According to the climatic characteristics of the Qinghai-Tibet Plateau and in accordance with engineering practice and theory, this paper attempts to analyzethe choosing principlesand the technical applicabilityof rip...According to the climatic characteristics of the Qinghai-Tibet Plateau and in accordance with engineering practice and theory, this paper attempts to analyzethe choosing principlesand the technical applicabilityof riprap subgrade in Qinghai-Tibet Railway permafrost regions.展开更多
Stability of earth dams during earthquakes has been a major concern for gcotechnical engineers in seismic active regions. Liquefaction induced slope failure occurred at the upstream slope of a major earth dam in the s...Stability of earth dams during earthquakes has been a major concern for gcotechnical engineers in seismic active regions. Liquefaction induced slope failure occurred at the upstream slope of a major earth dam in the suburb of Beijing, China, during the 1976 Tangshan Earthquake. The gravelly soil with loose initial condition liquefied under relatively small ground vibration. In recent years, a major seismic rehabilitation project was carried out on a similar earth dam nearby using dumped quarry stone. Seismic stability analysis was carried out using model test, finite element simulation, and pseudostatic slope stability program after taking into account the influence of excess pore pressure.展开更多
This paper examines scour and scour countermeasures at bridge piers and abutments. Abutment scour is by far more complex than its counterpart associated with piers because of the possibility of the presence of a flood...This paper examines scour and scour countermeasures at bridge piers and abutments. Abutment scour is by far more complex than its counterpart associated with piers because of the possibility of the presence of a floodplain. Notwithstanding this, the mechanism of scour at both piers and abutments is very similar; moreover, the failure mechanisms associated with both armoring and flow-altering countermeasures are not very different. In rivers with a floodplain, abutment scour becomes much more complex. In cases where the abutment ends at or near to the floodplain, it can initiate bank erosion, which clearly is an important erosion problem that is quite distinct from the customary scour at either an abutment in rivers without a floodplain or a pier. For this reason, abutment scour can be very site-specific while pier-scour is more generic in nature. To this end, the ability to identify the type of abutment scour that may form in a particular channel is closely related to an engineer's ability to propose devices for effective scour countermeasure.By summarizing research efforts on using riprap as a pier or abutment countermeasure over the past few decades, this paper highlights the deficiencies of riprap in arresting pier scour. To this end, different failure mechanisms are identified. They are shear failure, winnowing failure, edge failure, bedform-induced failure and bed-degradation induced failure. Each failure mechanism can singly or, more likely, combine to cause the eventual breakdown of the riprap layer. The study shows that a riprap layer is vulnerable to other failure mechanisms even though it is adequately designed against shear failure, rendering it ineffective in arresting scour.展开更多
Bed protection in apron downstream was installed to use riprap or gabion mattress. In the case of bed protection using riprap, the decision on the riprap diameter is very important because riprap diameter means the ca...Bed protection in apron downstream was installed to use riprap or gabion mattress. In the case of bed protection using riprap, the decision on the riprap diameter is very important because riprap diameter means the capacity to withstand the flow. Initial formulas for the decision on the riprap diameter applied velocity and weight as main factors. Since the main factors gradually expanded to depth, bed slope, and turbulence intensity, decision formulas for the riprap diameter were detailed. Because turbulence intensity was considered to be a main factor of the formula, the decision formulas for the riprap diameter could be expanded to apply to bed protection around hydraulic structures. Escarameia and May conducted a study on the riprap diameter of a strong turbulence area around the downstream of hydraulic structures. For the formula of Escarameia and May, the basis of the formula was the Izbash type, and the main factor was turbulence intensity. This study was an experimental study for deciding the riprap diameter installed around apron downstream and was based on the study results of Escarameia and May. The experiment measured the velocity upon change of discharge and riprap diameter to the installed weir model and analyzed the correlation of threshold velocity by diameter. The experimental formula in this study expanded the turbulence intensity limits of the Escarameia and May formula and increased application to turbulence intensity in weir downstream.展开更多
文摘According to the climatic characteristics of the Qinghai-Tibet Plateau and in accordance with engineering practice and theory, this paper attempts to analyzethe choosing principlesand the technical applicabilityof riprap subgrade in Qinghai-Tibet Railway permafrost regions.
文摘Stability of earth dams during earthquakes has been a major concern for gcotechnical engineers in seismic active regions. Liquefaction induced slope failure occurred at the upstream slope of a major earth dam in the suburb of Beijing, China, during the 1976 Tangshan Earthquake. The gravelly soil with loose initial condition liquefied under relatively small ground vibration. In recent years, a major seismic rehabilitation project was carried out on a similar earth dam nearby using dumped quarry stone. Seismic stability analysis was carried out using model test, finite element simulation, and pseudostatic slope stability program after taking into account the influence of excess pore pressure.
文摘This paper examines scour and scour countermeasures at bridge piers and abutments. Abutment scour is by far more complex than its counterpart associated with piers because of the possibility of the presence of a floodplain. Notwithstanding this, the mechanism of scour at both piers and abutments is very similar; moreover, the failure mechanisms associated with both armoring and flow-altering countermeasures are not very different. In rivers with a floodplain, abutment scour becomes much more complex. In cases where the abutment ends at or near to the floodplain, it can initiate bank erosion, which clearly is an important erosion problem that is quite distinct from the customary scour at either an abutment in rivers without a floodplain or a pier. For this reason, abutment scour can be very site-specific while pier-scour is more generic in nature. To this end, the ability to identify the type of abutment scour that may form in a particular channel is closely related to an engineer's ability to propose devices for effective scour countermeasure.By summarizing research efforts on using riprap as a pier or abutment countermeasure over the past few decades, this paper highlights the deficiencies of riprap in arresting pier scour. To this end, different failure mechanisms are identified. They are shear failure, winnowing failure, edge failure, bedform-induced failure and bed-degradation induced failure. Each failure mechanism can singly or, more likely, combine to cause the eventual breakdown of the riprap layer. The study shows that a riprap layer is vulnerable to other failure mechanisms even though it is adequately designed against shear failure, rendering it ineffective in arresting scour.
文摘Bed protection in apron downstream was installed to use riprap or gabion mattress. In the case of bed protection using riprap, the decision on the riprap diameter is very important because riprap diameter means the capacity to withstand the flow. Initial formulas for the decision on the riprap diameter applied velocity and weight as main factors. Since the main factors gradually expanded to depth, bed slope, and turbulence intensity, decision formulas for the riprap diameter were detailed. Because turbulence intensity was considered to be a main factor of the formula, the decision formulas for the riprap diameter could be expanded to apply to bed protection around hydraulic structures. Escarameia and May conducted a study on the riprap diameter of a strong turbulence area around the downstream of hydraulic structures. For the formula of Escarameia and May, the basis of the formula was the Izbash type, and the main factor was turbulence intensity. This study was an experimental study for deciding the riprap diameter installed around apron downstream and was based on the study results of Escarameia and May. The experiment measured the velocity upon change of discharge and riprap diameter to the installed weir model and analyzed the correlation of threshold velocity by diameter. The experimental formula in this study expanded the turbulence intensity limits of the Escarameia and May formula and increased application to turbulence intensity in weir downstream.
