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1.

Backward erosion piping (BEP) is a failure mechanism that can affect the safety of water-retaining structures. It can occur when a local anomaly on the downstream side of an embankment causes a concentration of seepage flow at that location. Shallow pipes may then form, progressing in the upstream direction and leading to a collapse of the water-retaining structure. A novel and economically appealing measure against BEP is the coarse sand barrier (CSB), which is now being developed in a multiscale experimental programme in the Netherlands. The method involves placing a trench filled with coarse sand below the blanket layer on the downstream side of the embankment. The CSB prevents the upstream progression of the pipe and significantly enhances resistance to BEP. This paper presents medium-scale laboratory tests involving a range of sands, barrier depths and relative densities. The piping process and the observations of pipe progression in the presence of a CSB are presented, followed by a conceptual model. The presence of a CSB changed the erosion pattern. It resulted in pipe formation perpendicular to the flow direction over the entire width of the barrier before the barrier was damaged. The findings also demonstrate the effect of material properties on pipe initiation, progression and pipe depth. Measurements of the pipe depth are presented and analysed, revealing the significance of pipe depth for understanding the piping process. This analysis shows considerable erosion in the downstream background sand and demonstrates that erosion profiles and measured pipe depths are significantly larger than in BEP tests without a CSB.

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2.

Backward erosion piping (BEP) is a form of internal erosion which can lead to failure of levees and dams. Most research focused on the critical head difference at which piping failure occurs. Two aspects have received less attention, namely (1) the temporal evolution of piping and (2) the local hydraulic conditions in the pipe and at the pipe tip. We present small-scale experiments with local pressure measurements in the pipe during equilibrium and pipe progression for different sands and degrees of hydraulic loading. The experiments confirm a positive relation between progression rate and grain size as well as the degree of hydraulic overloading. Furthermore, the analysis of local hydraulic conditions shows that the rate of BEP progression can be better explained by the bed shear stress and sediment transport in the pipe than by the seepage velocity at the pipe tip. The experiments show how different processes contribute to the piping process and these insights provide a first empirical basis for modeling pipe development using coupled seepage-sediment transport equations.

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3.
The Effects of Fines on the Behaviour of a Sand Mixture   总被引：1，自引：0，他引：1  
Intergranular void ratio, e s, can be used as an alternative indicator to assess the mechanical properties of composite matrix of coarse and fine grains. In this paper, an intensive laboratory study of saturated coarse rotund sand and fine angular sand mixtures with various mix ratios is investigated by a series of oedometer and direct shear tests. Oedometer tests performed on the mixtures show that fines percentages and stress conditions affect the compression behaviours. Tests indicated that, up to a fraction of fines, which is named as transition fines content (FCt), compression behaviour of the mixture is mainly governed by the sand grains. As the percentage of fines exceeds FCt finer grains govern the compression. Performed direct shear tests revealed that there is a relationship between the FCt and shear strength, which is harmonic with the oedometer test results.  相似文献   

4.
Suffusion involves fine particles migration within the matrix of coarse fraction under seepage flow, which usually occurs in the gap-graded material of dams and levees. Key factors controlling the soil erodibility include confining pressure (p′) and fines content (Fc), of which the coupling effect on suffusion still remains contradictory, as concluded from different studies considering narrow scope of these factors. For this reason, a systematical numerical simulation that considers a relative wide range of p′ and Fc was performed with the coupled discrete element method and computational fluid dynamics approach. Two distinct macroresponses of soil suffusion to p′ were revealed, ie, for a given hydraulic gradient i = 2, an increase in p′ intensifies the suffusion of soil with fines overfilling the voids (eg, Fc = 35%), but have negligible effects on the suffusion of gap-graded soil containing fines underfilling the voids (eg, Fc = 20%). The micromechanical analyses, including force chain buckling and strain energy release, reveal that when the fines overfilled the voids between coarse particles (eg, Fc = 35%) and participated heavily in load-bearing, the erosion of fines under high i could cause the collapse of the original force transmission structure. The release of higher strain energy within samples under higher p′ accelerated particle movement and intensified suffusion. Conversely, in the case where the fines underfilled the voids between coarse particles (eg, Fc = 20%), the selective erosion of fines had little influence on the force network. High p′ in this case prevented suffusion.  相似文献   

