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1.
The stress—strain behaviour of frozen soils is often described by means of creep curves from uniaxial or triaxial creep tests. Ten or twelve tests of similar samples are required to obtain a good relationship between stress σ, strain ε, temperature T and time t or strain rate ε. To reduce the required number of samples it is possible to apply the compression load in creep tests stepwise. Therefore creep curves for different stress levels can be obtained from one sample. In this paper the bearing capacity of cylindrical samples of frozen medium sand under constant uniaxial compression stress and under stepwise increased stresses is compared. It is shown how to use these different creep curves to describe the stress—strain behaviour of frozen soils. 相似文献
2.
As a clean form of energy able to replace oil, the demand for LNG (Liquefied Natural Gas) has been increasing. LNG must be stored in a cryogenic temperature of —162°C. The storage tanks now existing throughout the world can be divided into above-ground and inground types. In the Tokyo area, there are now 22 in-ground LNG storage tanks, either in operation or under construction, which are constructed with primary consideration given to safety and earthquake-proof design because of the circumstances around the LNG terminals. In the feasibility study of a very large-scale, in-ground LNG storage tank, comparative preliminary studies were made of various construction methods. Among them, the method using artificial ground freezing was proposed, in which it was planned to utilize the frozen soil as the means of ground water control and the temporary retaining wall. To confirm the feasibility of the design, a model tank test was conducted by freezing the actual tank yard. The yard ground, composed of sand and silt layers, was artificially frozen 10 m in diameter and 50 m in depth; in the frozen soil a shaft of 4 m in diameter was sunk to a depth 26 m below the ground level for various tests and measurements. The purpose of the test was mainly to confirm the construction method and to examine the agreement between theory and practice. Although this construction method has not been adopted in the actual tank work, the feasibility of the method itself has been confirmed as a result of the test. In this paper, the outline and major results of the test and analysis are described. 相似文献
3.
In connection with the building of a railway tunnel through the City of Oslo, temporary improvement of the soft clay by freezing was considered in order to reinforce the tunnel ceiling in an area where the rock cover was insufficient. The same solution was also considered for another part of the tunnel where the problem was to prevent bottom heave failure in a deep excavation. As this marine clay deposit has a very high salt content (about 25 g/l pore liquid), it was reasonable to believe that the strength of the frozen clay would be relatively low compared to previously published data concerning fresh clay soils. To investigate the stress—strain properties of frozen Oslo clay, a fairly comprehensive research programme was carried out; including two different temperature levels and using different testing techniques. The clay was tested in compression, tension, bending and shear, respectively. The tests were run very slowly, time to failure was normally 70–100 days. This paper presents the main test results, which indicate that there exists a fairly well defined critical shear stress level for a given freezing temperature. As long as the stresses do not exceed this stress level, the creep deformations are small and the creep rates are constant or decreasing with time. On the other hand, higher shear stresses lead to very extensive deformations or failure. 相似文献
4.
Artificial ground freezing at low temperatures provides a solution to such complicated problems as strengthening foundations, improvement of their reliability and the provision of the watertightness of the ground. Ground cooling and freezing directly changes the stress—deformation state of foundations and underground constructions. Basic diagrams on ways and means of forming low temperature frozen zones of a definite shape in the ground are given in the paper. Peculiarities of the work of the seasonally functioning heat-exchange devices and systems are discussed. The development and refinements of methods of calculation and long-term forecast of temperature fields in artificially cooled ground massifs is of great importance. Experimental data on migration phenomena in freezing soils and the methods of the numerical modeling of cooled massifs are discussed. The paper is illustrated by diagrams, test results and calculation data. 相似文献
5.
Twin 6.5 m diameter tunnels were driven through saturated soil at a depth of 25 m under a street intersection with the aid of horizontal freezing. The frozen soil section was about 30 m long. Because of groundwater pressure the horizontal freeze holes were drilled with sealed casings. A new drill bit was introduced to form a tight plug at the end of the casing. The soil around the perimeter of the tunnel bores was frozen by vaporizing freon in the freeze tubes. A 2.5 m thick ice wall in sand and moraine was developed during the freezing period of 55 days. The tunnel bores were excavated under protection of the frozen arch by cautious drilling and blasting. The advance was 1.2–1.8 m per round. Permanent tunnel linings were constructed by bolting together cast iron segments. 相似文献
6.
