Soils and Foundations最新文献_第2页

Modifying behavior of calcined waste phosphorus slag on the dispersivity and mechanical properties of dispersive soil 煅烧废磷渣对分散土分散性和力学性能的改良作用

IF 3.3 2区工程技术 Q2 ENGINEERING, GEOLOGICAL

Soils and Foundations

Pub Date : 2024-10-15 DOI: 10.1016/j.sandf.2024.101524

Dispersive soil is a common problem soil in engineering projects, which has the potential risk of causing serious engineering failures. In this paper, calcined waste phosphorus slag (CPS) was chosen to enhance the mechanical properties and reduce soil dispersivity. Dispersive soil samples with 1 % to 10 % CPS content were prepared and cured for 0 to 28 days. The dispersivity identification test was used to assess soil sample dispersivity. The compressive and tensile strength, conductivity, and pH were determined for the soil. Microstructural and mineral composition were analyzed using SEM/EDS, TG/DTG, and XRD analysis. The natural dispersive soil was selected to verify the effect of CPS in improving soil. Experiments show that the CPS inhibits soil dispersivity and converts it into non-dispersive soil. Both compressive and tensile strength increases significantly with the increase in the content of CPS and curing time. The tensile strength of the soil samples cured for 28 days increased by about 76 % and the compressive strength by about 61 % as the mixed content of CPS was increased from 1 % to 10 %. Results show that CPS can improve the strength and modify the dispersivity of soil, its optimal mixing content is 5 %. In addition, using CPS in dispersive soil could also solve the disposal problem of phosphate slag, which is a win-to-win solution.

分散性土壤是工程项目中常见的问题土壤，具有导致严重工程故障的潜在风险。本文选用煅烧过的废磷渣（CPS）来增强土体的力学性能，降低土体的分散性。制备了 CPS 含量为 1 % 至 10 % 的分散性土壤样本，并将其固化 0 至 28 天。分散性鉴定测试用于评估土壤样品的分散性。还测定了土壤的抗压和抗拉强度、电导率和 pH 值。使用 SEM/EDS、TG/DTG 和 XRD 分析法对微观结构和矿物成分进行了分析。为了验证 CPS 在改良土壤方面的效果，我们选择了天然分散土壤。实验表明，CPS 可抑制土壤的分散性，并将其转化为非分散性土壤。随着 CPS 含量和固化时间的增加，抗压和抗拉强度都有显著提高。随着 CPS 混合含量从 1% 增加到 10%，固化 28 天的土壤样本的抗拉强度增加了约 76%，抗压强度增加了约 61%。结果表明，CPS 可提高强度并改变土壤的分散性，其最佳混合含量为 5%。此外，在分散性土壤中使用 CPS 还能解决磷矿渣的处置问题，可谓一举两得。

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引用次数: 0

Effect of suction on time-dependent behavior of intact loess under oedometric conditions: Strain rate dependency and stress relaxation 吸力对气压条件下完整黄土随时间变化的行为的影响：应变速率依赖性和应力松弛

IF 3.3 2区工程技术 Q2 ENGINEERING, GEOLOGICAL

Soils and Foundations

Pub Date : 2024-10-10 DOI: 10.1016/j.sandf.2024.101520

Many geotechnical failures are associated with degradation of the soil strength over time. The time-dependency behavior of unsaturated loess is often required to evaluate the long-time behavior of geotechnical engineering in loess areas. To investigate such strain rate response and stress relaxation behavior of intact loess, a series of oedometric compression and relaxation tests were conducted under different suctions and strain rates. Water retention behaviors and microstructures were also measured to characterize the tested loess. The more rapid strain rate, leading to larger yield stress at relatively low suctions (0 and 50 kPa) and roughly paralleled one-dimensional normal compression lines (1D-NCL) conformed to the isotache approach. In contrast, the weakening effect of a more rapid strain rate on the clay cementation, resulted in smaller yield stress when the suction was larger than 100 kPa, which was an apparent deviation from the conception of the isotache. The reason might be that the microstructure developed during the long term (slow strain rate) under the relatively larger suction, which may increase the inter-particle bonding and structural strength. The relaxation behavior of unsaturated loess depended on suction and prerelaxation stress, which cannot be well described by the model with a soil constant viscosity I_v. The results of two viscous effects (rate-dependency and relaxation) in loess demonstrated that they could not altogether be explained within the isotache concept.

