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1.
A very soft ground constructed by dredging and hydraulic fill has characteristics such as high water content, high initial void ratio, and very little effective stress. Estimating, with thorough considerations about consolidation properties and the initial stress associated with each layer's distinctive stress history, is essential in order to predict a reasonable consolidation settlement of soft ground. By investigating a construction project for national industrial complexes at a coastal area in southern Korea that experienced reclamation and ground improvement adapting PVD, various laboratory tests to find consolidation properties were performed with undisturbed samples collected from the entire depth of the marine clay fill layer and original clay layer. Through the investigation, this report suggests relationships of heterogeneity of permeability in both vertical and horizontal directions, void ratio-effective stress, and void ratio-permeability. Considering the fact that the original clay layer was under the process of consolidation by load due to hydraulic fill from the top, estimating the appropriate initial stress of each layer is critical to predict the future process of consolidation settlement determined by time. In order to obtain the initial stresses of two layers with different stress histories related to consolidation, cone penetration and dissipation tests were conducted.  相似文献   

2.
Conventional drainage consolidation methods cause significant energy consumption and environmental issues. In this paper, a method combining siphon drainage and surcharge loading is proposed to drain water from soft soil with vertically installed prefabricated vertical drains (PVDs) and a siphon tube. To investigate the availability and effectiveness of this method, a laboratory physical modeling test was conducted to investigate the drainage and consolidation behavior. The laboratory modeling test results of this method were compared with the calculated results of the ideal sand-drained ground consolidation method to clarify the advantages and mechanism of this method. Comparison results show that the pore pressure and settlement in the proposed method developed faster than the calculation results of ideal sand-drained consolidation theory. About 10?m thickness of unsaturated zone can be formed by siphon drainage which produce a surcharge loading effect on the soil below the flow profile. Drainage is a very slow process in soft soil, and siphon drainage can work continually. Siphon drainage combined with surcharge loading is potentially a good alternative to drain water from soft clay economically and environmentally.  相似文献   

3.
Abstract

In practice, how to quickly improve the bearing capacity of piles in a short time is of great significance. In view of this, a technique of setting grooves and installing PVDs (prefabricated vertical drains) at the surface of the pile is proposed in this investigation to accelerate the consolidation of the surrounding soil. A radial and circular consolidation model is established for permeable piles. The finite cosine transform, finite Weber transform, and discretization method are used to obtain a semi-analytical solution for the consolidation model with a mixed drainage boundary condition at the surface of the pile. The sensitivity of the consolidation process to the strip number and the width of PVDs is discussed. The results show that the technique of installing PVDs in piles could potentially improve the bearing capacity. When the area of drainage channels is fixed, the bearing capacity of permeable piles can be more effectively improved by using a higher strip number of PVDs and a smaller PVD width.  相似文献   

4.
The presence of a fractured zone at a tunnel face can threaten the stability of the tunnel by causing water leakage and degradation of the soil strength. In this case, to stabilize the tunnel face, the pore water pressure is generally reduced and the loss of soil particles is prevented by installing drainpipes. The installation of drainpipes, however, can cause the concentration of flow channels and other ground instability problems. In this paper, a novel pin-holed pipe anchor is proposed to overcome the problems occurring in subsea tunnels. The pin-holed pipe anchor is a pipe-type support member designed to reinforce the ground while simultaneously enabling flow into the tunnel. Here, the design requirements of the pin-holed pipe anchor were examined through material tests, and the structural–hydraulic characteristics of the pin-holed pipe anchor were investigated through a model test. Furthermore, the applicability of the pin-holed pipe anchor to an actual tunnel was evaluated by numerical analysis of actual tunnels. Through selection of an appropriate perforated drainage area and bonded length, the pin-holed pipe anchor contributed to the improvement of the structural and hydraulic stabilities of the tunnel.  相似文献   

5.
A pressure relief technique has been proposed to reduce hydrostatic pressures by opening drainage holes around a water tank. This solution is evaluated by laboratory experiments and numerical parametric investigation. After seepage flow is allowed, the hydraulic head acting on the water tank is reduced due to seepage losses. The drainage holes should be opened on the base slab near the sidewalls, and at a certain height on the sidewalls. Given a fixed total opening area, the number of drainage holes with smaller diameter should be allowed near the edge of the water tank to increase the efficacy of the approach. The properties of the surrounding soil influence the results significantly, where a cushion layer with a higher hydraulic conductivity and a greater thickness is beneficial to the stability of the water tank, and a backfill layer with adequate thickness and hydraulic conductivity should be selected. An illustrative example is given in the end to demonstrate the advantage of the proposed antiflotation design strategy compared to the conventional enhanced self-weight method, and more economic design using less reinforcement and concrete can be achieved.  相似文献   