人工冻土的物理力学指标是地铁隧道工程冻结壁设计参数和开挖的依据。通过对宁波轨道交通一号线联络通道②～⑤海相沉积软土地层人工冻土的室内单轴抗压强度和抗剪强度试验,获得了冻结前后②～⑤土层的比热容、导热系数、内摩擦角和粘聚力的对比结果以及不同温度条件下冻土的极限抗压强度、弹性模量和泊松比结果。试验结果表明:②～⑤土层人工冻结土的物理力学指标较原状土有很大的提高,人工冻土极限抗压强度、弹性模量随温度的降低而增大,近似呈线性关系。各土层泊松比、温度的变化对冻土泊松比影响较小,随温度的降低有一定的减小。在-10℃条件下,冻结前淤泥质土、粘土层的内摩擦角和粘聚力有了大幅的提高,而③1砂土层的内摩擦角增幅较小。 相似文献
7.
The stress—strain and strength behavior of frozen soils is most often studied in a conventional uniaxial or triaxial compression test. However, available experimental evidence shows that the results obtained in such a test may be considerably affected by the test conditions, i.e., by the specimen shape and the method of axial load transfer to the specimen ends, both of which affect the uniformity of stress and strain distribution in the sample. The methods proposed for solving the problem of load transfer to the specimen ends differ considerably for brittle and ductile materials, respectively. Since a frozen soil may behave either as a brittle or as a ductile material, depending on strain rate, temperature and confining pressure, it is considered that the load transfer method selected should correspond to the expected sample behavior. In this paper, the results of a series of compression and creep tests are presented, in which the effects of specimen shape and end conditions on the behavior of a frozen sand were systematically investigated and compared. a frozen sand were systematically investigated and compared. 相似文献
8.
两种试验模式下的冻土应力-应变曲线均呈双曲线型,但其变形过程明显不同,FC模式 (传统冻土力学试验模式)下的屈服强度明显小于K 0DCF模式 (深土冻土力学试验模式)下的.FC模式下,加载应力路径下的破坏变形明显大于K 0DCF模式下的,而减载应力路径下的破坏变形小于K 0DCF模式下的.在试验围压范围内,两种试验模式下的莫尔包络线均满足莫尔 -库仑准则,且无论是加载还是减载应力状态,K 0DCF模式下的剪切强度总是大于FC模式下的,且随着σ的增大,K 0DCF模式下加载与减载下剪切强度的差值比FC模式下τ的差值小.通过一定的对应关系可将两种模式下的强度与变形联系起来. 相似文献
9.
冻结法施工在上海隧道建设中(如隧道旁通道、地下泵房等的设计与施工)得到广泛应用,也曾引发过严重的地质灾害(如上海地铁4号线外滩段的地质灾害)。因此安全、经济、合理地将冻结法用于上海软土地区隧道建设中已经成为上海工程建设中的一个重要的研究课题。本文以上海复兴东路越江隧道旁通道冻结法施工中遇到的第⑥层粉质粘土及第⑦层粉细砂为研究对象,针对设计冻结壁重要强度参数无侧限瞬时抗压强度,进行了室内试验研究,揭示了两种土的冻结强度随温度的变化关系,同时研究了粉细砂的冻结强度随含水率的变化规律。 相似文献
10.
选用四种不同固结方式,并在－５０℃条件下,对冻结砂土样进行三轴压缩试验,试验发现固结过程对冻土的强度与变表有明显影响。经历Ｋ０ＤＣＦ的冻土其强度最大,友坏变形最小,经历ＦＣ的试样强度最小,破坏变形最大;经历ＥＤＣＦ和ＥＵＤＣＦ的产介于中间。 相似文献
11.
Relying on the application of the artificial freezing method on subway tunnel construction, a series of triaxial creep tests were carried out to study the creep behavior changes of Shanghai soft clay subjected to artificial freeze–thaw action. On this basis, MIP tests were conducted with the soil samples before and after creep for comparison to investigate the microstructure changes. The results indicate that freeze–thawed soil produces smaller creep deformation and instantaneous deformation than the unfrozen soil. On a micro-level, during the creep process, the soil skeleton reaches a new structure balance with smaller pore volume and pore area. But the diameter of the maximum pore increases. The change rate of total intrusion volume is a pivotal micro-parameter to evaluate creep strain as there is a good linear relationship between them. 相似文献
12.
