To ensure the application of microbial self-healing concrete (MSHC) in practical engineering, it is imperative to investigate its constitutive model and the effect of microbial self-healing agent (MSHA) dosage on concrete properties. In this study, a constitutive model for MSHC is established using a Weibull-lognormal statistical distribution, and the effect of MSHA dosage on concrete performance is investigated. Results show that MSHA dosages of 0.30 m(3) and 0.45 m(3) serve as critical thresholds for compressive strength and splitting tensile/flexural strength, respectively, beyond which mechanical properties decline sharply. The optimal MSHA content was determined to be 0.33 m(3) per unit volume of concrete. Based on the constitutive model and ordinary concrete parameters, the mechanical behaviour of MSHC at any MSHA dosage can be effectively predicted. With the optimal dosage, MSHC healed cracks narrower than 1.02 mm after 28 days, achieving area and permeability repair rates of 96.02% and 77.65%, respectively.

Ground fissures are extraordinary urban geological disasters, and their harmful effects on underground structures have been highlighted in many cities. Differential settlements between strata can cause a void phenomenon at the bottom of a pipe gallery structure, significantly threatening the project’s construction and operation. This study analyzes the void phenomenon at the bottom of a pipe gallery structure, and a calculation method for the bottom void range is proposed. Through a model test, the stress and deformation laws of the pipe gallery structure under the conditions of orthogonal (90°) and oblique (45°) ground fissure displacements are analyzed. The results show that, owing to the dislocation of the ground fissure, the bottom void range of the pipe gallery is 2.87–3 times the length of the bottom edge of the pipe gallery section under the orthogonal condition and 3.125–3.5 times the length under the oblique condition. Under the dislocation of the ground fissure, the top plate of the structure is under tension; the bottom plate is under compression, and the strains on the side plates are significantly less than those on the top and bottom plates. The maximum contact pressure between the structure and the surrounding soil is distributed on the top plate of the hanging wall and the bottom plate of the footwall near the ground fissure. This study provides a theoretical basis for the optimal design of pipe gallery structures crossing ground fissures and has theoretical significance and application value.

Establishing a constitutive model that reflects the local bonding breakage process has always been a core task in soil mechanics and is crucial for solving engineering stability issues. Based on thermodynamic principles and breakage mechanics,this paper proposes a macro-micro thermodynamic constitutive model. This model quantitatively describes the thermodynamic behavior of local bonding breakage and the non-uniform distribution of stress-strain at the microscale. It improves the prediction accuracy of the model for deformation characteristics,which is similar to the Cambridge model in mathematical form. Firstly,based on the law of conservation of thermodynamic energy,the mathematical expression of structural breakage work during compression deformation was determined. It was found that the dissipated energy of breakage can be mainly divided into two parts:the frictional effect between bonded elements and frictional elements,and the irreversible transformation from bonded elements to frictional elements. Furthermore,a macro-micro constitutive model framework considering the thermodynamic behavior of local bonding breakage was established. Secondly,based on the constitutive framework and the deformation mechanism of loess (frictional,bonded,and damaged),the expressions for free energy,dissipated energy,and damage dissipated energy were determined. The damage yield function and elastic-plastic constitutive model considering the evolution laws of volume breakage and shear breakage were derived. Finally,the established model was used to predict the experimental data of other scholars,and its rationality and simulation advantages were verified through comparison. This model aligns better with thermodynamic principles,and its parameters are easy to determine.

The pipe gallery structure is a shallow underground structure, which is the dynamic response characteristics and failure of the pipe gallery structure caused by the vibration of the surface vehicle load are more significant. In this paper, taking an underground comprehensive utility tunnel construction as the research object, give the shallowly buried pipe gallery structure vibration characteristics and deformation mechanism under the condition of vehicle load. Meanwhile, this paper derived a model of the shallowly buried pipe gallery structure dynamic response affected by vehicle vibration characteristics, and the rationality was verified by carry out the model test. Some important points:①the stress characteristics of the top of the shallow buried pipe gallery structure are mainly as follows: both ends are pressure, while the middle is tension; ②the stress characteristics of the bottom are opposite to that of the top; ③the strain value of the pipe gallery structure is the largest in the range of 6 times the pipe diameter, and the dynamic response of the pipe gallery structure gradually decreases with the increase of soil depth; ④Under the same depth condition, the below position of the vehicle is the most unfavorable; and the influence of load frequency on the dynamic response of the whole pipe gallery structure and stratum is more intense at low frequency. This paper provides a reference for the stability analysis and safety evaluation of shallowly buried pipe gallery structures under vehicle vibration load.

