Analytical model for predicting time-dependent lateral deformation of geosynthetics-reinforced soil walls with modular block facing

To date,few models are available in the literature to consider the creep behavior of geosynthetics when predicting the lateral deformation(d)of geosynthetics-reinforced soil(GRS)retaining walls.In this study,a general hyperbolic creep model was first introduced to describe the long-term deformation of geosynthetics,which is a function of elapsed time and two empirical parameters a and b.The conventional creep tests with three different tensile loads(Pr)were conducted on two uniaxial geogrids to determine their creep behavior,as well as the a-Pr and b-Pr relationships.The test results show that increasing Pr accelerates the development of creep deformation for both geogrids.Meanwhile,a and b respectively show exponential and negatively linear relationships with Pr,which were confirmed by abundant experimental data available in other studies.Based on the above creep model and relationships,an accurate and reliable analytical model was then proposed for predicting the time-dependent d of GRS walls with modular block facing,which was further validated using a relevant numerical investigation from the previous literature.Performance evaluation and comparison of the proposed model with six available prediction models were performed.Then a parametric study was carried out to evaluate the effects of wall height,vertical spacing of geogrids,unit weight and internal friction angle of backfills,and factor of safety against pullout on d at the end of construction and 5 years afterwards.The findings show that the creep effect not only promotes d but also raises the elevation of the maximum d along the wall height.Finally,the limitations and application prospects of the proposed model were discussed and analyzed.

Physical model test and application of 3D printing rock-like specimens to laminated rock tunnels

Weak structural plane deformation is responsible for the non-uniform large deformation disasters in layered rock tunnels,resulting in steel arch distortion and secondary lining cracking.In this study,a servo biaxial testing system was employed to conduct physical modeling tests on layered rock tunnels with bedding planes of varying dip angles.The influence of structural anisotropy in layered rocks on the micro displacement and strain field of surrounding rocks was analyzed using digital image correlation(DIC)technology.The spatiotemporal evolution of non-uniform deformation of surrounding rocks was investigated,and numerical simulation was performed to verify the experimental results.The findings indicate that the displacement and strain field of the surrounding layered rocks are all maximized at the horizontal bedding planes and decrease linearly with the increasing dip angle.The failure of the layered surrounding rock with different dip angles occurs and extends along the bedding planes.Compressive strain failure occurs after excavation under high horizontal stress.This study provides significant theoretical support for the analysis,prediction,and control of non-uniform deformation of tunnel surrounding rocks.

The quaternion beam model for hard-magnetic flexible cantilevers

The recently developed hard-magnetic soft(HMS)materials manufactured by embedding high-coercivity micro-particles into soft matrices have received considerable attention from researchers in diverse fields,e.g.,soft robotics,flexible electronics,and biomedicine.Theoretical investigations on large deformations of HMS structures are significant foundations of their applications.This work is devoted to developing a powerful theoretical tool for modeling and computing the complicated nonplanar deformations of flexible beams.A so-called quaternion beam model is proposed to break the singularity limitation of the existing geometrically exact(GE)beam model.The singularity-free governing equations for the three-dimensional(3D)large deformations of an HMS beam are first derived,and then solved with the Galerkin discretization method and the trustregion-dogleg iterative algorithm.The correctness of this new model and the utilized algorithms is verified by comparing the present results with the previous ones.The superiority of a quaternion beam model in calculating the complicated large deformations of a flexible beam is shown through several benchmark examples.It is found that the purpose of the HMS beam deformation is to eliminate the direction deviation between the residual magnetization and the applied magnetic field.The proposed new model and the revealed mechanism are supposed to be useful for guiding the engineering applications of flexible structures.

Calculation of Intervertebral Disc Pressure in the Thoracic and Lumbar Spine in Elderly Women with Kyphosis Using a Novel Musculoskeletal Model with Isolated Thoracic Vertebrae and Rib Cage

