Time-dependent behavior and permeability evolution of limestone under hydro-mechanical coupling

Excessively high pore water pressure presents unpredictable risks to the safety of rock tunnels in mountainous regions that are predominantly composed of limestone. Investigating the creep characteristics and permeability evolution of limestone under varying hydrated conditions is crucial for a better understanding of the delayed deformation mechanisms of limestone rock tunnels. To this end, this paper initially conducts a series of multi-stage triaxial creep tests on limestone samples under varying pore water pressures. The experiment examines how pore water pressure affects limestone’s creep strain, strain rate, long-term strength, lifespan, and permeability, all within the context of hydraulicmechanical(HM) coupling. To better describe the creep behavior associated with pore water pressure, this paper proposes a new nonlinear fractional creep constitutive model. This constitutive model depicts the initial, steady-state, and accelerated phases of limestone’s creep behavior. Finally, the proposed model is applied to the numerical realization of deformation in limestone tunnel, validating the effectiveness of the proposed constitutive model in predicting tunnel’s creep deformation. This research enhances our understanding of limestone’s creep characteristics and permeability evolution under HM coupling, laying a foundation for assessing the longterm stability of mountain tunnels.

Fully fluid-solid coupling dynamic model for seismic response of underground structures in saturated soils

The seismic response characteristics of underground structures in saturated soils are investigated.A fully fluid-solid coupling dynamic model is developed and implemented into ABAQUS with a user-defined element to simulate the dynamic behavior of saturated soils.The accuracy of the model is validated using a classic example in literature.The performance of the model is verified by its application on simulating the seismic response characteristics of a subway station built in saturated soils.The merits of the model are demonstrated by comparing the difference of the seismic response of an underground structure in saturated soils between using the fully coupling model and a single-phase medium model.The study finds that the fully coupling model developed herein can simulate the dynamic response characteristics of the underground structures in saturated soils with high accuracy.The seismic response of the underground structure tends to be underestimated by using the single-phase medium model compared with using the fully coupling model,which provides a weaker confining action to the underground structure.

FLUID-SOLID COUPLING MATHEMATICAL MODEL OF CONTAMINANT TRANSPORT IN UNSATURATED ZONE AND ITS ASYMPTOTICAL SOLUTION

The process of contaminant transport is a problem of multicomponent and multiphase flow in unsaturated zone. Under the presupposition that gas existence affects water transport, a coupled mathematical model of contaminant transport in unsaturated zone has been established based on fluid_solid interaction mechanics theory. The asymptotical solutions to the nonlinear coupling mathematical model were accomplished by the perturbation and integral transformation method. The distribution law of pore pressure, pore water velocity and contaminant concentration in unsaturated zone has been presented under the conditions of with coupling and without coupling gas phase. An example problem was used to provide a quantitative verification and validation of the model. The asymptotical solution was compared with Faust model solution. The comparison results show reasonable agreement between asymptotical solution and Faust solution, and the gas effect and media deformation has a large impact on the contaminant transport. The theoretical basis is provided for forecasting contaminant transport and the determination of the relationship among pressure_saturation_permeability in laboratory.

Thermal-hydro-mechanical coupling damage model of brittle rock

Based on fluid mechanics, thermodynamics and damage mechanics, thermal-hydro-mechanical(THM) coupling damage model of brittle rock is established by analyzing THM coupling mechanism, where THM coupling damage variable DTHM is dominated by TH coupling damage variable DTH, TM coupling damage variable DTM and HM coupling damage variable DHM, and DTH is firstly expressed in term of dimensionless total thermal conductivity of the water Nu. Permeability test, uni-axial compression test and THM coupling test are conducted to measure the permeability, elastic modulus and THM coupling stress-strain curves of brittle rock. The tested values of THM coupling elastic modulus THME? are in good agreement with the predicted values of THM coupling elastic modulus ETHM, which can verify the newly established THM coupling damage model.

Analytical evaluation of steady-state solute distribution in through- diffusion and membrane behavior test under non-perfectly flushing boundary conditions

The through-diffusion and membrane behavior testing procedure using a closed-system apparatus has been widely used for concurrent measurement of diffusion and membrane efficiency coefficients of low-permeability clay-based barrier materials.However,the common assumption of perfectly flushing conditions at the specimen boundaries could induce errors in analyses of the diffusion coefficients and membrane efficiencies.In this study,an innovative pseudo three-dimensional(3D)analytical method was proposed to evaluate solute distribution along the boundary surfaces of the soil-porous disks system,considering the non-perfectly flushing conditions.The results were consistent with numerical models under two scenarios considering different inflow/outflow positions.The proposed model has been demonstrated to be an accurate and reliable method to estimate solute distributions along the bound-aries.The calculated membrane efficiency coefficient and diffusion coefficient based on the proposed analytical method are more accurate,resulting in up to 50%less relative error than the traditional approach that adopts the arithmetic mean value of the influent and effluent concentrations.The retar-dation factor of the clay specimen also can be calculated with a revised cumulative mass approach.Finally,the simulated transient solute transport matched with experimental data from a multi-stage through-diffusion and membrane behavior test,validating the accuracy of the proposed method.

