被困空腔对T-bar循环贯入软黏土流动特性影响的试验研究

为观测和分析T-bar循环贯入过程中被困空腔对软黏土流动特性的影响,利用Laponite RD、焦磷酸钠和去离子水配制透明黏土,自制由加载设备、CCD相机、激光器和控制系统组成的T-bar循环贯入试验装置,开展T-bar在透明黏土中的循环贯入试验。结果表明:T-bar初次贯入过程中,被困空腔影响土体绕探头的流动,土体不能进入全流动状态;T-bar初次上拔过程中,被困空腔与探头发生脱离,悬浮于探头上方,对土体流动的影响逐渐减弱,T-bar上拔2倍探头直径深度时土体流动不再受被困空腔影响,进入到全流动状态;第2—第10次循环贯入过程中,被困空腔稳定悬浮于土中,不影响土体流动,T-bar贯入1倍探头直径深度时土体流动表现为全流动状态;被困空腔对于T-bar循环贯入测试结果无显著影响,在T-bar初次贯入被困空腔阶段下通过T-bar循环贯入测试软黏土重塑强度是合理的。

Genetic programming for predictions of effectiveness of rolling dynamic compaction with dynamic cone penetrometer test results

Rolling dynamic compaction (RDC),which employs non-circular module towed behind a tractor,is an innovative soil compaction method that has proven to be successful in many ground improvement applications.RDC involves repeatedly delivering high-energy impact blows onto the ground surface,which improves soil density and thus soil strength and stiffness.However,there exists a lack of methods to predict the effectiveness of RDC in different ground conditions,which has become a major obstacle to its adoption.For this,in this context,a prediction model is developed based on linear genetic programming (LGP),which is one of the common approaches in application of artificial intelligence for nonlinear forecasting.The model is based on in situ density-related data in terms of dynamic cone penetrometer (DCP) results obtained from several projects that have employed the 4-sided,8-t impact roller (BH-1300).It is shown that the model is accurate and reliable over a range of soil types.Furthermore,a series of parametric studies confirms its robustness in generalizing data.In addition,the results of the comparative study indicate that the optimal LGP model has a better predictive performance than the existing artificial neural network (ANN) model developed earlier by the authors.

Resilient modulus prediction of soft low-plasticity Piedmont residual soil using dynamic cone penetrometer

Dynamic cone penetrometer（DCP） has been used for decades to estimate the shear strength and stiffness properties of the subgrade soils. There are several empirical correlations in the literature to predict the resilient modulus values at only a specific stress state from DCP data, corresponding to the predefined thicknesses of pavement layers（a 50 mm asphalt wearing course, a 100 mm asphalt binder course and a200 mm aggregate base course）. In this study, field-measured DCP data were utilized to estimate the resilient modulus of low-plasticity subgrade Piedmont residual soil. Piedmont residual soils are in-place weathered soils from igneous and metamorphic rocks, as opposed to transported or compacted soils.Hence the existing empirical correlations might not be applicable for these soils. An experimental program was conducted incorporating field DCP and laboratory resilient modulus tests on "undisturbed" soil specimens. The DCP tests were carried out at various locations in four test sections to evaluate subgrade stiffness variation laterally and with depth. Laboratory resilient modulus test results were analyzed in the context of the mechanistic-empirical pavement design guide（MEPDG） recommended universal constitutive model. A new approach for predicting the resilient modulus from DCP by estimating MEPDG constitutive model coefficients（k;,k;and k;） was developed through statistical analyses. The new model is capable of not only taking into account the in situ soil condition on the basis of field measurements,but also representing the resilient modulus at any stress state which addresses a limitation with existing empirical DCP models and its applicability for a specific case. Validation of the model is demonstrated by using data that were not used for model development, as well as data reported in the literature.

Quantification of displacement and particle crushing around a penetrometer tip

Particle crushing occurs near the tip of a penetrometer and influences the development of the tip resistance.To study particle crushing near a penetrometer tip,a cone penetrometer was monotonically jacked and then load-tested in medium dense and dense silica sand samples prepared in a halfcylindrical calibration chamber with viewing windows.During the tests,images of the advancing penetrometer and the surrounding soil were taken using digital cameras and analyzed to obtain the displacement and strain fields around the penetrometer using the Digital Image Correlation(DIC)technique.Subsequently,soil samples were collected near the tip of the penetrometer using a novel agarimpregnation technique and digitized using an X-ray microscope.The digitized samples were analyzed to reconstruct the three-dimensional models of individual particles,generating the gradation and relative breakage parameters of the sand around the cone penetrometer.

