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1.
The self-supported earth-retaining structure using stabilizing piles (SSR is used from here) has the advantages of less deformation and less internal force compared with conventional cantilever retaining structure. It is easier to conduct the excavation when SSR is used for an excavation instead of using braced excavation with struts. The SSR is better than other methods to the 10 m shallow excavation depth in terms of economical and constructional efficiency when the ground is not very soft. However, this SSR method lacks a theoretical basis in terms of geotechnical engineering. The objective of this study is to develop a method of analysis by laboratory model tests. A variety of model tests were performed in order to analyze the behavior of SSR and the ground, and to measure the stress acting on stabilizing piles relative to excavation steps and earth pressures on the wall. The analysis reveals the failure mechanism of a wedge and then suggests a method for calculating a virtual supported point. These findings were incorporated into a method for analyzing retaining wall, stabilizing piles, and beams connecting two structures. Future research is geared toward developing a design program that uses the analytical methodology for this SSR.  相似文献   

2.
ABSTRACT

Despite a number of geotechnical investigations that have been carried out in the Busan new port area of South Korea, the local practicing engineers have been unable to deduce successfully the geotechnical properties of the clays due to their spatial variation. In the area, clay deposits, so-called Pusan clays, are unusually thick, varying from 20 m to 70 m in thickness. For this study, comprehensive geological and geotechnical investigations were carried out with sophisticated sampling techniques, in situ and laboratory tests as well as geological analyses at an additional three locations. As a result of the investigations, it was found that depositional environments are closely related to the relative changes in sea level and have different features depending on location and depth. The clays consist of soft and stiff clays in the upper and the lower layers, respectively, which are classified as normally consolidated and cemented clay. Moreover, most of the geotechnical properties undergo small changes due to their depositional environment. Information about these effects would be quite helpful to understand the spatial variation of geotechnical properties as well as the effect of sample disturbance. Some correlations which reflect the geological history of the deposts were conducted for physical indexes and mechanical properties.  相似文献   

3.
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4.
The foundation soils for most of the North Sea gravity platforms installed so far have been very stiff over-consolidated clays and dense sand. Two actual platform sites are described that are representative of these soil conditions. It is shown how the design soil parameters required for a geotechnical analysis of the platform foundation have been selected for these two sites. The results of in situ testing, laboratory tests and experience from existing platforms are used, with the main emphasis placed on procedures used at the Norwegian Geotechnical Institute.  相似文献   

5.
Foundations of offshore oil and gas production platforms or wind parks are in the majority of cases piled-based. Piles are mainly driven to a certain design depth using hammers. However, there are many situations were driven piles cannot be properly installed. Plug formation or presence of rock layers and/or boulders preclude the correct installation. Since time is a key factor in offshore operations, offshore drilled piles are not very common. Their high level of uncertainty is mainly due to the complexity to assess a pile drillability analysis. For these reasons, assessing the drilling time needed to overcome the problems is very important. The following research compared first of all several well-known equations used for estimating the tunnel boring machine (TBM) excavation rate. Second, a novel approach has been used, which is based on the estimation of the specific energy. After having performed continuous automatic diagraphy tests in Turin subsoils (Italy), values of friction angles and compressive strength were obtained. Specific energy was calculated at the scale of the continuous automatic diagraphy test as a function of ξ, which is a coefficient depending on the geotechnical parameters assumed by Nishimatsu. It is therefore possible to estimate the drilling rate for different values of friction angle and cohesion.  相似文献   

6.
Despite a number of geotechnical investigations that have been carried out in the Busan new port area of South Korea, the local practicing engineers have been unable to deduce successfully the geotechnical properties of the clays due to their spatial variation. In the area, clay deposits, so-called Pusan clays, are unusually thick, varying from 20 m to 70 m in thickness. For this study, comprehensive geological and geotechnical investigations were carried out with sophisticated sampling techniques, in situ and laboratory tests as well as geological analyses at an additional three locations. As a result of the investigations, it was found that depositional environments are closely related to the relative changes in sea level and have different features depending on location and depth. The clays consist of soft and stiff clays in the upper and the lower layers, respectively, which are classified as normally consolidated and cemented clay. Moreover, most of the geotechnical properties undergo small changes due to their depositional environment. Information about these effects would be quite helpful to understand the spatial variation of geotechnical properties as well as the effect of sample disturbance. Some correlations which reflect the geological history of the deposts were conducted for physical indexes and mechanical properties.  相似文献   