Numerical Simulations and Model Tests of the Mooring Characteristic of A Tension Leg Platform Under Random Waves

Analyzing the dynamic response and calculating the tendon tension of the mooring system are necessary for the structural design of a tension leg platform （TLP）. The six-degree-of-freedom dynamic coupling responses and the mooring characteristics of TLP under random waves are studied by using a self-developed program. Results are verified by the 1：40 scaling factor model test conducted in the State Key Laboratory of Ocean Engineering at Shanghai JiaoTong University. The mean, range, and standard deviation of the numerical simulation and model test are compared. The influences of different sea states and wave approach angles on the dynamic response and tendon tension of the mooring system are investigated. The acceleration in the center and corner of the deck is forecasted.

Experimental Study on Scouring and Silting Deformation of Artificial Beach Under Storm Surge−Wave Coupling

With the increasing construction of artificial beach in coastal areas, it is of practical significance to study the beach surface deformation of artificial beach profile. Previous studies only focus on a single wave dynamic factor, and it is difficult to predict the beach deformation of artificial beach profile under the storm surge-wave co-action. To solve this problem, the cross-section physical model test method was used to study the beach surface deformation of a typical artificial beach profile in Shuangdao Bay, Weihai, Shandong Province, after continuous wave actions till they stabilize. The characteristics of beach surface deformation under the conditions of constant water levels, laddershaped water level combined with corresponding wave elements and storm surge-wave co-action are compared and analyzed. A beach profile model which satisfies the theory of Bruun model is proposed. The test results show that the maximum scour depth of beach under storm surge-wave co-action is smaller and the scour range is obviously larger than that under the condition of constant water levels or ladder-shaped water level. The evaluation of the maximum scour depth by traditional model test tends to be conservative while the evaluation of the scour range is insufficient.The research results can provide scientific reference for designing artificial beaches.

Experimental Study on Anchoring Physical Properties of Different Anchoring Lengths Coupled with Temperature and Pressure

Aiming at deep roadway anchorage solids, laboratory similar model tests were used to reveal the mechanical properties of anchorage solids with different anchorage lengths under the coupling effect of temperature and pressure, and SPSS statistical analysis software was used to conduct linear regression analysis of the ultimate anchorage force obtained from the tests. The results show that: through multiple linear regression analysis, the influence degree of temperature and pressure coupling on the ultimate anchorage force is arranged in order of anchoring length > surrounding rock strength > temperature > side pressure coefficient, and the linear regression equation of the model is obtained. Compared with the linear regression equation of simulation results, the model has a high explanatory ability.

工程尺度缓冲材料热-水-力多场耦合数值模拟研究

缓冲材料作为填充在废物罐与地质体之间重要的人工屏障,对高放废物处置库的长期安全至关重要。以工程尺度缓冲材料热-水-力多场耦合大型模型试验系统(China-Mock-up)为研究对象,采用有限元数值模拟软件LAGAMINE,考虑试验过程中复杂的边界条件与材料属性,实现了近5 a试验数据的定量模拟。模拟结果可准确预测试验系统内部不同特征点温度随室温周期性波动及线性增长这一动态变化规律;能够较好反映不同特征点相对湿度随时间的行为演化趋势,在加热器附近区域呈现出先干燥后饱和的现象,远离加热器区域则逐渐增大;模拟的总应力与实测试验数据间表现较好地一致性,能够反映试验台架内部不同特征点的总应力随时间逐渐增大这一演化过程。揭示了多场耦合条件下缓冲材料(膨润土)温度、湿度及应力的相互作用关系,为深入认识处置库环境下缓冲材料行为演化特征提供了重要的参考依据。

高地应力-化学侵蚀耦合作用下炭质板岩蠕变试验及非线性蠕变损伤模型

为克服高程障碍并降低施工风险,可采用长大隧道穿越崇山峻岭,但这些隧道往往处于深埋高地应力环境,并受到化学侵蚀影响。为了解决此问题,以丽江—香格里拉炭质板岩大变形隧道为研究对象,采用室内试验和理论推导,研究深埋炭质板岩隧道受化学侵蚀作用下的围岩变形特性。在Poyting-Thomson体蠕变体的基础上,根据模型元件的力学特性,叠加了损伤元件、化学损伤元件和非线性元件,提出高地应力-化学侵蚀耦合作用下炭质板岩非线性蠕变损伤本构关系。研究结果表明:1)炭质板岩试样受化学侵蚀影响显著,侵蚀90 d试样所产生的轴向蠕变应变为侵蚀0 d试样的2.02倍,侵蚀60 d试样所产生的径向蠕变为侵蚀0 d试样的1.85倍;2)受侵蚀的炭质板岩试样在三轴压缩状态下破裂以斜向贯通裂隙为主,并产生一定的滑移错动裂隙,且沿轴线的拉伸劈裂破坏受围压作用抑制明显,未产生竖向贯通裂隙。

