [3, 5]. This paper takes Yuankou Reservoir dam as the research object to monitor the horizontal displacement, settlement displacement and internal deformation of the upstream dam slope. The temporal and spatial development law of dam deformation is emphatically analyzed, and the overall deformation safety state of the dam is evaluated. The purpose is to provide reference for the safe operation of the reservoir dam. 2 Project summary.

Yuankou Reservoir is located in Wuyi County, Jinhua City, Zhejiang Province, China. It is a medium-sized reservoir mainly for flood control and irrigation. The dam is 509 m long, 6 m wide at the crest, and 43.30 m high at the maximum. The designed normal water level of the reservoir is 208.20 m, the corresponding storage capacity is 22.2 million m3, the designed flood water level is 212.12 m, and the checked flood water level is 212.50 m. The dam is a clay core wall dam with sand and gravel shell. The height of the clay core wall is 210.00 m, and the cross-section is approximately isosceles trapezoid. In order to increase the drainage capacity of the non-impermeable area of the dam, the part above 203.0 m elevation of the upstream slope of the original dam and the part above 205 m elevation of the downstream dam slope were excavated and backfilled with rockfill. The dam section is shown in Fig. 1.

Fig. 1
A structure dam in a triangular shape. Labeled parts, Left and right outer side, enrockment, strong permeable dam shell. On the left inner side, is stone silky clay. On the right inner side, there is a pebble dam with bedrock.

Internal structure and material of the dam3 monitoring point arrangement

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1.1 Layout of Dam Surface Deformation Monitoring Points

Three surface deformation observation sections were arranged parallel to the dam axis. The first deformation observation section (0 + 1) was located on the upstream side of the dam, 1.31 m away from the dam axis. The numbers of each measurement point are LD13, LD18, LD23, LD28, LD33, LD38 and LD43. The second deformation observation section (0 + 30) is located at the downstream side of the dam, 30.11 m away from the dam axis. The numbers of each measurement point are LD4, LD8, LD12, LD17, LD22, LD27, LD32, LD37 and LD42. The third deformation observation section (0 + 62) is located at the upstream side of the dam, 62.01 m away from the dam axis, and the numbers of each measurement point are LD2, LD6, LD10, LD15, LD20, LD25, LD30, LD35 and LD40.

A total of 25 surface deformation observation points. One working basis point and one checking basis point are arranged on the rocks at both ends of the above three sections. A total of six working basis points and six checking basis points. Two leveling basis points are arranged at the same time.

1.2 Layout of Deformation Monitoring Points in Upstream Dam Slope

Two monitoring sections (0 + 245 and 0 + 380 m) are set up 245 and 380 m away from the right bank of the dam to monitor the downstream dam slope deformation. Two survey pipes were arranged for each section, and a total of four survey pipes were arranged.

2 Analysis of Monitoring Results

2.1 Observation of Dam Surface Deformation

The vertical deformation of the dam is basically proportional to the height of the dam. The settlement is large where the dam is high and small where the dam is low. It accords with the general deformation law of earth-rock dam. The changes of dam settlement over the years are shown in Fig. 2. The downstream dam has less low settlement, and the settlement is between 3 and 33 mm. The downstream side of the dam crest has the largest settlement, and the settlement is between 65 and 96 mm. The subsidence displacement is fast in the early stage and slow in the late stage. Most of the points showed a subsidence trend before 2013, after which the settlement tended to be stable. The settlement rate of the last year is 0 ~ 7 mm/ year, and the settlement rate of the measuring point upstream of the dam crest is 3 ~ 7 mm/ year. The overall sedimentation rate is small.

Fig. 2
3 graphs with curves in a zigzag manner from 0. a, the highest peak for L D 43. b, highest peak for L D 10. c, highest peak for L D 4.