许多岩土工程的失效都与土壤强度随时间的推移而下降有关。要评估黄土地区岩土工程的长期行为，往往需要研究非饱和黄土的时间依赖行为。为了研究完整黄土的应变率响应和应力松弛行为，我们在不同吸力和应变率条件下进行了一系列气压压缩和松弛试验。此外，还测量了试验黄土的保水行为和微观结构。在相对较低的吸力（0 和 50 kPa）和大致平行的一维法向压缩线（1D-NCL）下，较快的应变速率导致较大的屈服应力，符合等压法。相反，当吸力大于 100 kPa 时，较快的应变速率对粘土胶结的削弱作用导致屈服应力较小，这明显偏离了等压法的概念。原因可能是在相对较大的吸力下，微观结构在长期（慢应变速率）过程中形成，这可能会增加颗粒间的结合力和结构强度。非饱和黄土的松弛行为取决于吸力和松弛前应力，而土壤恒定粘度 Iv 模型无法很好地描述这一点。黄土中两种粘性效应（速率依赖性和松弛）的结果表明，它们不能完全用等缓概念来解释。

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引用次数: 0

Assessment of foundation damage during earthquakes using acoustic emission monitoring: An experimental study on the shaking table test 利用声发射监测评估地震期间地基破坏情况：振动台试验研究

IF 3.3 2区工程技术 Q2 ENGINEERING, GEOLOGICAL

Soils and Foundations

Pub Date : 2024-10-09 DOI: 10.1016/j.sandf.2024.101473

Assessing structural foundation damage following an earthquake is critical for safety evaluation. However, assessing the damage to pile foundations with traditional visual inspections and non-destructive testing methods is challenging. This study evaluated the use of acoustic emission (AE) monitoring for damage detection and location in foundation structures during earthquake simulations by conducting shaking table experiments. Scaled models of foundation structures with and without surrounding soil were used in the experiments, and the performance of the AE monitoring system was evaluated by comparing the AE parameters via visual inspection. The experimental results showed that the AE monitoring system could effectively predict the initiation of cracks in foundation structures that experienced an earthquake. In addition, an appropriate filtering criterion for the shaking table experiments was established based on the AE characteristics of the foundation structures during the earthquake simulation, thereby improving the performance of the AE monitoring system for damage location. Consequently, this study contributed to a better understanding of the applicability of AE monitoring systems to foundation structures during earthquakes.

评估地震后结构地基的损坏情况对于安全评估至关重要。然而，使用传统的目视检查和非破坏性测试方法评估桩基损坏情况具有挑战性。本研究通过振动台实验，评估了在地震模拟中使用声发射（AE）监测来检测和定位地基结构的损坏情况。实验中使用了有周围土壤和无周围土壤的地基结构比例模型，并通过比较视觉检测的声发射参数评估了声发射监测系统的性能。实验结果表明，AE 监测系统可以有效预测地震中地基结构裂缝的产生。此外，还根据地震模拟过程中地基结构的 AE 特性，为振动台实验建立了适当的滤波准则，从而提高了 AE 监测系统的损坏定位性能。因此，本研究有助于更好地理解地震期间 AE 监测系统对地基结构的适用性。

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引用次数: 0

A machine learning-based method for predicting the shear behaviors of rock joints 基于机器学习的岩石节理剪切行为预测方法

IF 3.3 2区工程技术 Q2 ENGINEERING, GEOLOGICAL

Soils and Foundations

Pub Date : 2024-10-09 DOI: 10.1016/j.sandf.2024.101517

In this study, machine learning prediction models (MLPMs), including artificial neural network (ANN), support vector regression (SVR), K-nearest neighbors (KNN), and random forest (RF) algorithms, were developed to predict the peak shear stress values and shear stress-displacement curves of rock joints. The database used contained 693 records of peak shear stress and 162 original shear stress-displacement curves derived from direct shear tests. The results demonstrated that the MLPMs provided reliable predictions for shear stress, with the mean squared errors (MSEs) between their predicted and measured shear stress varying from 0.003 to 0.069 and the coefficients of determination (R² values) varying from 0.964 to 0.998. The feature importance values indicate that the joint surface roughness coefficient (JRC) is the most important influential factor in determining the peak shear stress, followed by the joint wall compressive strength (JCS), basic friction angle (

φ_{b}

), and shear surface area (A_s). Similarly, for the shear stress-displacement curve, the JRC is the dominant factor, followed by A_s,

φ_{b}

, and JCS. Additional direct shear tests were conducted for model validation. The validation shows that the MLPM predictions demonstrate improved consistency with the experimental results in relation to both the peak shear stress and peak shear displacement.

