A novel method for geometric quality assurance of rock joint replicas in direct shear testing-Part 2:Validation and mechanical replicability

Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies.However,a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking.In this study,a novel method is presented for geometric quality assurance of replicas.The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results.In Part 1 of this study,two quality assurance parameters,smf and V_(Hp100),are derived and their usefulness for evaluation of geometric deviations,i.e.geometric reproducibility,is shown.In Part 2,the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior,which qualifies the parameters for usage in the quality assurance method.Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σ_(mf)<0.06 mm and
|V_(Hp100)|
<0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength.The wear in these replicas,which have similar morphology as the rock joint,is in the same areas as in the rock joint.The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties,possibly from differences in toughness.It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics,which makes them useful in parameter studies.

Effects of water saturation and loading rate on direct shear tests of andesite

For estimating the long-term stability of underground framework,it is vital to learn the mechanical and rheological characteristics of rock in multiple water saturation conditions.However,the majority of previous studies explored the rheological properties of rock in air-dried and water saturated conditions,as well as the water effects on compressive and tensile strengths.In this study,andesite was subjected to direct shear tests under five water saturation conditions,which were controlled by varying the wetting and drying time.The tests were conducted at alternating displacement rates under three vertical stresses.The results reveal that the shear strength decreases exponentially as water saturation increases,and that the increase in shear strength with a tenfold increase in displacement rate is nearly constant for each of the vertical stresses.Based on the findings of the shear tests in this study and the compression and tension tests in previous studies,the influences of both water saturation and loading rate on the Hoek-Brown failure criterion for the andesite was examined.These results indicate that the brittleness index of the andesite,which is defined as the ratio of uniaxial compressive strength to tensile strength,is independent of both water saturation and loading rate and that the influences of the water saturation dependence and the loading rate dependence of the failure criterion can be converted between each other.

ANALYSIS OF SIZE EFFECT,SHEAR DEFORMATION AND DILATION IN DIRECT SHEAR TEST BASED ON GRADIENT- DEPENDENT PLASTICITY

The paper concerns the issue of size law,localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single shear band,and based on gradient-dependent plasticity,an analytical solution on size effect or snap-back is obtained. The results show that the post peak response becomes steeper and even exhibits snap-back with increasing of length. For small specimen,the relative shear displacement when specimen failure occurs is lower than that of larger specimen and the shear stress-relative displacement curve becomes steeper. The theoretical solution on non-uniformity of strains in shear band is obtained and evolution of the relative shear displacement is represented. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain,the dilation and compaction within shear band are analyzed. Relation between apparent shear strain and apparent normal strain and relation between shear displacement and vertical displacement are established.

Mesomechanical simulation of direct shear test on outwash deposits with granular discrete element method

The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. According to the results of laboratory direct shear test on the remolded samples, the soil particle parameters of numerical model based on in-situ particle size cumulative curves and 3D granular discrete element method were determined. Then, numerical experiments on different lithology, stone content and gradation composition were conducted. The results show that it is not a flat surface but a shear band that yields in the sample. The curve of particle velocity vs distance from the designed shear surface of test model that is taken as a datum plane in the vertical section of sample shows in "S" shape. The shear disturbance area is about twice the maximum diameter of stone blocks. The greater the stiffness of stone is, the rougher the shear surface is. The shear strength of outwash deposits is largely controlled by lithology and stone content, and the bite force between stone blocks is the root reason of larger friction angle. It is also shown that strain hardening and low shear dilatancy occur under high confining pressure as well as possibility of shear shrinkage. But it is easy to behave shear dilatation and strain softening under low confining pressure. The relationship between particle frictional coefficient and stone content presents an approximately quadratic parabola increase. The strain energy first increases and then drops with the increase of frictional energy. The cohesion increases with soil stiffness increasing but decreases with stone stiffness increasing. Numerical results are consistent with the laboratory test results of remolded samples, which indicate that this method can be a beneficial supplement to determine the parameters of engineering deposit bodies.