7.
Stable backfill materials for the heat sensitive structures of buried power cables, hot water pipes, and gas pipelines are suggested to have low permeability and high heat transfer characteristics. The hydraulic and thermal conductivities of backfill materials or clay liners are important parameters in proper design and construction of geotechnical structures involved with heat transfers. In this study, to investigate the optimal natural backfill or liner materials, thermal and hydraulic conductivities of kaolin–silica mixtures examined based on the results from laboratory tests under different consolidation conditions. From the experiment results, the thermal conductivity increases while hydraulic conductivity decreases with increasing density during consolidation process. As a result, back-fill materials with high kaolin content under low consolidation stress were desirable materials for burial of heat sensitive structures.  相似文献   

8.
The shoring system that consists of soldier piles and anchor tiebacks is often used in deep excavations in sandy deposits. However, uncertainties often exist in the design of such shoring systems. In this article, a simplified-robust geotechnical design method is proposed to account for these uncertainties in the shoring system design. Specifically, for a given deep excavation, uncertain soil parameters and surcharges are treated as noise factors, and the parameters of soldier piles and tieback anchors are treated as design parameters. Robust design is then implemented as a multiobjective optimization problem, in which the design robustness is sought along with cost efficiency and safety requirements. A trade-off between design robustness and cost efficiency exists and the optimization usually leads to a Pareto front. By applying the knee point concept, the most preferred design that meets the safety requirements and yields the best compromise between design robustness and cost efficiency can be identified on the Pareto front. Improvements made to the existing robust geotechnical design method include an efficient formulation of the design robustness and a new procedure for finding the most preferred design in the design pool. The new simplified-robust geotechnical design method is illustrated with a real-world excavation case study.  相似文献   

9.
A scale model of a flexible circular net with different weights attached to the bottom was tested in a flume tank. Global forces and net deformation were measured for different steady current velocities. Three different sizes of bottom weights were used in the tests. The results from these tests are presented and discussed with the emphasis on the dependency between the forces and the geometry. Comparison is also made to empirical based formulas for calculation of drag and lift forces on net structures. Findings show that i) the forces on, and deformation of a flexible net structure are mutually highly dependent on each other; ii) estimates of global forces on a flexible net structure calculated using simple drag formulas derived from stiff net panel experiments give large errors when compared to experimental measurements; iii) numerical models taking into account the dependency between force and deformation should be used to obtain accurate estimates of forces on flexible net structures; and iv) the forces on a flexible net structure are dependent on Reynolds number, and their dependency are similar to that of a regular cylinder.  相似文献   

10.
ABSTRACT

The Yellow River Delta, which is the second-largest delta in China, has experienced varying degrees of land subsidence since the late 1970s. Although recent studies have identified the natural consolidation and compaction of sediment among the most important contributors to geologic processes, their processes have rarely been quantified. We estimated the sediment compaction over different time ranges to determine the temporal evolution of subsidence parameters (i.e., cumulative compaction). Estimates of primary consolidation, secondary consolidation, and the degree of consolidation in 152 boreholes revealed the spatial–temporal characteristics of sediment compaction and consolidation using geotechnical parameters collected from 152 boreholes, soil mechanics equations and the Kriging interplolation method. In addition, these estimates were partially constrained and cross-validated using the interferometric synthetic aperture radar (InSAR) results from early 2007 to late 2010 which were provided in a previous study. By performing a comparison analysis between theoretical evaluations of compaction for borehole data and InSAR observations, we were able to quantify subsidence due to sediment compaction. The comparison results suggest that the theoretical solutions agreed well with the measurements recorded by the well-validated, advanced InSAR method and that the deviations between the InSAR technique and geotechnical evaluations ranged from ?22 to 3?mm. The results reveal that the land subsidence of the chosen borehole sites during the investigative period was dominated by the primary consolidation and compaction of sediment. The underprediction of subsidence may be explained by fluid withdrawal, oil exploitation and engineering construction. To speculate, more geological disasters may occur if the current subsidence condition extends into the future.  相似文献   