本研究开发了机器学习预测模型（MLPM），包括人工神经网络（ANN）、支持向量回归（SVR）、K-近邻（KNN）和随机森林（RF）算法，用于预测岩石节理的剪应力峰值和剪应力-位移曲线。所使用的数据库包含 693 条剪应力峰值记录和 162 条原始剪应力-位移曲线，均来自直接剪切试验。结果表明，MLPM 可提供可靠的剪应力预测，其预测剪应力与测量剪应力之间的均方误差（MSE）从 0.003 到 0.069 不等，判定系数（R2 值）从 0.964 到 0.998 不等。特征重要性值表明，接头表面粗糙度系数（JRC）是决定峰值剪应力的最重要影响因素，其次是接头壁抗压强度（JCS）、基本摩擦角（φb）和剪切表面积（As）。同样，对于剪应力-位移曲线，JRC 是主要因素，其次是 As、φb 和 JCS。为验证模型，还进行了其他直接剪切试验。验证结果表明，在峰值剪应力和峰值剪切位移方面，MLPM 预测结果与实验结果的一致性有所提高。

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引用次数: 0

Experimental study on mechanical behavior of silty-fine sand reinforced by a new type of permeable polymer material under dry-wet cycles 新型渗透性聚合物材料加固的淤泥细砂在干湿循环条件下的力学行为实验研究

IF 3.3 2区工程技术 Q2 ENGINEERING, GEOLOGICAL

Soils and Foundations

Pub Date : 2024-10-07 DOI: 10.1016/j.sandf.2024.101519

Silty-fine sand in the Yellow River floodplain is prone to geological hazards such as collapse, subsidence, gushing water, and sand routing triggered by groundwater seepage. As a new type of grouting material, permeable polymer is effective for solving silty-fine sand geologic hazards. With the rise and fall of the water table, capillary water, and transpiration, the reinforced silty-fine sand will be subjected to dry-wet cycles. Investigating the strength loss mechanism of specimens reinforced with permeable polymer during dry-wet cycles is essential for mitigating silty-fine sand geological hazards. The strength characteristics of permeable polymer grout-reinforced silty-fine sand specimens under dry-wet cycles and its extreme case (long-time immersion) were analyzed from macro and micro perspectives employing unconfined compressive strength (UCS) test and scanning electron microscope (SEM). The functional calculation model between the specimens and the initial grouting conditions under dry-wet cycles was constructed, and the main influencing factors of the UCS loss of the specimens were obtained. After permeable polymer grouting, the porosity of silty-fine sand is reduced effectively and the porous structure is changed. The grouted specimens maintain structural integrity and demonstrate excellent water stability even after dry-wet cycles.

黄河冲积平原上的淤泥质细沙容易发生崩塌、沉陷、涌水以及地下水渗漏引发的溃沙等地质灾害。作为一种新型灌浆材料，透水性聚合物可有效解决淤泥质细砂地质灾害问题。随着地下水位的升降、毛细管水和蒸腾作用，加固后的淤泥质细砂将经历干湿循环。研究透水聚合物加固试样在干湿循环过程中的强度损失机理对于减轻淤泥质细砂地质灾害至关重要。本研究采用无压抗压强度（UCS）试验和扫描电子显微镜（SEM），从宏观和微观两个角度分析了透水性聚合物灌浆料加固的淤泥质细砂试样在干湿循环及其极端情况（长时间浸泡）下的强度特性。构建了干湿循环条件下试件与初始灌浆条件之间的函数计算模型，并得出了试件无侧限抗压强度损失的主要影响因素。聚合物渗透灌浆后，淤泥质细砂的孔隙率有效降低，多孔结构发生改变。即使在干湿循环后，灌浆试样仍能保持结构的完整性，并表现出优异的水稳定性。

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引用次数: 0

Prospective method to estimate shear stress in the ground using two earth pressure cells 利用两个土压力单元估算地层剪应力的前瞻性方法

