大吨位基桩抗压载荷试验中的锚桩预应力保护技术

竖轴向承载力是桩基础设计的重要参数,现场静载试验是目前确定桩基承载力的主要手段之一。本文依托黄陵延安段高速公路洛河特大桥试桩工程,通过对原有工程桩施加预应力,形成了以工程桩为锚桩的锚拔体系。加载过程中试桩应力、锚桩应力及桩顶位移测试,结果表明,结合预应力技术,以工程桩作为锚桩构成桩基础静载试验的锚拔体系是可行的,同时提出了施加预应力大小的原则、方法以及确保后期曾作为锚桩的工程桩有足够承载能力应采取的必要措施。     

Orthotropic frost heaving force distribution characteristics for tunnel structures under hydro-thermo-mechanical coupling;

In cold regions,the frost heave of surrounding rock could lead to additional force on lining struc⁃ tures,which impairs the durability and safety of tunnels. This paper analyzed the distribution characteristics of tunnels’frost heave force in seasonally frozen regions. Firstly,energy conservation and mass conservation prin⁃ ciples were introduced,and a hydro-thermal-mechanical coupling model of frozen surrounding rock considering orthotropic frost heaving deformation was constructed. The reliability of the model was verified with the monitor⁃ ing result of the Qingshashan tunnel. Furthermore,the numerical model of the Dongtianshan tunnel was con⁃ structed,and distribution characteristics of temperature fields,water fields,and frost heave force were studied. In addition,various influencing factors on the tunnel’s frost heave force were analyzed,including the minimum temperature,the initial formation water content,the modulus ratio of the frozen and unfrozen surrounding rock,and the orthotropic frost heave coefficient. The simulation results show that the frozen depth of the tunnel is not uniform,the smallest at the arch foot and the largest at the center of the inverted arch. The maximum frozen depth difference was 48 cm. The frozen depth difference was due to the largest geometric curvature at the arch foot. At the same time,due to the minimum freezing depth and largest geometric curvature at the arch foot,the bending and folding of the arch foot of the lining are the most significant,and the von Mises stress at the arch foot is the largest. During one freezing-thawing period,the water content change includes four stages：freezing,thawing,stagnating and dissipating. After 20 freeing-thawing periods,in the water stagnating stage,the volu⁃ metric water contents at the lining top and sides increased by 10. 46% and 4. 21%,respectively,and the volumet⁃ ric water contents at the arch foot and lining bottom decreased slightly. The frozen surrounding rock produced both normal and tangential stress on the lining. Among them,the top arch and inverted arch are mainly manifest⁃ ed as compressive stress,while the compressive stress of the arch foot is minor and partially represented as ten⁃ sile stress. The frost heave force distribution patterns under different minimum air temperatures,initial water contents,modulus ratios between frozen and unfrozen surrounding rock,and orthotropic coefficients of frost heave deformation are the same. Normal stress distributions outside the lining are“mushroom-shaped”as a whole. The decrease in temperature could extend the freezing area,and the increase of orthotropic frost heave deformation coefficient could concentrate frost heave strain’s direction,which could significantly promote the frost heave force. The modulus ratio between frozen and unfrozen surrounding rock was negatively related to frost heave force,and the initial water content was positively related to frost heave. The orthotropic coefficient of frost heave deformation has the most significant influence on the value and distribution of frost heave force. After 20 years of freeze-thaw cycles,the difference of water field under different initial formation water content reduced,which leads to the little difference in frost heaving force of the tunnel under different initial formation water contents. The frost heave force distribution is mainly the result of the competition between the temperature field and the lining geometry. The minimum freezing depth leads to the smallest frost heave force at the arch foot. However,the deformation of the lining causes the arch foot to press against the surrounding rock,which could increase the compressive stress on the arch foot. For the tunnel with a small lining thickness,the extrusion effect of the arch foot to the outer surrounding rock is more prominent,which leads to a more considerable frost pressure at the arch foot. Overall,the frost heave force distribution of tunnels in cold regions should consider the influence of temperature conditions,water conditions,anisotropy of surrounding rock frost heave deformation,and lining geometry. Copyright © 2023 Institute of Microbiology, CAS. All rights reserved.     