黄土地基遇水湿陷后具有不均匀沉降特征,对修建于其上的预制管廊结构会产生不可避免的危害.地基湿陷使得预制管廊结构可能出现开裂、错台、扭转甚至廊体坍塌,影响预制管廊工程的安全运营.针对这一现象,本文通过不同配比配制四种不同湿陷性的人工黄土,经过试验后得到与原状黄土湿陷性相似的配比.并将其作为试验用土,开展湿陷性黄土地基对预制管廊结构受力性能影响的研究工作.研究表明,人工配制湿陷性黄土能够较好的模拟原状黄土特殊性质,在管廊受力方面,相较于顶底板横向应变,基底全幅浸水对于管廊前、后侧板应变影响幅度较小;浸水湿陷过程中会打破管廊与周围土体原有的受力平衡状态,引起应力重分布现象,且顶板和底板极易发生受拉破坏;在黄土地基发生不均匀沉降后,预制管廊结构会呈受弯、受扭状态.

Virtual simulation experiments have become an important component of experimental teaching in science and engineering, and are increasingly valued by various universities. In response to the characteristics of the concrete structure course and the difficulties in experimental teaching, combined with student feedback and teacher experience summary, an exploration was conducted on the mixed experimental teaching mode of concrete structure based on the Simdroid virtual simulation platform. This paper designs a student-centered teaching mode that combines online and offline practical teaching. This mode breaks the limitations of time and space, increases the fun and flexibility of experimental teaching, enhances students' learning enthusiasm and initiative, and effectively improves the teaching effect of concrete structure experiments.

The mechanical behavior of underground pipe gallery is a key research issue due to the static/dynamic states which exist in a ground fissure area. This study took an underground pipe gallery project in Xi'an, China as the research object. We analyzed the stress/strain characteristics of the pipe gallery structure and surrounding soil under static/dynamic conditions by the numerical simulation methods in detail. Based on the results, we proposed a theoretical calculation model for the pipe gallery structure considering the influence of the ground fissure, and combined with engineering examples for calculation and discussion. Subsequent results showed that: (1) the effective activity range of ground fissure on the deformation of the pipe gallery structure was mainly from 0.0 m (horizontal direction of ground fissure) to 32.0 m. In activity range, the pipe gallery structure is prone to failure, owing to the large soil deformation in the vertical direction; (2) with the increase of ground fissure settlement, a stress reduction area near the ground fissure appeared at the bottom of the hanging wall of the pipe gallery structure, and a local void phenomenon was revealed. The length of the local void is 6.0 m to 8.0 m under the maximum settlement (0.8 m) of the ground fissure; (3) Compared with the static conditions, the vertical and horizontal displacements of the pipe gallery structure and surrounding soil under the seismic action were little, and there were tension-compression and torsion-shear effects in corner of the square pipe gallery structure (with a stress concentration phenomenon). The deformation law of pipe gallery structure and surrounding soil considering ground fissure and the theoretical model of pipe gallery structure established in this paper can provide reference for practical engineering.

为分析粗骨料料浆泌水率在不同影响因素下的变化特征和泌水率与料浆坍落度之间的关系,在室内开展了粗骨料充填料浆泌水率特性的试验研究.分析了物料组成、质量浓度及水泥含量对料浆泌水率的影响规律,并进一步探索了粗骨料料浆泌水率与坍落度之间的关系.结果表明:尾砂料浆泌水率随着料浆浓度的不断增大呈现不断降低的趋势,并且泌水率的降幅随着水泥掺量的增加逐渐降低;当泌水率相近时,尾砂料浆的质量浓度明显低于粗骨料料浆的质量浓度,说明掺入废石后能够有助于矿山实现高浓度料浆充填;粗骨料料浆的泌水率随着质量浓度的增加也呈现不断减小的趋势,但泌水率的降幅随着粗骨料掺量的增加呈不断减小的趋势;料浆的泌水率随着水泥含量的增加不断降低,并且浓度的增加会导致泌水率的降幅出现增大趋势;料浆的坍落度随着泌水率的增加表现出逐渐增大趋势.因此,可通过泌水率参数的变化定性判断料浆的输送性能.

为研究直螺栓连接预制管廊的纵向受力性能,引用隧道纵向刚度计算的纵向等效连续化模型,对其进行改进,使其适用于直螺栓连接的预制管廊,从而得到考虑螺栓预应力影响的纵向等效拉压刚度和弹性弯曲刚度.推导出了预制管廊在弹性极限弯矩作用下,截面最大拉应力、截面最大压应力、接头最大变形、接头螺栓最大拉应力和接头螺栓最大变形的表达式.运用所得表达式,结合工程实例参数,分析了管廊截面尺寸、管壁厚度、节段长度和螺栓个数对其受弯矩作用时中性轴的位置和纵向等效刚度的影响程度和趋势.结果表明,管廊抗弯刚度受截面宽高比影响较大;通过增加管壁厚度来提高管廊等效刚度的方法不经济;在满足设计要求条件下,适当增大预制节段的长度和增多连接螺栓数量可以有效提高管廊的纵向刚度,并能够很好地改善管廊截面受力状态,同时不失经济性,为直螺栓连接预制拼装管廊结构的设计合理性和工程适用性提供理论支持.

