A refined deviatoric hardening plastic model for sand

The classical deviatoric hardening models are capable of characterizing the mechanical response of granular materials for a broad range of degrees of compaction.This work finds that it has limitations in accurately predicting the volumetric deformation characteristics under a wide range of confining/consolidation pressures.The issue stems from the pressure independent hardening law in the classical deviatoric hardening model.To overcome this problem,we propose a refined deviatoric hardening model in which a pressure-dependent hardening law is developed based on experimental observations.Comparisons between numerical results and laboratory triaxial tests indicate that the improved model succeeds in capturing the volumetric deformation behavior under various confining/consolidation pressure conditions for both dense and loose sands.Furthermore,to examine the importance of the improved deviatoric hardening model,it is combined with the bounding surface plasticity theory to investigate the mechanical response of loose sand under complex cyclic loadings and different initial consolidation pressures.It is proved that the proposed pressure-dependent deviatoric hardening law is capable of predicting the volumetric deformation characteristics to a satisfactory degree and plays an important role in the simulation of complex deformations for granular geomaterials.

J^＊ INTEGRAL OF THE SPECIFIC DEVIATOR STRAIN ENERGY AND ITS APPLICATION

First the deviator strain energy is introduced, then the problem of plane-crack critical growth was discussed, a path independent line integral J* was defined, furthermore its conservation was proved strictly. As application examples, Mode-I stress intensity factors of cracked beams were obtained with present approach. The results are shown to agree well with those available in the open literature.

纤维加筋膨胀土的蠕变规律及模型预测

膨胀土是具有流变性质的灾害性土,其蠕变行为直接影响到工程结构的稳定性和安全性。为探究剑麻纤维加筋膨胀土的蠕变特性及应力-应变数学模型,采用室内固结排水三轴蠕变试验,分别进行了不同含水率、不同围压和不同偏应力条件下素膨胀土和剑麻纤维加筋膨胀土的蠕变特性研究,根据蠕变特征曲线提出了基于Mesri蠕变经验模型的剑麻纤维加筋膨胀土的修正蠕变模型。结果表明:相同条件下,剑麻纤维加筋土的蠕变变形量明显小于素土的蠕变变形量,说明掺入剑麻纤维可有效提高膨胀土的结构性能和抗变形能力;素土和剑麻纤维加筋土的蠕变变形量随含水率增大而增大,而随围压的增大呈减小趋势;素土和剑麻纤维加筋土在受到偏应力时均会产生瞬时应变量和蠕变变形量,其蠕变变形量随偏应力的增大而增大;素土和加筋土的蠕变曲线分4个阶段,分别为弹性变形阶段、稳态蠕变阶段、衰减蠕变阶段和加速蠕变阶段;高偏应力下,基于传统Mesri蠕变经验模型的剑麻纤维加筋土蠕变预测误差高达37.95%,对Mesri蠕变经验模型进行修正后预测误差降至1.5%内,说明修正模型能较好地描述剑麻纤维加筋土的蠕变特性。此研究结果可为膨胀土工程提供理论参考。

Retrospective and prospective review of the generalized nonlinear strength theory for geomaterials

Strength theory is the basic theory for calculating and designing the strength of engineering materials in civil,hydraulic,mechanical,aerospace,military,and other engineering disciplines.Therefore,the comprehensive study of the generalized nonlinear strength theory(GNST)of geomaterials has significance for the construction of engineering rock strength.This paper reviews the GNST of geomaterials to demonstrate the research status of nonlinear strength characteristics of geomaterials under complex stress paths.First,it systematically summarizes the research progress of GNST(classical and empirical criteria).Then,the latest research the authors conducted over the past five years on the GNST is introduced,and a generalized three-dimensional(3D)nonlinear Hoek‒Brown(HB)criterion(NGHB criterion)is proposed for practical applications.This criterion can be degenerated into the existing three modified HB criteria and has a better prediction performance.The strength prediction errors for six rocks and two in-situ rock masses are 2.0724%-3.5091%and 1.0144%-3.2321%,respectively.Finally,the development and outlook of the GNST are expounded,and a new topic about the building strength index of rock mass and determining the strength of in-situ engineering rock mass is proposed.The summarization of the GNST provides theoretical traceability and optimization for constructing in-situ engineering rock mass strength.