Constitutive modelling of fine-grained gassy soil: A composite approach

Fine-grained marine sediments containing large undissolved gas bubbles are widely distributed around the world. Presence of the bubbles could degrade the undrained shear strength (s_u ) of the soil, when the gas pressure u_g is relatively high as compared with the effective stress in the saturated soil matrix. Meanwhile, the addition of bubbles may also increase s_u when the difference between u_g and pore water pressure u_w becomes smaller than the water entry value, causing partial water drainage from the saturated matrix into the bubbles (bubble flooding) during globally undrained shearing. A new constitutive model for describing the two competing effects on the stress-strain relationship of fine-grained gassy soil is proposed within the framework of critical state soil mechanics. The gassy soil is considered as a three-phase composite material with compressible cavities, which allows water entry from the saturated matrix. Bubble flooding is modelled by introducing an additional positive volumetric strain increment of the saturated clay matrix, which is dependent on the difference between pore gas and pore water pressure based on experimental observations. A modified hardening law based on that of the modified Cam clay model is employed, which in conjunction with the expression for bubble flooding, can describe both the detrimental and beneficial effects of gas bubbles on soil strength and plastic hardening in shear. Only two extra parameters in addition to those in the modified Cam clay model are used. It is shown that the key features of the stress-strain relationship of three fine-grained gassy soils can be reproduced satisfactorily.     

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Pseudo-fractal interpolation for risk analysis

This paper describes a new method of analyzing the risk incurred when the outcome of a decision depends on interpolated values, for example, on the flow through an aquifer sparsely sampled for permeability or on the ratio of waste to ore in a mineral deposit sparsely sampled for grade. The method uses large families of interpolations constructed between sample values using adaptations of the well-known midpoint displacement method for generating pseudo-fractional Brownian motion trajectories. The parameters defining each family are chosen interactively by specialists to incorporate their expert knowledge. Each family, or ensemble, then defines a population of values for any global characteristic (functional) such as flow rate or waste ratio. The probabilities of various outcomes are estimated by counting them and calculating their ratios. For example, if 900 out of 1000 are acceptable the chance of success is estimated to be 90%.     

软件综合评价的层次分析模式的建立

从软件综合价值工程分析入手，利用ＡＨＰ方法建立起软件综合评价模式，该模式符合评价技术理论，能够较好地反映软件的高科技特性品质和商品产业化的趋势要求。实例表明，该模式具有良好的可操作性，对于软件综合评价理论的建立具有一定意义     

改进ELECTRE方法在软件工程质量研究中的应用

本文利用改进的Electre评价排序方法,试图在软件开发工程质量评价中寻求一条由定性到定量评价的新途径。通过分析和应用,认为在软件开发工程中,软件详细设计的语言工具选择时,此方法是可行和有效的。     

崇明越江隧道岩土工程概要

对上海崇明越江隧道工程沿线的工程地质和水文地质条件进行概略总结,并对场地内的不良地质及其对策进行了分析评价。     

Using value engineering to optimize flood forecasting and flood warning systems: Golestan and Golabdare watersheds in Iran as case studies

Flood occurrence has always been one of the most important natural phenomena, which is often associated with disaster. Consequently, flood forecasting (FF) and flood warning (FW) systems, as the most efficient non-structural measures in reducing flood loss and damage, are of prime importance. These systems are low cost and the time required for their implementation is relatively short. It is emphasized that for designing the components of these systems for various rivers, climatic conditions and geographical settings different methods are required. One of the major difficulties during implementing these systems in different projects is the fact that sometimes the main functions of these systems are ignored. Based on a systematic and practical approach and considering the components of these systems, it would be possible to extract the most essential key functions of the system and save time, effort and money by this way. For instance, in a small watershed with low concentration and small lead time, the main emphasis should be on predicting and monitoring weather conditions. In this article, different components of flood forecasting and flood warning systems have been introduced. Then analysis of the FF and FW system functions has been undertaken based on the value engineering (VE) technique. Utilizing a functional view based on function analysis system technique (FAST), the total trend of FF and FW functions has been identified. The systematic trend and holistic view of this technique have been used in optimizing FF and FW systems of the Golestan province and Golabdare watersheds in Iran as the case studies.     

The Cathedral of S. Giorgio in Ragusa Ibla (Italy): characterization of construction materials and their chromatic alteration

The Cathedral of St. Giorgio in Ragusa Ibla (Sicily) is one of the most important Baroque monuments of eastern Sicily. The restoration of the monument underway has put forward notable questions regarding the stone materials used and their state of degradation. The façade appears to be made mainly of a creamy white calcarenite, and of mortars and plasters. However, detailed analysis has highlighted a more complex use of the raw material. The mortar and plaster have a different composition in regards to their architectural use while the natural stone material is distinguished not only by a creamy-white calcarenite but also by a dark coloured bituminous calcarenite (pitch rock), which now appears whiter because of superficial chromatic alterations. This process was reproduced in the laboratory using an accelerated aging technique on samples of bituminous calcarenite, which allowed the cause of the alternation to be identified as photo-oxidation of the asphaltenes. Following this process of photo-oxidation, other forms of chromatic alterations affected the façade (brown–orange-coloured patinas). FTIR, Scanning Electron Microscope and thin section microscopic observation allowed the characterization of also the products of this process to be carried out, highlighting the complex mechanism which the processes underwent.