11.
ABSTRACT

The lateral deflection of a cylindrical diaphragm wall and the associated ground movement induced by deep excavation are analyzed by performing site instrumentations and numerical analyses in the coastal area of Korea. Wall lateral deflection, rebar stress, and pore water pressure were measured and analyzed in eight directions. Variations of soil properties with the decrease of confining pressure are compared by performing various in situ tests before ad after excavation. To calculate the wall lateral deflection accurately, the effects of small strain nonlinearity, confining pressure, and the hysteresis loading/unloading loop developed during excavation are considered in the proposed numerical analysis. By comparing numerical results with measured ones, the importances of considering small strain nonlinearity and confining pressure reduction in the nonlinear (FEM) are emphasized. Also, the effects of wall stiffness on the performance of cylindrical diaphragm walls are studied for future similar excavation in the coastal area.  相似文献   

12.
Abstract

Compression behavior of sediments is crucial to geological engineering applications for ascertaining the deformation characteristics of the particular depositional environments. Unfortunately, obtaining the geotechnical parameters required to assess the compression behavior of sediments can be a costly and time-consuming undertaking. This study developed a general prediction equation that simulates the compression behavior of sediments. This developed equation is an exponential decline model that relates an increase of the shear-wave velocity to an increase of the mean effective stress. Consequently, the decrease of void ratio is presented as a continuous function of the shear-wave velocity. For this research, laboratory-derived sediment samples created to mimic actual sediments were isotopically consolidated during a consolidated undrained triaxial compression tests. The samples were prepared in the laboratory by mixing different percentages of fines and controlling the ratio of clay-to-silt fractions. Shear-wave velocity tests were performed during this consolidation testing using bender elements. The experimental constants needed for the prediction equation were well correlated to the depositional factors specifically characterized by percent fines, silt percent, and liquid limit that define better complexity of depositional processes.  相似文献   

13.
Abstract

The possibility of seafloor failure under external loadings on a gently sloping continental shelf is controlled, to a large extent, by the geotechnical characters of subbottom sediments (e.g., shear strength, compressibility, and liquefaction potential) and structural factors (e.g., sedimentary stratification). By means of undis‐turbing coring, in‐situ acoustic measurement, and subbottom profiling, the authors conducted an investigation into the seafloor instabilities and possibilities of sediment slope failure within the continental shelf off the Pearl River mouth, which is one of the most important areas for offshore development in the northern South China Sea. Based on in‐situ and laboratory measurements and tests for sediment physical properties, static and dynamic behavior, and acoustic characteristics, the analyses indicate: (1) subbottom sediments that originated from terrigenous clay during the Pleistocene are compact and overconsolidated, and the mean sound velocity in such sediments is relatively high; (2) the maximum vertical bearing capacity of subbottom sediments is efficiently conservative on the safe side for dead loads of light structures, and the trench walls are stable enough while trenching to a depth of about 2 m below the seafloor under still water; and (3) it is quite improbable that the subbottom sediments liquefy under earthquake (M ≤ 6) or storm wave loading.  相似文献   

