东黄山国际小镇串珠状隐伏溶洞顶板稳定性研究

地下岩溶发育破坏了岩体的完整性,导致岩体的强度和承载力大幅度降低,对工程场地地基稳定性构成潜在的威胁.本文依托东黄山国际小镇基础设施项目,在采用多种勘察手段相结合的方法确定岩溶发育特征的基础上,选取代表性的溶洞,采用按溶洞顶板安全厚度判别的定性评价方法和按顶板坍塌自行填塞判别、顶板抗弯安全厚度判别、按顶板抗剪安全厚度判别3种半定量评价方法对溶洞顶板安全厚度进行综合判别,对岩溶地基进行稳定性评价.研究结果表明:研究区揭露岩溶主要以覆盖型串珠状溶洞为主,多为充填型溶洞,选取的117个典型溶洞大多处于稳定状态,在自然状态下顶板稳定性较好,发生坍塌的可能性小.     

混凝土硫酸盐侵蚀破坏机理与预防措施

根据腐蚀产物将水泥混凝土硫酸盐侵蚀分为钙矾石型和碳硫硅酸钙型两大类,分析了不同类型硫酸盐侵蚀的发生条件、化学反应机理和混凝土外观破坏特征,并从原材料选择、配合比设计等方面提出不同类型硫酸盐侵蚀破坏的预防措施,从而为实际混凝土工程硫酸盐侵蚀破坏原因分析和耐久性设计提供参考。     

温度对掺石粉水泥基材料硫酸盐侵蚀的影响

将水泥-石灰石粉样品置于不同温度质量分数为5%的MgSO4溶液中,研究温度对掺石灰石粉水泥基材料硫酸盐侵蚀的影响.结果表明:温度对掺石灰石粉水泥基材料硫酸盐侵蚀机理及性能退化影响显著.室温(20±1)℃下,样品发生钙矾石/石膏型硫酸盐侵蚀.低温(5±2)℃下,样品发生碳硫硅钙石型硫酸盐侵蚀,腐蚀产物以碳硫硅钙石、石膏为主,材料性能劣化也更为严重.     

广东惠州岩溶分布特征及地质意义

可溶岩分布区地面塌陷和地面沉降等地质灾害是城市建设面临的重大地质问题之一,同时岩溶含水层利用与保护也是当前的科学研究热点。本文在综合分析区域构造、地层岩性、水文地质条件与岩溶发育关系的基础上,结合现有钻探资料,系统总结了惠州地区的岩溶分布特征和发育规律。结果表明：惠州地区的碳酸盐岩沉积受地层岩性及地质构造和地下水共同控制,有祼露型、覆盖型和浅埋藏型3种类型,以覆盖型和浅埋藏型为主。岩溶发育带分布标高有由北向南逐渐降低的趋势,主要受当地侵蚀基准面控制,强岩溶发育带相对埋藏深度集中在地面以下150 m范围内,并具有多层结构,垂向上岩溶发育带标高主要为-120～+115 m,埋深为0～250 m,主要分为3层,其中溶洞发育埋深介于0～50 m的溶洞占60.2%;发育埋深介于50～100 m占26.6%;发育埋深介于100～150 m占13.2%。研究成果可为惠州地区国土空间规划以及重大工程选址建设、岩溶塌陷防治和岩溶热矿水资源勘查提供科学依据。     

硝酸侵蚀衬砌喷射混凝土中性化过程及机理

以一般大气环境喷射混凝土永久衬砌长大公路隧道为工程背景,开展汽车尾气中氮氧化物对喷射混凝土衬砌结构中性化过程及机理研究。以pH值为2的硝酸溶液为侵蚀介质,对喷射混凝土开展浸泡试验。以侵蚀喷射混凝土的物理力学性能及离子含量为表征指标,分析喷射混凝土中性化过程。采用X射线衍射、热分析及扫描电镜,分析及表征喷射混凝土中性化区的物相组成及微观形貌,研究喷射混凝土中性化发展过程及机理。结果表明,硝酸侵蚀喷射混凝土中性化演化过程可分为中和反应阶段、水化产物分解阶段、混凝土表面剥蚀等3个阶段。期间,喷射混凝土pH值逐渐下降,NO_3~-含量升高。随着侵蚀的进行,水化硅酸钙及氢氧化钙的含量降低,硝酸钙、硝酸型水化氮铝酸钙及高岭石的相对含量增大,微观结构被破坏,中性化速度加快,物理力学性能降低。     