Large-scale direct shear testing of geocell reinforced soil

The tests on the shear property of geocell reinforced soils were carried out by using large-scale direct shear equipment with shear-box-dimensions of 500 mm×500 mm×400 mm (length×width×height). Three types of specimens, silty gravel soil, geocell reinforced silty gravel soil and geocell reinforced cement stabilizing silty gravel soil were used to investigate the shear stress-displacement behavior, the shear strength and the strengthening mechanism of geocell reinforced soils. The comparisons of large-scale shear test with triaxial compression test for the same type of soil were conducted to evaluate the influences of testing method on the shear strength as well. The test results show that the unreinforced soil and geocell reinforced soil give similar nonlinear features on the behavior of shear stress and displacement. The geocell reinforced cement stabilizing soil has a quasi-elastic characteristic in the case of normal stress coming up to 1.0 GPa. The tests with the reinforcement of geocell result in an increase of 244% in cohesion, and the tests with the geocell and the cement stabilization result in an increase of 10 times in cohesion compared with the unreinforced soil. The friction angle does not change markedly. The geocell reinforcement develops a large amount of cohesion on the shear strength of soils.

Numerical simulation of direct shear tests on mechanical properties of talus deposits based on self-adaptive PCNN digital image processing

The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of talus deposits that widely exist in the hydro-power engineering in the southwest of China were first reconstructed by small particles according to the in-situ photographs based on the self-adaptive PCNN digital image processing,and then numerical direct shear tests were carried out for studying the mechanical properties of talus deposits.Results indicate that the reconstructed meso-structures of talus deposits are more consistent with the actual situation because the self-adaptive PCNN digital image processing has a higher discrimination in the details of soil-rock segmentation.The existence and random distribution of rock blocks make the initial shear stiffness,the peak strength and the residual strength higher than those of the "pure soil" with particle size less than 1.25 cm apparently,but reduce the displacements required for the talus deposits reaching its peak shear strength.The increase of rock proportion causes a significant improvement in the internal friction angle of talus deposit,which to a certain degree leads to the characteristics of shear stress-displacement curves having a changing trend from the plastic strain softening deformation to the nonlinear strain hardening deformation,while an unconspicuous increase in cohesion.The uncertainty and heterogeneity of rock distributions cause the differences of rock proportion within shear zone,leading to a relatively strong fluctuation in peak strengths during the shear process,while movement features of rock blocks,such as translation,rotation and crossing,expand the scope of shear zone,increase the required shear force,and also directly lead to the misjudgment that the lower shear strength is obtained from the samples with high rock proportion.That,however,just explains the reason why the shear strength gained from a small amount of indoor test data is not consistent with engineering practice.

Direct shear tests of coarse-grained fillings from high-speed railway subgrade in cold regions

In order to study the shear behavior of coarse-grained fillings taken from the subgrade bottom layer of a cold region high-speed railway,large scale direct shear tests were conducted with different normal pressures,water contents and temperatures.The results indicate that the relationship between shear displacement and shear stress changed from strain-softening at lower normal pressures to strain-hardening at higher normal pressures,in both unfrozen and frozen states.This phenomenon was mainly due to the shear dilatation deformation effect.The shear displacement-shear stress curves show similar stages.Besides,the shear stress rapidly increased and there was not an increment in the shear displacement during the initial stage of the shear process in the frozen state.In both the unfrozen or frozen states at the same water contents,the shear strength increased with increasing normal pressure.