14.
Evaluation of slope stability, especially in the absence of a proper bed such as marine soils, is one of the most important issues in geotechnical engineering. Using geogrid layers to enhance the strength and stability of embankments is regarded as a commendable stabilization method. On the other hand, groundwater level erratically fluctuates in coastal areas. Therefore, the aim of this research is to study the effects of groundwater level changes on stability of a geogrid-reinforced slope on loose marine soils in Qeshm Island, Iran. At first, geotechnical properties of the site were obtained by comprehensive series of geotechnical laboratory and in situ tests. Then, by simultaneous changes of groundwater level and several parameters such as embankment slope, loading, geogrid length, geogrid number, and tensile strength of geogrid, different characteristics such as embankment safety factor (SF), vertical and horizontal displacements at embankment top and embankment base were studied. It was observed that groundwater level had significant effects on behavior of the embankment. For most of the observations, by decreasing the groundwater level, the displacements decreased and consequently safety factor increased. Increasing the length, number, and tensile strength of geogrid led to the reduction of displacements and an increase in the safety factor.  相似文献   

15.
ABSTRACT

Oil and its derivatives contaminate many soils and not only affect their chemical and biological properties but also their geotechnical properties. As oil contamination may deteriorate the functioning of piles, this paper addresses the effects of oil contamination on soil–pile interactions. Axial compressive bearing capacities of two close-ended, instrumented piles were investigated in different oil-contaminated sand using frustum confining vessel. Three different oils (gasoil, crude oil, and used motor oil) at different contamination levels were considered and using some strain gauges, the toe, shaft, and the net total bearing capacity of piles, as well as load distributions along the pile length, were derived. The results show that the presence of oil between soil particles has considerable adverse effects on bearing capacities of model piles, especially the shaft bearing capacity. The oil viscosity and percentage, as well as the contaminated sand bed thickness around the piles, are the most influential parameters. The higher the oil viscosity and oil content, the lower the values of the piles’ bearing capacities in comparison to the uncontaminated sand. With some modifications on the bearing capacity parameters of CFEM method, a good agreement was observed between measured and calculated bearing capacity values.  相似文献   

16.
In this paper, the movements of the analytical models of complete underwater tracked vehicle (UTV) and cutter bar (CB) tool systems on a surface as well as their movements up and down a slope in the up-cutting mode operation are fully studied and analyzed. First, the mathematical expression of the mechanics, for which the forces, moments, and energy from the CB to the UTV are analyzed, is related. Next, analyses on the systemic parameters and their sensitivity are conducted to observe the variations of the operational and geometric parameters, as well as the cutter-tool and material-condition effects on the force, moment, and power components. Also, a design process composed of seven typical steps is proposed as the reference of a trencher-machine design. The important design parameters of the trenching machine such as the length of the CB, the nose radius of the CB, and the height of the pivot point are designed according to the proposed design process; furthermore, these parameters are used for the estimation of the slope-angle range when the trencher system is working on the slope. To demonstrate the application of derived equations to practical problems of the machine design, a number of numerical simulations are performed. Through the numerical simulations, the important parameters of the system such as the tangential force, Ft, the tractive thrust, H, the normal reaction, V, the cutting moment, Mc, the maximum carrier weight, W, and the available power are analyzed. From these, as a reference data for the designing of a trencher machine, the previous design of the system can be improved.  相似文献   

17.
The characteristics of ocean wind waves place certain constraints upon devices designed to convert their energy to a useful form. Here we consider the nature of these constraints and the theoretical analysis of a wave power generator that conforms to the design criteria. We also present the results of field tests with several models of the wave power generator. The experimental results support the theory and indicate that such a wave pump is suitable for power generation in a variety of circumstances.  相似文献   

18.
Abstract

Where undissolved gas occurs within fine‐grained marine sediments it usually takes the form of discrete bubbles that are much larger than the normal void spaces. The possibility of buoyancy‐induced movement of these relatively large bubbles must be included when considering the transport of gas through marine sediments. A theoretical analysis shows that, under static loading conditions, bubbles larger than a critical size should have sufficient buoyancy to move upward through a fine‐grained sediment stratum, whereas bubbles smaller than the critical size should remain fixed in position. The critical radius is directly proportional to sediment shear strength, and bubbles of a realistic size should move upward only in extremely weak sediments. Further theoretical analysis shows that the critical bubble size is reduced under cyclic loading conditions, but movement of typical‐sized bubbles should still be restricted to sediments of low shear strength. A simple laboratory experiment provides support for the conclusions of the theoretical analysis. The results indicate that buoyancy‐induced movement of relatively large gas bubbles in fine‐grained sediments is most likely to occur under storm loading conditions and is unlikely to occur at depths greater than a few meters below the seabed.  相似文献   