Background: Degeneration of the intervertebral disc is one of the causes of kyphosis. Several biomechanical studies have investigated the mechanisms of development of spinal deformity using simulation models. Realistic musculoskeletal models are helpful for investigating the pathophysiology and changes in internal forces in patients with kyphosis. However, the association between intervertebral disc pressure and kyphosis has not been fully elucidated to date. Purpose: To calculate intervertebral disc pressure in elderly women with kyphosis using a novel and precise thoracolumbar three-dimensional musculoskeletal model. Materials and Method: Ten female patients with a mean age of 80.0 ± 6.5 years who visited our hospital for medical examination of osteoporosis were included. The subjects were divided into the normal and kyphosis groups depending on their sagittal vertical axis. Intervertebral disc pressures in the thoracic and lumbar spines of subjects were analyzed by inverse dynamics analysis using a novel three-dimensional musculoskeletal model, and were compared between the groups. Result: Significant differences in lumbar lordosis (LL) were observed between the two groups. Furthermore, the kyphosis group was older and shorter. In the kyphosis group, the upper thoracic vertebrae (T1 - T6) showed significantly higher intervertebral pressure than the normal group. Conclusion: Intervertebral disc pressure in the thoracic and lumbar spines of patients with spinal deformities was evaluated using a novel thoracolumbar three-dimensional musculoskeletal model. Using this novel model with separated thoracic spine and modified muscle path reflecting actual physiological curvature, disc pressure closer to the realistic condition was obtained. Intervertebral disc pressure in the upper thoracic spine in the kyphosis group was significantly increased compared with that in the normal group. Moreover, intervertebral disc pressures in the upper thoracic spine correlated negatively with LL.

Dynamic skin deformation simulation using musculoskeletal model and soft tissue dynamics

Deformation of skin and muscle is essential for bringing an animated character to life. This deformation is difficult to animate in a realistic fashion using traditional techniques because of the subtlety of the skin deformations that must move appropriately for the character design. In this paper, we present an algorithm that generates natural, dynamic, and detailed skin deformation(movement and jiggle) from joint angle data sequences. The algorithm has two steps: identification of parameters for a quasi-static muscle deformation model, and simulation of skin deformation. In the identification step, we identify the model parameters using a musculoskeletal model and a short sequence of skin deformation data captured via a dense marker set. The simulation step first uses the quasi-static muscle deformation model to obtain the quasi-static muscle shape at each frame of the given motion sequence(slow jump). Dynamic skin deformation is then computed by simulating the passive muscle and soft tissue dynamics modeled as a mass–spring–damper system. Having obtained the model parameters, we can simulate dynamic skin deformations for subjects with similar body types from new motion data. We demonstrate our method by creating skin deformations for muscle co-contraction and external impacts from four different behaviors captured as skeletal motion capture data. Experimental results show that the simulated skin deformations are quantitatively and qualitatively similar to measured actual skin deformations.

竖向土工加筋体对碎石桩承载变形影响的模型试验研究

在碎石桩桩顶一定深度内包裹竖向土工加筋体形成筋箍碎石桩,能有效提高碎石桩的承载能力,控制复合地基沉降量。采用分级加载方式,设计并完成了两组较大比例室内模型试验,对比分析了筋箍碎石桩和传统碎石桩的承载变形特性,进而探讨了筋箍碎石桩的加筋机理和鼓胀变形模式,重点分析了竖向土工加筋体的应力应变特征。分析结果表明:竖向土工加筋体能有效约束碎石桩的侧向鼓胀,在微小侧向变形内提供足够的径向约束应力;筋箍碎石桩的最大鼓胀变形多发生于加筋体以下区域,其破坏模式与筋体材料、桩体、桩周土体及其相互作用和协调变形密切相关;筋箍碎石桩的桩顶和桩底桩土应力比均明显大于传统碎石桩,上部土工加筋体在提高桩体刚度的同时,可有效地将上部荷载传递至桩底较好土层。

套筒长度对加筋碎石桩复合地基路堤变形和稳定性的影响

采用离心模型试验研究套筒长度对加筋碎石桩复合地基路堤变形和稳定性的影响。研究结果表明:(不加筋)碎石桩复合地基路堤下的桩体主要发生鼓胀变形,导致路堤整体产生显著沉降,但未出现剪切滑移趋势;半长加筋碎石桩复合地基路堤边坡及靠近坡肩下的桩体由于抗弯刚度不足,其在路堤荷载下产生弯曲变形及倾倒,同时位于路堤中心、主要承受竖向荷载的桩体则在加筋套筒底部未加筋部位产生明显的鼓胀变形,从而导致路堤产生很大的沉降,其桩顶和桩间土沉降量是碎石桩复合地基路堤的1.7倍左右;全长加筋碎石桩复合地基路堤边坡下桩体在路堤荷载下向外弯曲,由于其抗弯和抗压刚度较大,路堤沉降较小。在实际应用中,应对桩体采用全长加筋方式,以减小加筋碎石桩复合地基路堤的沉降,提高稳定性。