Design and verification of portable direct shear tester with application to remolded colluvium geomaterials

The mechanical properties of colluvium strongly govern the stability of colluvial slopes, and they arc essential for the related analysis and design. Nevertheless, their measurement is not easy on account of heterogeneity in property and difficulty of sampling. This study attempted to evaluate the shear strength of remolded colluvium by means of a simple direct shear test in the field. A portable direct shear tester was designed to overcome the inconvenience and expensiveness of the conventional large-scale in-situ direct shear test. It can be easily assembled and applied for the silnplc field direct shear test. For calibration, the results of the portable direct shear tester were compared with the results of the laboratory direct shear tester for four different types of soil samples, i.e. standard sand, slate debris, arenaceous shale debris and mixture of gravel and sand. Correlation formulas were established based on the calibration, enabling the portable direct shear tester to measure and estimate the shear strength of remoldcd colluvium in field. This study primarily focuses on the colluvium in Central Taiwan, including the lateritic Dadu Terrace and the arcnaceous shale of Taiping-Wufcng mounts. The portable direct shear tester was applied to sites selected in these areas, and the results were furthcr analyzed and discussed.

Presentation of Empirical Equations for Estimating Internal Friction Angle of GW and GC Soils in Mashhad, Iran Using Standard Penetration and Direct Shear Tests and Comparison with Previous Equations

Presentation of empirical equations for estimating engineering properties of soils is a simple, low cost and widely-used method. One of the major concerns in using these equations is evaluating their accuracy in different conditions and regions which often lead to doubts about obtained results. Most of these equations were derived in special laboratories, different climate conditions and in soils with different geotechnical and geological engineering properties and were generalized to other conditions. The main question is that whether these methods are also applicable to other conditions. Using local equations and narrowing the usage range of various methods based on each region’s properties are appropriate methods to solve these problems. This leads to simplified and faster analysis and high reliability in the obtained results. In this paper, empirical equations were derived to estimate internal friction angle, based on SPT numbers of Mashhad City’s soils in Iran, using SPT and direct shear tests results from 50 samples (25 GW and 25 GC soil samples). The results showed similar values for predicted?φ?values by SPT test and?φ?values determined by direct shear tests.

Mathematical Modeling of Shear Stress and Direct Shear Test for Compressible Soil: Case of Soil Bordering the Wouri River

This paper focuses on the development of the mathematical model of shear stress by direct shear test for compressible soil of the littoral region, which will be a great tool in the hand of geotechnical engineers. The most common use of a shear test is to determine the shear strength which is the maximum shear stress that a material can withstand before the failure occurs. This parameter is useful in many engineering designs such as foundations, roads and retaining walls. We carried out an experimental laboratory test of ten samples of undisturbed soil taken at different points of the border of Wouri river of Cameroon. The samples were collected at different depths and a direct shear test was conducted. The investigations have been performed under constant vertical stresses and constant sample volume with the aim to determine the frictional angle and the cohesion of the compressible soil which are so important to establish the conditions of buildings stability. Special care was taken to derive loading conditions actually existing in the ground and to duplicate them in the laboratory. Given that the buildings constructed in this area are subjected to settlement, landslide, and punch break or shear failure, the cohesion and the frictional angle are determined through the rupture line after assessed the mean values of the shear stress for the considered ten samples. The bearing capacity of the soil, which is the fundamental soil parameter, was calculated. From the laboratory experimental results, the least squared method was used to derive an approximated mathematical model of the shearing stress. Many optimizations methods were then considered to reach the best adjustment.

Study on Shear Strength Characteristics of Basalt-Concrete Bonding Interface Based on in-situ Direct Shear Test