A Proposed Framework for Optimised Utilisation of Materials for Low Volume Roads Using the Dynamic Cone Penetrometer

In order to minimise the cost of constructing low volume roads (LVRs), it is essential that optimum use is made of locally available, naturally occurring materials. However, conflicts often arise between material acceptability, as defined by conventional test methods and specifications, and material suitability in terms of actual engineering performance as a “fit-for-purpose” road construction material. To avoid such conflicts, it is crucial to adopt appropriate test methods and specifications for selecting construction materials. This paper presents a materials evaluation framework for optimizing the utilisation of materials in LVR pavements based on the use of the Dynamic Cone Penetrometer (DCP). This approach enables materials to be selected on the basis of their “fitness-for-purpose”. It avoids suitable materials from being rejected based on one or other of the traditionally specified parameters not being complied with, even though their strength, as measured by the DCP penetration rate (DN value in mm/blow) of the soil, may be adequate. Investigations of the properties of a wide range of locally available materials that have been used successfully in the construction of LVRs have confirmed the validity of the materials evaluation framework.

Development of a New Dynamic Lightweight Penetrometer for the Determination of Mechanical Properties of Fine-Grained Soils

Dynamic cone penetrometer is mainly used as an in situ device and laboratory application, in a mould, has rarely been reported due to the confining effect. In this study, a dynamic lightweight cone penetrometer that can be used in a CBR （California bearing ratio） mould in the laboratory as well as in the field, with similar results, was developed. The results show that the influence of the mould confinement can be eliminated when the hammer mass is 2.25 kg. A strong correlation was found between CBR values and the new dynamic lightweight penetrometer index, for six fine-grained soil samples, with different moisture contents, used in this study.

Application of automated cone penetrometer for railway investigation using correlations with DCPI and deflection modulus

Portable in-situ devices have been used for characterizing low accessible field,such as the railway subgrade.In this study,the automated cone penetrometer(ACP)was designed for the application on the railway subgrade.ACP is composed of the cone tip,driving rod,and hydraulic hammer system.The hydraulic motor lifts and drops the 294.3 N hammer from a height of 200 mm such that the potential energy of 58.9 N m impacts the driving rod.The N-value(NACP)from the ACP test was compared with the dynamic cone penetration index(DCPI)from the dynamic cone penetrometer(DCP)test.The test results show that the NACP and DCPI profiles show opposite trend owing to the inverse concept of the unit.From the correlation of DCPI and NACP,the limitation of DCPI reveals owing the minimum manually measured value of 1 mm/blow.Additionally,the evaluation of the deflection modulus(EFWD)using NACP is more efficient than that using DCPI.Based on the result of this study,we suggest that ACP can be used for strength and stiffness evaluation of railway subgrade rapidly and reliably.

Obtaining 2D Soil Resistance Profiles from the Integration of Electrical Resistivity Data and Standard Penetration Test (SPT) and Light Dynamic Penetrometer (DPL) Resistance Tests—Applications in Mass Movements Studies

In Brazil and various regions globally, the initiation of landslides is frequently associated with rainfall;yet the spatial arrangement of geological structures and stratification considerably influences landslide occurrences. The multifaceted nature of these influences makes the surveillance of mass movements a highly intricate task, requiring an understanding of numerous interdependent variables. Recent years have seen an emergence in scholarly research aimed at integrating geophysical and geotechnical methodologies. The conjoint examination of geophysical and geotechnical data offers an enhanced perspective into subsurface structures. Within this work, a methodology is proposed for the synchronous analysis of electrical resistivity geophysical data and geotechnical data, specifically those extracted from the Light Dynamic Penetrometer (DPL) and Standard Penetration Test (SPT). This study involved a linear fitting process to correlate resistivity with N10/SPT N-values from DPL/SPT soundings, culminating in a 2D profile of N10/SPT N-values predicated on electrical profiles. The findings of this research furnish invaluable insights into slope stability by allowing for a two-dimensional representation of penetration resistance properties. Through the synthesis of geophysical and geotechnical data, this project aims to augment the comprehension of subsurface conditions, with potential implications for refining landslide risk evaluations. This endeavor offers insight into the formulation of more effective and precise slope management protocols and disaster prevention strategies.