隧道突涌水灾害缩尺物理模型试验研究综述

随着我国经济的快速发展,隧道工程建设越来越多地面临着大埋深、高地应力、高地温、高渗透压力等复杂地质环境,运用物理模型试验开展复杂环境下隧道突涌水灾变机理与安全防控研究已成为岩石力学的热点问题。结合近年来国内外针对隧道突涌水灾变缩尺物理模型试验开展的研究工作,重点对该类物理模型的流固耦合相似理论、相似材料研制、渗透压加载方法等内容进行了系统梳理,并对下一步的可能发展方向进行展望。参考部分文献和突水典型案例后,总结了流固耦合相似准则和高地应力下的相似准则、相似材料选用方案及材料配比、试验中的水压加载方案,认为未来关注的重点包括考虑温度场的物理模型试验相似准则的研究和涌水涌泥与突水突泥间渐变过程的研究2个方面。

细长桁架臂卸载反弹动应力分布规律及试验

为研究细长桁架臂在卸载冲击下的动态响应变化规律,提出了基于等效梁振型函数的桁架臂动应力分布计算模型。根据等效梁振型函数,探讨了卸载后桁架臂动应力分布假设,分析了影响桁架臂卸载反弹动响应的相关参数。以装备细长桁架臂的动臂塔机为对象,建立了桁架臂精细化有限元模型和起重机刚柔耦合模型,通过仿真辨识了应力分布模型的关键参数。实施了动臂塔机系列载荷卸载冲击试验,桁架臂上主弦杆的动应力试验值与理论计算结果误差小于7%,表明动应力分布理论模型与实际相符。通过理论模型预测了极限工况下桁架臂上主弦杆动应力分布状态,发现在最大载荷卸载条件下起重臂动应力峰值超过结构承载极限,为卸载条件下起重机关键结构的优化设计提供依据。

舰艇水下爆炸破损分布特性

舰艇在作战过程中受到武器攻击,从爆炸产生的破口持续多向进水,影响舰艇的不沉性。为了探究水下爆炸破损分布特性,开展了驳船近场水下爆炸试验,利用声固耦合法计算了冲击波与气泡射流载荷联合作用下全船结构的毁伤,得到整船塑性变形区域的凹陷深度为85 cm,L形破口宽30 cm,破口面积为0.2 m2。对比了试验和仿真数据,计算破口尺寸的相对误差小于20%,破口位置吻合较好,验证了模型的准确性。利用该模型进行了不同爆距下爆炸仿真计算,提出了驳船在近场水下爆炸载荷作用下的分布式损伤模式,明确了舰船结构的毁伤除整体折断和局部大型破口外还有广泛分布的小裂缝存在于舱壁、舷侧外板等部位。随着冲击因子从5.74减小至1.91,舱底破口尺寸减小,舱内裂缝增多;当冲击因子在1.91~2.87之间时,舱底破损为分散式的小型破口。舷侧、舱壁与舱底的连接处为薄弱部位,小裂缝分布较多,在舰艇设计过程中可重点加强防护。

Numerical modeling and experimental investigation of a two-phase sink vortex and its fluid-solid vibration characteristics

A sink vortex is a common physical phenomenon in continuous casting,chemical extraction,water conservancy,and other industrial processes,and often causes damage and loss in production.Therefore,the real-time monitoring of the sink vortex state is important for improving industrial production efficiency.However,its suction-extraction phenomenon and shock vibration characteristics in the course of its formation are complex mechanical dynamic factors for flow field state monitoring.To address this issue,we set up a multi-physics model using the level set method(LSM)for a free sink vortex to study the two-phase interaction mechanism.Then,a fluid–solid coupling dynamic model was deduced to investigate the shock vibration characteristics and reveal the transition mechanism of the critical flow state.The numerical results show that the coupling energy shock induces a pressure oscillation phenomenon,which appears to be a transient enhancement of vibration at the vortex penetration state.The central part of the transient enhancement signal is a high-frequency signal.Based on the dynamic coupling model,an experimental observation platform was established to verify the accuracy of the numerical results.The water-model experiment results were accordant with the numerical results.The above results provide a reference for fluid state recognition and active vortex control for industrial monitoring systems,such as those in aerospace pipe transport,hydropower generation,and microfluidic devices.

