Assessment of liquefaction potential based on shear wave velocity:Strain energy approach

Liquefaction assessment based on strain energy is significantly superior to conventional stress-based methods.The main purpose of the present study is to investigate the correlation between shear wave velocity and strain energy capacity of silty sands.The dissipated energy until liquefaction occurs was calculated by analyzing the results of three series of comprehensive cyclic direct simple shear and triaxial tests on Ottawa F65,Nevada,and Firoozkuh sands with varying silt content by weight and relative densities.Additionally,the shear wave velocity of each series was obtained using bender element or resonant column tests.Consequently,for the first time,a liquefaction triggering criterion,relating to effective overburden normalized liquefaction capacity energy(WL=s’c)to effective overburden stresscorrected shear wave velocity(eVs1)has been introduced.The accuracy of the proposed criteria was evaluated using in situ data.The results confirm the ability of shear wave velocity as a distinguishing parameter for separating liquefied and non-liquefied soils when it is calculated against liquefaction capacity energy(WL=s’c).However,the proposed WL=s’c-Vs1 curve,similar to previously proposed cyclic resistance ratio(CRR)-Vs1 relationships,should be used conservatively for fields vulnerable to liquefaction-induced lateral spreading.

Micro-failure process and failure mechanism of brittle rock under uniaxial compression using continuous real-time wave velocity measurement

In this study,the micro-failure process and failure mechanism of a typical brittle rock under uniaxial compression are investigated via continuous real-time measurement of wave velocities.The experimental results indicate that the evolutions of wave velocities became progressively anisotropic under uniaxial loading due to the direction-dependent development of micro-damage.A wave velocity model considering the inner anisotropic crack evolution is proposed to accurately describe the variations of wave velocities during uniaxial compression testing.Based on which,the effective elastic parameters are inferred by a transverse isotropic constitutive model,and the evolutions of the crack density are inversed using a self-consistent damage model.It is found that the propagation of axial cracks dominates the failure process of brittle rock under uniaxial loading and oblique shear cracks develop with the appearance of macrocrack.

Surface-mounted bender elements for measuring horizontal shear wave velocity of soils

The bender element testing features its in-plane directivity, which allows using bender elements to measure the shear wave velocities in a wider range of in-plane configurations besides the standard tip-to-tip alignment. This paper proposed a novel bender element testing technique for measuring the horizontal shear wave velocity of soils, where the bender elements are surface- mounted and the axes of the source and receiver elements are parallel to each other. The preliminary tests performed on model ground of silica sand showed that, by properly determining the travel distance and time of the shear waves, the surface-mounted bender elements can perform as accurately as the conventional "tip-to-tip" configuration. Potentially, the present system provides a promising nondestructive tool for characterizing geomaterials and site conditions both in laboratory and in the fields.

Correlation of liquefaction resistance with shear wave velocity based on laboratory study using bender element

Recent studies using field case history data yielded new criteria for evaluating liquefaction potential in saturated granular deposits based on in situ, stress-corrected shear wave velocity. However, the conditions of relatively insufficient case histories and limited site conditions in this approach call for additional data to more reliably define liquefaction resistance as a function of shear wave velocity. In this study, a series of undrained cyclic triaxial tests were conducted on saturated sand with shear wave velocity Vs measured by bender element. By normalizing the data with respect to minimum void ratio, the test results, in-corporated with previously published laboratory data, statistically revealed good correlation of cyclic shear strength with small-strain shear modulus for sandy soils, which is almost irrespective of soil types and confining pressures. The consequently determined cyclic resistance ratio, CRR, was found to be approximately proportional to Vs4. Liquefaction resistance boundary curves were established by applying this relationship and compared to liquefaction criteria derived from seismic field measure-ments. Although in the range of Vs1>200 m/s the presented curves are moderately conservative, they are remarkably consistent with the published field performance criteria on the whole.

An improved method of evaluating liquefaction potential with the velocity of shear-waves

According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic shear modulus, which shows the relation of Gmax (kPa) with (σd/2)1/2(kPa)1/2. When applied to soils from different sites, the correlation can be normalized in reference to its minimum void ratio (emin). Accordingly, an improved method is established to evaluate the liquefaction potential with shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the maximum acceleration during earthquakes, which can be used to explain the phenomenon that the possibility of liquefaction decreases with the increment of the depth. Compared with previous methods this method turns out simple and effective, which is also verified by the results of cyclic triaxial tests.