IF 3.3 2区工程技术 Q2 ENGINEERING, GEOLOGICAL

Soils and Foundations

Pub Date : 2024-10-01 DOI: 10.1016/j.sandf.2024.101504

Many sophisticated numerical methods have been developed to evaluate soil responses. However, the lack of referential stress–strain behavior under complicated in-situ ground conditions makes it difficult to validate the obtained responses sufficiently. For example, under a long embankment, with imposing plane strain conditions in depth, allowing for both horizontal displacement toward the slope toe and settlement, the stress components change as a result of the interaction between one soil part and adjacent soil parts. Since those stress conditions themselves are unknown, no laboratory experimental data can be provided to validate a constitutive model. Therefore, the author considered that studying the stress conditions in the ground would play an important role in confirming the calculated results obtained by a numerical method. Soil stress cells have sometimes been utilized to measure the earth pressure in an experimental model, but such measurements have often proven to be unreliable or unrealistic. However, the preciseness of earth pressure meters has recently been examined and improved. Recently, centrifuge tests were conducted to estimate the shear stress in a horizontally layered model ground during shaking. By using a pair of earth pressure meters and the concept of Mohr’s stress circle, it was possible to estimate the shear stress at any point in the ground. The shear stress estimated by this method was seen to agree well with the results obtained by a calculation based on the force balances of the supposed soil blocks from the ground surface. As a result, it was confirmed that the proposed method is a promising way to estimate the shear stress in the ground and is worthy of further investigation.

目前已开发出许多复杂的数值方法来评估土壤响应。然而，由于缺乏复杂原地条件下的应力-应变行为参考，很难对所获得的响应进行充分验证。例如，在长堤坝下，在深度上施加平面应变条件，同时允许向坡脚的水平位移和沉降，应力分量会因一个土体部分和相邻土体部分之间的相互作用而发生变化。由于这些应力条件本身是未知的，因此无法提供实验室实验数据来验证构成模型。因此，作者认为研究地层中的应力条件对于确认数值方法计算出的结果具有重要作用。有时会利用土壤应力单元来测量实验模型中的土压力，但事实证明这种测量往往不可靠或不现实。不过，最近对土压计的精确性进行了研究和改进。最近，我们进行了离心机试验，以估算地震时水平分层模型地面的剪应力。通过使用一对土压力计和莫尔应力圈的概念，可以估算出地面任意一点的剪应力。通过这种方法估算出的剪应力与根据地表假定土块的力平衡计算得出的结果十分吻合。因此，可以确认所提出的方法是估算地层剪应力的一种可行方法，值得进一步研究。

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引用次数: 0

Relationship between void characteristics and re-liquefaction resistance: An image analysis study 空隙特征与抗再液化能力之间的关系：图像分析研究

IF 3.3 2区工程技术 Q2 ENGINEERING, GEOLOGICAL

Soils and Foundations

Pub Date : 2024-09-23 DOI: 10.1016/j.sandf.2024.101506

To scrutinize the impact of void characteristics on re-liquefaction resistance, a series of constant-volume cyclic bi-axial tests was conducted on an assembly of plastic rods. The first and second liquefaction stages involved the application of isotropic compression at 100 kPa followed by constant-volume cyclic loading with the deviator stress set at 30 or 60 kPa. This study introduced an innovative image analysis method to quantify four void characteristics: anisotropy index (

I_{e}

) and average void element size (

A_{e}

) for the element-based analysis, and local anisotropy index (

I_{e, i j}

) and local void ratio (

e_{ij}

) for the grid-based analysis. The newly developed anisotropy index was seen to facilitate the assessment of the primary alignment and degree of anisotropy in void elements. The results confirmed that an increase in re-liquefaction resistance is evident in specimens with lower average

e_{ij}

, coefficient of variation (CV) of

e_{ij}

, and

I_{e}

, indicating denser, more homogeneous, and isotropic conditions. Nevertheless, specimens with a greater degree of anisotropy were found to be more susceptible to re-liquefaction. The development of strain in the early stages of cyclic loading was found to be predominantly influenced by the anisotropy index, underscoring the imperative need for an enhanced method that can predict liquefaction resistance, as well as re-liquefaction resistance, and incorporates the anisotropy index.

