复合固化砂土力学及水稳性能试验研究

为探究经水泥、石灰和改性聚丙烯纤维复合固化砂土的力学及水稳性能,进行了系列室内试验,结果表明:随水泥掺量增加,固化砂土无侧限抗压强度和劈裂抗拉强度增大,但增长幅度减小,用一定量石灰取代水泥会降低水泥土强度,纤维可以提高水泥土强度,尤其是抗拉强度;水泥可大幅提高砂土抗剪强度和抗压回弹模量,随着纤维掺量的增加,固化土抗剪强度低于水泥土,黏聚力和回弹模量先增大后又减小,内摩擦角与黏聚力表现出负相关性;0.3%纤维加筋8%水泥固化土可以满足简易机场对基层材料的要求。     

纤维加筋固化黄土浸水强度试验研究

为探究水泥、石灰以及多种纤维复合固化黄土的水稳定性能,进行了浸水无侧限抗压强度试验和浸水无侧限劈裂抗拉强度试验。试验结果表明:加砂对复合固化黄土的水稳定性能不利;水泥固化效果优于其他固化剂;纤维可以提高浸水水泥固化土的浸水抗压强度和浸水劈裂抗拉强度,其中0.15%和0.30%纤维掺量的水泥固化黄土浸水抗压强度较高,但继续提高纤维掺量会导致抗压强度降低;纤维长度越长则复合固化黄土浸水抗压强度和劈裂抗拉强度越高,两种及两种以上的纤维混杂掺入会导致固化黄土浸水抗压强度和劈裂抗拉强度降低;水泥可以大幅提升固化土浸水劈裂抗拉强度,19mm聚丙烯纤维加筋固化土浸水劈裂抗拉强度较高,提高纤维掺量可以提高浸水劈裂抗拉强度,两种及两种以上的纤维混杂不能提高浸水劈裂抗拉强度。     

碱激发粉煤灰-钢渣粉协同固化膨胀土力学特性与微观机理研究

针对北疆供水一期工程的膨胀土受干湿-冻融循环作用引起力学特性劣化诱发的工程灾变问题,本工作采用钢渣粉、粉煤灰两种工业废渣作为固化材料,NaOH作为碱性激发剂对膨胀土进行改良,通过开展无侧限抗压强度、直接剪切、侧限压缩、SEM扫描电镜和X射线衍射试验,探究碱性激发工业废渣固化膨胀土的力学特性和微观结构机理。试验结果表明：(1)随着不同改良试剂的依次加入,孔隙结构得到改善,黏聚力不断增大,当粉煤灰质量掺量约为15%,钢渣粉掺量约为18%,烧碱掺量约为5%时,改良的膨胀土结构整体性最为致密,黏聚力达到峰值,土体抗压抗剪强度达到最高,固化效果最为显著。(2)最优配合比的改良土随着养护龄期的延长,生成的水化硅酸系列凝胶增多,胶结程度增强,孔隙含量减少,土体密实性和整体结构得到明显改善,抗压和抗剪强度均有较大幅度的提高,说明龄期对改良土体强度的形成有大幅度的影响。(3)通过对不同试验材料掺量下最佳改良土体的微观机理分析,可知随钢渣粉和烧碱的加入有针棒状的水化硅酸钙以及无定形状的硅铝酸盐凝胶物质生成,胶结联结土颗粒形成团聚体,颗粒间接触点增加,土体结构稳定性增强,从宏观力学行为上表现为固化土体整体强...     

高分子固化剂-玄武岩纤维/砂土复合材料强度特性

通过单轴抗压、快速剪切和抗拉试验,对高分子固化剂（PCA）-玄武岩纤维/砂土复合材料（Sand mixed with polymers and basalt fiber,PBS）的强度特性进行较深入的研究,对比分析了高分子固化剂含量、玄武岩纤维含量（与砂的质量比）和砂土密度对复合砂土材料强度的影响,并结合试验结果和SEM分析了PCA-BF/砂土的强度增强机制。试验结果表明:PCA-BF/砂土的抗压强度、抗剪强度和抗拉强度与纯砂土相比均有明显增强,且残余抗压强度随高分子固化剂含量增大而不断提高;随着高分子固化剂含量和玄武岩纤维含量增加,PCA-BF/砂土强度先快速增大,当PCA和纤维含量分别达到3%和0.6%时增幅变缓;随砂土密度的增大,PCA-BF/砂土的抗压强度和抗剪强度持续增大,而抗拉强度先减小后增大再减小,在砂土密度为1.55 g/cm3时达到最大抗拉强度。高分子固化剂能够在砂粒之间形成空间网络,使分散的砂土颗粒连接成为一体,且纤维与土体混合后能够起到拉筋作用,从而共同作用有效改善了复合砂土材料的强度特性。      