Investigation of long-wavelength elastic wave propagation through wet bentonite-filled rock joints

The saturation of the compacted bentonite buffer in the deep geological repository can cause bentonite swelling,intrusion into rock fractures,and erosion.Inevitably,erosion and subsequent bentonite mass loss due to groundwater inflow can aggravate the overall integrity of the engineered barrier system.Therefore,the coupled hydro-mechanical interaction between the buffer and rock during groundwater inflow and bentonite intrusion should be evaluated to guarantee the long-term safety of deep geological disposal.This study investigated the effect of bentonite erosion and intrusion on the elastic wave propagation characteristics in jointed rocks using a quasi-static resonant column test.Jointed rock specimens with different joint conditions(i.e.joint surface saturation and bentonite filling)were prepared using granite rock discs sampled from the Korea Underground Research Tunnel(KURT)and Gyeongju bentonite.The long-wavelength longitudinal and shear wave velocities were measured under different normal stress levels.A Hertzian-type power model was used to fit the wave velocities,and the relationship between the two fitted parameters provided the trend of joint conditions.Numerical simulations using three-dimensional distinct element code(3DEC)were conducted to better understand how the long-wavelength wave propagates through wet bentonite-filled rock joints.

Comparison of Vs and SPT Soil Liquefaction Assessments of NCEER: Including Hypothesis Testing

Soil liquefaction is one of the complex research topics in geotechnical engineering and engineering geology. Especially after the 1964 Niigata earthquake (Japan) induced many soil liquefaction incidents, a variety of soil liquefaction studies were conducted and reported, including the liquefaction potential assessment methods utilizing the shear wave velocity (Vs) or SPT-N profiles (SPT: standard penetration test). This study used the Vs and SPT methods recommended by the National Center for Earthquake Engineering Research (NCEER) to examine which is more conservative according to the assessment results on 41 liquefiable soil layers at sites in two major cities in Taiwan. Statistical hypothesis testing was used to make the analysis more quantitative and objective. Based on three sets of hypothesis tests, it shows that the hypothesis—the SPT method is more conservative than the Vs method—was not rejected on a 5% level of significance.

水平孔多参数综合测试仪器研发与应用

为研究引大济岷工程隧洞岩体特征、岩溶发育特征、地应力特征和地下水特征等,在泸定取水中线方案的引水线路中布置水平钻孔8个,共计2300 m。为满足对水平孔综合测试的需求,研制了一套适用于水平钻孔的存储式综合测井仪器。本文分析了水平孔多参数综合测试仪器各参数测量的基本工作原理;详细阐述了各功能单元的电路构成选型,主要采用DSP微处理器和大规模集成电路,结合传感器技术实现多种参数的综合测量,包括:水平钻孔的压力、温度、自然伽马、声波波速、孔内电视图像。综合测试仪器集成了模拟传感器、模拟调理电路、数据采集、数据处理、信息存储、数据通讯、信息交换、测控软硬件、电脑显示等功能,是水平孔综合测试不可缺少的技术。在引大济岷工程的水平定向孔中成功应用,一趟起下钻解决了水平钻孔的井斜、方位角、压力、温度、自然伽马、孔内电视测试的难题,尽最大可能保证了钻孔的安全及降低了劳动强度。

干砂地基初始应力对爆炸波传播影响的模型试验

为了研究砂土地基初始应力对爆炸波压力峰值、上升时间、传播速度和初始应力动态卸载等传播规律的影响,开展多组干砂地基常重力和超重力爆炸模型试验.试验结果表明,初始自重应力会抑制爆炸波近区压力峰值的增长,而对远区的影响较小.初始应力的增加使得爆炸波上升时间更长,更易由冲击波衰减为弹塑性波,并使得爆炸波波速增大.超重力试验通过还原砂土地基的原型自重应力,能够模拟爆炸荷载诱发砂土地基初始应力动态卸载的过程,形成爆炸压力和土体初始应力动态卸载拉应力的耦合波,动态卸载拉应力持续时间更长.与爆炸波压应力的比冲量相比,初始应力动态卸载拉应力的比冲量随着传播距离的增加逐渐成为爆炸能量的主要部分,其产生的破坏作用不可忽视.