5.
This paper presents a computational method able to effectively model both the simultaneous processes typically observed in backward erosion piping, ie, the pipe tip propagation and the conduit cross-section enlargement. The numerical method is based on the novel formulation of a problem of localized erosion along a line propagating in a multidimensional porous medium. In this line, a conduit with evolving transverse size is embedded, which conveys a multiphase flow. The two systems, porous medium and pipe, are bridged by exchange terms of multiphase fluid mass and by a shared fluid pressure field. On the contrary, different fields are considered to describe flows, which are assumed as Darcian in the porous medium and turbulent in the conduit. These two flows drive pipe propagation and enlargement, respectively, as modeled by means of proper erosion kinetic laws. The corresponding numerical formulation is based on the combination between one- and multidimensional finite elements, to model the erosion conduit and the porous medium, respectively. Several simulations are proposed to demonstrate the ability of the proposed approach in reproducing available experimental data of real-scale tests on levees. Our results point out the crucial role played by the combined influence of pipe propagation and enlargement, as well as of three-dimensional (3D) effects. We also assess the mesh independence of the proposed numerical solution, particularly as concerns the calculated pipe propagation history.  相似文献   

6.
Measurements of sand transport by wind on a natural beach   总被引：6，自引：0，他引：6  
Bagnold's (1954) and Kawamura's (1951) formulae may be used for the calculation of the sand movement on a natural beach, provided the shear stress velocity U* > 0·D4 m/s. Great discrepancies have been found between calculated and measured sand transport rates for U* < 0·D4 m/s, mainly because of the capillary forces acting on a wet beach. The measured critical shear velocity U*c at the beginning of sand movement on a clean dry beach agrees very well with that predicted by Bagnold's formula. On a dry beach where the sand grains are stuck together, U*c was found to be about 10% higher. On a wet beach U*c appeared to depend on the moisture content of the surface layer. Grain size is a determining parameter in the U*c-moisture content relation. When the angle a between the wind direction at sea and the dune face is between 15° and 85° the streamlines of the wind will bend in the vicinity of the dune face. In consequence this may influence the direction of sediment movement.  相似文献   

7.
By applying the Griffith stress criterion of brittle failure, one can find that the uniaxial compressive strength (σc) of rocks is eight times the value of the uniaxial tensile strength (σt). The Griffith strength ratio is smaller than what is normally measured for rocks, even with the consideration of crack closure. The reason is that Griffith’s theories address only the initiation of failure. Under tensile conditions, the crack propagation is unstable so that the tensile crack propagation stress (σcd)t and the peak tensile strength σt are almost identical to the tensile crack initiation stress (σci)t. On the other hand, the crack growth after crack initiation is stable under a predominantly compressive condition. Additional loading is required in compression to bring the stress from the crack initiation stress σci to the peak strength σc. It is proposed to estimate the tensile strength of strong brittle rocks from the strength ratio of R = \fracs\textc | s\textt | = 8\fracs\textc s\textci . R = {\frac{{\sigma_{\text{c}} }}{{\left| {\sigma_{\text{t}} } \right|}}} = 8{\frac{{\sigma_{\text{c}} }}{{\sigma_{\text{ci}} }}}. The term \fracs\textc s\textci {\frac{{\sigma_{\text{c}} }}{{\sigma_{\text{ci}} }}} accounts for the difference of crack growth or propagation in tension and compression in uniaxial compression tests. \fracsc sci {\frac{{\sigma_{c} }}{{\sigma_{ci} }}} depends on rock heterogeneity and is larger for coarse grained rocks than for fine grained rocks. σci can be obtained from volumetric strain measurement or acoustic emission (AE) monitoring. With the strength ratio R determined, the tensile strength can be indirectly obtained from | s\textt | = \fracs\textc R = \fracs\textci 8. \left| {\sigma_{\text{t}} } \right| = {\frac{{\sigma_{\text{c}} }}{R}} = {\frac{{\sigma_{\text{ci}} }}{8}}. It is found that the predicted tensile strengths using this method are in good agreement with test data. Finally, a practical estimate of the Hoek–Brown strength parameter m i is presented and a bi-segmental or multi-segmental representation of the Hoek–Brown strength envelope is suggested for some brittle rocks. In this fashion, the rock strength parameters like σt and m i, which require specialty tests such as direct tensile (or Brazilian) and triaxial compression tests for their determination, can be reasonably estimated from uniaxial compression tests.  相似文献   

8.
OuYang  Haoran  Dai  Guoliang  Qin  Wei  Zhang  Chengfeng  Zhu  Wenbo  Gong  Weiming 《Acta Geotechnica》2022,17(9):3927-3946