深部孤岛充填工作面沿空掘巷围岩偏应力演化与控制

目的 为解决深部孤岛充填工作面沿空掘巷围岩控制问题,方法 以邢东矿12216运料巷为背景,采用FLAC3D数值模拟软件,研究孤岛面临侧采空区在不同充填率条件下沿空掘巷围岩偏应力分布规律,模拟分析孤岛工作面充填开采时,工作面超前段围岩受动压影响时的偏应力演化特征。结果 结果表明:(1)孤岛工作面沿空掘巷巷道煤柱帮受临侧采空区充填效应影响较大,临侧采空区充填率增加使煤柱上偏应力峰值区呈椭圆形并逐步向采空区侧转移;(2)孤岛充填工作面沿空掘巷顶底板偏应力场形成一个朝向采空区侧的弧形低值带;(3)孤岛充填动压扰动时期,最大偏应力区位于实体煤一侧,距工作面前方8 m左右,距巷道4.3 m左右,峰值可达34 MPa。结论 结合数值模拟分析结果,提出采用“高强度锚杆+大直径高延伸率锚索”协同支护方式,现场工程实践表明,该支护方式沿空巷道围岩控制效果良好。

钙质砂三轴排水试验围压与剪切速率对应力特性影响研究

以海南省三沙市西沙群岛钙质砂为研究对象开展不同剪切速率的三轴固结排水试验,研究钙质砂剪切应力特性。试验结果表明:围压越大偏应力峰值出现的越晚,相同围压剪切速率越快应力峰值越大,应力下降也越快应力下降比越大,剪切速率对应力的峰值大小及残余剪切强度有一定影响,低围压下剪切速率对偏应力峰值影响更大。围压越小偏应力比越大,相同围压剪切速率越大偏应力比增长越快,当剪切速率低于一定速度时,偏应力比的变化并不受剪切速度的影响。相同围压条件下,由于排水剪切时围压和孔压保持不变,偏应力和平均有效应力关系为斜率3的直线,不同剪切速率破坏线趋势相同,剪切速率越大破坏线角度越大,但相差不大,破坏线为接近斜率1.75的直线,钙质砂内摩擦角为42°。剪切过程平均有效应力先增大后减小,剪切过程表现出剪缩到剪胀的变化过程,剪缩阶段不同剪切速率下孔隙比下降速率相近,剪切速率在剪胀阶段对孔隙比影响较大,剪切速率越大,孔隙比变化越大。

中间主应力系数对页岩气渗流特性及气体滑脱效应的影响

页岩气的渗流特性极大地影响着采收率,但对页岩气渗流特性的研究大多是在不同围压条件下开展的,其结果尚不能揭示中间主应力对渗透率的影响。因此,选用涪陵页岩气区块志留系龙马溪组页岩露头立方体岩石试件,采用自主研发的“多功能真三轴流固耦合试验系统”开展了页岩真三轴流固耦合试验,利用Klinkenberg方程拟合试验数据分析不同中间主应力系数对页岩气渗流特性和气体滑脱效应的影响。试验结果表明:①当偏应力较小时,中间主应力对页岩渗透率演化的影响较小,而当偏应力增加时,其影响越大且越不可忽略;②滑脱系数—固有渗透率的关系式与试验数据的拟合结果显示二者具有良好的相关性,可用于对同区块页岩滑脱系数的预测;③当偏应力小于或等于35 MPa时,滑脱效应贡献率保持在65%以上,表明此时滑脱效应主导着页岩中气体的渗流。

