Abstract. Eulerian and Lagrangian numerical moisture tracking models, which are primarily used to quantify moisture contributions from global sources to specific regions, play a crucial role in hydrology and (paleo)climatology studies on the Tibetan Plateau (TP). Despite their widespread applications in the TP region, potential discrepancies in their moisture tracking results and their underlying causes remain unexplored. In this study, we compare the most widely used Eulerian and Lagrangian moisture tracking models over the TP, i.e., WAM2layers (the Water Accounting Model – 2 layers) and FLEXPART-WaterSip (the FLEXible PARTicle dispersion model coupled with the “WaterSip” moisture source diagnostic method), specifically focusing on a basin governed by the Indian summer monsoon (Yarlung Zangbo River basin, YB) and a westerly-dominated basin (upper Tarim River basin, UTB). Compared to the bias-corrected FLEXPART-WaterSip, WAM2layers generally estimates higher moisture contributions from westerly-dominated and distant sources but lower contributions from local recycling and nearby sources downwind of the westerlies. These differences become smaller with higher spatial and temporal resolutions of forcing data in WAM2layers. A notable advantage of WAM2layers over FLEXPART-WaterSip is its closer alignment of estimated moisture sources with actual evaporation, particularly in source regions with complex land–sea distributions. However, the evaporation biases in FLEXPART-WaterSip can be partly corrected through calibration with actual surface fluxes. For moisture tracking over the TP, we recommend using high-resolution forcing datasets, prioritizing temporal resolution over spatial resolution for WAM2layers, while for FLEXPART-WaterSip, we suggest applying bias corrections to optimize the filtering of precipitation particles and adjust evaporation estimates.
Selecting and designing the most suitable support systems are crucial for securing underground openings, limiting their deformation and ensuring their long-term stability. Indeed, the rock excavations imposed by the erection of deep tunnels generate various harmful effects such as stress perturbation, damage, fractures, rockbursts, convergence deformation, and so on. To combat such effects by helping the surrounding rocks of these structures to hold up, rock bolts are typically utilized as pioneer support systems. However, the latter must be efficient and sustainable to properly fulfil their vital roles. A thorough understanding of the existing rock bolt types or models and the relevant factors influencing their failure is highly required for appropriate selection, design and applications. It is observed that, despite numerous studies carried out, there is a lack of comprehensive reviews concerning the advances in such rock support systems. This paper provides an insight into the most pertinent rock bolt types or models and describes the potential factors influencing their failure. Additionally, it discusses the durability of rock bolts, which has a huge impact on the long-term stability of deep rock tunnels. Furthermore, the paper highlights some proposals for future trends.
During tunnel construction in cold regions, the good adhesion of surrounding rock-lining interface is one of the important preconditions to evaluate the durability of tunnel lining. However, the repeated fatigue damage between rock and concrete due to the freeze-thaw action leads to debonding at the interface, which significantly affects the protective effect of shotcrete. Accordingly, based on the combination of sandstone-concrete as the object, through the development of sandstone-concrete interface freeze-thaw cycling test, and combining the nuclear magnetic resonance (NMR) test and scanning electron microscopy (SEM) analysis, the mechanism of debonding by freeze-thaw damage at the sandstone-concrete interface was systematically revealed. The conclusions drawn are as follows: (1) With the increase of freeze-thaw times, the content of micropores and macropores at the interface gradually increases, while the content of mesoporous gradually decreases. At the same time, the decrease of freeze-thaw temperature also aggravates the growth of interface cracks, and the freeze-thaw damage of interface is closely related to the minimum freeze-thaw temperature. (2) The damage of the sandstone side becomes more serious under multiple freeze-thaw actions. Concrete as a water retaining plate inhibits the migration of water to its interior, and a pot cover effect exists at the interface to provide better storage space for water accumulation. (3) The C-S-H group is the main source of the bond force of sandstone-concrete interface, and the freeze-thaw effect aggravates the fracture of the C-S-H group, which leads to the interface debonding. This study could provide an experimental basis and theoretical support for systematically recognizing the evolution mechanism of freeze-thaw damage and debonding of shotcrete in tunnels in cold regions.
Abstract. Evaporation from global oceans is an important moisture source for glaciers and headwaters of major Asian rivers in the Tibetan Plateau (TP). Although the accelerated global hydrological cycle, the altered sea–land thermal contrast and the amplified warming rate over the TP during the past several decades are known to have profound effects on the regional water balance, the spatial distribution of oceanic moisture contributions to the vast TP remains unclear. This hinders the accurate quantification of regional water budgets and the reasonable interpretation of water isotope records from observations and paleo archives. Based on historical data and moisture tracking, this study systematically quantifies the absolute and relative contributions of oceanic moisture to long-term precipitation in the TP. Results show that the seasonal absolute and relative oceanic contributions are generally out of phase, revealing the previously underestimated oceanic moisture contributions brought by the westerlies in winter and the overestimated moisture contributions from the Indian Ocean in summer. Quantitatively, the relative contribution of moisture from the Indian Ocean is only ∼30 % in the south TP and further decreases to below 10 % in the northernmost TP. The absolute oceanic contribution exhibits a spatial pattern consistent with the dipole pattern of long-term precipitation trends across the Brahmaputra Canyon region and the central-northern TP. In comparison, relative oceanic contributions show strong seasonal patterns associated with the seasonality of precipitation isotopes across the TP.