Three curves of surface deformation, settlement and displacement with time

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The horizontal displacement of dam surface deformation measurement points over the years is shown in Fig. 3. After the reservoir impoundment, the horizontal displacement of the dam surface is the largest at the 0 + 350 m section (1.0 m upstream of the dam axis), which is 57.0 mm, pointing to the downstream of the dam. The cumulative minimum displacement is − 13 mm, pointing upstream of the dam. Most of the horizontal displacement deformation was completed before 2013, and the basic process was stable in the later period. During the past year, the maximum horizontal displacement was located on the upstream side of the crest, at a distance of 7 mm, pointing upstream. Overall, the displacement is relatively small. The horizontal displacement on both sides of the dam in the cross section is relatively small. The horizontal displacement in the middle of the dam is large. The displacement of the left and right parts of the longitudinal section is relatively small, and the displacement of the middle dam section is large. It conforms to the general deformation law of dam. The maximum horizontal displacement of the dam is 57 mm, pointing downstream. The overall displacement is small. The annual maximum horizontal displacement is 7 mm, and the dam is in a safe and stable state.

Fig. 3
3 graphs for L D 13, 18, 23, 28, 33, 38 and 43. The curves move in a stable direction from left to right with some ups and downs. Highest curves, a, L D 43. b, L D, 12. c, L D 20.

Curve of horizontal displacement of section surface deformation with time

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2.2 Internal Deformation of Upstream Dam Slope

Dam internal deformation is mainly related to dead weight, pore pressure, filling height, construction scheme and construction water content.The sedimentation is mainly affected by humidification and rheology, and is also related to the upstream real-time water level, rate of change, precipitation and temperature. The data measured at section 0 + 245 and section 0 + 380 were sorted out and calculated to obtain the distribution map of upstream and downstream horizontal displacements along the elevation of each measuring point (Fig. 4). The horizontal displacement is positive to the downstream and negative to the upstream. It can be seen from the figure that before 2013, the horizontal displacements of sections 0 + 245 and 0 + 380 basically showed a downstream displacement trend, and then showed a stable trend. During normal operation, the deep horizontal displacement of the dam is basically related to the reservoir water level. At high water, the dam moves downstream; At low water levels, the dam moves upstream. The maximum downstream displacement of section 0 + 245 m is 44.6 mm, and the elevation is near 206.0 m. The maximum displacement in the downstream direction of section 0 + 380 m is 39.5 mm, and the elevation is 208 m. The horizontal displacements of the two sections conform to the general law of deformation during normal storage period, and the horizontal displacements are small. This indicates that the upstream dam slope is in a stable state.

Fig. 4
Two graphs of 10 curves that flow from the x-axis at 0 to the top for elevation and displacement. The curves range from different dates 2008 to 2017 and they represent the deformation curve of upstream dam slope.

Deformation curves of upstream dam slope of two sections with elevation variation (a represents the 0 + 245.0 section, b represents the 0 + 380.0 section)

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3 Conclusion

  1. (1)

    The dam settlement varies from 3 to 96 mm over the years, and the overall settlement is small. The subsidence displacement is fast in the early stage and slow in the late stage. The sedimentation rate in the last year is 0 ~ 7 mm/ year. The annual settlement rate of the observation point on the upstream side of the dam crest is 3 ~ 7 mm/ year. The overall sedimentation rate is small. Dam deformation is basically proportional to height. The settlement of high dam position is large, the settlement of low dam position is small. It accords with the general deformation law of earth-rock dam.

  2. (2)

    In the cross section, the horizontal displacement on both sides of the dam is relatively small, while the horizontal displacement in the middle of the dam is large. The maximum horizontal displacement is 57 mm, pointing downstream, and the overall displacement is small. The maximum horizontal displacement rate is 7 mm/ year, and the dam is safe and stable state.

  3. (3)

    Before 2013, the horizontal displacements of the two sections showed a downstream trend. Then its displacement shows a stable trend. At the section 0 + 245 m, the maximum downstream displacement is 44.6 mm and the elevation is near 206.0 m. At the section 0 + 380 m, the maximum displacement in the downstream direction was observed to be 39.5 mm, which was located at the elevation of 208 m. During normal operation, the deep horizontal displacement of the dam is related to the reservoir water level. The horizontal displacements of the two sections conform to the general law of dam construction period and normal storage period, and the horizontal displacements are small. This indicates that the upstream dam slope is a stable state.