Path Planning and Tracking Control for Parking via Soft Actor-Critic Under Non-Ideal Scenarios

Parking in a small parking lot within limited space poses a difficult task. It often leads to deviations between the final parking posture and the target posture. These deviations can lead to partial occupancy of adjacent parking lots, which poses a safety threat to vehicles parked in these parking lots. However, previous studies have not addressed this issue. In this paper, we aim to evaluate the impact of parking deviation of existing vehicles next to the target parking lot(PDEVNTPL) on the automatic ego vehicle(AEV) parking, in terms of safety, comfort, accuracy, and efficiency of parking. A segmented parking training framework(SPTF) based on soft actor-critic(SAC) is proposed to improve parking performance. In the proposed method, the SAC algorithm incorporates strategy entropy into the objective function, to enable the AEV to learn parking strategies based on a more comprehensive understanding of the environment. Additionally, the SPTF simplifies complex parking tasks to maintain the high performance of deep reinforcement learning(DRL). The experimental results reveal that the PDEVNTPL has a detrimental influence on the AEV parking in terms of safety, accuracy, and comfort, leading to reductions of more than 27%, 54%, and 26%respectively. However, the SAC-based SPTF effectively mitigates this impact, resulting in a considerable increase in the parking success rate from 71% to 93%. Furthermore, the heading angle deviation is significantly reduced from 2.25 degrees to 0.43degrees.

不同应力养护条件对水泥土力学性能影响试验研究

为更好地了解水泥土在养护时期所受应力大小对其后期力学性能的影响,研发恒温等压或偏压条件下水泥土试样的养护装置和相应的试验方法。基于改制的恒温恒压水泥土试样养护装置,制作等压和偏压养护条件下不同龄期的水泥土试样。通过无侧限压缩试验(UCT),获得等压和偏压养护条件下水泥土试样的应力-应变曲线及其无侧限抗压强度(UCS)和变形模量E_(50)随龄期的演化规律。试验结果表明:等压养护时围压σ_(c)从0.1 MPa增加到0.3 MPa,水泥土试样在龄期为7 d和14 d时的无侧限抗压强度和变形模量E_(50)均随着围压的增加而增大,但28 d龄期水泥土样的UCS和E_(50)随围压σ_(c)的增长而减小,甚至0.3 MPa围压养护试样的UCS已低于无围压养护试样的UCS,水泥土存在“高围压养护长期强度降低效应”;不同轴压比λ下偏压养护的水泥土样,其60 d龄期的UCS在偏压较小(即λ<λ_(c),λ_(c)为临界轴压比)时逐渐增加,而在偏压较大(即λ>λ_(c))时逐渐下降,即水泥土又存在“小偏压养护强度增加,大偏压养护强度降低的效应”。通过对试验结果进行回归分析,分别建立等压养护下计入围压参数σ_(c)的水泥土UCS和E_(50)的演化方程、偏压养护下水泥土UCS和E_(50)与轴压比λ的经验关系式。研究成果对于深刻理解环境条件对水泥土力学性能的影响机制和指导工程实践,具有较好的理论和工程实际意义。

反压诱导有效应力增生模式与土体强度关联机制研究

反压施加是提高土体饱和度的常用有效方法,但易引起土体强度参数表观偏离。采用标准球形玻璃珠砂,开展基准固结不排水(consolidated undrain,CU),固结排水(consolidated drained,CD)及干样试验,对偏应力与孔压(或体积应变)数据进行实时精准测记与对比分析,借助p′-q应力路径图,显著呈现并定量分析了反压施加对土体力学特性的影响规律,初步厘清了反压施加对土体强度的影响机制。反压设置对CU试验结果影响显著,孔压发展形态控制着偏应力发展的形态,最终影响强度参数的确定,但应力路径始终约束在修正类剑桥模型的框架范围内。孔压发展模式和速率主要受限于反压设置大小及试样相对密实度,反压越大,孔压潜在变化幅度越大,进而导致偏应力变化区间增大;相对密实度越大,孔压发展速率越大,偏应力增速渐大。初始状态相同时,CU试验孔压发展与CD试验体积应变发展趋势高度一致,展示了试样体积应变势在不同边界条件下的共同本质。初步给出了临界状态时CU残余强度定量预测公式,根据相对密实度及反压值可初步定量评定残余孔压值,进而可确定CU残余强度。