土工袋装砂桩复合地基室内模型静载试验

为了研究袋装桩型复合地基的受力变形特性,对袋装砂桩和传统砂桩处理的软土复合地基进行了分级静力加载室内模型试验.分析了各级试验荷载下的沉降、桩土应力比以及袋体张力分布等变化规律.试验结果表明:袋装砂桩的性能明显优于传统砂桩的性能.将试验结果与现有的弹性理论和弹塑性理论分析结果进行对比.通过相互间的沉降和桩土应力比的比较,发现弹性理论过高地估计了复合地基的性能,而弹塑性理论与试验结果更为接近;弹塑性理论所提供的袋体张力与试验结果也比较相近.弹塑性理论适合评估袋装桩型复合地基的主要受力变形性能,可用于实际工程的设计计算.

基于同心拱模型的桩承式加筋路堤简化分析方法

为准确、便捷地分析桩承式加筋路堤中加筋体的受力和变形特性,提出了一种正方形和正三角布桩形式下的三维简化分析方法.首先考虑加筋体的空间变形形态,假设内部区域和条带区域加筋体的变形曲面分别为旋转抛物面和抛物柱面;然后根据同心拱模型基本原理,推导出作用在加筋体上方荷载的简化表达式;最后通过求解加筋体在三维空间内竖向力的平衡方程,得出加筋体的最大竖向变形和最大拉力、桩顶平均应力、桩间土平均应力以及荷载传递效率.利用所提方法对2个工程案例进行计算,并将计算值与实测值进行对比分析.结果表明,应用该简化分析方法所得的计算值与实测数据吻合良好,荷载传递效率的最大计算误差约为6%,从而验证了该方法的有效性.

路堤下桩–网连接方式对筋材受力变形的影响

基于现场试验,采用有限元软件PLAXIS2D建立桩承式加筋路堤数值模型,对比分析了路堤荷载下普通加筋和固网加筋时,筋材荷载传递、变形特性及筋–土界面摩擦特性。研究结果表明:对于软土地基上高填方路堤,固网加筋能更好地发挥筋材荷载传递效应;普通加筋时筋材变形曲线可用椭圆描述,筋材下表面筋–土界面应力比n约为40%,上表面n在10%~20%之间;固网加筋时,筋材下表面n约为10%,而上表面n小于10%。基于筋材变形特性及筋–土界面摩擦特性,提出了一种筋材拉力计算方法,并通过数值模拟结果对所提方法的合理性进行了验证。

考虑筋材蠕变-温度耦合效应的加筋土挡墙变形分析

基于既有土工合成材料筋材蠕变试验结果及蠕变特性分析,构建一种考虑蠕变-温度耦合效应的筋材本构模型,并利用二维瞬态热传导方程,建立计算加筋土挡墙温度的有限差分公式,进而确定加筋土挡墙温度并结合筋材本构模型计算面板水平位移和筋材最大应变,综合分析了初始温度、温度幅值、筋材层间距、墙顶超载、填土内摩擦角和导热率等因素对挡墙水平位移和筋材应变的影响。计算结果表明:挡墙竣工后初次环境温度升温过程使面板水平位移和筋材最大应变增加明显,后续温度周期性变化时挡墙变形增长缓慢;挡墙初始温度越高,其初期变形增加明显,而增加温度幅值导致面板长期变形量增加明显;增加墙顶超载、筋材层间距或减小填土摩擦角,导致相同时间内面板水平变形增加明显;填土导热率对面板水平位移和筋材最大应变的影响较小;环境温度周期性变化下,3 a内挡墙最大水平位移δ_(max)与墙高H比值δ_(max)/H变化范围在0.9%~1.5%;筋材最大应变靠近面板且最大值接近10%的限值,实践中应重点关注靠近面板的筋材长期性能变化对加筋土挡墙变形和稳定性影响。

包裹式加筋土挡墙的变形特性及影响因素研究

通过离心模型试验和FLAC2D数值模拟,研究软土地基包裹式加筋土挡墙的变形特性及其影响因素。离心模型试验表明,包裹式加筋土挡墙工后的侧向变形较小,包裹式的加筋墙面起到了传统面板的作用。采用基于离心模型试验的FLAC2D数值模拟,通过改变筋材的长度、布置间距(竖向)和刚度,探讨三者对挡墙变形特性的影响,结果表明,筋材的布置间距对挡墙变形的影响最显著,在实际工程中3个参数都应该控制在一定范围内。研究结果可为相关工程提供一定的参考及建议。