Understanding the shear behavior of thermally desorbed diesel-contaminated soil is critical for evaluating its engineering reuse as fill materials. In this study, diesel-contaminated and uncontaminated soils were subjected to thermal desorption treatment at temperatures ranging from 105 to 600 ℃. Physicochemical and microscopic tests, including gas chromatography, organic matter analysis, X-ray diffraction, particle size distribution, and scanning electron microscopy, were conducted to elucidate the shear behavior and underlying mechanisms. The results reveal three main geotechnical contributions. First, the shear strength of both soils increases with temperature, with a significant enhancement observed between 400 and 500 ℃ due to kaolinite dehydroxylation and particle cementation. Second, in the low-to-intermediate temperature range (105–400 ℃), the lubricating effect of diesel and oil films weaken interparticle contacts, significantly reducing the shear strength and internal friction angle of contaminated soil while also delaying organic matter degradation and mineral transformation. Third, above 500 ℃, most diesel is removed, and the contaminated soil exhibits a more uniform particle size distribution, leading to higher shear strength parameters than those of uncontaminated soil. Image-based porosity analysis further confirms the dual role of diesel in pores: filling pores at low temperatures, exposing pores during volatilization, and promoting sintering and densification after complete removal. These findings provide a theoretical basis for optimizing thermal desorption remediation processes and for safely reusing remediated soil as backfill in residential foundation platforms and road subgrades.

The deformation characteristics of soil after thermal desorption are crucial for the evaluation of engineering properties, but the evolution mechanism is currently unclear. This study focuses on the thermal desorption of contaminated soil, conducting Geo-dynamic Systems consolidation-rebound tests to reveal the evolution mechanism of consolidation–rebound deformation and pore pressure characteristics, and exploring the evolution mechanism through pore structure, particle size distribution, and Cation Exchange Capacity tests. Results show that the consolidation characteristics of uncontaminated soil increase and then decrease with heating temperature, with 400 °C as a turning point. In contrast, the consolidation deformation of contaminated soil continues to decrease. The vertical deformation of the soil in the pre/early consolidation stage is greater before 400 °C, while after 400 °C, the deformation continues to increase with consolidation pressure, and higher heating temperatures enhance the soil’s rebound deformation ability. Pore water pressure changes in two stages, with temperature ranges of 100–300 °C and 300–600 °C, and with increasing heating temperature, the characteristics of pore pressure change from clay to sand. Mechanism tests reveal that inter-aggregate pores affect initial deformation, while intra-aggregate pores affect later deformation, both showing a positive correlation. Aggregate decomposition increases initial deformation capacity at 100–400 °C while melting body fragmentation increases later deformation capacity at 500–600 °C. CEC decreases with increasing heating temperature, reducing inter-particle resistance and increasing soil deformation capacity. Particle size distribution and Cation Exchange Capacity impact consolidation–rebound pore pressure.

以北部湾吹沙型填海场地为背景,通过浸泡-加载联动试验和有限元计算方法研究了外界条件差异对北部湾吹填场地卓越周期的影响.结果表明:在远场长周期地震动作用下,北部湾吹填场地反应最为强烈,其加速度反应谱峰值放大了近两倍,卓越周期向长周期方向偏移且相对偏移量最小,产生共振危害几率增大;输入地震动幅值增大,吹填场地对其短周期高频部分抑制效应和长周期低频部分放大作用变强,场地卓越周期向长周期方向演化的趋势增加;随着堆载预压加固荷载增大,场地地表中心动力响应减弱,卓越周期呈减小的趋势,预压处理达到一定程度后,场地由Ⅳ类场地变为Ⅲ类场地.

In this study, mercury intrusion porosimetry (MIP) and X-ray micro-computed tomography (XRμCT) were used to characterize the pore structures and investigate the permeability characteristics of clay after aging and contamination with diesel. The results of the MIP tests showed that aging leads to reductions in porosity and average diameter, as well as an increase in tortuosity. The XRμCT analysis yielded consistent results; it showed that aging renders pores more spherical and isotropic and pore surfaces smoother. This weakens the pore connectivity. Micromorphological analysis revealed that aging led to the rearrangement of soil particles, tighter interparticle overlapping, and a reduction in pore space. The combination of MIP and XRμCT provided a comprehensive and reliable characterization of the soil pore structure. An increased diesel content increased the porosity and average diameter and reduced the tortuosity of the pores. Mechanistic analysis showed that aging weakens interparticle cohesion; this causes large agglomerates to break down into smaller agglomerates, resulting in a tighter arrangement and a subsequent reduction in porosity. An increase in diesel content increases the number of large agglomerates and pore spaces between agglomerates, resulting in increased porosity. Both aging and diesel content can weaken the permeation characteristics of soil.

