Zhang, X. Y. (American Bureau of Shipping) | Yong, F. (National University of Singapore) | Li, Y. P. (Hohai University) | Yi, J. T. (Chongqing University) | Lee, F. H. (National University of Singapore) | Chen, X. (Beijing Jiaotong University) | Wang, S. Q. (American Bureau of Shipping)
The quest for reliable and cost-effective solution of installing piles in deepwater led to the development of dynamically installed piles that embed themselves into the seabed through free-fall. Several variations of dynamically installed piles have been devised and successfully entered into service at deepwater offshore sites. The most notable one is the torpedo pile patented by Petrobras.
To facilitate the design and installation of the dynamically installed piles, ABS has developed Guidance Notes to provide geotechnical design and structural assessment methods. This paper presents an overview of the guidance and details of the technical development that forms the basis of the recommended methods.
In support of the development of the guidance, finite element analyses and centrifuge tests were conducted to study pile/soil interaction and to verify and further improve the prediction methods for pile pullout capacity. The pile inclination after installation, which has a significant effect on the pile pullout capacity and is of significant concern to the offshore industry, was thoroughly studied. Since the dynamic installation process results in lower short-term pullout capacity of the pile, it is recommended that the piles be installed for a sufficiently long period to allow the development of the pullout capacity. A prediction of the pile capacity restoration over time was developed based on the results of a series of centrifuge tests. A framework on the normalized vertical and horizontal component is proposed to predict the pile pullout capacities subjected to different loading angles.
Pei, Qitao (Changjiang River Scientific Research Institute) | Ding, Xiuli (Changjiang River Scientific Research Institute) | Luo, Wei (Hohai University) | Huang, Shuling (Changjiang River Scientific Research Institute) | Zhang, Yuting (Changjiang River Scientific Research Institute)
Grouting method is a common way to deal with engineering geological hazard, such as rockfall, inrush of clay and water. It is of great significance to accurately identify diffusion characteristics of slurry for engineering design and safety construction. This paper selects the cement-silicate slurry as grouting material. The slurry with fast curing grouts can be taken as Bingham liquid with the time-dependent behavior of viscosity in static water environment. Combining the constitutive equations of generalized Bingham fluid, continuity equations, motion equations etc., a theoretical diffusion model of grouting in the dip crack at constant grouting rate is established by considering the uneven spatial distribution of viscosity. On the basis, the temporal and spatial distribution equations of viscosity and pressure in the diffusion region of slurry are derived. Then, the relationship among grouting time, the radius of slurry diffusion and grouting pressure are obtained. Finally, the impact of dip angles of crack on the diffusion characteristics of slurry at constant grouting rate is studied. The results may be constructive to the determination of grouting parameters of cement- silicate slurry in practical grouting engineering.
Grouting method is an effective way to reinforce weak rock masses and control of groundwater by exclusion. It has been widely used in the disaster treatment of geotechnical engineering, especially for underground projects. Also, the double liquid with fast curing grouts (e.g. cement- silicate slurry) is the most common material for grouting (Shimoda and Ohmori, 1982; Li, et al., 2007).
Engineering practice shows that the radius of slurry diffusion, grouting pressure and grouting rate, under different geotechnical conditions, are closely related to engineering design and safety construction. Many scholars have done in-depth research on the diffusion characteristics of slurry in geotechnical media. Based on the constitutive equations, the slurry can be divided into the following categories: Newtonian fluid, Bingham fluid, power-law fluid and so on (Ni, et al., 2005; Fransson, et al., 2007; Dahlo and Nilsen, 1994). In addition, according to the motion equations, the grouting mode can be divided into permeation grouting, compaction grouting, splitting grouting, dynamic water grouting, etc.(Funehag and Gustafson, 2008; Miller and Roycrof, 2004; Zhang, et al., 2015; Ruan, 2005). During the grouting process, the grouting pressure is mainly determined by water pressure. As the viscosity of slurry with fast curing grouts grows larger, the shear stress of slurry changes greatly in a short period of time, the effect of which on grouting pressure cannot be ignored. Besides, the occurrence of crack exposed in rock masses often presents irregular spatial distribution. However, when it comes to the diffusion mechanism of slurry with fast curing grouts by considering the time-dependent behavior of slurry viscosity, the occurrence of crack is often assumed to be horizontal. The self-weight of slurry, filling the dip crack, is not taken into consideration. Thus, the temporal and spatial diffusion characteristics of grouting cannot be reasonably reflected.
