Lateral earth pressure of granular backfills on retaining walls with expanded polystyrene geofoam inclusions under limited surcharge loading

Existing studies have focused on the behavior of the retaining wall equipped with expanded polystyrene(EPS)geofoam inclusions under semi-infinite surcharge loading rather than limited surcharge loading.In this paper,the failure mode and the earth pressure acting on the rigid retaining wall with EPS geofoam inclusions and granular backfills(henceforth referred to as EPS-wall),under limited surcharge loading are investigated through two-and three-dimensional model tests.The testing results show that different from the sliding of almost all the backfill in the EPS-wall under semi-infinite surcharge loading,only an approximately triangular backfill slides in the wall under limited surcharge loading.The distribution of the lateral earth pressure on the EPS-wall under limited surcharge loading is non-linear,and the distribution changes from the increase of the wall depth to the decrease with the increase of the limited surcharge loading.An approach based on the force equilibrium of a differential element is developed to predict the lateral earth pressure behind the EPS-wall subjected to limited surcharge loading,and its performance was fully validated by the three-dimensional model tests.

Surface Pressure Loading Technology of Ship Structures

A hull structure is prone to local deformation and damage due to the pressure load on the surface.How to simulate surface pressure is an important issue in ship structure test.The loading mode of hydraulic actuator combined with high-pressure flexible bladder was proposed,and the numerical model of the loading device based on flexible bladder was established.The design and analysis method of high-pressure flexible bladder based on aramid-fiber reinforced thermoplastic polyurethane was proposed to break through the surface pressure loading technology of ship structures.The surface pressure loading system based on flexible bladder was developed.The ultimate strength verification test of the box girder under the combined action of bending moment and pressure was carried out to systematically verify the feasibility and applicability of the loading system.The results show that the surface pressure loading technology can be used well for applying uniform pressure to ship structures.Compared with the traditional surface loading methods,the improved device can be applied with horizontal constant pressure load,with rapid response and safe process,and the pressure load is always stable with the increase of the bending moment load during the test.The requirement for uniform loading in the comprehensive strength test of large structural models is satisfied and the accuracy of the test results is improved by this system.

Earth Pressure Distribution and Sand Deformation Around Modified Suction Caissons(MSCs) Under Monotonic Lateral Loading

The modified suction caisson(MSC) is a novel type of foundation for ocean engineering, consisting of a short external closed-top cylinder-shaped structure surrounding the upper part of the regular suction caisson(RSC). The MSC can provide larger lateral bearing capacity and limit the deflection compared with the RSC. Therefore, the MSC can be much more appropriate to use as an offshore wind turbine foundation. Model tests on the MSC in saturated sand subjected to monotonic lateral loading were carried out to investigate the effects of external structure sizes on the sand surface deformation and the earth pressure distribution along the embedded depth. Test results show that the deformation range of the sand surface increases with the increasing width and length of the external structure. The magnitude of sand upheaval around the MSC is smaller than that of the RSC and the sand upheaval value around the MSC in the loading direction decreases with the increasing external structure dimensions. The net earth pressure in the loading direction acting on the internal compartment of the MSC is smaller than that of the RSC at the same embedded depth. The maximum net earth pressure acting on the external structure outer wall in the loading direction is larger than that of the internal compartment, indicating that a considerable amount of the lateral load and moment is resisted by the external skirt structure.

An innovative test method for mechanical properties of sandstone under instantaneous unloading confining pressure