19.
Abstract

The continental slope off the coast of Israel is riddled with numerous large slump scars at depths greater than 400 m. Recent scar slumps are situated in the steepest central portions of the continental slope (400–450 m depth, α = 6°), frequently disfiguring older slump scars in its lower portions. The slumping materials were probably largely transported downslope in the form of density currents, and occasionally by sliding of large sediment chunks. Upslope retrogressive slumping phases progressively disfigure the shape of the slump scars until they totally disappear, causing net reduction of the thickness of the sedimentary column. To provide a basis for the quantitative analysis of slumping, laboratory vane tests, triaxial consolidated, undrained compression tests with pore‐pressure measurements, drained direct shear tests, and consolidation tests were performed oh undisturbed samples. Because the sediments consist of normally consolidated silty clays, the geotechnical properties measured on the core samples can be readily extrapolated for greater depths, assuming the sediments are homogeneous. Angles of internal friction measured by direct shearing under drained conditions are ?d =24°‐25°, designating the maximum possible angle of a stable infinite slope. These angles are appreciably higher than the steepest slopes in the investigated area, and a drained slumping mechanism is therefore considered unlikely. The slopes of the slump scar walls are about 20°; therefore, in the absence of active erosional, sedimentological, or tectonic agents, these walls have long‐term stability (drained shear). Undrained shear failure resulting in slope instability may be attributable to rapid changes in slope geometry (undercutting or oversteepening of the slope), fluctuations in pore pressure, or accelerations associated with earthquakes. Undrained shear‐strength parameters were determined by both laboratory consolidated‐un‐ drained triaxial tests and by miniature vane shear tests. The angles of internal friction that were measured are ?cu =15°‐17°, and the cu/p o values range between 0.22 and 0.75. An analysis of the force equilibrium within the sediments leads to the conclusion that horizontal earthquake‐induced accelerations, as little as 5–6% of gravity, are sufficient to cause slope failure in the steepest slope zone (400–450 m depth, α=6°, cu/p o=0.25). Collapse resulting from liquefaction is unlikely, as the sediments are normally consolidated silty clays with intermediate sensitivity, St =2–4.

The existence of slump scars in the lower portion of the continental slope, characterized by gentle slopes (α=1°‐3°) and sediments with high shear strength (cu/p o=0.30–0.50) is attributed to large horizontal accelerations (k= 12–16% of gravity). Owing to the wide range of geotechnical properties of the sediments (cu/p o= 0.20–0.75) and the inclination of the continental slope (α=1°‐6°), the same earthquake may generate a wide range of horizontal accelerations in different portions of the continental slope, and slumping may occur wherever the stability equilibrium is disrupted.  相似文献   

20.
Abstract

Fault fracture zones have always been a key problem in the construction of submarine tunnels. To efficiently summarize the safety impact of different construction schemes on a submarine tunnel crossing a fault fracture, a theoretical model using numerical simulation has been established via the benching tunnelling construction method, three-step method, Center Diaphragm method (CD method), both sides heading method, Cross Diaphragm method (CRD method) and two kinds of supporting methods: pre-grouting and shotcreting. Numerical simulation studies on the excavation and support of submarine tunnels crossing fault fracture zones have been carried out. The research indicates: the fracture zone is the main area where sedimentation instability occurs; the CRD method has the lowest horizontal convergence under the support of the diaphragm; increasing the grouting strength is more effective in controlling the deformation of the surrounding rock than increasing the range of the pre-grouting and the thickness of the shotcrete in the initial support is increased, and its resulting effect is obvious. To optimize the construction scheme, we compared the settlement, horizontal convergence and surrounding rock stress of the tunnel according to the simulation results of different excavation support methods, which could provide theoretical guidance for better on-site construction techniques.  相似文献   

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