Pang, Mengqiang (Hohai University) | Ba, Jing (Hohai University) | Yu, Cun (Hohai University) | Zhou, Jian (Hohai University) | Wang, Enjiang (Hohai University) | Jiang, Ren (China Petroleum Exploration and Development Research Institute, Langfang Branch)
The attenuation (Q−1) of medium is a parameter more sensitive to pore fluid than seismic velocities for gas-bearing reservoirs, thus accurate estimation of seismic attenuation is very meaningful for exploration of natural gas reservoirs. In this paper, we used the quality factor to carry out the seismic identification of carbonate reservoirs and estimate the Q values point by point of the target layer by using S transform and improved frequency shift method. In addition, the two-dimensional Q profiles of some survey lines and the three-dimensional Q section of the whole area were extracted. The results show that the Q value is low in the gas-bearing area with high-porosity, and the attenuation is anomalously high. And in the non-gas-bearing area with low-porosity, the Q value is higher, with no attenuation anomaly. The analysis method of attenuation effectively reflects the absorption characteristics and gas-bearing differences of the stratum, and can be effectively used in reservoir prediction.
Presentation Date: Monday, October 15, 2018
Start Time: 1:50:00 PM
Location: Poster Station 5
Presentation Type: Poster
Zhou, Jian (Hohai University and University of Houston) | Ba, Jing (Hohai University) | Castagna, John P. (University of Houston) | Yu, Cun (Hohai University) | Jiang, Ren (RIPED-Langfang) | Ge, Qiang (RIPED-Langfang)
Seismic amplitude analysis could provide valuable information regarding physical properties of reservoir rocks that is related to seismic reflection characteristics, e.g. porosity. However, for thin-layer reservoirs, limited seismic resolution and related wavelet tuning often hinders accurate interpretation of seismic amplitudes. We show that for generalized simple layer, i.e. without the same magnitudetop and base reflections, amplitude of composite top-base reflection signal is affected by both perturbations to thinlayer reservoir and overburden rocks. The complex tuning behavior can be simplified using the fact that any arbitrary seismic signal can be uniquely decomposed using the Fourier transform into odd and even components that have distinct sensitivities to variation in thin-layer and overburdenproperties. Numerical analysis based on true log parameters in a tight-dolomite reservoir in the Sichuan Basin, China show that amplitude at peak frequency of the seismic data odd part (OAPF) is more sensitive to thin-reservoir porosity change compared to that of original signal (total waveform, TAPF) and even part of the waveform (EAPF). When applied in analyzing real seismic data, conventional TAPF is not obviously correlated to porosity variations. However, the OAPF attribute responds well to the porosity measured in boreholes, and also relates to apparent seismic attenuation. These results suggest that, for thin layers, amplitude-based interpretation and inversion may benefit from isolation of even and odd amplitude attributes.
Presentation Date: Monday, October 15, 2018
Start Time: 1:50:00 PM
Location: 209A (Anaheim Convention Center)
Presentation Type: Oral
The responses of static and dynamic moduli of porous rocks to the changes of differential pressure have been explained by the effects of pore microstructure, i.e., the effects of cracks (soft pores) and intergranular (stiff) pores. Specifically, cracks play a major role on the elastic properties in rocks. By using the Mori-Tanaka theory, this work relates rock elastic properties to the pore microstructure. Since the static moduli dependency of elastic properties is more sensitive than that of dynamic moduli, we propose to estimate the distribution of pore aspect ratios by using the static bulk modulus, where the David’s model is extended and applied. The theory is applied to data from the Navajo and Weber sandstones. The results show that the distribution of pore aspect ratio and crack porosity obtained with the static bulk modulus are higher than those estimated with dynamic moduli, suggesting that the estimations from static bulk modulus are probably closer to the reality of rocks, since those from dynamic moduli are generally considered as underestimates of the true amounts.