CM型抗侵蚀防水剂在硫酸电解铜工程中的应用

含硫酸蒸气和凝聚物会对电解铜厂的混凝土厂房产生严重腐蚀,使厂房及构件造成腐蚀性脱落、剥皮、强度降低、钢筋锈蚀,严重影响建筑物的使用寿命。为解决这一问题,在某工程设计中采用了42．5强度等级的普通水泥和32．5强度等级的矿渣水泥掺用CM型抗侵蚀防水剂,配制耐腐蚀混凝土。梁、柱、吊车梁、预制顶板用普通水泥掺加CM型抗侵蚀防水剂,掺量为水泥重量的6％～8％（替代水泥率）,设计为C30混凝土。基柱、一层板柱、标高8．1m上部、高位池（硫酸液池用树脂做防护层）、地面等用矿渣水泥,CM型抗侵蚀防水剂的掺量为水泥重量的6％～8％（替代水泥率）,设计为C20～C25混凝土。电解槽四排总宽18m,长90m,整个车间100多m长,高度15m。该工程建成投产3年后,混凝土棱角、表层及平整度都完好如初,未见有受腐蚀的迹象。     

土体内侵蚀稳定性分形判据

涌水突泥是隧道开挖过程中一种最为常见且危害巨大的地质灾害形式。当隧道开挖至岩溶或断层等地质构造时,会在渗透作用下引起致灾体内的细颗粒流失,并逐渐形成优势通道,进而诱发渗透失稳型涌水突泥。准确判断土体内侵蚀稳定性对预防该类型涌水突泥至关重要。研究利用土体级配的分形特性,推导已有常用判据的分形表达式,并根据现有试验结果,提出了一种具有较高精度的分形判据。研究成果可为隧道渗透失稳型涌水突泥的防治提供理论依据。     

坦桑尼亚公路项目冲沟形成研究分析及危害处理措施

冲沟侵蚀是一种非常常见的土壤侵蚀形式,严重影响了土地的使用,并可能对基础设施造成很大威胁。论文通过采集现场土样,分析其塑性性能、内摩擦角和黏聚力,并基于可蚀性因子公式研究其可蚀性等级;通过现场测绘和分水岭模型研究其地表水流向和径流量,以此明确地表水径流量与冲沟形成关系。最终得出结论:冲沟的侵蚀是由于地表雨水不断对研究区域的土壤进行冲刷形成。由此提出阻止冲沟的进一步侵蚀的措施,旨在保护公路路基安全。     

碳硫硅钙石的形成及其对混凝土性能的影响

研究了石灰石粉对混凝土抗硫酸盐侵蚀性能的影响．石灰石粉取代水泥用量为0,20％,40％．180d浸泡试验表明：石灰石粉掺量越高,侵蚀溶液温度越低,混凝土遭受硫酸盐侵蚀破坏的程度越严重;掺石灰石粉的混凝土在0～10℃的条件下可引起碳硫硅钙石类型的硫酸盐侵蚀破坏．     

复合盐侵蚀衬砌喷射混凝土耐久性退化研究

我国西部地区土壤及地下水中含有高浓度、及Cl,与隧道衬砌喷射混凝土发生一系列物理化学反应,造成其结构耐久性能退化。为系统研究复合盐侵蚀喷射混凝土耐久性能退化规律及机理,分别以10%Na2SO4溶液和5%Na2SO45%MgSO43.5%NaCl混合溶液为侵蚀介质,采用干湿交替法,开展喷射混凝土耐久性试验。、及Cl与氢氧化钙和铝相反应生成水镁石、石膏和Friedel盐,延缓钙矾石形成。复合盐侵蚀喷射混凝土物理力学性能退化速度明显小于硫酸盐侵蚀。硫酸盐侵蚀喷射混凝土以表面水泥砂浆和骨料的剥落为主,复合盐侵蚀主要以表面龟裂最终断裂为主,且裂缝中充满白色结晶盐。分析侵蚀喷射混凝土矿物组成和微观结构,硫酸盐侵蚀喷射混凝土产物主要为钙矾石和石膏,而复合盐侵蚀喷射混凝土产物组成复杂,包括碳硫硅钙石、水镁石、石膏、钙矾石、水化硅酸镁和结晶盐。硫酸盐侵蚀喷射混凝土中含量高于复合盐侵蚀,而混凝土pH值低。     

Sandy barriers, climate change and long-term planning of strategic coastal infrastructures, Îles-de-la-Madeleine, Gulf of St. Lawrence (Québec, Canada)

The case study of Îles-de-la-Madeleine is presented to illustrate one aspect of the challenge facing coastal communities with regard to relative sea-level rise and climate change, namely the management of strategic infrastructures located within the coastal zone. GIS mapping has been carried out in two sites where the main road system of this archipelago, Highway 199, is located on sandy barriers and where the road has been threatened by chronic erosion problems for several decades. Our results confirm the dynamic nature of the barriers components (habitats, inlets and tidal deltas) and document the impacts of road-related modifications to the coastal system. These alterations have resulted in significant changes to coastal habitats, including loss due to coastal squeeze between the retreating shoreline and the coastal protection structures. Resort to riprap structures also impacted the evolution of the coastline and further coast hardening might jeopardize the morpho-sedimentary equilibrium of the barriers. To ensure the sustainability of coastal resources and secure Highway 199, it appears that a change is required, from an ad hoc type of management of coastal erosion towards the inclusion of the management of the road system within a long-term and integrated planning of the coastal zone.     

