Engineering activities in permafrost regions have a major impact on the local permafrost environment. The construction and operation of the China-Russia Crude Oil Pipeline (CRCOP) have changed the surface conditions and the soil’s thermal state. However, the response of the permafrost environment to CRCOP is less studied. This article carries out ground temperature monitoring, ground surface deformation (GSD) and pipeline deformation observations, electrical resistivity tomography (ERT) measurements, and unmanned aerial vehicle (UAV) surveys to study permafrost thawing, talik development, topographic change, and pond distribution. The results indicated that the oil temperature has increased yearly and the permafrost around the pipeline has degraded quickly. The artificial permafrost table (APT) has decreased at a rate of 0.68 m/a at a location 2 m away from the center of pipeline, and reached –11.4 m deep by 2022. The talik around CRCOP Ⅰ was larger than that around CRCOP Ⅱ and the two taliks were gradually approaching each other. Permafrost-thawing-induced pipeline subsidence and surface settlement have led to thermokarst depressions and water accumulation. The sinking rates of CRCOP Ⅰ and Ⅱ are approximately 0.2 m/a and 0.45 m/a, respectively. The ground surface settlement rate on the right-of-way of pipeline (on-ROW) is about 5.49 cm/a. Settlement rate in ponding areas is 8.18 cm/a, significantly larger than 4.81 cm/a in non-ponding areas. The ponding area on-ROW accounts for 67.4% and it on CRCOP Ⅰ is larger than that on CRCOP Ⅱ. Pipeline construction, high oil temperature, and permafrost thawing have led to the development of geohazards, which have potential to be worsen under the influence of fires, climate warming, and human activities. Multisource data provides ground verification for satellite images to extract deformation and ponding information along pipelines, and provides a scientific basis for assessing the thermal impact of pipelines and geohazard development.
In this study, A time-domain seismic response analysis method and a calculation model of the underground structure that can realize the input of seismic P, SV and Rayleigh waves are established, based on the viscoelastic artificial boundary elements and the boundary substructure method for seismic wave input. After verifying the calculation accuracy, a comparative study on seismic response of a shallow-buried, double-deck, double-span subway station structure under incident P, SV and Rayleigh waves is conducted. The research results show that there are certain differences in the cross-sectional internal force distribution characteristics of underground structures under different types of seismic waves. The research results show that there are certain differences in the internal force distribution characteristics of underground structures under different types of seismic waves. At the bottom of the side wall, the top and bottom of the center pillar of the underground structure, the section bending moments of the underground structure under the incidences of SV wave and Rayleigh wave are relatively close, and are significantly larger than the calculation result under the incidence of P wave. At the center of the side wall and the top floor of the structure, the peak value of the cross-sectional internal force under the incident Rayleigh wave is larger than the calculation result under SV wave. In addition, the floor of the underground structure under Rayleigh waves vibrates in both the horizontal and vertical directions, and the magnification effect in the vertical direction is more significant. Considering that the current seismic research of underground structures mainly considers the effect of body waves such as the shear waves, sufficient attention should be paid to the incidence of Rayleigh waves in the future seismic design of shallow underground structures.
Abstract. The thermal state of permafrost in the present and future is fundamental to the ecosystem evolution, hydrological process, carbon release, and infrastructure integrity in cold regions. From 2011, we began to establish a permafrost monitoring network along the China-Russia crude oil pipelines (CRCOPs) route at the eastern flank of the northern Da Xing'anling Mountains in Northeast China. Based on meteorological data near the southern limit of latitudinal permafrost (SLLP), ground temperature data in 20 boreholes with the depths of 10–60.6 m, soil volumetric liquid water contents and 2-D electrical resistivity tomography (ERT) data, we compiled an integrated dataset of the ground thermal state along the CRCOPs route. Study results demonstrate that permafrost in the vicinity of SLLP has experienced marked warming (2011–2020) to climate change, manifested as the rising permafrost temperatures at depth. Local thermal disturbances triggered by the construction and operation of CRCOPs have resulted in significant permafrost warming and subsequent thawing on the right-of-way (ROW) of the pipeline. This permafrost thaw will persist, but it can be alleviated by adopting mitigative measures, such as insulation layer and thermosyphons. The in-situ observational dataset is of great value for assessing the variability of permafrost under the linear disturbances of the CRCOPs and related environmental effects, for understanding hydro-thermal-mechanical interactions between the buried pipelines and permafrost foundation soils, and for evaluating the operational and structural integrity of the pipeline systems in the future. The dataset is available at the Third Pole Environment Data Center (http://doi.org/10.11888/Cryos.tpdc.272357 (Li, 2022)).
This paper reports the dewatering scheme of a deep excavation in sandy pebble strata. The excavation is in high permeability strata and is close to the Yellow River, making the dewatering difficult during construction. At present, few researchers have specially studied the dewatering scheme of deep excavations in strong permeable strata near the water resource. Field pumping test was conducted before the excavation activity, and the permeability coefficient of the strata was obtained by reverse analysis. According to the characteristics of the project, the dewatering scheme of “ ” was proposed. The influence of vertical waterproof curtain and base grouting on dewatering was analyzed by numerical simulation. In the construction process, the field water table and ground settlement were measured. The results show that (1) the groundwater table versus permeability coefficient curve shows three different stages and (2) the dewatering scheme of “ ” is effective for deep excavation in strong permeable strata.
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