With the rapid development of urban transportation facilities, their construction inevitably encounters unfavorable conditions, such as rivers and lakes. When using the weir construction method to build transportation facilities in lakes, the design scheme for the pit slope excavation inside the cofferdam is related to the success or failure of the construction. In this study, the design scheme for pit excavations in lakes is discussed and analyzed using numerical simulation and on-site monitoring against the background of Jinji Lake Tunnel. The findings are as follows. (1) The greater the distance between the pit and the cofferdam, the smaller the impact of pit excavation on the cofferdam is; when the excavation depth is 10 m and the distance is more than 47 m, the deformation of the whole pile is less than 15 mm. (2) Under the condition that the platform width is kept the same, the smaller the height and width ratio is, the greater the safety factor will be, and under the condition that the height and width ratio is kept the same, the longer the platform width is, the greater the safety factor will be. (3) When the pit and cofferdam are far away from each other, different slope release design schemes have different effects on cofferdam deformation and stability. The results of this research can provide references and guidance for the design and construction of similar projects. 

Research on Deformation Characteristics and Design Optimization of Super-Large Cofferdam Enclosure Structure

Diamondiferous kimberlites occur in the Wafangdian area in the eastern part of the North China Craton (NCC). In order to better constrain their magmatic source and emplacement time, we have investigated apatite from two kimberlites, i.e., the #110 dike kimberlite and the #50 root-zone kimberlite by measuring in situ their U–Pb and Sr–Nd isotopic compositions. The crystallization ages of the #110 and #50 apatites are 460.9 ± 16.8 Ma and 455.4 ± 19.3 Ma, respectively. For the #50 apatite, 87Sr/86Sr = 0.70453–0.70613 and εNd(t) = −2.74 to −4.52. For the #110 apatite, 87Sr/86Sr = 0.70394–0.70478 and εNd(t) = −3.46 to −5.65. Based on the similar distribution patterns of the rare earth elements (REEs) and the similar Sr-Nd isotope compositions of the apatite, it is believed that the #110 and #50 kimberlites have the same source region and the kimberlite magmas in Wafangdian were derived from an enriched mantle source (EMI). The primary magmatic composition has little effect on the emplacement pattern. It is more likely that the geological environment played an important role in controlling the retention and removal of volatile components (H2O and CO2). This led to the different evolutionary paths of the kimberlite magma in the later period, resulting in differences in the major element compositions of the apatite. High Sr concentrations may be associated with hydrothermal (H2O-rich fluid) overprinting events in the later magmatic period; the higher light rare earth element (LREE) concentration of the #50 apatite reflects the involvement of the REE3+ + SiO44− ⇔ Ca2+ + PO43− replacement mechanism. Two emplacement patterns of the #110 dike kimberlite (#110 apatite, low Sr, and high Si) and the #50 root-zone (#50 apatite, high Sr, and low Si) kimberlites were identified via major element analysis of the #110 apatite and #50 apatite. 

Geochemistry, Sr-Nd Isotope Compositions, and U-Pb Chronology of Apatite from Kimberlite in Wafangdian, North China Craton: Constraints on the Late Magmatic Processes

Cofferdam is a building in the form of earth, stone, concrete or masonry filling and holds water, prevents flooding, provides irrigation. The building has many functions such as for agriculture, power generation, and tourist attractions. Cofferdam will also be very helpful in flood control which will control flood water so that it will not overflow excessively which endangers the surrounding community. Besides having great benefits. If the cofferdam collapses (broken) it will cause flash floods that result in casualties. Therefore the cofferdam must be designed safely and technically feasible. The research approach used in this study is a quantitative approach using the 2012 GEO-SLOPE program. The conclusions from the analysis of slope seepage and seepage stability are the Critical Safety Factors for cofferdam stability according to the results of the analysis after running SLOPE/W are 1.711 &amp; 1.512 because it is higher than 1.5 (SNI 8460:2017 Geotechnical Requirements Design, This means that the stability of the cofferdam is safe. The modeling results show that the seepage discharge is 1.81x10-7 m3/s = 1.81x10-4 liters/sec = 15.64 liters/day which is smaller than the maximum allowable discharge of 50 liters/day. So it can be concluded that the seepage discharge is safe. 