Spatiotemporal characteristics of cultivated land use eco-efficiency and its influencing factors in China from 2000 to 2020

Improving cultivated land use eco-efficiency(CLUE)can effectively promote agricultural sustainability,particularly in developing countries where CLUE is generally low.This study used provincial-level data from China to evaluate the spatiotemporal evolution of CLUE from 2000 to 2020 and identified the influencing factors of CLUE by using a panel Tobit model.In addition,given the undesirable outputs of agricultural production,we incorporated carbon emissions and nonpoint source pollution into the global benchmark-undesirable output-super efficiency-slacks-based measure(GB-US-SBM)model,which combines global benchmark technology,undesirable output,super efficiency,and slacks-based measure.The results indicated that there was an upward trend in CLUE in China from 2000 to 2020,with an increase rate of 2.62%.The temporal evolution of CLUE in China could be classified into three distinct stages:a period of fluctuating decrease(2000-2007),a phase of gradual increase(2008-2014),and a period of rapid growth(2015-2020).The major grain-producing areas(MPAs)had a lower CLUE than their counterparts,namely,non-major grain-production areas(non-MPAs).The spatial agglomeration effect followed a northeast-southwest strip distribution;and the movement path of barycentre revealed a"P"shape,with Luoyang City,Henan Province,as the centre.In terms of influencing factors of CLUE,investment in science and technology played the most vital role in improving CLUE,while irrigation index had the most negative effect.It should be noted that these two influencing factors had different impacts on MPAs and non-MPAs.Therefore,relevant departments should formulate policies to enhance the level of science and technology,improve irrigation condition,and promote sustainable utilization of cultivated land.

高偏应力煤巷围岩拉剪破裂特征及分区控制方法研究

为获得高偏应力巷道围岩拉剪破裂特征并提出优化支护方案,以山西某矿孤岛工作面为背景,采用理论分析、数值模拟、相似模拟相结合的研究手段,分析了高偏应力条件下巷道围岩拉剪破裂分布特征及演化规律,揭示了托顶煤巷道围岩拉剪破裂机制,提出了高偏应力条件下巷道围岩沿掘进方向的全长分区控制方法。研究结果表明:(1)当侧压系数λ为0.60时,巷道围岩两帮呈“楔形”破坏,顶底出现明显卸荷并在巷道围岩四角点处产生应力集中;侧压系数λ逐渐减小至0.24的过程中,巷道围岩以两帮破坏为基础,在剪切应力作用下“蝶叶”逐渐发育,并最终形成蝶形破裂。(2)开挖破坏区围岩的浅部存在拉剪混合破裂区域,以张拉破裂为主;围岩深部为剪切破裂。围岩破裂演化过程可划分为3个阶段,分别为环自由面的自身破坏阶段、“蝶叶”孕育扩展阶段和“蝶叶”扩展稳定阶段。(3)定义了基于巷道全长分区的应力阈值,提出了掘进巷道全长分区支护方法,可为后续采煤工作面巷道的差异化支护提供理论参考。