微胶囊-玄武岩纤维/水泥复合材料的力学性能

以水泥、玄武岩纤维和脲醛/环氧树脂微胶囊为主要材料,制备水泥基复合材料标准试样,研究纤维掺量、纤维长度、微胶囊质量分数、水灰质量比和养护龄期对复合材料抗折强度和抗压强度的影响,利用正交实验确定微胶囊-玄武岩纤维/水泥自修复复合材料力学性能的最优配比。实验结果表明：抗折强度随着纤维掺量的增加而增加,抗压强度随着纤维掺量增加而减小;随着纤维长度的增加,抗折强度略有增加,抗压强度略有降低;抗折强度随着微胶囊质量分数的增加呈现出先增加后减小的趋势,而抗压强度则呈现下降趋势;抗折强度与抗压强度随养护龄期的增加而呈增加的趋势;材料经损伤后修复,抗折强度修复率为117%,恢复率为103%,抗压强度修复率为71%,恢复率为97%。     

纤维聚苯乙烯泡沫颗粒轻质土的制备及力学性能

为促进轻质土在岩土工程中的广泛应用,添加改性聚丙烯纤维改善其力学性能,通过无侧限抗压强度试验分析探讨了纤维聚苯乙烯泡沫（EPS）颗粒轻质土强度-变形特性、受压破坏模式和无侧限抗压强度的影响因素,并运用SEM从微观层次上分析了其力学机制。结果表明:不同EPS颗粒、纤维及水泥掺量时,纤维EPS颗粒轻质土的应力-应变曲线不同;EPS和水泥掺量是强度的主要影响因素,其次为纤维掺量;强度随EPS掺量的增大而显著降低,随水泥掺量增大而显著提高;未加纤维的EPS颗粒轻质土松散且易破碎,强度骤然丧失;添加纤维能提高轻质土的峰值强度、残余强度、整体性和韧性,改善其脆性破坏模式;但EPS掺量较高（大于干土质量的3%）时,纤维与水泥土粘结有限,EPS颗粒轻质土力学性能改善效果较弱;EPS颗粒为空心蜂巢结构,纤维表面布满针状的水泥水化物并形成空间网状结构。所得结论表明纤维改善了轻质土力学性能。      

水泥砂浆固化粉质黏土分离式Hopkinson压杆试验与分析

为研究掺砂量（与干土的质量比）对水泥粉质黏土冲击压缩强度及能量吸收特征的影响,采用Φ 50 mm分离式Hopkinson压杆（Split Hopkinson pressure bar,SHPB）试验装置对不同掺砂量的水泥粉质黏土进行了0.4 MPa冲击气压下的冲击压缩试验。结果表明：普通水泥粉质黏土（未掺砂）动态应力-应变曲线大致分为弹性阶段、屈服硬化阶段及破坏阶段,而随着掺砂量的逐渐增加,水泥砂浆固化粉质黏土动态应力-应变曲线中屈服阶段愈加不明显,出现了理想的塑性阶段;水泥砂浆固化粉质黏土的冲击压缩强度随掺砂量的增大而先增大后减小,在掺砂量为10%时达到最大平均动强度9.56 MPa,较普通水泥土强度提高9.79%;水泥砂浆固化粉质黏土的吸收能随冲击压缩强度的增大而增大,两者具有较好的指数关系。     

煤矸石改良黄土的力学和抗冻融性能

【目的】提出用煤矸石改良黄土的解决方案,解决煤矸石存量逐年增大且利用率低、季冻区黄土地基病害严重的双重难题。【方法】分析煤矸石改良黄土的反应机制,通过无侧限抗压强度、直剪、固结压缩和湿陷性试验,分析煤矸石改良黄土试件的无侧限抗压强度、抗剪强度、黏聚力、内摩擦角、压缩系数和湿陷系数等力学性能指标,确定煤矸石的最优掺量;以黄土原料为对照组,将最优掺量的煤矸石改良黄土试件进行冻融循环试验,再次进行无侧限抗压强度和直剪试验,分析冻融循环后最优试件的力学和抗冻融性能。【结果】当煤矸石质量分数为20%,养护龄期28 d时,煤矸石改良黄土的无侧限抗压强度为585 kPa,抗剪强度为287 kPa,压缩系数约为0.19 MPa^-1,黏聚力为63.755 kPa,内摩擦角为29.646°,湿陷性完全消除;进行冻融循环试验后,随着冻融循环次数的增大,无侧限抗压强度逐渐减小,冻融循环次数为11时的无侧限抗压强度、抗剪强度、黏聚力损失率分别为26.9%、 7.4%、 18.6%,内摩擦角变化较小,煤矸石改良黄土的力学和抗冻融性能较好。【结论】煤矸石活性较低,改良后的黄土的强度虽然提升幅度...     