弹性地基梁法是计算地下结构的常用方法,但是在地裂缝活动下管廊结构底部产生脱空,弹性地基梁法的使用条件不再适用.基于Euler-Bernoulli-Bousslnesq模型和链杆法,将管廊与地基的接触看作是无穷多次超静定结构,通过将无穷多次超静定结构转化为有限次超静定结构,建立管廊结构在地裂缝作用下底部脱空的计算模型,由管廊结构与地基接触部分相对位移为零的条件,给出了管廊结构底部脱空范围的计算方法,并与既有地裂缝作用下管廊模型试验结果进行对比验证,由对比分析结果可知,管廊底部脱空范围计算方法所得结果与模型试验结果基本一致,最大误差不超过-18.75％,表明管廊底部脱空范围计算方法具有一定的适用性和有效性,可为地裂缝区域的管廊结构设计提供一些参考借鉴.

To study the evolution law and internal mechanism of the mechanical behavior of the structure and surrounding strata of an underground utility tunnel under the dislocation of ground fissures, and the failure mode of the tunnel structure, based on theoretical analysis and model tests, this study proposes a new method for determining the rationality of model test parameters and selecting the optimal dislocation rate, and then carries out an underground pipe gallery model test under multiple influencing factors such as dislocation displacement and mutual angle. First, by comparing the theoretical solution of the internal force of the pipe gallery structure under initial conditions, the rationality of the model test parameters can be preliminarily verified. Second, the physical unidirectional compression experiments of the geological structure of ground fissures at high, medium, and low speeds were carried out, and it was observed that the low speed (0.0005 mm/s) could better reflect the active characteristics of ground fissures in Xi’an. Based on the above experimental parameters, the mechanical behavior of underground pipe gallery under the influence of orthogonal (90°) and oblique (45°) was studied, and the following conclusions were obtained. (1) The structural strain at the top of the upper plate changes from tension to compression with an increase in the cross momentum when it was orthogonal and from tension to compression when it was oblique. (2) With the increase in staggered momentum, the contact pressure near the top of the structure near the ground fracture at the orthogonal and oblique angles increases considerably, and both angles demonstrate a void at the bottom of the upper pipe gallery structure. (3) The soil near the ground fissure is more severely affected by the dislocation, and the stress disturbance at the far end was the smallest. (4) With an increase in dislocation displacement, the law of surface subsidence was consistent between the orthogonal and oblique, i.e., the upper surface deformation showed a convex distribution. The lower plate showed a concave distribution. Based on the above conclusions, through in-depth summary and analysis, the longitudinal failure mode of the pipe gallery structure under orthogonal and oblique crossings was obtained: extrusion failure mode of the pipe gallery structure under an orthogonal condition and torsion–tension–extrusion failure under an oblique condition.

The prediction of foundation settlement is an important topic in loess filling engineering. Based on a filled foundation in Yan’an, China, this study explores the consolidation characteristics of compacted loess with different compaction energy and consolidation pressure through consolidation tests, analyzes the strain-time curve and refines the curve within 2 h, separates the primary and secondary consolidations, and obtains the critical time point between the primary and secondary consolidations. Deformation rate and cumulative deformation S t were introduced to analyze the  −  S t curve at the secondary consolidation stage; the secondary consolidation coefficient was employed to describe the secondary consolidation characteristics of compacted loess. According to the secondary consolidation characteristics, a prediction model of loess settlement considering different compaction energy and fill thickness was proposed, and the applicability of the model was further analyzed. The model will facilitate in guiding the design and construction of loess filling engineering.

In the geogenetic overburden excavation of underground space projects (such as comprehensive pipe corridors or subways), the foundation stress is in an unloading state. The effect(s) from the unloading on the coefficient of subsidence in the loess area should be considered. In this study, to explore the effect of unloading on the collapsibility of loess, the collapsible loess in the Guanzhong area was considered as the research object. An expression for the unloading collapse coefficient was established based on the unloading stress ratio, unloading collapse ratio, and other parameters. The influence of the unloading on the loess collapse coefficient was studied using an indoor collapsibility test, and the function form and parameters for the expression were determined. As combined with the field test, the accuracy of the expression for the unloading coefficient was verified based on the test value for the specific collapsibility, calculated value for the specific collapsibility, and calculated value for the unloading collapsibility.