The compressive and tensile strengths of frozen clay are important parameters for frozen wall design in artificial freezing
excavation of tunnels and foundation pits. Up to now, nobody has conducted the compressive and tensile test of frozen clays
in Shanghai area. In this paper, the unconfined compressive and tensile tests of frozen clay specimens drilled from the soil
horizons 3–5 in Shanghai area were conducted in Zwick-Z020kN High-low Temperature Materials Testing Machine and Frozen Soil
Triaxial Testing Machine, the corresponding constitutive equations were suggested; the temperature-unconfined uniaxial compressive
strength relation was discussed; the strain rate–unconfined uniaxial compressive strength and strain rate–uniaxial tensile
strength relations were studied. The relation between moisture content, dry density and unconfined uniaxial compressive strength
was analyzed, too. In addition, the uniaxial compressive elastic modulus of Shanghai frozen clays and its influence factors
were discussed. The research work of the current paper is very helpful for the design and theoretical studies of artificial
freezing excavation in soft soil areas. 相似文献
14.
冻结岩石的变形破坏特性是冻结法施工过程中的基础力学问题,在荷载作用下不同冻结温度岩石的力学特性和变形特征差异性较大,严重影响冻结壁的安全与稳定。因此,研究冻结岩石的损伤本构关系,对指导冻结法设计与施工具有重要意义。为分析荷载作用下冻结岩石变形破坏的全过程,采用Weibull分布描述岩石材料的非均质性,基于Drucker-Prager破坏准则,建立三轴应力状态下岩石损伤本构模型,结合冻结砂岩三轴压缩试验,重点分析本构关系中均质度系数m、平均强度F 0与冻结温度和围压的变化关系,对损伤本构方程进行修正,并基于此模型研究冻结砂岩的损伤演化规律。结果表明:在相同围压下,随着冻结温度的降低,砂岩峰值强度显著增大,峰值应变减小,压密阶段逐渐减弱,弹性变形阶段斜率增加,岩石脆性破坏特征明显。在相同冻结温度下,均质度系数m和平均强度F 0随围压升高无显著变化,而随着冻结温度的降低,m和F 0分别呈现指数增长和线性增长,说明随着冻结温度的降低,砂岩冻结越充分,内部自由水冻结成冰占比及冰体强度增长幅度越大,尤其在0~–10℃内提升效果显著,冻结作用提高了砂岩的均质性和平均强度。基于不同冻结温度砂岩的力学特性和变形规律,对不同冻结温度砂岩的损伤本构方程进行了修正。依据修正本构模型研究发现,损伤演化曲线能够很好地反映冻结砂岩压缩试验的压密、线弹性、屈服变形及应变软化各阶段的变形特征,验证了模型的合理性。研究结果为低温环境下岩石力学特性研究及地下冻结工程设计施工提供有益的参考。 相似文献
15.
Depending on artificial freezing method applied in subway tunnel construction, a series of stress-controlled cyclic triaxial tests were conducted on freezing–thawing mucky clay to investigate their resilient and plastic strain behavior. In terms of practical engineering, this study focuses on three significant influencing factors which are artificial freezing temperatures, dynamic stress amplitude and loading frequency. This study demonstrates how these influence factors effect on the resilient strain or dynamic elastic modulus and accumulated plastic strain which are crucial to better understanding the strain behavior of freezing–thawing soil. The results indicate that the value of freezing temperature has slight influence on dynamic elastic modulus, but the freeze–thaw action can truly decrease the dynamic elastic modulus of soil, and soil with higher freezing temperature possesses larger accumulated axial strain. Besides, the dynamic elastic modulus decreases remarkably with the increasing of the cyclic stress amplitude, while the accumulated plastic strain behaves adversely. In addition, loading frequency has the least effect compared with other two factors, but lower frequency can generate larger accumulated plastic strain. 相似文献
16.
青藏铁路全线开通运营以来,对处于高寒地区的永久冻土隧道之一的风火山隧道的质量状态首次进行了无损检测。风火山隧道处于高寒永久冻土区,隧道全部处于冻岩中,两端洞口主要为砂岩与泥岩,并且为富冰冻土。受到季节性冻融的影响,隧道病害比较突出,主要表现为衬砌裂缝,漏水涌水,衬砌酥松剥落。为了准确地掌握风火山隧道衬砌结构质量状态,本文首次应用于风火山隧道衬砌结构的质量检测。该检测设备一改传统破坏式的检测方法,具有快速、简捷、无损、灵活的特点。通过对现场数据处理分析,可以精确探测衬砌厚度,查明衬砌背后存在的空洞和回填不密实区域。检测结果表明,隧道在高寒恶劣环境中,衬砌总体外观质量尚好,但是在两端洞口段有渗水现象;衬砌背后空洞缺陷等级为严重地段测线长度为20m,等级为极严重地段测线长度为98m;衬砌背后回填不密实缺陷等级为严重地段测线长度为41m,等级为极严重地段测线长度为33m。检测结果与实际病害情况基本相符。 相似文献
17.