With the increase of underground engineering construction depth,the phenomenon of surrounding rock sudden failure caused by supporting structure failure occurs frequently.The conventional unloading con-fining pressure(CUCP)test cannot simulate the plastic yielding and instantaneous unloading process of supporting structure to rock.Thus,a high stress loading-instantaneous unloading confining pressure(HSL-IUCP)test method was proposed and applied by considering bolt’s fracture under stress.The wall thickness of confining pressure plates and the material of bolts were changed to realize different confin-ing pressure loading stiffness(CPLS)and lateral maximum allowable deformation(LMAD).The superio-rity of HSL-ICPU method is verified compared with CUCP.The rock failure mechanism caused by sudden failure of supporting structure is obtained.The results show that when CPLS increases from 1.35 to 2.33 GN/m,rock’s peak strength and elastic modulus increase by 25.18%and 23.70%,respectively.The fracture characteristics change from tensile failure to tensile-shear mixed failure.When LMAD decreases from 0.40 to 0.16 mm,rock’s residual strength,peak strain,and residual strain decrease by 91.80%,16.94%,and 21.92%,respectively,and post-peak drop modulus increases by 140.47%.The test results obtained by this method are closer to rock’s real mechanical response characteristics compared with CUCP.

Construction of Micropiles Using Pressure Techniques

This paper discusses the technique of casting concrete ofmicropiles with pressures and the consequence of comparisons with normal way of casting concrete （casting with gravity）. Preliminary geotechnical studies have been made in specific area in Sudan to predict the soil parameters and then an experimental work has been done for an estimated number ofmicropiles with different diameters and different techniques of placing concrete with various amount of pressure. This study was carried out to learn the usefulness of this technique in the field of structural foundations in Sudan. Capacities of micropiles were compared in cases of non-pressure casting （normal way of casting concrete） and pressure casting. Through the results, it was found that the entry of pressure factor in the operation of casting concrete increases the capacities of micropiles. The increased value of ultimate load depends on the amount of pressure applied.

Experimental study on dynamic mechanical property of cemented tailings backfill under SHPB impact loading

Cemented tailings backfill(CTB) have increasingly been used in recent years to improve the stability of mining stopes in deep underground mines. Deep mining processes are often associated with rock bursting and high-speed dynamic loading conditions. Therefore, it is important to investigate the characteristics and dynamic mechanical behavior of CTB. This paper presents the results of dynamic tests on CTB specimens with different cement and solid contents using a split Hopkinson pressure bar(SHPB). The results showed that some CTB specimens exhibited one to two lower stress peaks after reaching dynamic peak stress before they completely failed. The greater the cement-to-tailings ratio is, the more obvious the strain reaction. This property mainly manifested as follows. First,the dynamic peak stress increased with the increase of the cement-to-tailings ratio when the impact velocity was fixed. Second, the dynamic peak stress had a quadratic relationship with the average stress rate. Third, the cement-to-tailings ratio could enhance the increase rate of dynamic peak stress with strain rate. In addition, the dynamic strength enhancement factor K increased with the increase of strain rate, and its value was larger than that of the rock samples. The failure modes of CTB specimens under low-speed impact were tensile failure and X conjugate shear failure, where were nearly the same as those under static uniaxial and triaxial compression. The CTB specimens were crushed and broken under critical strain, a failure mode similar to that of low-strength concrete. The results of the experimental research can improve the understanding of the dynamic mechanical properties of CTB and guide the strength design of deep mining backfills.

H-M Bearing Capacity of A Modified Suction Caisson Determined by Using Load-/Displacement-Controlled Methods

This paper presents a series of monotonically combined lateral loading tests to investigate the bearing capacity of the MSCs （modified suction caissons） in the saturated marine fine sand. The lateral loads were applied under load- and displacement-controlled methods at the loading eccentricity ratios of 1.5, 2.0 and 2.5. Results show that, in the displacement-controlled test, the deflection-softening behavior of load-deflection curves for MSCs was observed, and the softening degree of the load-deflection response increased with the increasing external skirt length or the decreasing loading eccentricity. It was also found that the rotation center of the MSC at failure determined by the load-controlled method is slightly lower than that by the displacement-controlled method. The calculated MSC capacity based on the rotation center position in serviceability limit state is relatively conservative, compared with the calculated capacity based on the rotation center position in the ultimate limit state. In the limit state, the passive earth pressures opposite the loading direction under load- and displacement-controlled methods decrease by 46% and 74% corresponding to peak values, respectively; however, the passive earth pressures in the loading direction at failure only decrease by approximately 3% and 7%, compared with their peak values.