6.
This article presents a case history of determination of effective depth of prefabricated vertical drains (PVDs) under embankment loading on a very soft clay deposit in central China, near Jiujiang, Jiangxi Province. The height of the embankment was 5.3 m and construction time was about one year. The PVDs were installed to a depth of 8.5 m at a spacing of 1.5 m in a triangular pattern. Field observations and the finite element method (FEM) were employed to analyze the performance of the soft deposit during embankment construction. The influential depth of the embankment loading was evaluated based on settlement, excess pore pressure, and stress increase in subsoil, both from the observed data and FEM analysis. The effective PVD depth was determined in the following ways: (1) the depth of 5% subsoil settlement of surface settlement; (2) vertical stress increase in subsoil of 25% in-situ stress; and (3) consolidation time/PVD depth relation by FEM. Based on the analysis, the effective depth of PVDs was determined to be between 10 and 12.8 m for this field case.  相似文献   

7.
A remarkable combined dry jet mixing (DJM) and prefabricated vertical drains (PVDs) method was used to enhance the performance for soft ground improvement. In the combined method, PVDs are first installed and then DJM columns are installed between the PVDs at larger spacing. This combined method improves the effectiveness of the ground improvement and creates a more economical solution. This paper presents a case study of the combined method for marine clay improvement in Lianyugang of China. The excess pore water pressure in soils created by the installation of DJM columns with and without PVDs was monitored and compared. In situ standard penetration tests were conducted in the DJM columns and before-and-after piezocone penetration tests were performed in soils surrounding the columns. Long-term settlement monitoring under embankment loading was carried out for the ground improved by combined method and DJM method alone. The field tests, settlement monitoring and economic benefit analysis results demonstrated that the DJM-PVD method is technologically sound and cost-effective as compared with the conventional DJM method.  相似文献   

8.
Studies of Daphnia distribution and function could help people manage and protect water quality. We investigated how spatial distribution and filtering efficiency of Daphnia in the transition and lacustrine zones of the Nanwan Reservoir (China). Samplings were conducted seasonally for 2 years from six sites in the reservoir. Daphnia abundance and biomass were significantly higher in the lacustrine zone than in the transition zone. Similar composition and biomass of edible phytoplankton were found in the two zones, suggesting that food quantity could not explain high Daphnia distribution in the lacustrine zone. The variations of water velocity and food quality could help explaining Daphnia patchy distribution in the reservoir. On the one hand, rapid water velocity can cause the Daphnia decrement in the transition zone. On the other hand, the ratio of particulate organic carbon (POC) to chlorophyll a (chl a) concentration was significantly higher in the transition zone, indicating more allochthonous material constituted the food source for Daphnia. The lower quality food likely suppressed Daphnia development in the transition zone. A linear regression between Daphnia abundance and Secchi depth (SD) may suggest a cause-effect relationship where increased filtering efficiency was responsible for increased water clarity to some extent.  相似文献   

9.
Difficulties in the prediction of time-distribution of consolidation settlement will be introduced by using the Murayama test embankment case of Japan. In particular, it will be discussed why the prediction of consolidation rate is difficult in multi-layered soil with complex and variable mechanical properties like organic soil or peat. It can be inferred that uncertainties, which are embedded intricately in the consolidation problem as well as given ground condition, would be major causes for consolidation settlement. After that, the author focused on the movement of pore water under the various conditions of hydraulic conductivity in the soils, and how it can affect the time-distribution of the consolidation settlement. For the applied key methodology on the consolidation settlement problem, we propose the hybrid consolidation simulation controlling the movement of pore water with high accuracy and, finally, the aim of this article is to discuss the methodological approaches obtained by the study, including the basic concept and accurate movement of pore water under various conditions of soil layers and hydraulic conductivity.  相似文献   

10.
采用超声水位和PIV流速测量技术,对不同水力坡度下非淹没丁坝近区的水流结构进行了试验研究。结果表明,随着水力坡度的降低,在坝头处,紊动强度较大的区域逐渐向主流区及上游扩散;在坝后,跌水最低点逐渐下移,漩涡中心向丁坝侧边壁靠近。回流区长度与宽度的变化和水力坡度的变化无明显对应关系,但坝头近壁区的流速与坝后回流区的长度及宽度存在高度响应的线性关系。研究成果揭示了丁坝在不同水力坡度下调整水流结构的机理,同时对各家测量得到的回流区长度不等有了较明确的答案,为工程中丁坝的设计及河道岸线的规划提供了科学依据。  相似文献   