To help meet the need for the reuse of thermally desorbed soil from contaminated sites, this paper presents a laboratory simulation of the thermal desorption treatment of diesel-contaminated soils. The simulated treatment was based on the thermal desorption treatment of contaminated soil around chemical plants. X-ray micro-computed tomography and mercury pressure porosimetry were used to characterize changes in the pore structure of soil contaminated with diesel fuel and treated with thermal desorption. The changes in pore structure were rationalized in terms of macroscopic shrinkage of soil, matrix suction, particle gradation, and clay minerals. Additionally, permeability properties were explored. The main results were as follows: Thermal desorption altered the pore structure of the soil. With separate heating of different soil samples, the increase in heating temperature enlarged internal pore space, porosity, and average pore diameter, enhanced pore connectivity, and reduced tortuosity of the soil. Continuous heating of identical soil samples at intervals and progressively higher temperatures led to reductions in pore space, porosity, and pore average diameter as well as pore connectivity, and increased tortuosity. Matrix suction and clay minerals were the main factors responsible for changes in the pore structure. The mechanism of matrix suction was the main reason for very different trends in changes in the pore structure. Clay minerals were not influential until temperatures exceeded 400 °C. The permeability coefficients showed two very different trends with temperature under the two heating regimes.

ABSTRACTIn karst topography, hidden caves or underground rivers may imperil the safety of tunnels. It is critical to accurately detect the location and geometric shape of hidden karst caves for assessing the safety of tunnels. This paper reports a case where a large karst cave was exposed during the construction of the Nongmo tunnel in Duan County, Guangxi, China. A 2D ground‐penetrating radar survey was employed to preliminarily detect the distribution of hidden karst caves along the tunnel axis. Advanced drilling was used to obtain the velocity of electromagnetic waves and verify the 2D ground‐penetrating radar detection. Ground‐penetrating radar 3D grid detection was carried out for further detecting the geometric shape of the hidden karst caves. Rotary thrust power ratio, which is a function of drilling speed, rotating speed, propulsion pressure and torque, was proposed to reflect the integrity of the surrounding rocks. It was found that the depth of the peak value in the rotary thrust power ratio curve is consistent with that of the amplitude jump in ground‐penetrating radar A‐scans and in time–frequency distributions. The results of 3D attributes analysis indicate that due to the variation of highlights in different ground‐penetrating radar signal attributes, the obtained karst cave shapes using different attributes would be various. A multi‐attributes fusion method was proposed to generate a data volume considering various attributes. The 2D geometric shapes at different depths were obtained using the anomalous body lineament in the generated date volume slices. The 3D geometric shapes were reproduced by combining the obtained 2D geometric shapes at various depths. Based on different detection and analysis methods, the outline shape of karst caves at YK364 + 199 ∼ YK364 + 184 of the Nongmo tunnel was revealed in detail.

为了研究高温作用对黏土抗剪性能的影响,采用高温炉对土体加热至105℃、200℃、300℃、400℃、500℃和600℃,待冷却后重塑制样,通过三轴剪切试验、成分分析测试、粒度分布测试和扫描电镜观察等手段获得抗剪性能指标及其影响机理.研究表明:105℃与200℃处理土体抗剪性能指标基本不变.200℃后处理的黏土重塑样初始切线模量随着温度增大始终增大.当温度由400℃升高至500℃时,应力-应变关系由硬化型转变为软化型.土体黏聚力c值随温度升高先减小后增大,400℃是黏聚力最低值温度.c值降低阶段是由高温作用下土中有机质降解、矿物成分脱水所致,增大阶段是由于高温作用后土粒咬合作用加剧形成表观黏聚力.土体内摩擦角ψ值随温度升高而增大(＞200℃),分析认为是与高温作用后土粒表面的粗糙程度和土粒咬合作用加剧相关.微观试验表明:105℃土体中具有絮凝结构.400℃土体粒间胶结作用不明显,土粒连接方式由面-面形式过渡到边-边与边-面形式.500℃与600℃土体孔隙减少,土粒间结合更为紧密.