基于CEL方法对T-bar测试浅层软土强度系数修正的讨论

软土强度测试是室内土工试验和现场原位测试的重要组成部分,T-bar贯入仪是一种能够简便准确得到软土不排水抗剪强度沿深度连续分布包络线的测试手段。文中基于CEL大变形计算结果,在与其他学者应用T-bar测试结果对比的基础上,验证了计算方法的可靠性;根据计算得到的T-bar系数随贯入深度的分布特点,提出了简便的修正方法,可用于T-bar测试浅层软土强度的修正。

土体强度对T-bar系数修正影响的研究

本文基于CEL大变形计算方法,计算了4种土体不排水抗剪强度条件下T-bar贯入过程,根据得到的T-bar系数随贯入深度的分布特点,提出了T-bar修正系数表达式中参数的拟合表达式,进而给出根据T-bar测试数据迭代计算软土不排水抗剪强度的方法。该研究结果可为其他类似工程提供借鉴。

既有建筑新增T-bar墙、板施工技术

行业内传统的安防做法通常为增大建筑结构墙体厚度、增强钢筋配置或加设钢板来提高安防等级,施工成本过高且占用室内使用面积,存在一定的弊端。如何快捷高效地提高建筑物的安防等级,尤其是在既有建筑内增设安防等级高的结构工程成为一大难题。以北京CBD超高层工程为例,通过在钢筋混凝土结构墙、板的钢筋之间增设新型高强T-bar材料,并通过合理的工序安排,可靠的措施保证结构成形质量,形成一种符合高安防等级要求的结构体系,达到UL安防认证标准,可为其他类似工程提供借鉴。

高功率高效率速调管输出耦合器的优化与设计

输出耦合器作为速调管关键部件,其性能直接关系到速调管的整体表现。然而,耦合器故障却是速调管及多种真空电子设备中最为常见的问题之一,特别是在高连续波功率运行场景下,这一问题更为突出。针对连续波650 MHz/800 kW高效率速调管,对输出耦合器进行优化设计,并在单注和多注速调管耦合器测试方面取得了重要突破:单注速调管输出耦合器在连续波模式下的测试功率已达到690 kW以上,为了进一步增加功率容量,采用T-bar结构过渡,并对耦合器进行优化设计,使陶瓷附近电场分布更均匀;而多注速调管矩形波导窗输出耦合器最高测试功率达到全驻波115 kW。此外,通过对耦合器的结构、材料以及散热方式进行分析与优化,积极探索提升耦合器功率容量的多种可能途径,进一步增强了速调管的稳定性和可靠性。

糯玉米茎秆穿刺强度QTL分析与基因组选择

茎秆穿刺强度是衡量玉米茎秆机械强度和抗倒伏能力的重要指标之一,本研究以衍生于糯玉米自交系衡白522和通系5的198个重组自交系为试验材料,对茎秆穿刺强度进行数量性状位点(QTL)分析和基因组选择研究。单个环境QTL分析共检测到4个控制糯玉米茎秆穿刺强度的QTL,每个QTL的表型变异贡献率均小于10.00%,且仅在单个环境中被检测到;多个环境QTL分析共检测到8个QTL与环境互作,其加性效应总共可解释24.64%的表型变异,加性效应与环境互作贡献率为17.51%;上位性QTL分析共检测到4对QTL与QTL互作,可解释8.25%的表型变异。基因组选择中,当训练群体占群体总数的80%,随机选择500个标记即可获得较高的预测准确性;但是根据单个环境QTL分析结果,选择机率常用对数值排名前200的标记,即可大幅度提高基因组选择预测准确性。

自落式贯入仪率相关系数标定方法

自落式贯入仪(free-falling penetrometer,FFP)作为一种新型地质勘察技术,可以高效快速地获取海底沉积物的力学性质参数。FFP贯入过程中锥尖阻力受贯入速率影响,数据处理时需借助速率因子将动贯入阻力转化为与静力触探试验(cone penetration test,CPT)等效的准静态贯入阻力,但目前速率因子中的率相关系数尚无明确测试方法。基于牛顿运动定律对率效应进行理论分析,并利用南海北部陆坡淤泥质沉积物开展室内贯入试验;并采用对数函数和幂次函数拟合锥尖阻力与贯入速率关系,提出了自落式贯入仪率相关系数的标定方法。研究结果表明,释放高度和探头质量都会影响最终贯入深度,但贯入过程中的锥尖阻力变化受探头质量影响较小,提出的率相关系数标定方法能够更准确获取FFP贯入的率相关系数。在实际应用中可采用室内试验标定的系数修正原位试验数据,为FFP实际应用提供技术支持。

海洋静力触探仪标准装置研究及不确定度评定

为解决海洋静力触探仪量值溯源问题,结合设备测量过程中受温度影响的分析,根据量值溯源技术路线,设计构建了可在模拟海洋温度条件下开展海洋静力触探仪校准的标准装置。在对该标准装置的稳定性和开展试验的重复性考核的基础上,对校准试验结果进行了不确定度评定分析,分析表明海洋静力触探仪标准装置所复现的孔隙水压力标准值扩展不确定度为0.017 MPa(k=2),锥尖阻力标准值扩展不确定度为0.031~0.270 kN(k=2),侧壁摩阻力标准值扩展不确定度为0.031~0.036 kN(k=2),构建的标准装置性能指标满足海洋静力触探仪的量值溯源需求。