压剪作用下PVA纤维再生混凝土力学性能试验研究

为了研究压剪作用下外掺聚乙烯醇(PVA)纤维对再生混凝土力学性能的影响,以再生粗骨料取代率、压应力比和PVA纤维体积掺量为变化参数,设计并制作144个立方体试件进行压剪试验。观察了试件的破坏形态,得到了荷载-位移曲线及垂直变形-剪切位移曲线,分析了不同变化参数对抗剪强度、峰值位移的影响规律。结果表明：0.1%体积掺量的PVA纤维对再生混凝土的抗剪强度提高了10%;随着压应力比的增大,试件的抗剪强度呈增大趋势,平均增大了2.03倍;与普通混凝土相比,再生混凝土试件的抗剪强度平均降低了13%;当再生粗骨料取代率为100%时,PVA纤维最佳掺量为0.1%;提出了纤维掺量为0.1%时压剪作用下PVA纤维再生混凝土抗剪强度计算公式。     

聚乙烯醇纤维增强偏高岭土-水硬石灰砂浆材料性能的研究

针对偏高岭土-水硬石灰砂浆材料抗拉强度低、极限延伸率小、性脆的问题,为了提高其韧性和稳定性,增强其抗裂能力,设计并制备了聚乙烯醇(PVA)纤维掺杂偏高岭土-水硬石灰砂浆材料,开展了PVA纤维不同掺量、不同长度下偏高岭土-水硬石灰砂浆材料收缩率、波速、抗压强度、抗折强度及劈裂抗拉强度的试验研究,通过扫描电镜观察分析了PVA纤维在偏高岭土-水硬石灰砂浆材料中的微观作用机理。结果表明:PVA纤维改变了偏高岭土-水硬石灰砂浆的收缩率和内部结构。试样的抗折强度和劈裂抗拉强度随着纤维增加而增大,抗压强度会在纤维长度一定时随着掺量的增多而降低。PVA纤维对砂浆材料整体性有明显改善,受压后仍能够保持着较好的原样性,纤维和砂浆基体之间产生了机械铆合作用,具有较好黏结性。     

机场道面抢修用聚氨酯稳定集料的试验研究

以机场道面意外损毁的抢修为目的，进行了聚氨酯发泡快速稳定道面基层回填料的试验研究。试验结果表明，常温下用聚氨酯发泡稳定碎石集料，2h无侧限抗压强度达到2．05MPa，对道面结构的有限元分析表明，试验所用材料可满足道面基层的力学性能要求。     

改进相位编组直线算法提取遥感图像中的机场目标

本文在分析了机场影像的重要特征之后,改进了相位编组直线提取算法,在机场跑道检测中,利用改进算法精确提取出跑道平行直线对,然后采用区域生长算法确定机场的整个结构。实验证明,这种改进的算法具有更好的抗噪性能,对于影像质量要求有更加宽松的范围,更具有实用性能。     

机场内部飞机噪声监测与评价

对某军用机场内部噪声环境影响进行评价,机场内部布设七个位置点进行噪声测量,在实际监测的基础上,采用计权等效连续感觉噪声级和A计权声级的最大值为评价量对机场飞机噪声现状进行评价,同时介绍了机场内部飞机噪声污染的危害及应采取的相关防治措施.     