轴扭耦合冲击器结构设计与室内试验

为提高PDC钻头切削齿在硬地层中的吃入深度、消除扭转振动带来的危害,在自激换向式扭冲总成结构的基础上,增设水力脉冲式轴冲总成,利用扭冲总成拨叉带动轴冲总成动盘阀同步旋转,使过流面积发生周期性变化,产生水力脉冲轴冲载荷,与扭冲载荷一起形成轴扭耦合冲击,设计出一种结构简单、冲击频率相同的新型轴扭耦合冲击器。同时,基于能量转换与守恒定律,建立了冲击器性能参数数学模型,并开展了轴扭耦合冲击器性能参数室内试验。试验结果表明,该轴扭耦合冲击器的压降、轴冲载荷与流量平方呈正比,扭冲载荷、冲击频率与流量呈线性增大关系,最大相对误差仅7.91%,验证了该数学模型的准确性。研究结果可为同类冲击钻井工具的开发提供理论指导。

泥水盾构排浆系统输送大粒径卵石管道的压力损失

泥水盾构在砂卵石地层掘进时,排浆管道将输送大量大粒径卵石,导致浆体产生不稳定湍流,这给管道压力损失的确定带来了挑战。该研究设计了环流试验装置,以CMC透明黏性浆液为实验用泥浆,建立了基于计算流体动力学与离散单元法(CFDDEM)耦合的三维数值模型;以粒径为5~80 mm的卵石为对象,分析了卵石粒径级配、浆液流速、卵石体积分数以及管道倾角对管道沿程压力损失的影响规律。研究结果表明:同一卵石粒径级配、卵石体积分数与管道倾角下,管道沿程压力损失随浆液流速的增加大致呈指数函数规律增加;对于水平管道,不同卵石粒径级配下的管道沿程压力损失差别较小;在低浆液流速(v <2 m/s)下,管道沿程压力损失随卵石体积分数的增大呈线性规律增加,在较高浆液流速(v≥2.0 m/s)下,管道沿程压力损失随卵石体积分数的增大呈指数函数形式增加;对于倾斜及竖直管道,同一卵石粒径级配、卵石体积分数与浆液流速下,管道沿程压力损失随着管道倾斜角度的增大首先表现为缓慢增加,然后呈急剧增加,其转折点的管道倾角为60°。此外,在泥浆浮力以及湍流的作用下,大粒径的卵石难以克服自身重力达到完全悬浮的运动状态,因此,大粒径卵石主要沿管道下壁面运动,且在管道弯头处压力存在明显的分层现象。

船用膜片联轴器的膜片组件简化建模方法及模态试验

针对船用膜片联轴器的膜片组件螺栓连接的复杂性问题,基于薄层单元法对膜片组件的有限元模型进行简化,提出一种新型简化建模方法——结构分割法。对模型静刚度进行计算,确定结构分割法中结合面单元的弹性模量和泊松比。该方法相较于传统的薄层单元法计算效率更高。将结构分割法模型的模态仿真结果与试验结果进行对比,结果表明,结构分割法模态分析得到的振型与试验测得的前三阶振型吻合较好,固有频率误差均在10%之内,验证简化模型仿真的正确性,可为船用膜片组件结合部动力学快速有效建模提供思路。

强夯置换对软土基坑边坡开挖稳定性的影响研究

强夯置换作为一种地基处理方法,主要用于提高地基承载力,减小沉降,而将其作为基坑支护的相关研究却鲜有报道。通过一系列室内模型试验探讨了不同强夯置换率、基坑边坡坡率条件下,强夯置换后软土基坑在开挖过程中的变形位移规律。通过构建墩土合并计算、墩土分开计算、墩土耦合3种有限元数值模型,对室内模型试验结果进行了对比验证。结果表明:水平位移向四周呈辐射式递减,室内模型试验与数值模拟的水平位移变化趋势一致且吻合度较高;坡体稳定系数随置换率的增加而不断上升;在墩与土之间加入界面单元提高了墩土之间的相互作用,可以有效提高数值模拟的准确性。

山东省高速公路与区域经济融合协调评价与发展策略研究

在揭示高速公路与区域经济融合协调发展必要性的基础上,以山东省16个地级市高速公路与区域经济相关数据为基础,采用耦合协调度模型和皮尔逊检验对山东省高速公路与区域经济融合发展的区域差异特征和相互作用的时间变化特征进行了评价,进而从不同角度对推动高速公路与区域经济融合协调发展、强化高速公路对区域经济发展的促进作用提出了具有现实可行性的策略建议。研究结果表明,山东省区域经济和高速公路发展处于强耦合、强作用阶段,而高速公路里程对国内生产总值增长的作用程度及其显著性整体呈现一定弱化趋势,山东省仍需提高高速公路与区域经济融合协调,强化高速公路对区域经济的促进作用。