Reliability Analysis Of Settlement For The Spillway Tunnel Of The Sand Dam

To solve the problem of water shortage in the sand area of northern Shaanxi province,the use of local materials to construct dams on the river and the construction of waterconservancy initiatives have been implemented. However, practice and research on theconstruction of hydraulic structures in the sand area is not much at present and manyunexpected problems often occur after completing the construction of hydraulic structures.Conducting research on the problems of hydraulic structures which have been built in the areais not only for the safety of the building to provide the scientific basis for reinforcement, butalso providing a reference for the construction of similar projects.Firstly, the paper applied cell "life and death" technology and the step loading method tosimulate the construction process of a reservoir spillway tunnel with a sand dam and calculatethe settlement values of the construction period of spillway tunnel. Secondly, the papersimulated the settlement of spillway tunnel of the storage period of different conditions andcompared the settlement value of the calculated and measured values to verify the correctnessof the numerical model. Finally, the paper applied PDS of the finite element software ANSYSto analyze the reliability of the settlement of the spillway tunnel under normal the water levelcondition. The laws related with the settlement of the spillway tunnel are obtained as follows:(1) After grading load of construction period, the settlement of the spillway tunnel isgradually increased in pace with filling the upper part of the dam. The simulated maximumsettlement value is24.35cm that appears near the dam axis. The settlement amount isgradually reduced away from the dam axis. The upstream section seams of the spillwaytunnel has been obviously uneven settlement.(2) When the elevation of the water in the reservoir is1064.00m, the simulatedmaximum settlement amount of the spillway tunnel is24.34cm and the settlement curve isalmost completely overlapping with the settlement curve of the construction period; When theelevation of the water in the reservoir is1082.00m, the simulated maximum settlementamount is25.10cm and the settlement curve in the vicinity and downstream part of the damaxis is almost overlapping with the settlement curves which are respectively obtained at thesixth and seventh load. The settlement of the upstream part is very large and significantlydifferent compared with the settlement results obtained in the previous two loads. (3) When the elevation of the water in the reservoir is1064.00m, the simulationsettlement values of the spillway tunnel are close to the settlement value obtained by actualobservations and the trend of the two settlement curves is unanimous. The settlement at bothends of the spillway tunnel is relatively small and the two settlement curves are almostoverlapping. The settlement in the middle part is large and the two settlement curves bringabout certain deviation. The simulation settlement values of the spillway tunnel are slightlylarger than the observed values. The simulated and measured maximum settlement valuesappear in the same observation point. The settlement of simulation results is basicallyconsistent with observations settlement of the actual project and the law of the settlement isconsistent.(4) After the simulation analysis of1000Monte Carlo for the Numerical model, theaverage value, maximum value and minimum value of the maximum settlement amount of thespillway tunnel under the normal water level condition are respectively25.36cm,35.02cmand19.59cm. The largest settlement values are mainly between22cm and30cm under theconfidence level of95%.(5) The impact of the compression modulus of the dam foundation layer of dense sand tothe largest settlement of the spillway tunnel is most significant in the significant level of2.5%and the sensitivity coefficient is0.787that accounts for45.81%of the total impact factors.Secondly, the main impact factors are the material density of the dam and the compressionmodulus of loose sand of the dam foundation and the sensitivity coefficients are respectively-0.507and0.255that respectively accounts for29.51%and14.84%of the total impact factors.The other several factors that influence the maximum settlement amount of the spillwaytunnel are not significant.(6) Engineering measures taken to increase the compression modulus of the damfoundation can significantly inhibit the spillway tunnel settlement and this method is the mosteffective and feasible way to prevent the continued settlement of the spillway tunnel.