Theoretical And Experimental Research On The Stability CWR In Permafrost Area Of Qinghai-Tibet Railway

The Golmud-Lhasa Section of Qinghai-Tibet railway passes through the hinterland of Tibet Plateau. It is 1142 kilometers long and with an average altitude of about 4380 meters, including 546.4km permafrost regions. Lately, CWR (continuous welded rail) has been covered on Qinghai-Tibet railway in permafrost zone with 316.4 km’s long. Permafrost zone of Qinghai-Tibet railway has its unique characteristics like low temperature and oxygen, changeable climate, big day/night temperature difference, long annual negative temperature, stronger solar radiation, more steep gradients, thicker ballast bed, more thawing settlement of subgrade and so on, these climatic and environmental conditions and the particularity of the track structure is very unfavorable for the stability and maintenance of CWR.However, research on the CWR in permafrost zone is immature and it leads to the lack of evidence for designing, laying and maintaining of CWR, which makes it hard to guarantee the commuting safety. This paper is focused on the scientific conundrum in designing, laying and maintenance of CWR caused by the climate, geological conditions, and operation characteristics in plateau section, combining with the structure of CWR in permafrost regions, in order to study the stability of CWR, comprehensively apply site inspection, in situ monitoring, laboratory tests and methods of theoretical and numerical analysis to research design parameters and the state of the track, field testing and monitoring technologies and stability theory of CWR in Permafrost Regions, and the main results are shown as follows:(1) Rapid detection technology of state parameters for ballast bed has been proposed; and the Design parameters & variation law relate to CWR stability in permafrost zone have been acquired.Portable torque tooling and data acquisition instruments for measuring state parameters of ballast bed are developed, which provides a rapid detection method for ballast bed parameter evaluation. Field test and laboratory cryogenic property test for design parameters of CWR stability in permafrost zone are carried out, and state parameter of ballast bed of CWR, value and variation laws of initial CWR deflection and longitudinal resistance of fastener are acquired.(2) Stability analytical model of CWR that can accurately represent the actual bending state of CWR has been established.Based on differential equation method, the curve equation that can accurately reflect boundary conditions of the track bending is acquired. Applying consistent defect modal method modal to represent the initial CWR deflection, built a stability analysis model of CWR while the temperature applies the force. Based on the energy method, the stability formula of CWR is derived; the model can characterize the true state of the track bending, and fully reflect the causal relationship between temperature stress and deformation of the track.(3) The set-theoretic convex approach is first is applied to the stability analysis of CWR.Considering the design parameters as variables in a range, calculation method of the stable critical rail temperature bounds based on the theory of convex model and interval analysis theory is proposed. Based on interval analysis theory, reliability analysis model, and design parameters sensitivity analysis method with the feature of reliability are constructed based on the non-probabilistic reliability theory. And open up new avenues for the research of structure uncertainties of CWR.(4) Construction of the CWR’s long-term in situ monitoring method of the status of track displacement and the synchronous acquisition of rail temperature.Since long-term monitoring technology of CWR’s status still need to be improved, and developed, situ monitoring system of CWR state in permafrost regions is researched and developed, and gather the track displacement, beam end displacement, meanwhile it realizes the lasting observation and automatic data storage of rail displacement, bridge beam displacement, synchronous acquisition of rail temperature and bridge beam temperature, automatic storage of the continual real time monitoring and data under bad climate condition in plateau section, forming a complete set of situ monitoring techno logy of CWR status in permafrost zone.(5) Obtain of the value and evolution of the CWR state parameters in permafrost zone.Analyzing situ monitoring data of the state of the CWR in permafrost zone, this research finds that plateau climate and environmental characteristics’response and its internal relationship with CWR’s state, establishes the inter-annual variability quantitative (function) of temperature and track temperature, and finds the evolution law of CWR state in permafrost zone.(6) Propose designing, laying and maintenance methods for CWR in permafrost zoneBased on the latest research results of field testing, in-situ monitoring, and stability theory analysis obtained in permafrost regions, this research proposes the stress-free temperature of CWR, best season, time and the temperature range of rail maintenance and repair work of CWR, and has established design, laying and maintenance and repair methods for CWR in permafrost region.