The paper presents a constitutive model for simulating the high strain‐rate behavior of sands. Based on the concepts of critical‐state soil mechanics, the bounding surface plasticity theory and the overstress theory of viscoplasticity, the constitutive model simulates the high strain‐rate behavior of sands under uniaxial, triaxial and multi‐axial loading conditions. The model parameters are determined for Ottawa and Fontainebleau sands, and the performance of the model under extreme transient loading conditions is demonstrated through simulations of split Hopkinson pressure bar tests up to a strain rate of 2000/s. The constitutive model is implemented in a finite‐element analysis software Abaqus to analyze underground tunnels in sandy soil subjected to internal blast loads. Parametric studies are conducted to examine the effect of relative density and type of sand and of the depth of tunnel on the variation of stresses and deformations in the soil adjacent to the tunnels. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
18.
叠交隧道是涉及隧道之间、隧道与土体相互作用的复杂体系,其安全性将严重影响城市轨道交通建设。目前,对于叠交隧道振动台试验的研究集中在水平平行和交叉叠交隧道、单向和双向地震动输入。鉴于此,利用自行设计的层状三向剪切模型箱,对竖直平行叠交隧道开展三向地震作用下的振动台模型试验,研究地基土−叠交隧道模型体系动力特性、地基土加速度、叠交隧道加速度、地表沉降、地基土孔压、叠交隧道动土压力及叠交隧道应变等地震响应。结果表明：随着震波峰值加速度（peak ground acceleration,简称PGA）依次增加,地基土−叠交隧道模型体系的自振频率随之减小,而阻尼比随之增大;叠交隧道周围地基土加速度和孔压的梯度差随着地震波PGA的增大而增大,且上隧道周围梯度差比下隧道更大;地基土对加速度的放大效应随着地震波PGA的增大而减弱;相同地震波作用下,相同位置处的叠交隧道加速度傅里叶谱形状相似,但幅值随着地震波PGA的增大而增大。此外,与顶部和底部位置相比,腰部位置加速度傅里叶谱频段范围变宽,幅值峰值有所降低;地表沉降峰值随着地震波PGA的增大而减小,相比地基土两侧位置,中心位置的沉降峰值明显较小;地震波的类型对叠交隧道动土压力峰值和应变峰值影响较小;对于动土压力峰值,两隧道的最大值均为腰部,而上、下隧道的最小值分别为底部、顶部;对于应变峰值,上隧道在腰部明显大于顶部和底部,而下隧道在4个位置相差不大。 相似文献
19.
Cylindrical specimens of fine Ottawa sand (A.S.T.M. designation C-109), compacted at the optimum moisture content and saturated before unidirectional freezing, have been tested in uniaxial compression at a cold room temperature of —5.5°C and strain rates between 10 −7 and 10 −2 s −1. The results agree with an extrapolation of data obtained by Sayles and Epanchin [1], but are much higher than those obtained by both Goughnour and Andersland [2] and Perkins and Ruedrich [3] at strain rates below 10 −5 s −1. There is evidence that this may be due to variation in total moisture (ice) content, the conditions under which the specimens were frozen (closed system or an open system) and to the end effects at the platen—specimen interface. 相似文献
20.
Freezing was used in the jointing section of two shields (diameter 3.14 m) which ran across at right angles and at 25-m depth under the crossing of main roads for the construction of a 2.4-m diameter sewer tunnel. The object of freezing was to create a frozen barrier to prevent the inflow of water and fine sand into the area to be excavated. Thirty-five freeze pipes (length about 7 m) were placed from one shield conically in the direction of the flank of another shield with freeze pipes attached to its inside wall. The cooling unit was placed on unoccupied land at about 60 m distant from the jointing section and the freeze pipes were connected with the cooling unit by supply and return pipelines. The cooling unit had a cooling capacity of 79,000 kcal/h at an evaporation temperature of −27°C and a condensation temperature of +40°C. Freezing was continued for 180 days and the CaCl2 brine temperature was −25 to −30°C. These works were accomplished without the sinking of shaft and the use of injection, in complete safety with no traffic restriction on the road surface. 相似文献
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