Abstract The distress development of highway embankments in permafrost regions presents accumulative and abrupt characteristics according to the survey data of the Qinghai-Tibet Highway (QTH). In view of this problem, this study proposes the concept of a temporal effect of embankments in permafrost regions. The concept represents the service life of an embankment by analyzing its distress history under different geological conditions, embankment scales, and structures. The maintenance history, reconstruction material, and distress data of the QTH over the past 60 years were collected in this article. The relations between highway distress and mean annual ground temperature (MAGT), permafrost degradation rate, and ice content were studied based on the survey data. The service life was determined by considering the previously mentioned factors. Besides, the newly developed distresses and their temporal effects were analyzed by using the treatment measure. The results showed that the MAGT and service life was negatively correlated. With MAGT increasing from −3.0°C to −0.5°C, mean annual service life decreased from >40 to <10 annum (a). As the permafrost degradation rate increased, the time of embankment distress occurrence was increasingly shortened. Secondly, when the permafrost degradation rate exceeded 15 cm/a, no section with a service life of >40 a existed. When the permafrost degradation rate exceeded 20 cm/a, the embankment was found to be in need of reconstruction in 10 a. Thirdly, the higher the ice content, the earlier the distress occurred and the higher the distress grade. Especially in warm and high degrading-rate permafrost regions, the embankment on an ice layer with soil inclusions showed severe distresses 2–3 a after pavement construction, and was in need of maintenance or reconstruction in 5–10 a. Finally, installing the special treatment measures could effectively delay the development process of embankment distress. The survey results indicated that the cooling efficiency of thermosyphon embankment, crushed-rock embankment, ventilation duct embankment, and thermal insulation-layer embankment could reach 95, 55, 90, and 90 %, respectively, and their distress prevention efficiencies were 70, 80, 60, and 70 %, respectively.
The comprehensive understanding of the variation law of soil thermal conductivity is the prerequisite of design and construction of engineering applications in permafrost regions. Compared with the unfrozen soil, the specimen preparation and experimental procedures of frozen soil thermal conductivity testing are more complex and challengeable. In this work, considering for essentially multiphase and porous structural characteristic information reflection of unfrozen soil thermal conductivity, prediction models of frozen soil thermal conductivity using nonlinear regression and Support Vector Regression (SVR) methods have been developed. Thermal conductivity of multiple types of soil samples which are sampled from the Qinghai‐Tibet Engineering Corridor (QTEC) are tested by the transient plane source (TPS) method. Correlations of thermal conductivity between unfrozen and frozen soil has been analyzed and recognized. Based on the measurement data of unfrozen soil thermal conductivity, the prediction models of frozen soil thermal conductivity for 7 typical soils in the QTEC are proposed. To further facilitate engineering applications, the prediction models of two soil categories (coarse and fine‐grained soil) have also been proposed. The results demonstrate that, compared with nonideal prediction accuracy of using water content and dry density as the fitting parameter, the ternary fitting model has a higher thermal conductivity prediction accuracy for 7 types of frozen soils (more than 98% of the soil specimens’ relative error are within 20%). The SVR model can further improve the frozen soil thermal conductivity prediction accuracy and more than 98% of the soil specimens’ relative error are within 15%. For coarse and fine‐grained soil categories, the above two models still have reliable prediction accuracy and determine coefficient ( R 2 ) ranges from 0.8 to 0.91, which validates the applicability for small sample soils. This study provides feasible prediction models for frozen soil thermal conductivity and guidelines of the thermal design and freeze‐thaw damage prevention for engineering structures in cold regions.
Summary As a type of mono-alkyl ester, biodiesel exhibits great potential to serve as the base oil of drilling fluids substituting for conventional oil-based drilling fluids (OBDFs). This paper presents a series of laboratory investigations of water-in-biodiesel (invert) emulsion as the basis of a high-performance, environmentally friendly, and low-cost biodiesel-based drilling fluid (BBDF). Biodiesel produced from waste cooking oil was used to formulate a BBDF because of its high flashpoint, reliable storage stability, acceptable elastomeric material compatibility, nontoxicity, and excellent biodegradability. In light of the results of tests used to measure various properties, the biodiesel invert-emulsion chemistry, including the required hydrophile/lipophile balance (HLB), optimal emulsifier, effects of different additives (organophilic clay, calcium chloride, and lime), as well as hydrolytic stability, was studied. A biodiesel invert emulsion that remains stable after hot rolling at 120°C for 16 hours can be prepared with correct combinations of additives, thereby offering a firm foundation for designing BBDFs. The novel emulsifier package developed in this work is introduced as an achievement in the comprehensive usage of waste cooking oil because its feedstock is identical to that of biodiesel. An initial economic analysis of the use of biodiesel for drilling is also presented. Details of the formulations and properties of BBDFs derived from this fundamental research are discussed in another paper (Part 2).
Summary This paper presents an environmentally friendly, biodiesel-based invert-emulsion drilling fluid (BBDF). On the basis of the stable emulsion previously optimized (which was presented in Part 1), several necessary additives, including an organophilic clay (OC), a fluid-loss (FL) -control agent and a rheological modifier (RM), were developed or selected to formulate the BBDF. Numerous laboratory tests of different properties were conducted to evaluate the properties of this drilling fluid. BBDF has a rheological behavior and filtration properties that meet the requirements of drilling operations. It exhibits good shale-inhibition ability, excellent lubricity, and tolerance to contaminants. Low toxicity and great biodegradability are the prominent advantages of this system. After evaluating the suitabilities of known rheological models for BBDF, a hydraulic simulation was carried out on the basis of the Herschel-Bulkley model. BBDF performs similarly to conventional oil-based drilling fluids (OBDFs) subject to deepwater drilling conditions. High performance and great environmental compliance make BBDF a promising option for marine or extended-reach drilling. In addition, novel OC produced from rectorite and nonionic surfactants was successfully introduced into this drilling fluid. This modified rectorite is expected to be a substitute for conventional organobentonite.
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