The behavior of calcareous sand under repeated impact considerably differs from that of silica sand. Notably, calcareous sand is important in engineering projects in the South China Sea, such as pile driving. To understand the behavior of calcareous sand under multiple impacts, the improved split Hopkinson pressure bar (SHPB) system was selected for one-dimensional impact tests of silica and calcareous sand with particle sizes of 0.25–0.50 mm. The sand specimens were impacted 1, 3, 7 and 10 times. The test results reveal that the dynamic apparent stiffness of silica sand is approximately 6–8 times that of calcareous sand. The dynamic apparent modulus values of the two sands increase with an increase in the number of impacts, N. For calcareous sand, the compression index Cc decreases with an increase in N, and silica sand shows the opposite trend. The yield pressure pc of calcareous sand under impact loading is approximately 40% of that of silica sand. With an increase in N, the energy absorption capacity, energy dissipation rate and damage variables of the two sands exhibit a downward trend. In addition, the energy absorption efficiency of calcareous sand is better than that of silica sand. During the process of impact, a large number of sand particles will break, and particle breakage will change the particle size distribution (PSD), thereby significantly affecting the physical and mechanical properties of the corresponding soil. Based on the test results and fractal theory, an evolution model is established to characterize the PSD evolution in the breakage state for uniformly graded calcareous sand. Moreover, a Markov chain model is proposed to describe the PSD evolution of nonuniformly graded specimens. The predicted results of both models show agreement with the experimental values.

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9.
王霜  陈建生  周鹏 《岩土力学》2015,36(10):2847-2854
对由弱透水黏土层、细砂层和强透水砂砾层组成的三层堤基进行了管涌发展的砂槽模型试验,为了便于观察分析,细砂层由各种颜色的细彩砂依次排列在砂砾石层上表面,通过改变彩砂层的厚度分析研究了不同细砂层厚度对管涌发生、发展机制及过程的影响。试验结果表明,三层堤基细砂层厚度的不同使管涌发生的临界水力梯度、涌砂量和通道发展的速度不同,与双层堤基有很大区别。临界水力梯度是由多种元素决定的,包括破坏土体的性质及其整体性等;细砂层的存在使流量在渗透变形初期对涌砂不敏感;在试验中发生的相同水位下多次间歇性涌砂,其原因一方面是颗粒在运动过程中发生堵塞,另一方面是通道边界的土体失去支撑发生应力释放,抵抗力随着时间逐渐减小。  相似文献   

10.
Discordant ultramafic pipes cut most of the layered sequence of the Bushveld Complex. We have studied one pipe in detail, the Tweefontein pipe, which cuts the Critical Zone, eastern Bushveld Complex, because it is well-exposed in a new road cutting. Field relations suggest that these pipes were emplaced while the layered rocks were extremely hot and incapable of brittle failure. The existence of displaced chromitite and anorthosite fragments in this discordant body is suggestive of an intrusive magmatic, rather than metasomatic, mode of emplacement. Initial Sr isotopic ratios of plagioclase from the pipe are in the range 0.7073 to 0.7079, which contrast with typical ratios of 0.7055 to 0.7065 for the Critical Zone, and >0.708 for Main Zone. These data preclude an origin for the pipe as residual magmas from the adjacent layered rocks. The compositions of, and extensive exsolution in, pyroxenes in the pipe indicate temperatures of formation comparable to those of the layered sequence itself, and that they underwent slow cooling comparable to the surrounding layered rocks, such that they both have similar closure temperatures. Preferential replacement of leuconoritic layers suggests a temperature of emplacement in excess of the plagioclase–pyroxene cotectic temperature. The per mil δ18O difference between plagioclase and pyroxene (Δplag–px) for samples from within the pipes ranges from 0.4 to 1.0, and averages 0.7 (for nine pairs), compared to Δplag–px of 0.4 to 0.6 for host rocks, again consistent with magmatic temperatures of formation. Oxygen isotope ratios for plagioclase and pyroxene in the pipes and layered host rocks are comparable, and preclude a significant fluid contribution from metamorphosed sediments in the floor of the Bushveld Complex in the formation of the primary mineralogy. The presence of hornblende, and occasional higher Δplag–px values than in the normal layered sequence rocks suggest lower temperature equilibration in the pipe, probably in the presence of a fluid. Higher absolute δ18O values for both minerals in a few of the pipe and host samples suggest reaction with a later fluid. These discordant ultramafic pipes are considered to form by emplacement of magma batches, which are Sr-isotopically distinct from those which produced the adjacent layered rocks of the Bushveld Complex, but were nevertheless extremely closely related in time to the main intrusive events. Dissolution of host rocks, rather than purely mechanical dilation, provided the space for pipe emplacement. However, the pipe may have acted ultimately as a channelway for low-temperature hydrothermal fluids related to later faulting in the immediate vicinity. Received: 10 October 1998 / Accepted: 22 May 2000  相似文献   