In rock engineering,the shear strength of the basalt-concrete bonding interface is a key factor affecting the shear performance of hydroelectric dam foundations,embedded rock piles and rock bolts.In this study,30 sets of in-situ direct shear tests were conducted on the basalt-concrete bond interface in the Baihetan dam area to investigate the shear strength characteristics of the basalt-concrete bonding interface.The bonding interface contains two states,i.e.,the bonding interface is not sheared,termed as se(symbolic meaning see Table 1);the bonding interface is sheared with rupture surface,termed as si.The effects of lithology,Joints structure,rock type grade and concrete compressive strength on the shear strength of the concrete-basalt contact surface were investigated.The test results show that the shear strength of the bonding interface(s_(e)&s_(i))of columnar jointed basalt with concrete is greater than that of the bonding interface(s_(e)&s_(i))of non-columnar jointed one with the same rock type grade.When the rock type grade isⅢ_(2),fcol is 1.22 times higher than fncol and ccol is 1.13 times greater than cncol.The shear strength parameters of the basalt-concrete bonding interface differ significantly for different lithologies.The cohesion of the bonding interface(s_(i))of cryptocrystalline basalt with concrete is 2.05 times higher than that of the bonding interface(s_(i))of breccia lava with concrete under the same rock type grade condition.Rock type grade has a large influence on the shear strength of the non-columnar jointed basalt-concrete bonding interface(s_(e)&s_(i)).cnol increases by 33%when the grade of rock type rises fromⅢ_(1)toⅡ_(1).the rock type grade has a greater effect on bonding interface(s_(i))cohesion than the coefficient of friction.When the rock type grade is reduced fromⅢ_(2)toⅢ_(1),f_(ncol)′increases by 2%and c_(ncol)′improves by 44%.The shear strength of the non-columnar jointed basalt-concrete bonding interface(s_(e)&s_(i))increases with the increase of the compressive strength of concrete.When concrete compressive strength rises from 22.2 to 27.6 MPa,the cohesion increases by 94%.

Numerical analysis of loess and weak intercalated layer failure behavior under direct shearing and cyclic loading

The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China.The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software.Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing,and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity.The macroscopic properties and damage patterns were obtained for six numerical configurations;namely,loess-weathered mudstone with 0°,10°,and-10°joints and weathered mudstone with 0°,10°,and-10°weak intercalated layers.The numerical test results revealed that,in the direct shear tests,the shear stress and shear displacement of the samples increased with the normal stress.In the cyclic shear tests with a total cycle number N=20,the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop.The numerical tests also revealed that,under cyclic shear,the normal stress and shear velocity affected the shear strength.The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations.Compared with the damage pattern of the direct shear tests,the damage of the cyclic shear tests mainly comprised shear cracks and fractures,some shaking consolidation settlement and fewer shear strain occurred around the joints.In the direct shear tests,more compression cracks and fractures occurred in the samples.The damage mainly developed along the joints,and shearing-off damage occurred.The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China.

Application of in situ direct shear device to shear strength measurement of rockfill materials

A simplified in situ direct shear test （DST） was developed for measuring the shear strength of soils in fields. In this test, a latticed sheafing frame replaces the upper half of the shear box used in the conventional direct shear box test. The latticed shearing frame is directly embedded in the ground to be tested after a construction process and is pulled with a flexible chain while a constant dead load is applied to the sample in the sheafing frame. This simplified in situ DST has been validated by comparing its results with those of triaxial tests on samples with parallel gradations under normal stresses less than 100 kPa. In this study, the DST was further validated by carrying out tests on samples with the same gradations, rather than on samples with parallel gradations, under normal stresses up to 880 kPa. In addition, the DST was performed inside fills in two applications.

Shear Strength of Unbound Crop By-Products Using the Direct Shear Box Apparatus

The return to old building methods by mixing crop by-products with mineral binders is arousing great interest in Europe since about 25 years.The use of these bio-aggregates based materials for the design of building envelopes is a valuable opportunity to deal with increasingly demanding thermal regulations.In addition,the regulatory framework is moving towards reducing the overall car-bon footprint of new buildings.Some traditional and historic buildings are based on timber framing with earth-straw as infill material for instance.Hemp concrete is a bio-based material that can be manually tamped in timber stud walls or more recently in the form of precast blocks.Owing to their low compressive strength,bio-based concretes using a large volume fraction of plant-derived aggregates are only considered as thermal and sound insulation materials.The structural design practice of wood frame walls does not assume any mechanical contribution of hemp concrete whereas it may contribute to the racking strength of the structure.In this context,more research is needed regarding the shear behavior of crop by-products and bio-based concretes.In this case,the objective of the study was to perform direct shear tests under three levels of normal pressure on hemp shiv and rice husk as unbound crop by-products.The results showed that the friction angle of the granular skeleton based on rice husk for a given relative displacement was significantly lower than that measured on hemp shiv.This is in accordance with what had been observed on bio-based concretes cast by mixing aggregates with lime and shear strength parameters measured by means of triaxial compression.