复杂应力场中圆形隧洞偏应力场分布规律

为了厘清深部圆形中导洞(设置于双向隧洞中间)围岩偏应力分布问题,结合岩石力学与摩尔-库仑屈服准则,推导平面三向应力场中圆形隧洞围岩主偏应力与塑性区半径解析解,研究不同工况下圆形隧洞围岩主偏应力的分布规律及塑性区边界处主偏应力的几何形态分布特征。结果表明:当隧洞所处的斜向应力场为竖向应力场0.5~1.0倍时,随着斜向应力场水平方位角α_(1)=α_(2)增加,径向1.0倍隧洞半径范围内顶底主偏应力在快速降低,腰部主偏应力在快速增加,径向1.0倍隧洞半径范围外隧洞围岩主偏应力先小幅下降后又逐渐增大,最终在围岩深部趋于某定值;隧洞围岩主偏应力对其塑性区形态分布影响显著,当斜向应力场水平方位角α_(1)=α_(2)为30°时,围岩塑性区形态分布较优,为圆形或椭圆形。

常偏应力路径下花岗岩风化土的力学特性

为了探究不同围压下花岗岩风化土力学特性性能,选取广西玉林市容县花岗岩风化土作为研究对象,通过对饱和重塑花岗岩风化土进行常偏应力排水剪切(CSD)试验,研究了不同围压下风化土的力学行为过程和破坏机理,并对CSD试验后的试样进行了扫描电镜(SEM)试验,揭示了CSD试验下风化土失效的微观机理。结果表明:在孔压上升初期,试样的轴向应变增长缓慢,偏应力几乎不变;随着孔压的不断升高,平均有效应力下降至失稳点,轴向应变突然增加,偏应力迅速衰减,试样呈现出瞬变破坏的形式;在降雨入渗时,围压程度的变化对土体行为有显著影响,低围压下,试样局部水压力增大,导致鼓胀破坏。而高围压下,试样呈现伴随有软弱面的剪切破坏。

A Distortion Self-Calibration Method for Binocular High Dynamic Light Adjusting and Imaging System Based on Digital Micromirror Device

Dear Editor,In order to realize the pixel level light adjusting control of the binocular high dynamic light adjusting and imaging system, this letter proposed a novel self-calibration method. By analyzing the optical design of the system, the causes of the distortion are given and a distortion model is established. Then, a quick and accurate self-calibration method is designed. The experiments indicate that the method can calibrate the two image sensors of the system at the same time,the average pixel deviation of the calibrated system is less than 0.5pixels and the maximum deviation is less than 1 pixel.

Spatiotemporal patterns and drivers of cultivated land conversion in Inner Mongolia Autonomous Region,northern China

Protection and optimization of cultivated land resources are of great significance to national food security.Cultivated land conversion in northern China has increased in recent years due to the industrialization and urbanization of society.However,the assessment of cultivated land conversion in this area is insufficient,posing a potential risk to cultivated land resources.This study evaluated the evolution and spatiotemporal patterns of cultivated land conversion in Inner Mongolia Autonomous Region,China,and the driving factors to improve rational utilization and to protect cultivated land resources.The spatiotemporal patterns of cultivated land conversion in Inner Mongolia were analyzed using the cultivated land conversion index,kernel density analysis,a standard deviation ellipse model,and a geographic detector.Results showed that from 2000 to 2020,the trends in cultivated land conversion area and rate in Inner Mongolia exhibited fluctuating growth,with the total area of cultivated land conversion reaching 7307.59 km^(2) at a rate of 6.69%.Spatial distribution of cultivated land conversion was primarily concentrated in the Hetao Plain,Nengjiang Plain,Liaohe Plain,and the Hohhot-Baotou-Ordos urban agglomeration.Moreover,the standard deviational ellipse of cultivated land conversion in Inner Mongolia exhibited a directional southwest-northeast-southwest-northeast distribution,with the northeast-southwest direction identified as the main driving force of spatial change in cultivated land conversion.Meanwhile,cultivated land conversion exhibited an increase-decrease-increase change process,indicating that spatial distribution of cultivated land conversion in Inner Mongolia became gradually apparent within the study period.The geographic detector results further revealed that the main driving factors of cultivated land conversion in Inner Mongolia were the share of secondary and tertiary industries and per-unit area yield of grain,with explanatory rates of 57.00%,55.00%,and 51.00%,respectively.Additionally,improved agricultural production efficiency and the coordinated development of population urbanization and industry resulted in cultivated land conversion.Collectively,the findings of this study indicated that,from 2000 to 2020,the cultivated land conversion in Inner Mongolia was significant and fluctuated in time,and had strong spatial heterogeneity.The primary drivers of these events included the effects of agriculture,population,and social economy.