复杂爆炸载荷致肺损伤试验研究

为研究真实工况下人员在爆炸冲击波作用下的动态响应特性,开展某型云爆弹静爆作用下工事内仿人形装置(Anthropomorphic Test Device,ATD)和绵羊的毁伤试验研究。采用爆炸测试装置和简易假人作为研究对象,通过6发爆炸试验分析爆炸冲击波在ATD表面传播规律,开展2种人员损伤预测模型的对比分析。研究结果表明:在本试验工况下,冲击波和崩落的混凝土碎块是主要的毁伤元;爆炸冲击波在ATD表面首先发生反射,随后绕射至其他部位,压力曲线表现出非典型冲击波特征,反射叠加效应明显;在典型冲击波特征正压作用时间区间内,由于Axelsson损伤模型线性阻尼项的影响,求解的胸壁运动速度呈现出先增大至峰值后降低的现象;Axelsson损伤模型与UFC 3-340-02规范相比,在人员损伤预测方面相对保守。所得研究结果可为工程应用及毁伤评估提供参考。

泊松比变化对基于波速混凝土损伤计算的影响

利用超声波波速计算材料损伤的方法有广泛的应用,然而现有研究中常忽略泊松比的变化。研究了泊松比变化对基于波速混凝土损伤计算结果的影响。首先,通过理论分析,在基于波速的损伤计算公式中引入泊松比修正系数;其次,通过对混凝土柱试件进行轴压试验,验证了考虑泊松比变化的必要性;最后,在试验数据的基础上提出了泊松比修正系数实用计算方法。结果表明:忽略泊松比变化的影响时,基于波速的混凝土损伤计算值与真实值的平均相对误差高达73%;采用泊松比修正系数后,该误差减小至21%。基于波速进行混凝土损伤计算时宜计入泊松比修正系数以提高计算精度。

超声波在新拌液态粉煤灰抗压强度研究中的应用

对掺石灰的一种新型液态粉煤灰材料进行无侧限抗压强度检测,通过试验研究石灰含量变化对试件抗压强度的影响,试验结果表明:当石灰含量为0、4%、8%和12%时,新拌液态粉煤灰的7 d和28 d抗压强度均逐渐增加,尤其是28 d时的强度显著大于7 d时的强度。利用超声波无损检测技术测得试件的超声波速,通过回归分析研究抗压强度与超声波波速之间的相关性,建立了二者不同龄期的理论关系式:7 d龄期的宜采用二次函数拟合,回归方程为f_(cu)=0.000000976692v^(2)-0.000830792v+0.45616;28 d龄期的宜采用一次函数拟合,回归方程为f_(cu)=0.002v-0.96639;整体实测数据关系宜采用二次函数拟合,回归方程为f_(cu)=0.00000117211v^(2)-0.000767908v+0.32397。7 d和28 d的相关性R^(2)均>85%,表明其抗压强度和超声波速度之间存在显著的相关性,为研究新拌液态粉煤灰的无损检测提供了理论基础。

基于人工神经网络的多源数据融合技术在浅层纵波速度调查中的应用

微测井是地震勘探中常用的一种近地表纵波速度调查方法,在场地条件和施工成本受限的情况下,该方法得到的速度解释剖面常存在横向分辨率不足的问题。利用静力触探法布设方便、成本低廉的优势,提出一种利用人工神经网络模型关联地层阻力和地层波速的方法,以期通过少量实测微测井实现大范围纵波速度结构的有效预测。该方法的实施流程如下:(1)两两配对静力触探和微测井数据以生成控制点位,以岩性变化为网络分裂条件,输入层神经元接收锥尖阻力、侧摩阻力和深度数据,输出层神经元接收纵波速度,在中间设置多个全连接隐藏层;(2)通过前馈训练机制更新隐藏层神经元参数;(3)将非控制点位的静力触探数据输入到训练好的神经网络模型以获取全区近地表纵波速度结构剖面。在苏北某场地进行方法测试和数据分析,结果证实岩性分层的精细度和训练样本量是决定模型表现的两个关键因素。人工神经网络法预测浅层纵波速度的准确率超过90%,在可靠性、分辨率以及鲁棒性方面都超越了现有的经验公式法,可以辅助判断地下虚反射界面和低降速带分布范围,是提高地震勘探浅层速度调查精度和效率的有益探索。

防渗墙塑性混凝土力学性能-波速拟合曲线研究

针对塑性混凝土防渗墙超声波无损检测的应用进行研究。首先设计了3个强度等级的掺膨润土塑性混凝土,通过正交试验探究膨润土掺量、水胶比、砂率、外加剂掺量对塑性混凝土工作性能的影响,确定了最终配合比。基于最终配合比制备混凝土试件并进行力学性能试验、超声波测试和超声波测试比对试验,将得到的强度-波速关系和弹性模量-波速关系进行函数拟合,建立力学性能-波速曲线。结果表明,拟合曲线主要符合二次函数和幂函数形式,得到的5~7 MPa强度-波速曲线(二次函数)和1~7 MPa弹性模量-波速曲线(二次函数)的拟合程度较好,相关系数R2均大于0.94。