Shear behaviour of a rock bridge sandwiched between incipient joints under the influence of hydraulic pressures

The rock bridges sandwiched in incipiently jointed rock mass were considered as barriers that block the fluid seepage,and provide certain shear strength reservation.For better revealing the influence of hydraulic pressure on the failure behaviour of rock bridges,direct shear tests were carried out through a newly proposed method on rock samples that contain two parallel incipient joints.By developing the gypsum-silicone pad coupling samples,a conventional triaxial test system was qualified to implement direct shear tests with satisfied sealing capability.The results showed that the rock bridges could be failed through the tensile failure,shear failure and mixed failure mechanism.The hydraulic pressure would facilitate the tensile failure mechanism and induce rougher fracture surfaces;while the normal stress would facilitate the shear failure mechanism and induce less rough fracture.The hydraulic pressure reduced the global shear strength of the rock block through reducing the efficient normal stress applied on the rock bridge area,which was highly dependent on the joint persistence,k.Moreover,because of the iterating occurrence of the hydraulic pressure lag with the fracture propagation,the rock bridge failure stage in the shear stress-shear displacement curves displayed a fluctuation trend.

砂土-混凝土接触面剪切带细观变形特征的试验研究

接触面剪切带的细观变形特征是研究结构物与土体相互作用的核心问题。为探明砂土-混凝土接触面剪切带变形特征,利用大型直剪仪开展砂土-混凝土接触面直剪试验,采用灌砂变形标记法实测砂土变形,依据标记线剪应变沿竖向的变化特征对砂土变形区域进行划分。在此基础上,研究粗糙度、法向应力和密实度对砂土-混凝土接触面剪切带细观变形特征的影响规律。研究结果表明:1)砂土可分为非剪切区、过渡区和应变集中区,应变集中区仅存在剪切面之上。2)规则型接触面的上剪切带厚度均值为33D_(50),远大于下剪切带9D_(50)和“光滑”接触面剪切带厚度20.4D_(50)。3)密实度对剪切带及其过渡区厚度的影响微弱,而粗糙度对其影响显著;法向应力、密实度对应变集中区厚度影响有限,应变集中区厚度随粗糙度的增大近似线性增大;应变集中区长度随粗糙度的增大先增大后减小,随密实度的增大近似线性增大,随法向应力增大而减小。4)随剪切位移增大,上剪切带厚度不断增大而下剪切带厚度先增大后保持基本不变,应变集中区的长度增大,但剪切位移对应变集中区厚度的影响有限。5)获得归一化剪切带厚度取值h_(t)/D_(50)与D_(50)的关系,在有限元模拟规则型结构与砂土的相互作用时,建议砂土体细化网格单元的范围不小于最大剪切带厚度37D_(50)。研究成果深化了砂土-规则型接触面剪切带变形特征的认识,可为大粗糙度、带肋桩的承载变形特性的精细化有限元模拟分析提供重要参考和依据。

高摩阻超静定土工格栅在粗粒土夹层中的剪胀作用研究

在加筋土工程中,采用异型格栅和设置粗粒土夹层可以有效增强筋土相互作用。然而粗粒土夹层厚度的确定方法仍有待进一步研究。基于一种带有凸起节点结构的高摩阻超静定土工格栅(high resistance hyperstatic geogrids,简称HRHG)与砾石的直剪试验结果,建立了剪切硬化筋土界面的剪胀本构模型,并进一步研究了筋土剪胀应力在土体内引起附加应力的分布规律。通过开展不同法向压力(30、50、80 kPa)下的直剪试验,研究了不同粗粒土夹层厚度(60、100、140、180 mm)对筋土相互作用的影响,并与筋土界面剪胀应力的分布规律进行了对比分析。结果表明,筋土界面剪胀本构模型可以有效计算剪缩位移和剪胀位移,且最终剪胀位移随法向压力增加而减小。由界面剪胀应力引起的粗粒土中附加应力随着与筋土界面距离的增加而降低,但是剪胀范围逐步增大。粗粒土夹层厚度的增加可以有效提高界面剪切强度,但存在最优夹层厚度使界面剪切强度的增幅迅速降低。最优夹层厚度随着法向压力的增加而减小。通过对比分析最优夹层厚度与剪胀应力比之间的关系,提出了基于筋土界面剪胀本构模型的确定最优夹层厚度的半经验公式,可为HRHG在工程中的设计或应用提供参考。