Cumulative Deformation of Soft Clay Under Cyclic Loading

Reconstituted specimens are prepared by means of vacuum preloading. Both static and cyclic triaxial tests are carried out, with the specimens consolidated under different principal stress ratios. A finite element method is put forward for calculating the cumulative deformation of soft clay under cyclic loading.

Failure of rock under dynamic compressive loading

Split Hopkinson Pressure Bar(SHPB) test was simulated to investigate the distribution of the first principal stress and damage zone of specimen subjected to dynamic compressive load. Numerical models of plate-type specimen containing cracks with inclined angles of 0°,45° and 90° were also established to investigate the crack propagation and damage evolution under dynamic loading. The results show that the simulation results are in accordance with the failure patterns of specimens in experimental test. The interactions between stress wave and crack with different inclined angles are different; damage usually appears around the crack tips firstly; and then more damage zones develop away from the foregoing damage zone after a period of energy accumulation; eventually,the damage zones run through the specimen in the direction of applied loading and split the specimen into pieces.

LoadRunner在蒙古语资源网负载压力测试中的应用与研究

系统的负载压力是系统性能指标的一个重要方面。根据用户对系统性能的需求设计了测试用例,用LoadRunner录制测试脚本,模拟用户并发访问网站页面操作,对蒙古语资源网进行了负载压力测试。通过分析测试结果,初步评估该网站的性能瓶颈,并提出改善网站性能的建议。

Development of a Test Rig for Axial Strains Measurement in Automobile Wheel

In automobile wheel application, a test rig is vital and used to simulate conditions of the wheel in service in order to affirm the safety and reliability of the wheel. The present work designed a test rig for measuring axial strains in automobile wheel. The wheel used was a five-arm wheel (6JX14H2;ET 42) and Tyre (175 × 65 R 14). Experimental (EXP) test was carried out, with a radial load of 4750 N and inflation pressure of 0.3 MPa, to measure the axil strains which were converted to maximum principal strain values and, compared with data from Finite Element Analysis (FEA) using Creo-Element/Pro 5.0 at wheel’s contact angles of 90 degree (FEA 90 deg), 40 degree (FEA 40 deg) and 30.25 degree (FEA 30.25 deg), respectively. Results show that at the wheel’s point of contact with the ground, maximum principal strain values were highest at the inboard bead seat with a value of about 5.69 × 10-4 mm/mm, followed by the values at the well of about 5.66 × 10-4 mm/mm. The value at the outboard bead seat was least at about 2.22 × 10-4 mm/mm, which was due to the presence of spikes at this location that tends to resist imposed radial loads. However, the highest mean maximum principal strain values at the locations of inboard, well and outboard, were about 2.11 × 10-4 mm/mm, 3.78 × 10-4 mm/mm and .99 × 10-4 mm/mm, respectively. With the highest single value of about 5.69 × 10-4 mm/mm, the inboard bead seat was the most strained location of the wheel. Overall results showed that all values of maximum principal strains were below the threshold value of about 1 × 10-2 mm/mm. The values obtained for EXP and FEA could be said to be in close agreement when compared with the threshold value. With this in mind, the rig is recommended for use in related experimental procedures.

三峡库区滑坡涌浪作用下桥墩波压特性研究

由于三峡库区的非开敞性,滑坡引起的涌浪衰减较慢,传播过程中可能对沿程桥墩产生巨大破坏。以涪陵长江二桥为依托,构建了比例尺为1∶70的库区河道水槽,试验模拟了滑坡涌浪对桥墩的作用。结果表明:桥墩上涌浪波压分为共振波压(P_(re))和脉动波压(P_(pu)),共振波压为涌浪冲击桥墩瞬间桥墩共振产生的高频振动波,频率为300.0~400.0 Hz;脉动波压为波浪作用过程产生的压力,频率为0.2~0.5 Hz;脉动波压在对岸桥墩上沿水深的分布近似为垂直分布,在同岸桥墩沿水深锯齿状减小,最大脉动波压分布在水面附近;共振波压沿水深分为单峰值、多峰值和无峰值3种,10万m^(3)以上大方量滑坡产生的共振波压为单峰值和多峰值分布,单峰值的峰值波压是水面波压的5.0倍,多峰值的峰值波压为水面波压的2.5倍~4.0倍,10万m^(3)以下滑坡产生的共振波压呈现无峰值分布;共振波压沿水深呈先增大后减小的“侧V”形;P_(re)/P_(pu)最大位置在距水面1/3水深位置,第二大位置在距水面1/5水深位置。该文提出了桥墩迎波面涌浪压力荷载计算模型,并针对三峡库区不同运行水位给出了相应水位条件下最大涌浪波压的计算公式。