为探讨不同固结压力、固结比及动荷载频率等条件下夹持厚层软土的动力特性,以广西北部湾吹沙填海场地下伏深厚软土层为研究对象,利用"浸泡-加载"试验装置制备一批不同固结压力和固结比的土样开展GDS动三轴试验,获取海积软土的动应力-动应变曲线、动弹性模量和阻尼比等动力参数的变化规律.结果表明,在同一动应变条件下,动应力、动弹性模量和最大动弹性模量随着固结压力和动荷载频率的增加而增大,随着固结比的增大而减小;阻尼比和最大阻尼比随着固结压力和动荷载频率增加而减小,随着固结比的增加而增大.基于Hardin-Drnevich公式建立了各影响因素变化下海积软土动弹性模量和阻尼比的数学模型,以期为吹沙填海场地卓越周期的演化特征研究提供数据支撑.

Adopting the expansive soil in Nanning, China, as the pollution-free background soil, and 0# diesel as the petroleum hydrocarbon pollutant, the effect of thermal treatment on the expansion characteristics of contaminated soil by diesel was studied. X-ray diffraction (XRD), mercury intrusion porosimetry method (MIP), scanning electron microscopy (SEM), and gas chromatography-flame ionization detection (GC-FID) were adopted in a study of the effect mechanism. The results reveal that at a constant diesel content, the steady-state no-load expansion ratio (Steady ER) of the thermal treated diesel-contaminated expansive soil (TT-ES) decreases with increasing heating temperature, and the expansion time history curve changes from a three-stage shape to a straight-line shape. The XRD test results show that the content of illite, which determines the expansion characteristics of the TT-ES, has not changed during the thermal treatment and cannot be used to explain the decrease of expansion characteristics of TT-ES. However, the change of its crystal structure can have an impact on the expansion characteristics. Within the heating temperature range from 500 ~ 800 °C, the cation exchange capacity decreases, which reduces the hydration reaction of the TT-ES, thereby decreasing the Steady ER. Within the full heating temperature range, the soil structure affects the time history curve shape and the Steady ER. When the heating temperature remains constant, the larger the diesel fuel amount was, the lower Steady ER. Similarly, the decrease in cation exchange capacity due to the incorporation of diesel oil and the change of the soil structure reduce the Steady ER.

层位特征是探地雷达路面检测的重要信息,而目前基于人工或相关算法的层位拾取方法存在主观性强、工作量大和每次仅能追踪一个层位等问题.为此,提出了一种基于探地雷达瞬时相位余弦的多层位自动追踪方法.首先,通过复信号分析获取了雷达数据的瞬时相位余弦;其次,利用子波余弦矩阵数据进行相似度分析后再计算其瞬时相位余弦,增强相位数据同相轴的横向连续性;然后,获取相位数据的空间位置、振幅和极性信息,并在信号幅值和同相轴特征等一系列约束条件下自动追踪横向连续的层位线;最后,通过比较深度方向相邻层位线上振幅的均方根平方值来确定层位数据及其极性,并通过设置层位线阈值和振幅阈值来提取强振幅连续的层位线数据.数值模拟和现场案例分析验证了本文方法的有效性和适应性.

Coastal cities in Beibu Gulf of China are creating new lands by reclaiming from coasts, and are located in a seismic zone. The reclaimed land consists of a thick layer of marine soft soil overlain by sand. Earthquake in a soft-soil field usually leads to catastrophe, depending on the consolidation of soil and the amplitude of earthquake. In this paper, a scale model with a typical soft-soil stratigraphic section is presented to study the seismic responses of a soft-soil field under different consolidation conditions. The scale model was sequentially applied with several seismic waves at different epicentral distances to test the horizontal acceleration at different depths. The test results show that consolidation state, the earthquake amplitude and the spectral characteristics can greatly affect the predominant period, the horizontal acceleration amplification factor, and the seismic design parameters. Therefore, the earthquake characteristic and the consolidation state of soil should be taken into consideration comprehensively to ensure the safety of surface buildings on the reclaimed land during the earthquake.

目前探地雷达数据处理更多地是直接引入其他领域的图像和信号处理方法,如中值滤波、小波变换和剪切变换等去噪方法.存在效率低、图像边缘保持差、噪声处理不彻底等缺点,且滤波效果取决于噪声的类型.为此,提出了一种结合探地雷达倾角信息和相关性信息的改进双边滤波算法.首先,分别基于梯度平方的结构张量算法和相似系数分析方法提取了探地雷达局部倾角信息和相关性信息;然后利用所提取的角度信息构建高斯角度相似权值函数,并将该函数代替双边滤波算法中的高斯空间权值函数,增强噪声压制的方向性;将双边滤波算法中的高斯像素相似度权值函数中心点代替为邻域内的中值,提高雷达图像中的奇异点噪声压制能力;最后在权值函数中结合相关系数信息,进一步压制强振幅噪声.数值模拟和实际数据分析结果表明,本文改进算法能够有效压制随机噪声和强振幅噪声,增强振幅的连续性.