11.
This study presents comprehensive geotechnical data of the natural marine sediments cored from the hydrate occurrence regions during the Ulleung Basin Gas Hydrate Expedition 1 (UBGH1), East Sea, offshore Korea in 2007. Geotechnical soil index properties of the Ulleung Basin sediments, including grain size distribution, porosity, water content, Atterberg limits, specific gravity, and specific surface area, were experimentally determined. These soil index properties were correlated to geotechnical engineering parameters (e.g., shear strength and friction angle) by using well-known empirical relationships. By performing standard consolidation tests on both undisturbed specimens (as recovered from the original core liner after hydrate dissociation) and remolded specimens, stress-dependent mechanical and hydraulic properties (e.g., compressibility and hydraulic conductivity) were measured. The experimental results provide important engineering parameters, and demonstrate the effect of hydrate presence and consequential dissociation to index properties, engineering parameters, and innate sediment structures.  相似文献   

12.
Abstract

First, this article presents a simulation experiment of hydraulic reclamation, and then a vacuum preloading (VP) test using the sedimentary soil obtained by the first experiment. In the VP test, the distribution and variation of different physico-mechanical parameters before and after the treatment were tested. According to the test results, the concept “non-Terzaghi soil” is proposed to explain the inhomogeneity and its mechanism rendered by “seepage separation.” And then a staged VP (SVP) drainage consolidation method has been introduced to improve the inhomogeneity and seepage curtain phenomena around prefabricated vertical drains (PVDs) during the consolidation. The test results demonstrate that the clogging problem around PVDs has been prevented and the consolidation efficiency has been promoted after the SVP test. It has been noticed that the cumulative drainage volume and the settlement displacement of SVP test were 27% and 24%, respectively, greater than that of VP test, and the soil tends to be more homogeneous. Moreover, it has been shown that the inhomogeneity degree of the permeability coefficient, unit weight, void ratio, water content, cohesion, internal friction angle, compression modulus, and the soil surface settlement in slurry after the SVP test were 3.10, 1.02, 1.03, 1.09, 2.30, 1.92, 1.19, and 1.02, whereas that after VP test was 397.27, 1.07, 1.40, 1.40, 4.74, 3.00, 1.76, and 1.22. Finally, the mechanism of SVP method has been discussed.  相似文献   

13.
Studying sedimentation and consolidation of dredged slurry has significant implications to the design of storage yard and subsequent ground improvement. In this study, settling velocity of soil particles in dredged slurry during sedimentation and consolidation processes was investigated using an improved multilayer extraction sampling (MES) method. A series of sedimentation column tests were performed on dredged slurry with three different initial water contents. Distributions of volume of soil particles and density of dredged slurry were first obtained by the MES method, settling velocity of soil particles was then calculated by volume flux function approach. It was found that the density and velocity inflection points can be used to distinguish the settling zone and the consolidation zone. The experimental results reveal that the velocity of soil particles was quite low and monotonically decreased with sedimentation height at low initial water content throughout the whole test period, whereas it was increased at 0–1 hours and almost remained constant at 1–7 hours in the settling zone at high initial water content. The effects of initial water content on sedimentation and consolidation mode of dredged slurry and the settling velocity of soil particles were discussed. The relationship between settling velocity of soil particles and particle diameter was also studied. It is indicated that the measured velocity of soil particles was much lower than that calculated by the Stokes equation, and it was related to 0.4881–0.5906 order of particle diameter at 0–1 hours and 0.1117–0.1825 order of particle diameter at 1–7 hours for the test slurries.  相似文献   

14.
This article presents a laboratory study of static behavior of silty-sand soils. The objective of this laboratory investigation is to study the effect of initial confining pressures and fines content on the undrained shear strength (known as liquefaction resistance) response, pore pressure, and hydraulic conductivity of sand–silt mixtures. The triaxial tests were conducted on reconstituted saturated silty-sand samples at initial relative density Dr = 15% with fines content ranging from 0 to 50%. All the samples were subjected to a range of initial confining pressures (50, 100, and 200 kPa). The obtained results indicate that the presence of low plastic fines in sand–silt mixture leads to a more compressible soil fabric, and consequently to a significant loss in the soil resistance to liquefaction. The evaluation of the data indicates that the undrained shear strength can be correlated to fines content (Fc), inter-granular void ratio (eg), and excess of pore pressure (Δu). The undrained shear strength decreases with the decrease of saturated hydraulic conductivity and the increase of fines content for all confining pressures under consideration. There is a relatively high degree of correlation between the peak shear strength (qpeak) and the logarithm of the saturated hydraulic conductivity (ksat) for all confining pressures.  相似文献   