为研究含水状态对脆延转化特性的影响,针对工程性质特殊的胡麻岭隧道红层软岩展开了系列试验,探究了干燥与天然含水状态试样脆延性区的强度变形规律.首先对干湿组红层软岩分别进行不同围压下的常规三轴压缩试验,进一步引入脆性指标对岩样脆性程度进行定量表征,并基于Mohr-Coulomb强度准则以及考虑结构强度的初始屈服面模型对各特征应力进行了分析.在此基础上通过试验,从宏细观尺度上探究了红层软岩脆延转化机理.研究表明:岩样干燥后,峰值强度增加了93.39％～145.35％,残余强度增加了77.83％～133.72％,脆延转化压力增加近40％,峰值应变降低了24.13％～88.92％;延性区的干湿试样的黏聚力近似为脆性区的1.8倍,但内摩擦角均小于脆性区,为脆性区的50.4％～90.5％;同时发现延性区试样在施加围压时已经进入了弹塑性变形阶段,且脆延转化压力等于等向固结压力.该研究内容可进一步丰富红层软岩的工程特性,并为穿越红层软岩地下工程的开挖支护提供理论依据.

为研究因工程场地高程差造成的折线型预制式管廊的地震稳定性问题,以西安纬一路段预制式地下管廊工程为例,使用ABAQUS软件对直线型和折线型管廊进行三维有限元动力计算,对比分析不同线型管廊在地震荷载作用下管廊结构的变形和加速度、拼接缝的变形、锚栓结构的受力及损伤特性的响应规律.研究发现:1)折线管廊在x轴(横向)、z轴(纵向)的最大水平位移分别在管廊埋深变化段靠近浅埋处和管廊埋深变化段靠近深埋处管廊底板附近,表明了管廊结构高程变化点为变形敏感点;2)折线管廊拼接缝在地震中和地震后的张拉变形很小,而横向和竖向滑移变形较大,其中横向水平滑移变形最大;3)折线段管廊的损伤值比直线段管廊混凝土管节的损伤值更大,且折线管廊损伤主要发生在倾斜段的管节,其中多以拉伸损伤为主.在实际设计工作中,应提高折线管廊区域的管廊强度.

为了分析城市地下综合管廊施工中锚栓和拼接缝受力变形规律,采用土体非线性弹性本构模型对土体的地层变形进行了表征,提出了一种装配式地下综合管廊施工过程的有限元数值模拟方法,实现了隐式计算方法中材料非线性及接触非线性问题的求解.结果表明:该分析方法避免了隐式计算方法中土体弹塑性本构模型及接触非线性问题导致的计算不收敛.反映了管廊施工过程中土体非线性力学行为以及管廊一土体之间的相互作用,为城市综合管廊建设提供了新的数值模拟方法.

结构性黄土的力学性能、工程特性与重塑土有显著区别,特别是在高应力作用下黄土的结构性对抗剪强度的发挥有显著影响.因此基于陕北某高填方工程黄土地基,对原状黄土与重塑黄土进行了室内高围压固结排水三轴试验.通过分析原状与重塑黄土的应力应变曲线和偏应力差值曲线,研究了结构性黄土的强度变化机理,结果表明黄土在低围压下结构性强度迅速发挥,并随着围压的增大、胶结物质持续破坏,内摩阻力发挥开始逐渐增强;基于结构性岩土材料破损机理的二元介质模型,通过引入抗剪贡献率ζv,修正并建立了高应力下结构性黄土的抗剪强度准则;并与试验结果进行对比,表明该强度准则能够一定程度上反映出结构性黄土在不同围压作用下粘聚分量与摩擦分量分步发挥的内在机理.

以秦巴山区某软岩公路隧道为工程背景,采用FLAC数值模拟和现场监测相结合的方法对该隧道合理施工方法进行了研究.建立3种不同施工方法下的计算模型,数值计算结果显示,相比于台阶法施工和单侧导坑法,采用留核心土法施工引起的隧道围岩变形较小,能够满足设计要求,从经济和施工工期角度来看,留核心土法是该地区软岩隧道最为合理的施工方法.为了验证数值计算结果的可行性,在隧道周围设置了变形监测点,实测结果表明,采用留核心土法施工后,隧道最大周边收敛14.81 mm,最大拱顶沉降值为27.11 mm,隧道变形在允许范围之内.隧道围岩变形的实测值与预测值变化趋势基本一致,表明FLAC数值模拟可在隧道施工前对隧道施工方法的合理性做出评价,具有超前指导意义.

Depended on the belt conveyer lane in Wenjiapo coal mine, the floor heave mechanics of large section soft rock roadway was researched using theoretical analysis and lab experiment. The type of floor heave was determined as hydro-expansiveness. The floor heave support scheme was proposed and the supporting parameters were given. With the FLAC3D numerical simulation, the feasibility of floor heave support program proposed was verified. The result of industrial test indicated that, the floor heave value was 22?4mm, which significantly reduced after floor heave treatment. The floor deformation was controlled effectively, meeting the deformation requirements of mine block.