Presentation Date: Tuesday, October 16, 2018
Start Time: 1:50:00 PM
Location: 202A (Anaheim Convention Center)
Presentation Type: Oral
Seismic interpretation is often based on the analysis of amplitude anomalies, and these can depend strongly on the seismic wavelet present in the data. However, if the wavelet polarity or phase is not known or if fine-scale impedance variations are complex, a direct interpretation of the anomaly can be difficult and ambiguous. The readily available Stratton data set contains a dome-like feature that may be interpreted as exhibiting a bright-spot indicator for a gas reservoir, yet on closer examination is probably due to a hard layer with a gradational base. This feature provoked our interest in modeling domes with various wavelet phases. We generated synthetic data from 1-D and 2-D models, for different impedance profiles, thicknesses, and wavelet phases. The results demonstrate that the seismic response from a layer with impedance contrast that decreases with depth is quite different from that of a layer with constant impedance contrast when the bed thickness is greater than 1/4 of wavelength. On the other hand, a thin bed with constant impedance contrast and a 90° wavelet may strongly resemble a thick bed with a gradational base and a 0° wavelet (and vice-versa). We believe that the anomaly we have observed in Stratton data represents a reef-type of structure with higher impedance than surrounding beds, with that difference decreasing gradually with depth.
Presentation Date: Tuesday, October 16, 2018
Start Time: 1:50:00 PM
Location: Poster Station 14
Presentation Type: Poster
In this paper, a modified PZIII model by considering the impact of principal stress rotation for the wave(current)-induced soil response in a sandy seabed is cited. Unlike the previous works, the proposed model considers the effect of PSR by treating it generating the plastic strain rate independently. Then, the proposed model was incorporated into the finite element analysis procedure DIANA-SWANDYNE II. Both wave and current loadings are considered in the present model. The proposed model was first validated through comparisons with the previous experimental data for the soil response under wave and current loading. Adapting the proposed model, effects of the PSR on the fluid-seabed interactions will be investigated.
Recently, the human exploration and development of ocean are more frequent due to the abundant marine resources and colossal development. However, in the complex marine environment, the constructions of offshore engineering projects have huge challenges in the present due to various uncertain factors. The cyclic dynamic load which is produced by wave and current propagation on the seabed surface will cause the fluctuation and accumulation of pore water pressure. When the pore pressure extreme growth, the effective stress will decrease, which will lead to instability of the soil as the consequence of the horizontal or vertical movement of the soil particles, resulting in instability of the soil (Sumer, 2014). Therefore, determining pore-water pressures within a porous seabed is particularly crucial for coastal geotechnical engineers involved in the design of the offshore infrastructures foundations. Numerous studies have been carried out to calculate the stability of the seabed in the past, including poro-elastic model and poro-elastoplastic model, but most of them did not consider the effects of PSR (Jeng, 2013).
The continuous rotation of the principal stresses in a seabed is an essential feature of the dynamic response of soil under cyclic wave loading. Unfortunately, due to the assumption of pure PSR, this process cannot be trapped by conventional elasto-plastic theory without changing the cyclic deviatoric stress amplitude of the plastic strain. However, several experimental results have confirmed that the plastic strains are generated merely through altering the principal stress orientation in both monotonic and cyclic rotational share tests (Ishihara and Towhata, 1983; Towhata and Ishihara. 1985; Sassa and Sekiguchi, 1999; Jafarian et al. 2012; Konstadinou and Georgiannou, 2013). However, the inhomogeneity materials determines the effect of PSR. If the seabed soil is always homogeneous, even if the wave loading is rotating, the principal stress axis may not produce a significant effect.
During the past few years, design and construction of large deep-water wharf has become an important subject. A new type of wharf structure with arched longitudinal beams has been proposed to adapt to open sea deep-water area. Previous studies of this new structure mainly focused on static calculation. In this study, a three-dimensional model of wharf with arched longitudinal beams is established by using ANSYS/LS-DYNA software. The p-y curve is employed to simulate the pile-soil interaction. Considering different pile torsional angles and positions, the wharfs dynamic characteristics is analyzed when the impact force is imposed upon the structure.
In recent years, a trend of large tonnage vessels is increasing in port engineering. The international routes are now sailing the fifth and sixth generation container ships and over 300,000 tons for bulk vessels and oil tankers (Leifer and Wilson, 2007). In China, at present, the number of berths which can handle vessels over 50,000 tons is about 260, but in fact, most of them cannot meet the requirements of large-tonnage vessels, and construction of deep water wharves is in urgent needed (Zhang, 2006). The deep-water wharf works under adverse conditions and is hard to be constructed, so design of deep-water wharf is an important research topic in port engineering (Zhai and Lu, 2006). A new type of wharf with arched longitudinal beams was proposed (Zhai and Lu, 2008), which can make full use of arch's overhead crossing and reinforced concrete compression resistance, improve the interval between transversal bents greatly, and decrease underwater construction quantity.