以不同非线性程度的简化土层剖面和日本KiK-net台网的台站场地为研究对象,分别采用FLAC3D和DEEPSOIL进行土层地震反应分析.通过对比地表反应谱和地震动峰值,验证运用FLAC3D软件进行一维土层非线性地震反应计算的可行性.计算结果表明:在简化土层剖面计算中,FLAC3D与DEEPSOIL计算结果较为接近;虚假共振现象导致DEEPSOIL非线性频域分析的地表反应谱峰值大于FLAC3D与DEEPSOIL时域分析的.在台站场地土层剖面的计算中,非线性场地的计算结果较黏弹性场地更为接近实测值.刚性基岩模型的计算结果在短周期范围较为准确,而采用露头运动参考点的柔性基岩计算结果在长周期范围内更为合理.

为了探究不同地下水位的场地条件下对吹砂填海场地动力响应的影响,以广西北部湾吹砂填海场地为研究对象,基于FLAC3D软件结合前期室内试验结果建立了场地模型,进行了数值模拟分析.在此研究中着重分析地下水位的变化对场地加速度放大系数、加速度反应谱和地震液化效应的影响,为减轻吹砂填海建设场地的震害程度提供参考依据.结果表明:随着地下水位埋深的增加,地表加速度放大系数呈现出逐渐减小的趋势,地震放大作用主要集中在短周期,卓越周期也在短周期处取得;随着地下水位埋深的减小,地震波高频成分被过滤,低频成分被放大,场地特征周期与卓越周期均有增大趋势;地下水位变化对吹填沙土层液化的产生和发展具有显著的影响,随着地下水位的上升,砂土表现出更强的液化效应,并且液化现象随着地震峰值加速度的增大逐渐沿土层深部发展.

This study investigates the pore structure characteristics of a marine soft soil of the Beibu Gulf, Guangxi Province, China and its variation with clay content. Pore-size distribution was measured by Mercury intrusion porosimetry (MIP) and analyzed based on fractal theory. The analysis of the results relies on the distinction of several types of pores: micropores, small pores, mesopores and macropores, separated by the critical pore diameters of 0.02 μm, 0.18 μm and 0.78 μm, respectively. Mesopores and small pores were dominant, accounting for more than 75% of the total pore volume. Small pore volume increases with clay content at the expense of the mesopore volume. Between 22.31% and 32.31% clay, the connectivity of pores improves with clay content, while the tortuosity of pores increases from 22.31% to 32.31% of clay and then decreases between 32.31% and 37.31% clay. Marine soft soil in the Beibu Gulf is characterized by multiple fractal dimensions. Macropores had a large (close to 3) fractal dimension, independent of clay content. Mesopores and small pores had a smaller fractal dimension comprised between 2.1 and 2.4, while the fractal dimension of micropores did not exceed 1.5. The fractal dimension of mesopores and micropores are influenced significantly by the clay content. The study of the porosity of the marine soft soil of the Beibu Gulf could serve as a useful basis for the prediction of its hydraulic properties.

There is a very strong link between the behavior of ground penetrating radar (GPR) wave propagation in zinc-contaminated soil and the dielectric properties of soil. This relationship can be of significant use in the practices of quick detecting the degree of pollution in zinc-contaminated soil. In this research, measurements were conducted on the zinc-contaminated soil samples with different soil index properties (i.e., zinc ion concentration, wet density and moisture content). The radar reflection wave data of the common midpoint and common-offset sounding mode were obtained by using the 600 MHz antenna, and the relative permittivity was measured using the vector network analyzer. The attribute analysis of radar reflection wave shows that the wave velocity is affected by wet density and moisture content, but independent of zinc ion concentration. Both the amplitude and the peak frequency decrease with the increase in zinc ion concentration, wet density and moisture content. For the soil dielectric properties, the metal ions can change the conductivity of solution in soil, affecting the imaginary part of relative permittivity, but with little effect on the real part. The positive correlations between the relative permittivity with density and moisture content are caused by the variation of three-phase composition of soil. Besides, the measured soil dielectric properties and the radar reflected wave attributes confirm each other, which can well explain the change rules of electromagnetic wave velocity, amplitude and central frequency. The presented results can increase understanding and confidence on GPR for quantitative monitoring and detecting of zinc-contaminated soil.