地震作用下陡岩崩塌颗粒离散元数值模拟研究

 基于江坪河水电站陡岩边坡,进行块体倾覆分析确定地震影响下潜在的破坏位置,推导地震波在颗粒介质内中传播时的边界条件设置公式,用二维颗粒离散元模拟分析地震作用下陡岩的崩塌灾害。结果表明：基于颗粒离散元的崩塌灾害分析方法可通过颗粒运动轨迹来判断边坡是否稳定,研究边坡破坏扩展过程,并可通过修改边界颗粒的属性来模拟入射地震波及透射边界,可最大限度模拟荷载–岩性–灾害发展的耦合作用;地震作用下顺坡向陡倾角卸荷裂隙发育是影响陡岩边坡稳定的控制性结构面,表层发生局部崩塌、块体失稳的可能性较大,其破坏机制为高烈度地震作用下从表层局部块体崩落开始,继而沿着节理裂隙快速扩展直至上部岩体产生崩塌,破坏规模则主要取决于顺层向裂隙的发育深度。该方法可为崩塌失稳边坡的稳定性研究及灾害预测提供理论依据。     

Quantitative assessment of the shoreline protection performance of geotextile sandbags at an in-situ coastal experimental station

The coast of China is periodically impacted by tropical cyclones and storm surges, and has experienced significant coastal erosion problems. Traditional “hard engineering” coastal protection measures used to protect Chinese sandy coasts from storm erosion are found to be expensive and less environmental and even make sandy beach disappearing. In this study, geotextile system as a more flexible material was developed and qualitatively compared with the traditional coastal protection measures. An in-situ permanent revetment was applied with durable geotextile sandbags on the coast of Chudao in China from October 2018 to October 2020, and it was designed for three different testing segments to optimize the stability and construction cost of geotextile sandbags. The field surveys were carried out to collect the in-situ data on beach profiles, wave dynamics, material durability, and sandbag revetment stability. In analyzing the two-year field data collected, it is found that the testing segment-2 wrapped with sheet of plastic geogrids is the most effective of the three testing segments in terms of their coat, structural stability and material durability, and that both the slope of the seabed and the design thickness of geotextile sandbag are the dominate factors responsible for the failure of sandbag structures.     

陕西西乡骆家坝天坑群喀斯特地质遗迹特征及成因

汉中天坑群的发现对于分析南北过渡带喀斯特地质环境具有重要意义。本文以骆家坝天坑群喀斯特为例,通过资料梳理和实地调查,总结喀斯特形态组合特征,深入分析喀斯特形成原因,揭示南北过渡带局部构造特征。结果表明:研究区天坑群主要发育于喀斯特台原面上,发育有最具特色的崩塌型天坑群。受新构造运动间歇式隆升影响,喀斯特的发育具有层状特征,天坑、竖井、溶洞和峰丛洼地的分布均呈现分层性。受构造作用的影响,研究区溶洞中干洞较多,退化作用明显。因此,未来要加强区域生态环境保护,防止溶洞地质灾害的频发。     

间断级配砂土中管线破损引起的渗流侵蚀模型试验

频发的路面塌陷事故对城市安全造成了巨大威胁,主要原因是地下管线破损引起周围土体的渗流侵蚀,进而产生了地下空洞所致。针对目前常见的地下无压管线破损问题,提出了一种研究间断级配砂土中破损管线周围渗流侵蚀特性的模型试验方法。基于试验中的水土流失变化和受侵蚀区域的发展规律,揭示了间断级配砂土中侵蚀过程可分为快速侵蚀阶段、稳定侵蚀阶段和收敛阶段,土体中由于侵蚀变形产生的松动区和空洞扩展规律与砂土流失变化一致。对比不同工况的侵蚀量和最终侵蚀状态,得到了土体饱和度和水位高度通过影响渗流力而改变侵蚀量和空洞形态,土体级配则决定了可流失细砂含量,从而影响侵蚀量和空洞大小,而当管线破损形状只导致细粒流失时,破损尺寸的增加将增多流失路径数量,进而增大了侵蚀量,但此因素影响较小。     

