Numerical analysis of applying special pavements to solve the frost heave diseases of high-speed railway roadbedsin seasonally frozen ground regions

The Haerbin-Dalian Passenger Dedicated Line is the first high-speed railway constructed in the seasonally frozen ground regions of northeastern China. Frost heave diseases occurred in the first winter of its operation(between October 2012 and January 2013), and frost heave was observed mainly in the roadbed fills that were considered not susceptible to frost heave. This paper proposes applying two special pavements — black pavement and insulation-black pavement — to improve the thermal regime of the roadbed. Three numerical models of the roadbed temperature field were built based on the field conditions of the Changchun section(D3K692+840 to D3K692+860). The results show that:(1) Compared with cement pavement, black pavement and insulation-black pavement could reduce the freezing index at the roadbed surface by 37% and 64%, respectively, which could influence the maximum frozen depth;(2) the maximum frozen depths under the black pavement and insulation-black pavement were respectively 1.3–1.4 m and 1 m. Compared with cement pavement, they could reduce the maximum frozen depth by 0.4 m and 0.7–0.8 m, respectively, which would reduce the permitted amount of frost heave by 4 mm and 7–8 mm, which would meet the deformation limit established by the Code for Design on Special Subgrade of Railway;(3) the freezing periods of the black pavement and the insulation-black pavement were, respectively, approximately four months and two months. Compared with cement pavement, they could reduce the freezing period by approximately 19 days and 40 days, respectively, and delay the initial freezing time by 9 days and 18 days; and(4) compared with cement pavement, black pavement and black-insulation pavement could reduce the frozen areas of roadbeds in the cold season, which suggests that these two special pavements could provide better thermal stability for roadbeds.     

浅谈超大超重罐槽柔性地基施工技术

航天员综合试验训练楼内基础中性浮力水槽,是我国航天员地面模拟太空失重环境训练重要设施,作者以中性浮力水槽为例,重点研究超大超重罐槽柔性地基施工技术控制难题,在大量的实地试验研究基础上,解决了工程施工过程中的许多关键性技术难题,保证了试验任务的按期完成。     

Rock varnish microlamination dating of late Quaternary geomorphic features in the drylands of western USA

Varnish microlamination (VML) dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts. In this study, we establish a generalized late Quaternary (i.e., 0–300 ka) varnish layering sequence for the drylands of western USA and tentatively correlate it with the SPECMAP oxygen isotope record. We then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late Quaternary geomorphic features in the study region. VML dating of alluvial fan deposits in Death Valley of eastern California indicates that, during the mid to late Pleistocene, 5–15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation. During the Holocene interglacial time, however, 0.5–1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate. VML dating of alluvial desert pavements in Death Valley and the Mojave Desert reveals that pavements can be developed rapidly (< 10 ky) during the Holocene (and probably late Pleistocene) in the arid lowlands (< 800 m msl) of these regions; but once formed, they may survive for 74–85 ky or even longer without being significantly disturbed by geomorphic processes operative at the pavement surface. Data from this study also support the currently accepted, “being born at the surface” model of desert pavement formation. VML dating of colluvial boulder deposits on the west slope of Yucca Mountain, southern Nevada, yields a minimum age of 46 ka for the emplacement of these deposits on the slope, suggesting that they were probably formed during the early phase of the last glaciation or before. These results, combined with those from our previous studies, demonstrate that VML dating has great potential to yield numerical age estimates for various late Quaternary geomorphic features in the western USA drylands.     

用非线性模型评价加筋柔性台背路堤

在考虑土的固结和土体的非线性应力应变关系的基础上,利用非线性有限元数值方法对土工织物加筋柔性台背路堤的受力性状和破坏机理进行了分析。分析结果表明,将铺有土工合成材料的桥台路堤,看作由土体、土工合成材料、土体-土工合成材料界面组成的、独立的平面应变三层连续体系,进行数值计算是行之有效的。计算结果显示,土工织物加筋可以有效减少桥台路堤50%的均匀沉降和66%的非均匀沉降,并能增加台背路堤的稳定性。现场监测表明,本文采用的数值模拟方法与实际工程具有一致性。     

公路施工中预防水泥混凝土路面断板措施探讨

路面发生断板,致使水泥混凝土路面使用性能下降,严重影响了公路运输的效益和行车安全,本文根据多年施工经验,提出在施工中预防断板的有效措施,供水泥混凝土路面施工参考。     

Application of matter-element analysis based on entropy right to evaluate the pavement condition in permafrost region

Evaluation of pavement performance is one of the most important issues in a pavement-management system.By employing the concept of entropy,the matter-element model for evaluating pavement is established,and the weights of the evaluation indices are obtained from surveying data.By calculating the degree of dependence of the matter-element model,the pavement performance evaluation can be obtained by this method.The results show that the matter-element model based on entropy right has good performance for evaluating the pavement condition in permafrost region.     

地下通道浅埋暗挖对城市道路结构的影响

城市地下通道浅埋暗挖法施工会导致地层变形和地表沉降。采用通用有限元软件ABAQUS,对地下通道浅埋暗挖施工过程进行数值模拟,根据围岩开挖引起的位移响应和应力响应计算,结合现场实测数据,评价地下通道浅埋暗挖法施工对城市道路路面结构的影响,并讨论长管棚超前预支护对减小围岩开挖引起的路面结构附加弯拉应力的意义。分析结果表明：浅埋地下通道,围岩软弱,暗挖施工会引起显著的地层损失和路表沉降,这会导致沥青混凝土路面结构内形成较大的附加弯拉应力;采用长管棚超前预支护可控制地层损失和路表沉降,并可减小由此引起的路面结构附加弯拉应力。     

滑模摊铺机在混凝土路面施工中的应用

泰曲路(泰安-曲阜)改造工程三合同段的混凝土路面采用滑模摊铺机进行施工,滑摸摊铺机在不用固定模板的情况下可以连续完成摊铺、振动、刮平、成形、抹光以及打设传力杆等工序,工艺先进,具有一定的推广价值。     

Scattering of oblique waves by permeable vertical flexible membrane wave barriers

The interaction of obliquely incident surface gravity waves with a vertical flexible permeable submerged membrane wave barrier is investigated in the context of three-dimensional linear water wave theory. From the general formulation of the submerged membrane barrier, the performance of bottom-standing, surface-piercing and fully extended membrane wave barriers are analyzed for various values of wave and structural parameters. The analytic solution of the physical problem is obtained using eigenfunction expansion method and a coupled boundary element-finite difference method has been used to get the numerical solution. In the boundary element method, since the boundary condition on the membrane barrier is not known a priori, the membrane response and velocity potentials are solved simultaneously using appropriate discretization with the help of finite difference scheme. The convergence of the analytic and numerical solution techniques is discussed. The study reveals that for suitable combination of wave and structural parameters, approximately (45–50)% incident wave energy can be dissipated irrespective of membrane barrier configurations. Further, in certain situations, nearly full wave reflection and zero transmission occur for all barrier configurations. The study will be useful in the design of flexible permeable membrane to act as an effective wave barrier for creation of tranquility zone in the marine environment.