11.
The stability of sublittoral, fine-grained sediments in a subarctic estuary   总被引：1，自引：0，他引：1  
The erodibility of natural estuarine sediments was measured in sit along a longitudinal transect of Manitounuk Sound, Hudson Bay, using the benthic flume Sea Carousel. Sedimentation processes along the transect varied from continuous, rapid, post-glacial sedimentation in the inner Sound, to glacial outcrops and seabed reworking of the outer Sound. The grain size and physical bulk properties reflect changes in depositional environment and correlate with sediment erosion threshold stress (τc), erosion rate (E), erosion type and still-water mass settling rate. There was a steady increase in τc (0·8–2·0 Pa) with distance down the Sound in parallel with the decreasing sedimentation rate (0·003–0·001 m yr?1) and increasing sediment bulk density (1650–2010 kg m?3). The near-surface friction coefficient varied up to 68° in proportion to the clay content of post-glacial material. Glacial sediments were characterized by variable results and generally higher friction coefficients. Seabed erosion in Sea Carousel began with surface creep of loose aggregates, pellets and organic debris. This was followed by Type I bed erosion at rates that varied between 0·0002 and 0·0032 kg m?2 s?1 (mean 0·0015). Type I peak erosion rate was inversely related to applied bed shear stress (τo). Type II erosion succeeded Type I, often after a broad transitional period. Simulations of suspended sediment concentration in Sea Carousel were made using four commonly used erosion (E) algorithms. The best results were obtained using Krone's dimensionless ratio relationship: E=M(τo/τc-1). Simulations were highly sensitive to the definition of erosion threshold with sediment depth [τc(z)]. Small errors in definition of τc(z) caused large errors in the prediction of suspended sediment concentration which far exceeded differences between the methods tested.  相似文献   

12.
The paper considers two techniques to model the Cone Penetration Test (CPT) end resistance, qc in a dense sand deposit using commercial finite element programmes. In the first approach, Plaxis was used to perform spherical cavity expansion analyses at multiple depths. Two soil models, namely; the Mohr–Coulomb (MC) and Hardening Soil (HS) models were utilized. When calibrated using simple laboratory element tests, the HS model was found to provide good estimates of qc. However, at shallow depths, where the over-consolidation ratio of the sand was highest, the relatively large horizontal stresses developed prevented the full development of the failure zone resulting in under-estimation of the qc value. The second approach involved direct simulation of cone penetration using a large-strain analysis implemented in Abaqus/Explicit. The Arbitrary Lagrangian Eulerian (ALE) technique was used to prevent excessive mesh deformation. Although the Druker–Prager soil model used was not as sophisticated as the HS model, excellent agreement was achieved between the predicted and measured qc profiles.  相似文献   

13.
管涌对堤防工程的危害极为严重,人类对管涌的认识也逐渐加深。目前,对管涌破坏开始的条件及其破坏后通道贯通的后果了解较多,然而,因其破坏及发展机制的复杂性,对于管涌发生后涌砂及流量的研究并不深入。通过自行设计的室内模型,改变上覆黏土的厚度对3组土性相同的无黏性土试样进行试验。对测压管水头、通道范围、涌砂量和流量等进行对比分析,研究孔隙率、渗透系数以及流量的变化规律,发现涌砂随时间变化满足非线性关系--Boltzmann模型。最后,利用渗透系数与孔隙率以及孔隙率与累计涌砂量的关系,推导并验证了流量随时间变化的理论公式。这对于认识管涌和有效控制管涌发展以及减灾避难有着非常重要的意义。  相似文献   