地基承载力特征值确定土变形模量的探讨

目前我国地基沉降计算主要采用土压缩模量来计算,再用经验系数对计算结果进行修正。这种方法对于一些结构性较强的硬土地基误差较大,主要原因是取样扰动影响。为此,探讨了变形模量与地基承载力特征值的理论联系,在笔者提出的确定变形模量经验方法基础上,总结出依据地基承载力特征值确定变形模量的方法,该方法具有理论依据,可便捷地通过岩土工程勘察报告中常提供的地基承载力特征值确定土的变形模量,能够更为准确计算地基沉降值。采用不同方法(压板试验法、压缩模量推求法、标贯击数法、承载力经验法、依据地基承载力特征值确定变形模量法)计算了若干试验案例,通过对不同方法结果的对比,初步验证了依据地基承载力特征值确定变形模量法是可行的。

活动门试验中土压力盒标定方法

为确保活动门试验结果的准确性,根据试验填土深度的不同,对一批相同型号的电阻式土压力盒进行了垂直方向上的分级加载和卸载标定,并考虑标定装置内壁摩擦力影响,修正了作用在土压力盒上的有效加载和卸载应力。通过对加卸载过程进行离散元模拟,证明有效加载和卸应力修正方法较为合理。标定试验结果表明,加载过程中微应变量-有效应力曲线呈线性变化,可使用线性函数拟合;卸载过程中微应变量-有效应力曲线存在明显的滞后现象,且滞后程度随有效加载应力的增大而增大,可使用单指数曲线拟合。标定土压力盒后,开展了填土试验,结果表明土压力盒不宜在压力过小或填土深度过小时使用。

复合壳体水中高静压试验及极限承载能力分析

[目的]旨在实现在水中高静压环境下对结构应变的准确测试,同时探究复合壳体在水中高静压环境下的极限承载能力大小以及不同初始缺陷的影响。[方法]首先,开展复合壳体水下高静压试验,提出基于高压防护装置的水下高静压3D-DIC测试方法,获得结构在15 MPa水压下的应变;然后,将其与有限元模型模拟结果进行对比,验证3D-DIC测试系统在水中高静压环境下的可行性以及数值模型的正确性;最后,在此基础上针对不同初始缺陷条件对复合壳体极限承载能力的影响开展仿真计算。[结果]结果显示,试验结果与数值仿真结果的平均误差为5.1%;不同模态下复合壳体的极限承载能力与添加的几何缺陷大小呈二次函数关系,其中,一阶模态下极限承载能力的变化梯度为1.48~2.12 MPa/mm,三阶模态下极限承载能力的平均变化梯度为1~4.32 MPa/mm。[结论]3D-DIC测试技术在水中高静压环境下可以对复合壳体进行准确的应变测量。在水中高静压环境下,几何初始缺陷在很大程度上影响复合壳体的极限承载能力,其中三阶模态的影响程度大于一阶模态。

波浪荷载作用下防波堤地基土动强度试验研究

通过模拟波浪荷载,对防波堤地基土做了等压固结不排水动三轴剪切试验,分析得出,循环剪应力比与破坏振次可用幂函数拟合,但拟合参数不是常数,与土类和围压有关;土体在剪切过程中孔隙水压力会不断增加,但始终没有达到初始的围压数值,达到破坏标准时,约为初始围压的60%~80%;动孔压比与振次比关系可用幂函数很好地拟合,拟合参数不是常数,与土性有关;3种土的动应变发展模式不同,粉质黏土的压应变一直大于拉应变,粉土是压应变与拉应变基本同时发展,砂土则在开始一段时间,轴向应变很小,压应变小于拉应变,中后期,轴向应变迅速增长,压应变逐渐超过了拉应变。