贯通型标准JRC双节理剪切力学及声发射特性研究

节理岩体的抗剪性能是影响工程岩体强度及稳定性的关键因素。基于3D打印技术制作标准JRC节理面模具和固定夹板,采取一体化浇筑方式制备不同节理面间距和不同粗糙度的双节理试样,结合声发射(acousticemission,AE)技术探究不同法向应力条件下粗糙双节理岩体剪切力学特性和破坏演化特征。结果表明:剪切应力-剪切位移曲线形态受节理粗糙度和法向应力共同影响。随JRC和法向应力的增加,剪切应力软化程度加重;法向应力较大时,峰后阶段剪切应力存在多次突降现象,突降值随法向应力的增加而增大。峰值剪切强度出现在双节理间岩石夹层断裂时刻,随JRC和法向应力的增加呈增大趋势,随节理面间距增加呈减小趋势。AE结果表明:岩石夹层断裂时刻AE能量大幅突增,AE能量峰值稍滞后于剪切应力峰值,随法向应力的增加,AE能量峰值和累积AE能量值增大;AE定位点空间上集中于岩石夹层部分,时间上频发于200~600 s内,随节理面间距的增加,AE定位点的集中范围扩大。

冻融作用下冰碛体剪切特性与围岩压力研究

冰碛体是由冰川作用搬运大量碎屑物质堆积形成的特殊岩土体。受赋存的地理及气候条件影响,冻融作用会对穿越该类围岩的隧道尤其是洞口段的工程建设带来挑战。笔者调研了中国西藏地区冰碛体围岩地质条件,设置冻融循环直剪试验研究了冻融循环次数与含水率对冻结冰碛体的力学特性和力学指标影响,引入冻融次数与含水率综合参数K,拟合得出黏聚力c公式。结果表明:冻融循环和含水率对冰碛体黏聚力c有较大影响。改进了太沙基理论,提出了适用于冰碛体围岩隧道洞口段的围岩压力计算公式。以昌林铁路某隧道为例,计算不同条件下的围岩压力,验证了公式的合理性。研究发现:冻融循环和含水率是影响冰碛体力学性能变化的重要因素,冻融作用对洞口段隧道围岩压力有不同程度的影响,在工程建设中应充分考虑。

岩性特征对混凝土坝体-基岩原位直剪试验力学特性影响分析

以广西巴马县坡月水库工程为研究对象,采用平推法开展不同法向应力(0.4、0.8、1.2、1.6、2.0 MPa)下混凝土坝体-基岩原位直剪试验,探究岩性特征对混凝土坝体-基岩力学特性的影响。结果表明,不同法向应力下试样的剪切应力-位移曲线均表现出试样内部初始缺陷受力微裂纹扩展的稳定扩展阶段、微裂缝逐渐扩展形成宏观裂缝的不稳定扩展阶段及混凝土与岩体分离的开裂阶段3个阶段;法向应力、岩体岩性对试样的断裂能均有显著影响。不同法向应力下,试样断裂能的范围为16.65~177.28 N/m,断裂能随着法向应力或灰色砂岩含量增大而增大,随泥质粉砂岩含量或风化程度增大而减小;混凝土坝体-基岩的抗剪强度随基岩中灰色砂岩含量增大而增大,随泥质粉砂岩含量或基岩风化程度增大而减小。研究结果可为类似研究提供试验参考。