14.
Soil degradation resulted from unreasonable land use and erosion has been a serious problem in the black soil region of northeastern China. This paper seeks to understand the relationships between topsoil properties and topography and land use for land management targeting at improving soil quality in this region. A total of 292 soil samples and 81 volumetric rings were taken from a typical small watershed of the region in June 2005 for examining total carbon (TC), total nitrogen (TN), soil texture (classified into gravel, sand, silt, and clay), and bulk density (ρ b), respectively. Spatial variability of these soil properties was evaluated with classical statistics and geostatistics methods. The results of classical statistics indicated that TC, TN, sand, silt, clay content, and ρ b were moderate variables while gravel had great variability. Soil properties were mainly correlated to slope position, elevation and land types. Geostatistical analyses showed that the spatial autocorrelation for TC, TN, and silt was weak, strong for clay and moderate for and ρ b sand, respectively. The spatial variations of soil properties are affected comprehensively by topographic factors, land use, erosion, and erosion control in this watershed. Past erosion, however, is the most important component to induce change of soil properties. In this small watershed, current soil and water conservation measures play an important role in controlling soil loss. But the restoration of soil properties was unsatisfactory. Comparing with untilled soil of this region, TC, TN, silt content are excessively low; whereas ρ b, sand and clay content are excessively high; gravel appears at most sampling locations. It is necessary for improving soil properties to protect forest and grassland and change cultivation system of farmlands.  相似文献   

15.
ABSTRACT In situ measurements of lakebed sediment erodibility were made on three sites in Hamilton Harbour, Lake Ontario, using the benthic flume Sea Carousel. Three methods of estimating the surface erosion threshold (τc(0)) from a Carousel time series were evaluated: the first method fits measures of bed strength to eroded depth (the failure envelope) and evaluates threshold as the surface intercept; the second method regresses mean erosion rate (Em) with bed shear stress and solves for the floc erosion rate (Ef) to derive the threshold for Em = Ef = 1 × 10?5 kg m?2 s?1; the third method extrapolates a regression of suspended sediment concentration (S) and fluid transmitted bed shear stress (τ0) to ambient concentrations. The first field site was undisturbed (C) and acted as a control; the second (W) was disturbed through ploughing and water injection as part of lakebed treatment, whereas the third site (OIP) was disturbed and injected with an oxidant used for remediation of contaminated sediment. The main objectives of this study were: (1) to evaluate the three different methods of deriving erosion threshold; (2) to compare the physical behaviour of lacustrine sediments with their marine estuarine counterparts; and (3) to examine the effects of ploughing and chemical treatment of contaminated sediment on bed stability. Five deployments of Sea Carousel were carried out at the control site. Mean erosion thresholds for the three methods were: τc(0) = 0·5 (±0·06), 0·27 (±0·01) and 0·34 (±0·03) Pa respectively. Method 1 overpredicted bed strength as it was insensitive to effects in the surface 1–2 mm, and the fit of the failure envelope was also highly subjective. Method 2 exhibited a wide scatter in the data (low correlation coefficients), and definition of the baseline erosion rate (Ef) is largely arbitrary in the literature. Method 3 yielded stable (high correlation coefficients), reproducible and objective results and is thus recommended for evaluation of the erosion threshold. The results of this method correlated well with sediment bulk density and followed the same trend as marine counterparts from widely varying sites. Mass settling rates, expressed as a decay constant, k, of S(t), were strongly related to the maximum turbidity at the onset of settling (Smax) and were also in continuity with marine counterparts. Thus, it appears that differences in salinity had little effect on mass settling rates in the examples presented, and that biological activity dominated any effects normally attributable to changes in salinity. Bedload transport of eroded aggregates (2–4 mm in diameter) took place by rolling below a mean tangential flow velocity (Uy) of 0·32 ms?1 and by saltation at higher velocities. Mass transport as bedload was a maximum at Uy = 0·4 ms?1, although bedload never exceeded 1% of the suspended load. The proportion of material moving as bedload was greatest at the onset of erosion but decreased as flow competence increased. Given the low bulk density and strength of the lakebed sediment, the presence of a bedload component is notable. Bedload transport over eroding cohesive substrates should be greater in estuaries, where both sediment density and strength are usually higher. Significant differences between the ploughed and control sites were apparent in both the erosion rate and the friction coefficient (φ), and suggest that bed recovery after disruption is rapid (< 24 h). τc(0) increased linearly with time after ploughing and recovered to the control mean value within 3 days. The friction coefficient was reduced to zero by ploughing (diagnostic of fluidization), but increased linearly with time, regaining control values within 6 days. No long‐term reduction in bed strength due to remediation was apparent.  相似文献   