不同能级强夯法处理新近吹填粉细砂地基现场试验

某矿石码头堆场表层由新近吹填形成的松散粉细砂组成,地下水位及黏粒含量均较高。为验证强夯法进行地基处理的可行性以及优化施工参数,拟在处理厚度为6和9 m的两个区域设立施工试验区,分别采用2000和4000 kN·m的夯击能进行强夯试验,施工同时监测夯击过程中孔隙水压力、夯沉量等变化情况,施工完成后进行现场标准贯入试验和荷载试验,并给出单位面积夯击能与夯沉量的双曲线关系式。结果表明,孔隙水压力消散时间约为2 d,每一点夯的最优夯击数为7~8击;处理后的地基承载力较处理前显著提高,且达到了设计文件中200 kPa的承载力要求。

250 km/h动车组气动载荷及动态气密特征的实车试验

为了对长期运行的现役列车车体疲劳及静强度提供载荷边界输入条件,并加强对车体气动载荷特性和车内压力舒适性的长期运用评估,采用实车试验的方法得到CRH5A型动车组线路气动载荷和频率特征及不同隧道运行工况下车内外压力波动和车内压力舒适性特征,结合实测数据和所提出的动态气密指数分析方法,计算整车动态气密指数。研究结果表明:在京沈客专沈阳—朝阳试验段,车体绝对气动压差变化范围为−2.53~0.71 kPa;车体外两侧压力无明显主频;间隔1 s和3 s的车内压力变化量最大值分别为294 Pa和383 Pa,尾车的车内压力波动最剧烈。列车通过黑山隧道、下窝堡隧道、扣莫明洞隧道、三棱山隧道4个典型长度隧道的整车动态气密性指数计算结果分别为10.46、12.13、11.06和14.40 s,对于同一列车而言,列车的动态气密指数未因所通过隧道长度的不同而有较明显的离散特征。

联排凹曲面屋盖的风荷载特性试验研究

为了探究凹曲面屋盖的风荷载特性并为实际工程提供抗风设计参考,对3种联排凹曲面屋盖进行刚性模型风洞测压试验,系统分析联排数及风向角对凹曲面屋盖升力系数、平均风压系数和极值风压系数的影响.结果表明:屋盖整体升力系数随着联排数的增加不断降低,各屋盖的升力系数受风向角影响较大.在不同联排数及风向角下,屋盖整体承受向上的风吸力,屋盖的平均风压系数表现出复杂的波动性;在迎风屋盖边缘处的气流分离现象明显,导致该处存在较大风吸力;越远离迎风侧的屋盖,平均风压系数的波动越小,稳定于-0.1.联排数对极值风压系数的影响不可忽略,尤其是极小值负压系数,边缘屋盖分区极小值负压系数的最小值为-5.1,中间屋盖分区极小值负压系数的最小值为-3.3.基于试验结果,总结给出不同联排凹曲面屋盖分区的平均风压系数和极值风压系数.

80 MN压剪试验机竖向加载模糊PID控制系统的设计

为了稳定、精确、可靠地实施超大力值竖向加载,以80 MN压剪试验机为对象,对其竖向加载装置的机械结构、液压系统以及控制系统进行总体设计;建立位置-压力双闭环PID控制算法的数学模型,并设计模糊PID控制器;最后,通过AMESim-Simulink对控制系统进行耦合仿真,获取位移与试验力的时域响应曲线,并在80 MN压剪试验机上进行竖向加载试验以验证控制系统的可靠性。结果表明:竖向加载模糊PID控制系统使竖向加载在220 s后达到稳态,位移误差与试验力误差均小于0.05%,此控制系统的稳定性、精确性和可靠性得到验证。