为了得到热脱附后柴油污染膨胀土的膨胀特性,以南宁膨胀土为背景土,制备不同掺量的柴油溶度污染土;并在模拟热脱附环境中进行实验室土壤修复,得到修复后的柴油污染膨胀土,最后进行无荷载膨胀率测试.同时利用XRD分析、压汞测试和气相色谱测试进行机理分析.试验结果表明:柴油掺量一定时,加热温度越高,无荷载膨胀率越低;加热温度一定时,柴油掺量越大,无荷载膨胀率越小.机理分析结果显示:柴油的掺入对黏土矿物基本没有影响;加热温度和柴油掺量的增加可增大柴油污染膨胀土孔隙率和孔隙平均直径,虽然加快了水分浸入,增强黏土水化作用,但是增大的膨胀空间,削弱了膨胀潜势,最终导致无荷载膨胀率降低.同时,残余"碳"存在,可减缓或者阻隔水与黏土矿物表面的水化作用,导致无荷载膨胀率降低.

To determine the high-temperature effect on the soil particle composition (SPC) and its mechanism in Nanning, China, a laboratory experiment was designed based on the high-temperature environment caused by forest fires and considering thermal desorption. The effect mechanism was examined based on the soil organic matter and soil minerals (kaolinite). The experimental results indicated that the SPC was not changed before 200°C. With increasing heating temperature, the content of silt and clay decreased, while the content of sand greatly increased after 200°C. The analysis believes that the reduction of the content of organic matter has promoted the reduction of the content of silt and clay to a certain extent. The decrease in the silt and clay content inevitably increased the sand content, but this was also related to the soil minerals (kaolinite), and a reaction occurred producing a cementing substance that absorbed both silt and clay to form new sand. The temperature effect on the SPC was divided into three parts. The first part was observed from 100 to 200°C, while the soil composition was unchanged. The second part was from 200 ~ 400°C. This part is related to the reduction of organic matter content. The third part was determined to be between 400 and 800°C, which was mainly related to clay minerals. The fusion of silt and clay during the formation of new sand resulted in a decrease in its content beyond 400°C.

Ground penetrating radar (GPR) is a geophysical exploration technique used in a wide range of applications such as polar exploration, hydrogeological surveys, and archeological prospection. In recent years, it has been applied to tunnel construction for forecasting geological anomalies in front of the tunnel face. However, the application of GPR, forecasting geological anomalies in karst tunnels, has always been restricted by the problem of ambiguity. In the paper, based on the GPR investigation of highway tunnels in the karst areas in Guangxi, China, several GPR data of typical karst geological anomalies were selected as the analysis objective. The purpose of this study is twofold: to analyze and summarize the GPR attribute characteristics of typical geological anomalies by studies of laboratory tests and to introduce a new method for identifying different types of karst geological anomalies automatically in karst tunnel construction. Firstly, the attribute analysis technology of GPR is introduced, and the propagation law of electromagnetic waves in karst geological anomalies is studied from three perspectives: the time domain, frequency domain, and time-frequency domain by using physical laboratory simulations. Then, an intelligent identification model for typical karst geological anomalies is established in accordance with a Gaussian process (GP). Results from the Gaussian classification of field cases indicate that the type of typical karst geological anomalies can be effectively identified via comparing model prediction probability. The findings of this research allow for quantitative description of the GPR interpretation of typical karst geological anomalies in tunnel advanced prediction.

It is difficult to solve the problem of multi-results when using ground penetrating radar (GPR) to forecast geological anomalies of karst tunnel due to numerous factors, such as the field detection environment, the complexity of karst geology and the interpretation technology and so on. Some representative cases from the previous projects were chosen as the studied object, the attribute characteristics of typical geological anomalies in karst tunnel construction were analyzed and summarized. The results of field tests indicated that the attribute characteristics were closely associated with karst geological anomalies. Among them, the center frequencies of GPR reflection waves in cavity karst caves, karst caves filled with dry loose clay and gravel and anhydrous fracture zones attenuated slowly with time, and the distribution ranges were 90-105 MHz, 85-100 MHz, and 70-110 MHz respectively. However, the center frequency of radar reflection waves in karst caves filled with soft plastic clay and water-saturated fracture zones decreased rapidly with time, and the distribution ranges were 60-80 MHz and 40-70 MHz respectively. After studying the method of quantitative representation for attribute features, a calculation method of radar wave absorption and attenuation parameter based on generalized S transform and wavelet spectral simulation was proposed. The analysis results of field tests indicated that each of the characteristic properties could reflect the features of the radar reflection wave of karst geological anomalies in some ways. Different geological anomalies in karst tunnel construction could be distinguished after integration of these characteristic parameters, which could enhance the accuracy of GPR interpretation in karst tunnel advanced geology prediction.