为了仔细研究空隙特性对抗再液化能力的影响，对塑料棒组件进行了一系列恒容循环双轴试验。第一和第二液化阶段包括施加 100 kPa 的各向同性压缩，然后是恒容循环加载，偏差应力设定为 30 或 60 kPa。本研究引入了一种创新的图像分析方法来量化四种空隙特征：基于元素分析的各向异性指数（Ie）和平均空隙元素尺寸（Ae），以及基于网格分析的局部各向异性指数（Ie,ij）和局部空隙率（eij）。新开发的各向异性指数有助于评估空隙元素的主要排列和各向异性程度。结果证实，平均 eij、eij 变异系数 (CV) 和 Ie 较低的试样抗再液化能力明显增强，这表明试样更致密、更均匀且各向同性。然而，各向异性程度较高的试样更容易发生再液化。在循环加载的早期阶段，应变的发展主要受各向异性指数的影响，这突出表明迫切需要一种能预测抗液化能力和抗再液化能力并包含各向异性指数的增强型方法。

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引用次数: 0

Pseudo-dynamic bearing capacity of strip foundations on rock masses considering the Rayleigh surface waves 考虑瑞利表面波的岩体上条形地基的伪动力承载力

IF 3.3 2区工程技术 Q2 ENGINEERING, GEOLOGICAL

Soils and Foundations

Pub Date : 2024-09-10 DOI: 10.1016/j.sandf.2024.101508

Evaluation of seismic bearing capacity is to be vital for design of strip foundations in earthquake areas. Combining the upper bound theorem of limit analysis, the discrete technique is successfully extended in this study to investigate the seismic ultimate bearing capacity of shallow strip foundations on rock masses considering the Rayleigh waves, in which the nonlinear HB failure criterion is used to describe the constitutive relation of rock masses. The failure model of foundation soil is generated using the discretization method, a “point by point” technique. The variations of shear modulus G of rock masses and seismic acceleration varying with the depth are taken into consideration. The generalized tangential technique is employed to avoid the difficulty resulting from the nonlinear HB failure criterion. A linear corresponding to the Mohr–Coulomb failure criterion, tangent to the nonlinear Hoek–Brown failure criterion, is used to derive the objective function that is to be minimized. By comparing with the existing results, the present approach is verified. The widely parametric studies are made to investigate the effect of different parameters, e.g. shear modulus G, m_i, GSI, $σ_{ci}$ , γ, D, V_R, on the seismic bearing capacity of strip foundations. The present method provides a reference for strip foundations designed in earthquake areas.

地震承载力的评估对于地震区带状地基的设计至关重要。本研究结合极限分析的上界定理，成功地将离散技术扩展到考虑雷利波的岩体上，研究浅层带状地基的地震极限承载力，其中采用非线性 HB 破坏准则来描述岩体的构成关系。地基土的破坏模型是通过 "逐点 "技术的离散化方法生成的。岩体的剪切模量 G 和地震加速度随深度的变化都被考虑在内。为避免非线性 HB 破坏准则带来的困难，采用了广义切向技术。与莫尔-库仑失效准则相对应的线性失效准则与非线性霍克-布朗失效准则相切，从而得出最小化的目标函数。通过与现有结果的比较，本方法得到了验证。通过广泛的参数研究，探讨了不同参数（如剪切模量 G、mi、GSI、σci、γ、D、VR）对带状地基抗震承载力的影响。本方法为在地震区设计带状地基提供了参考。

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引用次数: 0

Effect of silt uniformity on the liquefaction resistance of sand–silt mixtures 淤泥均匀性对砂-淤泥混合物抗液化性能的影响