机场内部飞机噪声影响评价与防治方法研究

军用喷气式飞机噪声危害显著，机场内部是受到飞机噪声危害最为严重的区域，但长期以来一直没有得到人们的重视。根据飞机噪声影响的特点，提出了一种基于双指标的机场内部飞机噪声评价方法。并在此基础上，结合噪声等值线图，提出机场内部飞机噪声防治的方法。结合某机场，具体分析了机场内部飞机噪声现状影响评价方法和机场飞机噪声的防治方法与步骤。     

Expedient airfield runway repair using folded fibreglass mat

For expedient airfield runway repair, the US Air Force has developed a folded fibreglass mat to cover craters repaired with a well-compacted granular base material. The objective of this study was to evaluate the adequacy of using polymer plugs to anchor the mat to a repaired asphalt pavement for heavy aircraft operations. The effort consisted of materials testing, field experiments and analytical modelling. An 89,800-kg (198,000-pound) load cart having the footprint of a single C-5 main gear was pulled on a mat with wheels locked to simulate full braking forces. Anchor bushings were instrumented to measure anchor loads. A simplified numerical model was developed for anchor load analysis which has been validated against the load cart test data. The anchor system sustained the braking forces from all the load cart tests without failure. The polymer plug anchors have adequate vertical pull-out capacity to resist the uplifting force from the ‘bow wave’ formation of the mat. The polymer plug anchors also have adequate resistance to fatigue loads.     

Estimating fatigue endurance limits of flexible airfield pavements

In perpetual pavements, damage from bottom-up cracking can be limited to the top surface lift through using a very thick surface layer or a binder-rich intermediate layer. This can be attained by maintaining tensile strains at the bottom of the hot-mix asphalt (HMA) layer below a certain value known as the fatigue endurance limit (FEL). This paper presents a method for estimating a strain-based FEL for flexible airfield pavements. The proposed method is based on the concept that a 50% reduction in HMA layer modulus would indicate initiation of fatigue cracking. Falling weight deflectometer (FWD) testing results, collected from National Airport Pavement Test Facility (NAPTF) flexible pavement sections, were analyzed to determine at which loading pass each section had a 50% reduction in HMA layer modulus (N_f50). NAPTF tensile strain data were also used to determine the tensile strain at N_f50 for each pavement section by averaging the peak tensile strains. The proposed approach was validated by comparing its results to those obtained using a common FEL estimation model known as the rate of dissipated energy change (RDEC) model. To further verify the results of the proposed approach, peak tensile strain was plotted vs. number of loading cycles for all sensors. Using these plots, the peak tensile strain at which the variability in the strain gauge data increased was used as an estimate of a possible FEL. The N_f50 tensile strains estimated using the proposed method were comparable to the values determined from RDEC and variability approaches.     

Oil-Shale Fly Ash Utilization as Independent Binder of Natural Clayey Soils for Road and Airfield Base Construction

ABSTRACT

This article describes physicochemical interactions of different natural clayey soils with oil-shale fly ash (OSFA) from thermal power plants, dealing with the strengthening processes of new materials. Toward this end, a range of traditional and modern research methods were used, i.e., definition of the ultimate strength under uniaxial compression and rupture by the Brazilian method, temporary changes in moisture content and linear deformation, water and frost resistance, free CaO and SO₃, CaCO₃, XRD, and SEM. It was established that the surfaces of the initial component (OSFA and soils) particles were dissolved in porous alkaline solutions. The dissolution products gave rise to new amorphous and crystal formations. After 28 days, the strength of the samples reached 2–12 MPa but, after 90 days, it rose to 4–31 MPa. It was found that the strength at every stage of hardening can be increased significantly by changing the proportion of the initial mixture's composition. The materials displayed very high water and frost resistance, with coefficients equaling or exceeding the 1.0 level, except the OFSA and loess combination. The materials developed are applicable for the construction of roads, airfields, and dam bases and for various types of foundations without traditional binders, such as cement, and without heating.     

Oil-Shale Fly Ash Utilization as Independent Binder of Natural Clayey Soils for Road and Airfield Base Construction

This article describes physicochemical interactions of different natural clayey soils with oil-shale fly ash (OSFA) from thermal power plants, dealing with the strengthening processes of new materials. Toward this end, a range of traditional and modern research methods were used, i.e., definition of the ultimate strength under uniaxial compression and rupture by the Brazilian method, temporary changes in moisture content and linear deformation, water and frost resistance, free CaO and SO₃, CaCO₃, XRD, and SEM. It was established that the surfaces of the initial component (OSFA and soils) particles were dissolved in porous alkaline solutions. The dissolution products gave rise to new amorphous and crystal formations. After 28 days, the strength of the samples reached 2-12 MPa but, after 90 days, it rose to 4-31 MPa. It was found that the strength at every stage of hardening can be increased significantly by changing the proportion of the initial mixture's composition. The materials displayed very high water and frost resistance, with coefficients equaling or exceeding the 1.0 level, except the OFSA and loess combination. The materials developed are applicable for the construction of roads, airfields, and dam bases and for various types of foundations without traditional binders, such as cement, and without heating.     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.