Previous studies on the new structure mainly focused on the static analysis with all-vertical-piled foundation, while ignored the structural response under the complex dynamic loads. The horizontal force mainly acts on the brace piles, so analysis on the brace piles arrangement influenced to the whole forced condition of wharf structure is necessary. In this study, the p-y curve is employed to simulate the pile-soil interaction. Considering different pile torsional angles and positions, the wharf's dynamic characteristics is analyzed when the impact force is imposed upon the structure, the most suitable brace piles arrangement and torsional angle are determined. The results will provide guidelines in design and construction of the deepwater wharf.
A storm surge barrier is planned to build at the entrance of the North Branch of the Yangtze Estuary for various purposes, e.g. preventions of extreme high water level due to storm and salt intrusion in dry season. A process-based model of the Yangtze Estuary is elaborated to simulate water levels during typhoon period with the storm surge barrier included in the model as hydraulic structure. Scenarios for different storm surge barrier width are examined by the model. By applying real time control method, the storm surge barrier operation, such as gate opening and closing, is also implemented in the model. The simulated high water level during typhoon Winnie (9711) period with different opening width are compared with the reference case, i.e. without barrier, and the observation data. The width of 3km is recommended based on the largest reduction of extreme high water level. The optimal operation program during typhoon period is recommended.
The Yangtze Estuary is located halfway up China's coastline (Fig. 1). It has ample water and sediment supply from upstream and obvious tidal influence, creating an estuary characterized by three major bifurcations and four outlets, with well-developed shoals, alternating channels, expanded sandbars, and a vast submerged delta. The part of the estuary considered in this study is the North Branch. The integrating management plan of the Yangtze Estuary is aim to the sustainable development of the entire estuary with the basic strategy of maintaining the present layout of the estuary.
In the last half century, the North Branch has been degraded under the influence of both the human interference (e.g. land reclamation) and nature morphology evolution, as become shallower and narrower. As a consequence, much less river discharge is flowing into the sea from this branch (<5% annually). This branch becomes flood dominant with more marine input, e.g. salinity, marine sediment. The saline water can sail upstream to the upper part of this branch and can even power into the South Branch under some circumstance, as is called salt intrusion from upstream in this estuary. In addition, with the branch being narrower and shallower, the coastal flooding, especially during typhoon period, become more severe than before. One of the alternatives for the management plan is to build a storm surge barrier at the entrance of the North Branch, so as to prevent the salt intrusion from the upstream of the estuary and the extreme high water level due to storms.
In this paper, we present a conceptual design of new underwater vehicle named as Underwater Benthic Vehicle (UBV) by the author. Different from traditional body-types, the vehicle has double spherical shells. What is most striking is that the vehicle can rolling forward on the seabed by inside-driven mechanism, combined with high mobility underwater. In order to meet the requirements of new operations, certain technical problems are discussed in this paper. All these work are good foundation for follow-up R&D and applications of UBVs.
With the rapid consumption of land resources, the oceans will be more and more important in the global growth. At the same time, the attempts of humans to explore and understand the oceans have never ceased. Underwater vehicles first appeared in 1950s and immediately launched an exploration revolution against the oceans (Jiang, 2000). Because of its advantages in the dangerous and unknown environment underwater, the vehicles have wide application in marine aspects. A large amount of underwater vehicles with a variety of shapes, sizes, weights, modes and depths are developed for different purposes. In short, underwater vehicles have become an important frontier of high and new marine technology (Qian, 2016).
The Fig.1 shows the pedigree of underwater vehicles in present, including Human-Occupied Vehicles (HOVs), Remote-Operated Vehicles (ROVs), Towed Vehicles (TOWs), Autonomous Underwater Vehicles (AUVs) and Gliders.
Among them, the HOVs first appeared. By taking scientists to deep sea, the HOVs greatly increase their subjective initiative and creativity at the scene (Liu, 2012). After that, due to inherent risk of HOVs, the ROVs developed rapidly under the impetus of offshore industry from the 1970s (Ge, 2016). While the depth increasing, the umbilical and LARS system become more and more complex and bring harsh terms to mother ships. At this time, the advantage of ROVs is lost gradually, and the range is also limited by the tethers (Xu, 2014). Therefore, the AUVs, including Gliders, become the focus of research in marine applications as ocean monitoring, underwater military and so on in the 1990s gradually.