15.
Hyporheic invertebrates were sampled in six small headwater streams draining pine, pasture, and native forest catchments. Sites were sampled in autumn and spring using three different hyporheic sampling methods (colonisation pots, pump sampling, and freeze‐coring). Total invertebrate abundance and taxon richness differed significantly among sites on both sampling occasions for pump samples, whereas freeze‐coring did not discriminate among sites, and pot samples showed significant differences in autumn, but not in spring. Differences among sites with respect to community composition were not consistent between sampling methods. Community ordination indicated that samples from colonisation pots tended to group together, whereas pump and freeze core samples were widely separated. Differences across land uses were also apparent (native forest sites formed a distinct cluster separated from pine and pasture sites). Results suggest that colonisation pots may provide a pathway for the entry of epigean organisms into the hyporheic zone even when hydraulic connectivity between surface and hyporheic zones is low. Invertebrate abundance was very low in pump samples, and this method also captured the fewest taxa of the three methods. The size bias known to exist with pump sampling techniques may restrict the usefulness of the method when comparing streams of differing hydraulic conductivity.  相似文献   

16.
长江水下三角洲浅表沉积层中的生物扰动构造   总被引：2，自引：0，他引：2  
为查明长江水下三角洲生物扰动类型、特征和分布规律,探讨生物扰动构造的可能影响因素,使用箱式采样器获取包括三角洲前缘、前三角洲、过渡带以及正常浅海的无扰动沉积岩心,利用高分辨X-ray成像技术对浅表沉积层中的生物扰动构造进行了研究。结果表明,长江水下三角洲发育虫孔构造和挖掘构造,虫孔构造直径0．5-2mm,长度数厘米至数十厘米,多数虫孔垂直于层理发育,挖掘构造形态呈漏斗状,其内沉积物混合强烈;生物扰动构造具有明显的分带性,三角洲前缘生物扰动指数〈1,前三角洲及过渡带扰动指数为2-3级,最高达4级,而紧靠前三角洲的正常浅海生物扰动指数为2级。生物扰动构造的发育主要受上覆水体盐度、悬浮体含量制约,在盐度接近正常浅海水体盐度、悬浮体含量中等的前三角洲、过渡带是生物扰动构造发育的有利环境。研究未发现底质沉积物类型、底质环境因子对生物扰动构造的明显制约作用。  相似文献   

17.
A model of sea ice growth as an expanded region of a phase transition (mushy zone) with a linear temperature profile is developed. The linear temperature distribution agrees with the mushy zone by introducing an equivalent porosity determined by its thermodynamical condition. This approach does not require any a priori information about the dependence of the porosity on the temperature and salinity; it rather allows us to obtain this relation from a solution of the mathematical problem. The model makes it possible to calculate the thickness of the growing ice and to estimate its main characteristics as well as the heat capacity of the underice layer under the conditions of undisturbed growth at any moment of the autumn-winter season up to its maximal thickness with account for the snow accumulation, basin depth, varying regime of cooling, and water salinity.  相似文献   

18.
Erective Sea Embankment with PCC Piles   总被引：2，自引：0，他引：2  
  相似文献   

19.
The degree of sediment disturbance in the South Pass area is correlated to the average hydraulic conductivity, shear strength, and thermal gradient. Hydraulic conductivity averages 18, 6, and 4 × 10–7 cm/s in the undisturbed, moderately disturbed, and most disturbed sediments, respectively. Shear strength also decreases with increasing disturbance, from 7.6 to 4.4 to 3.5 kPa. Excluding the four stations dominated by annual temperature variations, the remaining 19 thermal gradients correlate well with sediment disturbance. The average gradient is positive in all of the disturbed sediments (0.12 ± 0.07° C/m) and 0 in the undisturbed sediments (0.02 ± 0.05° C/m).  相似文献   

20.
The uncertainty and sensitivity of predicted positions and thicknesses of seawater-freshwater mixing zones with respect to uncertainties of saturated hydraulic conductivity, porosity, molecular diffusivity, longitudinal and transverse dispersivities were investigated in both head-control and flux-control inland boundary systems. It shows that uncertainties and sensitivities of predicted results vary in different boundary systems. With the same designed matrix of uncertain factors in simulation experiments, the variance of predicted positions and thickness in the flux-control system is much larger than that predicted in the head-control system. In a head-control system, the most sensitive factors for the predicted position of the mixing zone are inland freshwater head and transverse dispersivity. However, the predicted position of the mixing zone is more sensitive to saturated hydraulic conductivity in a flux-control system. In a head-control system, the most sensitive factors for the predicted thickness of the mixing zone include transverse dispersivity, molecular diffusivity, porosity, and longitudinal dispersivity, but the predicted thickness is more sensitive to the saturated hydraulic conductivity in a flux-control system. These findings improve our understandings for the development of seawater?freshwater mixing zone during seawater intrusion processes, and give technical support for groundwater resource management in coastal aquifers.  相似文献   

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