Simulation of Cofferdam Calculations Using Geo-Studio Application in Peusangan Hydropower Dam Construction

Study on the Impact of the Daily Operations of Complementary Hydro-Photovoltaic of Cascade Hydropower Stations on the Flow Fluctuation Characteristics in Reservoir Areas

Coupling analysis of earth-rock dam break risk factors based on the ISM-BN model

A reservoir area is mostly located in the canyon area, and the geological structure is complex. There are a large number of unstable slopes on the bank of the reservoir. The stability of bank slope is greatly affected by water storage and reservoir water regulation. In addition, sudden rainstorm and other external factors can reduce slope stability. In this article, the physical model test is used to study the seepage field and deformation characteristics of typical reservoir bank slopes with sand layers under different rainfall intensities, different water level fluctuation rates, and their coupling effects. The model has a length of 4.0 m, a width of 1.0 m, and a height of 0.9 m, and the piezometers and white balls are used to monitor the pore water pressures and displacements inside the slope model individually. The results show that the responsiveness of pore water pressure inside the slope lags behind both water level fluctuation and rainfall. The lag time is inversely proportional to the water level fluctuation rates under the single water level fluctuation condition, while it is proportional to water level fluctuation rates in the water level decline stage under the coupling effect condition. The rapid impoundment of the reservoir area has a strengthening effect on the stability of the reservoir bank slope. However, accelerated deformation of the slope occurs in the stage of water level decline, and the deformation rate is proportional to the water level fluctuation rates.

https://www.frontiersin.org/articles/10.3389/feart.2022.863370/pdf

Physical Model Test on the Deformation Mechanism of Reservoir Bank Slopes With Sand Layers Under Coupled Hydro-Mechanical Conditions

Due to the double disturbance effect of dredging and filling, there will be a problem with weir slope stability after the formation of a fill type saturated clay weir. In order to study the influence of water-level fluctuation on the instability and seepage failure of the dump-fill cofferdam, the saturated-unsaturated seepage theory and strength reduction method are embedded into the finite element system such that the fluid-solid coupling stability of the dump-fill cofferdam is analyzed. The results show that the influence of water-level fluctuation on the instability and seepage failure of the dump-fill cofferdam can be revealed by the coupling analysis excellently. The variation of the saturation line of the cofferdam is consistent with the variation of water-level rising, but the change response of the saturation line of the cofferdam has a lag property during the water-level decline process in that the water level changes faster. The maximum displacement of the cofferdam can be approximated as two stages, namely, the stable growth stage and the accelerated growth stage (slip initiation), in which the influence of the water-level fluctuation on the displacement of stable growth stage is more obvious. Based on the fluid-solid coupling analysis, the most dangerous sliding surface of the cofferdam is located at the position of the horse path, with a critical strength reduction coefficient of approximately 1.475. The possibility of seepage failure of the cofferdam will be increased if the water level exceeds the height of the impermeable wall.

/pdf/the-influence-of-water-level-fluctuation-on-the-instability-3vakp66s.pdf

The Influence of Water-Level Fluctuation on the Instability and Seepage Failure of Dump-Fill Cofferdam

Kimberlite in the Mengyin area serves as an excellent medium for studying the characteristics and evolutionary processes of the Paleozoic mantle. In order to determine the age of the primary calcite within the kimberlite, in situ carbonate U–Pb dating was conducted in the Mengyin area. The results indicate that the primary calcite in the kimberlite originated approximately 383 ± 18 Ma (MSWD = 6.6). This age constraint suggests that the eruption of the kimberlite took place during this period, leading to the thermal alteration of limestone xenoliths, ultimately forming marble. Consequently, it can be inferred that lithospheric thinning occurred no later than the Late Devonian period. Fluid inclusions found within the marble provide further insights into its formation. The recorded formation temperature of the marble ranges from 243°C to 370°C, with a salinity range of 2.57%–14.77% (NaCl). The pressure estimates fall within the range of 3.22–20.70 MPa, indicating a depth mainly between 900 and 1,000 m. Based on these findings, it can be inferred that the overall denudation depth in the west Shandong area, since the Late Devonian, is estimated to be approximately 900–1,000 m. Furthermore, the overall crustal rise rate is estimated to be approximately 3 m/Ma.

/pdf/preliminary-investigation-of-the-eruption-time-of-kimberlite-1rk3ais5.pdf

Preliminary investigation of the eruption time of kimberlite in the Late Devonian in Mengyin, Shandong

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Physical Model Test on the Deformation Mechanism of Reservoir Bank Slopes With Sand Layers Under Coupled Hydro-Mechanical Conditions

The Influence of Water-Level Fluctuation on the Instability and Seepage Failure of Dump-Fill Cofferdam

Preliminary investigation of the eruption time of kimberlite in the Late Devonian in Mengyin, Shandong