西辽河通辽段河床沉积物渗透系数的现场测定

采用不同方法对西辽河通辽段河床沉积物渗透系数进行现场测定,获取各点位的垂向渗透系数。并分别在探坑、土样坑、渗透仪渗水试验、竖管试验、渗坑法渗水试验、双环渗水试验位置处及其附近,先从河底表面取沉积物样,再从岩性明显变化的不同深度取样,带回实验室,进行颗粒分析,探讨河床沉积物渗透系数与颗粒级配之间的关系。结果表明:随着河床沉积物中砂石含量的增加其渗透系数也增大;反之,河床沉积物中黏土含量增加其渗透系数减小。沉积物的颗粒级配是影响渗透系数的重要因素,颗粒级配对于沉积物的孔隙尺寸、孔隙的形状及大小都有很大的影响。研究结果可为计算地表水与地下水的交换量提供可靠的水文地质参数,进而提高地下水资源评价结果的精度。

施钾量对高产夏玉米抗倒伏能力的影响

倒伏是玉米高产的重要限制因素之一。本研究旨在探讨施钾量对高产夏玉米抗倒伏能力的影响,为钾肥科学施用提供科学依据。选用登海661(DH661)和郑单958(ZD958),设置6个施钾水平,研究高产条件下施钾量对夏玉米基部茎节穿刺强度、伤流量和产量的影响,并观察基部第3茎节显微结构。结果表明,施钾肥能显著提高茎秆的穿刺强度,DH661和ZD958最大提高幅度分别为17.90%和25.57%,但不同茎节提高幅度不同。伤流液的强度随着施钾量的增大先增加后减小,开花前促进作用大,吐丝期DH661和ZD958施钾180kghm2时最高,分别比对照提高24.30%和29.68%。单位面积内维管束增加,特别是小维管束增多是提高茎秆穿刺强度的关键。施钾肥可以显著提高玉米产量,随施钾量的增加,籽粒产量呈先增高后降低的趋势,DH661和ZD958分别在施钾180kghm2和240kghm2时达到最高产量。

基于离散元法的贯入圆锥对沙土颗粒运动特性分析

为了预测土壤颗粒在圆锥指数仪贯入沙土过程中的运动特性,该文通过建立一个三维长方体料床模型用离散元法模拟了圆锥贯入沙土的全过程,讨论了料床指定初始位置上颗粒的运动轨迹,还将料床的位移场按照位移量大小分成4个区,分析了料床的横向、纵向以及合成的位移场,最后给出了不同贯入深度的料床速度场及力链分布规律。研究结果显示:受到圆锥向下贯入和左右壁面阻挡的共同作用,大多数颗粒在圆锥贯入过程中以纵向移动为主,横向上体现为近似线性梯度的受限扩散式移动,尤以锥尖附近的横向位移最明显;颗粒在纵向上均经历了先向下运动再向上运动的过程,在圆锥贯入过程中料床的纵向位移场,作为向上和向下位移区的分界线,一条"衣领"带状区域的颗粒近似静止;越靠近锥尖附近的颗粒接触力和速度越大,且随着贯入深度的增加,锥尖处的接触力增大。该文的研究为土壤圆锥指数实地测量时测量点间距的取值提供理论依据。

运用轻便动力触探仪研究黄土的岩土工程特性

运用可变能量轻便动力触探仪对黄土在天然状态及饱和状态下进行了一系列现场触探试验，并结合该仪器开展了黄土天然状态下及饱和状态下的静力分级加载载荷试验。在这些试验所获结果基础上，分析了黄土的岩土力学性质，尤其是黄土的湿陷性。对比用其它手段测得的湿陷参数，提出了一种运用触探仪现场测试黄土的力学强度，进而运用所测的力学强度对黄土的湿陷性进行间接评价的简单方法。

圆锥指数仪贯入沙土试验的离散元法模拟

利用离散元法对圆锥指数仪贯入沙土的试验进行了数值模拟研究。贯入试验与数值模拟结果所揭示的现象相吻合,即圆锥侧壁上的土壤摩擦阻力对总贯入阻力影响微小。离散元数值模拟结果显示,贯入圆锥锥尖部位的颗粒力链为强力链,颗粒的速度数值较大但方向杂乱,其他位置颗粒几乎静止;圆锥指数仪的贯入阻力随贯入深度增加而显著增大;土槽侧壁的正压力随贯入深度增加而增大;贯入速度变化对贯入阻力和土槽侧壁正压力的影响微弱。