IF 3.3 2区工程技术 Q2 ENGINEERING, GEOLOGICAL

Soils and Foundations

Pub Date : 2024-09-10 DOI: 10.1016/j.sandf.2024.101507

Literature review revealed that effects of particle segregation and silt uniformity on the liquefaction resistance of sand–silt mixtures are not well understood. Therefore, cyclic direct simple shear tests were conducted to investigate effects of silt uniformity and stratified structures on the liquefaction resistance of sand–silt mixtures with 0%–40% fines content (FC). For all uniform sand–silt mixtures, as FC increased up to 20%, liquefaction resistance decreased, while it increased as FC increased from 20% to 40%. The liquefaction resistance of the samples with uniform silt only in the top and bottom layers was slightly higher than that of a uniform sample (USM), while the cyclic strength of the samples with silt concentrated in the middle layer was greater (up to 23%) than that of other nonuniform samples. USM exhibited the least liquefaction resistance. In addition, the number of silt layers (NoSLs) substantially affected the liquefaction resistance of stratified structures: as NoSLs increased from 1 to 3 layers, the cyclic resistance ratio was reduced by 20%, 10%, and 7% for FC values of 20%, 30%, and 40%, respectively. The liquefaction resistance of the stratified samples was greater than that of USM. To quantify the effect of silt uniformity and NoSLs, the nonuniformity index (NUI) was introduced herein; the calculated NUI values showed that the increase in liquefaction resistance was well correlated with the increase in the NUI.

文献综述显示，颗粒离析和粉土均匀性对砂-粉土混合物抗液化性能的影响还不十分清楚。因此，我们进行了循环直接简单剪切试验，以研究粉土均匀性和分层结构对细粒含量（FC）为 0%-40% 的砂淤土混合物抗液化性能的影响。对于所有均匀的砂淤土混合物，当细粒含量增加到 20% 时，抗液化性降低，而当细粒含量从 20% 增加到 40% 时，抗液化性增加。仅在顶层和底层有均匀淤泥的样本的抗液化性略高于均匀样本（USM），而淤泥集中在中层的样本的循环强度（最高达 23%）高于其他非均匀样本。USM 的抗液化能力最小。此外，淤泥层数（NoSLs）对分层结构的抗液化能力也有很大影响：当 NoSLs 从 1 层增加到 3 层时，FC 值为 20%、30% 和 40% 时，抗循环比分别降低了 20%、10% 和 7%。分层样本的抗液化能力大于 USM。为量化淤泥均匀性和 NoSL 的影响，本文引入了非均匀性指数（NUI）；计算的非均匀性指数值表明，液化阻力的增加与非均匀性指数的增加密切相关。

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引用次数: 0

Elastoplastic finite element simulation of domino fault formation associated with tilting of highly structured ground 与高结构地层倾斜相关的多米诺断层形成的弹塑性有限元模拟

IF 3.3 2区工程技术 Q2 ENGINEERING, GEOLOGICAL

Soils and Foundations

Pub Date : 2024-08-23 DOI: 10.1016/j.sandf.2024.101475

Ground deformation on the Earth’s surface layer is strongly affected by the nonlinearity of geomaterials. However, the formation process of such deformation has yet to be described in a unified manner based on mechanics. The present study focuses on the normal faults in a submarine ground with highly developed soil skeleton structures and attempts to reproduce the process of normal fault formation associated with the tilting of a horizontally deposited submarine ground using an elastoplastic finite element simulation. The simulation was conducted using the soil–water coupled finite deformation analysis code GEOASIA, which incorporates an elastoplastic constitutive equation of the soil skeleton based on the modified Cam-clay model and the soil skeleton structure concept. The key findings are as follows:

1) Normal faults are formed from the ground surface to depth as shear bands, where shear strain is localized while exhibiting softening behavior with plastic volume compression.

2) Multiple normal faults are almost equally spaced and parallel to each other, with the inter-fault blocks rotating backward. The morphology of normal faults formed by the tilting of the ground shows domino-style characteristics.

3) The degree of the soil skeleton structure influences the formation of normal faults.

This study demonstrates that elastoplastic geomechanics can explain the formation process of ground deformation, which has usually been interpreted from the perspectives of geomorphology and geology.

地球表层的地面变形受到土工材料非线性的强烈影响。然而，这种变形的形成过程尚未得到基于力学的统一描述。本研究侧重于具有高度发达土壤骨架结构的海底地层中的法向断层，并尝试使用弹塑性有限元模拟再现与水平沉积海底地层倾斜相关的法向断层形成过程。模拟使用了水土耦合有限变形分析代码 GEOASIA，其中包含了基于修正的 Cam-clay 模型和土壤骨架结构概念的土壤骨架弹塑性构成方程。主要结论如下：1)法向断层从地表到地层深处形成剪切带，剪切应变局部化，同时表现出塑性体积压缩软化行为。这项研究表明，弹塑性地质力学可以解释地面变形的形成过程，而地面变形通常是从地貌学和地质学的角度来解释的。

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引用次数: 0