冲磨速率和角度对海工混凝土抗冲磨性能的影响

针对海水挟砂浪涌的服役环境,试验研究了冲磨速率及冲磨角度对桥梁墩柱海工混凝土抗冲磨性能的影响,并对不同胶凝材料体系混凝土抗冲磨强度进行了比较.结果表明：冲磨速率和冲磨角度对海工混凝土抗冲磨性能有较大影响.在胶凝材料体系不变的前提下,海工混凝土稳定磨损率随冲磨速率增大逐渐增大,抗冲磨强度随冲磨速率增大逐渐降低;海工混凝土稳定磨损率随冲磨角度增加逐渐增大,当冲磨角度小于60°时,稳定磨损率增加速率较大,超过60°后增加速率趋缓,当冲磨角度为90°时,稳定磨损率最大.在相同强度等级条件下,硅粉对混凝土抗冲磨强度的贡献最大,而矿粉与粉煤灰复掺也显著提高了混凝土的抗冲磨强度.     

离子侵蚀对再生混凝土多重界面区(ITZ)性能的影响

通过研究氯离子和硫酸根离子侵蚀下再生混凝土不同界面过渡区的显微结构以及显微硬度变化,揭示了离子侵蚀对再生混凝土结构和性能的影响机理.结果表明:再生混凝土经氯离子侵蚀后,骨料老界面、骨料新界面、砂浆新界面的显微硬度逐渐降低,过渡区宽度逐渐增加;氯离子侵蚀前后,同种界面过渡区显微硬度值随着新浇筑砂浆强度等级的增加而增大,且...     

Experimental study on suffusion under multiple seepages and its impact on undrained mechanical responses of gap-graded soil

An experimental investigation of multiple seepage-induced suffusion and its impact on the mechanical responses of internally unstable gap-graded soil, with a fines content of 25%, is presented in this paper. Using a modified triaxial erosion apparatus, with a redesigned seepage control system, erosion tests under multiple seepage conditions, as well as undrained monotonic and cyclic compression tests, are performed. It is found that multiple seepages cause an eroded mass without a marked change in volume and with a change in hydraulic conductivity as the number of seepage cycles increases. The monotonic compression tests show that eroded soil presents a smaller peak strength, residual strength, and a greater contractive response than non-eroded soil. The peak strength and stiffness of eroded soil are seen to decrease considerably as the number of seepage cycles increases. Multiple seepage-induced suffusion may create a collapsible soil structure in eroded soil, as shown by sudden decreases in deviator stress and stiffness, coupled by sharp increases in pore water pressure at small strain levels. As eroded soil might already be unstable, cyclic loading causes it to collapse, revealing a sudden increase in the generation of cyclic pore water pressure and a decrease in liquefaction resistance. The results highlight the importance of conducting laboratory tests to determine the impact of internal erosion on the strength and liquefaction resistance.     

A wave flume experiment for studying erosion mechanism of revetments using geotextiles

Unfavorable erosion to a revetment can affect the stability of the bank and may jeopardize the safety of adjacent structures, thus improvement work is needed to increase the stability of the revetment as well as reducing the possibility of failure. The use of geotextiles as a protection material for banks is not only environmentally friendly, but also stable in the long run. However, improper design of geotextiles may cause considerable loss of soil, which might result in failure. The actual flow behavior in revetments using geotextiles is rather complicated and can be categorized into three zones, namely, the uni-directional flow zone, the cyclic flow zone, and the tangential flow zone. In this study, a wave flume experiment was performed on model revetments using two kinds of geotextiles as the filter material to prevent erosion induced by cyclic flows. Soil migration behaviors were monitored. Furthermore, two kinds of cover blocks, riprap and concrete blocks, were carefully placed on the revetments in order to avoid puncture and abrasion of geotextiles during construction of revetments. The main purpose of this study is to elucidate the erosion control and filtration performance of soil-geotextile filtration systems under wave action. Two nonwoven needle punched geotextiles were tested. The geotextiles both have the same characteristic opening size, but have a different number of constrictions and different structures. One is a thin double-layer nonwoven material consisting of continuous filaments and the other is a thick one-layer nonwoven material consisting of short fibers.     

基于水动力场控制的岩溶塌陷预警预报研究

岩溶塌陷是山东省近年来濒发的主要地质灾害之一,主要分布于泰安、枣庄、临沂、莱芜等覆盖型岩溶发育区,其发展、发生主要受岩溶水不合理开采所致,水位是影响岩溶塌陷的重要因素。本文以临沂市城区的岩溶塌陷为例来探讨岩溶塌陷预警预报思路,首先是在完善的监测网络基础上,建立预警模型,通过水文地质模型预测可行的地下水开采方案,并模拟城区一带的岩溶塌陷区水位的变化趋势,人为控制地下水动力场,进而建立岩溶塌陷动力预警预报系统,可为减少或避免该灾害的发生及其防治提供科学依据。