16.
The variation and anisotropy in hydraulic conductivity and the coefficient of consolidation was investigated for two Swedish sulphide clays. A series of constant rate of strain oedometer tests was performed on samples trimmed in the vertical and horizontal direction. A methodology to evaluate the horizontal coefficients of consolidation c h via the horizontal hydraulic conductivity k h and the vertical compression modulus M v is proposed. Laboratory evaluations of c h are also compared with determinations of c h from in situ piezometer measurements in vertically drained sulphide clay. Furthermore, the validity of the empirical correlation between hydraulic conductivity change index C k and initial void ratio e 0, C k  = 0.5e 0 (Tavenas et al. in Can Geotech J 20(4):645–660, 1983b), was investigated for the sulphide clays. The results from the investigation show large ranges in measured hydraulic conductivities and coefficients of consolidation. However, the results indicate that the correlation C k  = 0.5e 0 is valid. The anisotropy in hydraulic conductivity and the coefficient of consolidation of the sulphide clays tested seems to be small. For design purposes, multiple tests for assessment of hydraulic conductivity and the coefficient of consolidation should be made, and a partial factor of safety, depending on the requisite level of safety and the spatial variability of the parameters, should be introduced. For design purposes in this type of clay, k h  = k v and c h  = c v are suggested.  相似文献   

17.
Clastic injection and surface expression of subsurface sediment remobilization is a phenomenon which is becoming increasingly recognized. However, understanding of the physical mechanisms that control these features remains limited, dominated by inference from outcrop and seismic studies. Here, this limitation is addressed through a set of experiments focused on the development and evolution of fluidization features in non‐cohesive bedded sequences. Fluidization and the onset of piping are shown to occur progressively through a sequence of discrete phases, with initial void formation, development of infiltration horizons, rupture and finally pipe formation. Critically, the style of piping, the stability of piping and the temporal evolution of venting are shown to exhibit considerable variability. In particular, pipes may either be stable or very mobile, migrating laterally over large distances; these produce deposits that are typically interpreted in outcrop as being the product of en masse liquefaction rather than localized, dynamic fluidization. These differing elements are synthesized to produce a model of sand extrudites. In addition, the implications of this model are explored.  相似文献   

18.
Granular materials like sand are widely used in civil engineering. They are composed of different sizes of grains, which generate a complex behaviour, difficult to assess experimentally. Internal instability of a granular material is its inability to prevent the loss of its fine particles under flow effect. It is geometrically possible if the fine particles can migrate through the pores of the coarse soil matrix and results in a change in its mechanical properties. This paper uses the three‐dimensional Particle Flow Code (PFC3D/DEM) to study the stability/instability of granular materials and their mechanical behaviour after suffusion. Stability properties of widely graded materials are analysed by simulating the transport of smaller particles through the constrictions formed by the coarse particles under the effect of a downward flow with uniform pressure gradient. A sample made by an initially stable material according to the Kenney & Lau geometrical criterion was divided into five equal layers. The classification of these layers by this criterion before and after the test shows that even stable granular materials can lose fine particles and present local instability. The failure criterion of eroded samples, in which erosion is simulated by progressive removal of fine particles, evolves in an unexpected way. Internal friction angle increases with the initial porosity, the rate of lost fine particles and the average diameter D50. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

19.
邕江防洪水堤是南宁市唯一抵御洪水侵害的防线,其堤基为河床和河漫滩相冲洪积物。下部中、粗砂层和圆砾层属管涌层;中部粉砂层、粉土层属流土层;上部粘性土层;底部为第三系泥岩层。本文通过对场地管涌县、流土层判别、水文地质条件概化、地下水回水位预测、盖层变形破坏预测和地下水水力坡降计算,来预测场地发生管涌地质灾害的可能性。  相似文献   

20.
细砂层埋深对堤基管涌影响的试验研究   总被引：1，自引：0，他引：1  
不同土层结构的堤基,其管涌发生和发展的情形不同。以前的研究多集中于双层堤基的情况。事实上,含夹砂层堤基中,位于砂砾石层内的细砂层会对堤基管涌的发生产生重大影响,并且这些影响随细砂层在砂砾石层中的位置不同而不尽相同。利用室内砂槽试验,模拟当细砂层位于砂砾石层内部不同深度时含夹砂层堤基管涌的发展过程,研究细砂层埋深对 堤基管涌的影响。试验结果表明,细砂层埋深存在一个临界深度,当细砂层埋深较浅时,堤基的临界水力梯度较小,易于发生管涌,且管涌发生以后,堤基被侵蚀的速率较大,出砂较多;堤基破坏的临界水力梯度随着细砂层埋深的增加而增大,当细砂层埋深大于临界埋深时,堤基的临界水力梯度基本不变,同时堤基抵抗管涌破坏的能力较强,其破坏形式与双层堤基 相类似。  相似文献   

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