剪切波速测试值差异性特征及对场地类别划分的影响研究

剪切波速测试是评估场地土层特性及其对地震波传播影响的关键手段,其测量值的差异性特征对场地类别的划分具有显著影响。通过对青岛某码头工程的岩土工程进行勘察,采集了剪切波速测试数据,并分析了各测点的频率分布形态特征以及正态检验,以确保数据准确性。研究结果为工程设计提供了科学依据,强调了在场地评估中剪切波速差异性的重要性,为工程实施提供了有益的技术支持。

低应变同条件下桩型实测波速差异大研究探讨

在工程实践中,有时会出现在设计强度、成桩工艺、养护条件以及龄期相同的桩型,实测低应变波速差异大的情况。这一现象不符合同条件下的桩型,实测波速在某一范围内分布这个常规认知。甚至曾经有过相关专家以实测波速偏差过大为由,质疑检测数据的真实性。通过研究发现,这个波速差异大,并不是检测数据不真实导致的,也不是同条件下的桩型这一条件不满足,更不是同条件下的桩型实测波速在某一范围内这个常规认知不对,而是因为横向尺寸效应引起的。横向尺寸效应能够引起基桩实测波速产生差异,在桩径较大,桩长较短的时候,尤其明显。论本结合实例,对横向尺寸效应影响低应变实测波速进行了分析。

岩土工程勘察技术探讨

现代建筑工程建设过程中,不良地质是影响工程建设的主要因素之一,有效对这些不良地质进行了解,可以为后续建筑工程的设计与施工打下良好基础。所以,建筑工程建设前,必须要开展良好的岩土工程勘察工作,以准确了解不良地质的具体情况。基于此,本文以某建筑工程的岩土工程勘察作为研究对象,通过对该工程基本情况的简单介绍,进而阐述了勘察工作的任务和要求、勘察工作量的布置情况及勘察具体内容。之后以此为基础,介绍了本工程中主要采用的勘察方法,为建筑领域更好地开展岩土工程勘察工作提供支持。

帮东河水库大坝趾板固结灌浆试验施工技术分析

以帮东河水库混凝土面板堆石坝为例,进行了现场固结灌浆试验,对试验灌浆效果进行分析评价,为正式生产固结灌浆提出符合规范标准的施工参数。结果表明:在灌浆前压水试验过程中,出现压入流量为70 L/min~90 L/min,孔口未反水,建议采用1∶1浆液进行开灌。该区内地下岩层较为松散、有大量裂隙、透水率高;设计灌浆压力作用下,压水试验(0.24 MPa)、灌浆过程中(0.3 MPa)趾板无抬动现象,可适当提高灌浆压力。此次试验灌浆效果较好,但耗浆量较大,建议就地取材掺入黏土或粉煤灰,降低成本,提高经济效益。试验孔经二次序钻灌大透水率明显降低,检查孔透水率合格,同样表明灌浆压力可适当提高。建议正式灌浆压力由原设计值0.3MPa提升至0.35MPa或0.4MPa,增加灌浆扩散范围,提升固结灌浆质量。对2个检查孔进行弹性波速质量检查,检测结果达标。

复杂地形地质条件下岩土工程勘察技术的应用研究

为可靠掌握复杂地形地质条件情况,文章以珠海大道(金湾互通以西段)快速化提升工程为例,通过PS波速测试方法和圆锥动力触探勘测技术分别实现土层物理力学参数和地基承载力、变形模量测量,依据测量结果为施工提供可靠依据,旨在最大限度地保证施工质量。

Experimental study on the e ect of fracture scale on seismic wave characteristics

In fractured reservoir beds, fracture characteristics affect seismic wave response. Fractured models based on the Hudson＇s fractured medium theory were constructed in our laboratory by a backfilling technique. For the same fracture density, the variations of the velocity and amplitude of the primary wave and shear wave parallel and perpendicular to the fracture were observed by altering the diameter （scale） of the penny-shaped fracture disk. The model test indicated that an increase of fracture scale increased the velocity and amplitude of the primary wave by about 2%. When the shear wave propagated parallel to the fracture, the velocity of the fast shear wave hardly changed, while the velocity of slow shear wave increased by 2.6% with increasing fracture scale. The results indicated that an increase of fracture scale would reduce the degree of anisotropy of the shear wave. The amplitudes of slow shear waves propagating parallel and perpendicular to fractures decreased with increasing fracture scale.