Computing large deviation prefactors of stochastic dynamical systems based on machine learning

We present a large deviation theory that characterizes the exponential estimate for rare events in stochastic dynamical systems in the limit of weak noise.We aim to consider a next-to-leading-order approximation for more accurate calculation of the mean exit time by computing large deviation prefactors with the aid of machine learning.More specifically,we design a neural network framework to compute quasipotential,most probable paths and prefactors based on the orthogonal decomposition of a vector field.We corroborate the higher effectiveness and accuracy of our algorithm with two toy models.Numerical experiments demonstrate its powerful functionality in exploring the internal mechanism of rare events triggered by weak random fluctuations.

Path Planning of Multi-Axis Robotic Arm Based on Improved RRT*

An improved RRT∗algorithm,referred to as the AGP-RRT∗algorithm,is proposed to address the problems of poor directionality,long generated paths,and slow convergence speed in multi-axis robotic arm path planning.First,an adaptive biased probabilistic sampling strategy is adopted to dynamically adjust the target deviation threshold and optimize the selection of random sampling points and the direction of generating new nodes in order to reduce the search space and improve the search efficiency.Second,a gravitationally adjustable step size strategy is used to guide the search process and dynamically adjust the step-size to accelerate the search speed of the algorithm.Finally,the planning path is processed by pruning,removing redundant points and path smoothing fitting using cubic B-spline curves to improve the flexibility of the robotic arm.Through the six-axis robotic arm path planning simulation experiments on the MATLAB platform,the results show that the AGP-RRT∗algorithm reduces 87.34%in terms of the average running time and 40.39%in terms of the average path cost;Meanwhile,under two sets of complex environments A and B,the average running time of the AGP-RRT∗algorithm is shortened by 94.56%vs.95.37%,and the average path cost is reduced by 55.28%vs.47.82%,which proves the effectiveness of the AGP-RRT∗algorithm in improving the efficiency of multi-axis robotic arm path planning.

巷道围岩偏应力分布规律及破坏机理探究

回采巷道围岩塑性区形态分布特征是巷道稳定控制的关键问题。以锦界煤矿31117工作面为工程背景,基于最大主偏应力以及巷道蝶形破坏理论,揭示了31117巷道出现大变形破坏的原因。研究结果表明,在不同应力场下,最大主偏应力存在圆形、椭圆形、X形3种破坏形态。同时,巷道围岩塑性区形态与最大主偏应力形态具有对应关系,以最大主偏应力为指标,可以在一定程度上揭示巷道围岩变形破坏机理。31117巷道在高偏应力作用下,导致巷道顶板两侧出现挤压破坏,基于偏应力分布形态,提出巷道关键控制技术。

近距离孤岛工作面沿空留巷偏应力分布规律及控制

为解决近距离条件下孤岛工作面复用沿空留巷围岩稳定性差、控制难的问题,以登茂通煤矿3107孤岛工作面复用沿空留巷为工程背景,通过数值模拟分析了复用沿空留巷围岩偏应力分布规律及其失稳破坏机制。结果表明:随着超前距离的减小,巷旁支护体、实体煤帮部应力高值区与2102采空区底板的贯通趋势增强,且偏应力峰值增大,破坏趋势增强。基于此提出了实体煤侧采用锚杆+注浆改性+锚索联合支护技术,巷旁支护采用单体支柱支护分区域控制技术。通过现场监测,最大两帮移近量分别为512.31、378.96 mm,锚杆、锚索支护构件结构稳定,有效保障了复用沿空留巷的围岩稳定性,可为类似条件下巷道控制提供借鉴。