Shear Strength Of Marine Clay Research Articles

Evaluation of undrained shear strength of marine clay by constant-volume direct box shear test

東京国際空港 D 滑走路新設事業における東京湾海底の粘土地盤の地盤調査データを用いて，定体積一面せん断試験で求められる強度の設計への適用性を検討した。不攪乱試料を原位置の有効土被り圧で圧密後0.25mm/min でせん断した強度 su(DST0)に補正係数 0.85 を乗じた値が設計せん断強度として妥当であることを確認した。正規圧密まで圧密したときのせん断強度について，定体積一面せん断試験と圧密非排水（CU）三軸圧縮試験による強度の比較を行った。その結果，圧密後の強度増加の推定には圧密非排水三軸圧縮試験による強度の 70%を用いるのが妥当であることがわかった。

Reliability analysis of submarine slope considering the spatial variability of the sediment strength using random fields

The properties of marine sediments vary spatially, and the undrained shear strength of marine clay increases linearly with depth because of depositional processes and the effective overburden pressure. To evaluate the stability of submarine slope considering the spatial variability of soil strength, the random field discretized by the Karhunen-Loève expansion is combined with the limit equilibrium method to conduct reliability analysis. For simplicity, our physical model does not include many complexities such as the effects of excess pore water pressure on the stability of submarine slopes. Stability estimates of the infinite slope model, under both static and seismic loading, are made with three types of one-dimensional stationary or non-stationary random fields. The two-dimensional slope model is also analyzed, where the shear strength varies with the positions of the strips because of the discrete random-field function for the soil material. In submarine slope reliability analysis, the non-stationary random field of the linearly increasing soil strength is used, instead of the commonly used stationary one. To obtain the failure probability through Monte Carlo simulations, a novel response surface method based on Gaussian process regression is introduced to build the surrogate model. The computational efficiency is significantly increased, because there is a considerable reduction of calls of the deterministic analysis. Therefore, the proposed method makes the prediction of submarine landslides which are usually rare events with very small probabilities more efficient.

Factors Affecting Post-cyclic Undrained Shear Strength of Marine Clay

Post-cyclic undrained shear strength is primarily controlled by the cyclic loading parameters and loading conditions. In the present paper, series of undrained constant strain cyclic triaxial test followed by strain-controlled monotonic shearing was carried out on normally consolidated marine clay specimens. An attempt was made to study the variation of post-cyclic undrained shear strength with the cyclic loading conditions namely staged cyclic loading and continuous cyclic loading. The effect of cyclic loading parameters such as cyclic strain amplitude, cyclic loading frequency and drainage after the undrained cyclic loading on post-cyclic strength and stiffness is also presented. It is observed from test results that the post-cyclic undrained strength and stiffness of the specimen is greatly influenced by the cyclic loading condition and drainage after cyclic loading. It was noted that due to the multiple stages of cyclic loading followed by pore pressure dissipation, the induced apparent overconsolidation ratio is higher for staged cyclic loading than the continuous cyclic loading conditions.

Numerical modelling of submarine landslides with sensitive clay layers

A large-deformation finite-element (FE) modelling technique is presented to model submarine landslides. A strain softening model for undrained shear strength of marine clay is incorporated in the FE modelling. The development of large plastic shear strain concentrated zones (shear bands) and their propagation with displacement of soil mass are simulated. FE simulations show that the existence of a weak layer might result in the initiation and propagation of shear bands leading to large-scale progressive landslides. Such progressive development of failure planes cannot be simulated using the limit equilibrium method of slope stability analysis. Depending upon the geometry and soil properties, a number of failure patterns are identified which are comparable with morphologic features seen in field observations. Based on this type of FE analysis and compared with seabed morphology, the developed failure planes could be identified where the shear strengths are expected to be lower because of pre-shearing than the shear strengths of the soil outside these zones, which could then be implemented in the modelling of seabed for offshore development projects in the areas where failure occurred in the past.

Evaluation of undrained shear strength of marine clay using cone penetration resistance at South Pars field in Iran

In this paper, several new models are developed based on a soft computing technique for predicting undrained shear strength (su) of marine clays at South Pars field, Persian Gulf, Iran. For this purpose, numerous piezocone penetration tests (PCPTs) data are used along with laboratory and in-situ measurements of su. In this regard, evolutionary polynomial regression (EPR) is used instead of conventional simple linear regression analysis in order to correlate su and cone tip resistance more precisely. According to five developed models (models I to V), it is found that the tip resistance corrected for pore water pressure effect (qt) yields slightly better estimation of su, compared to the raw cone tip resistance (qc) obtained directly from PCPT. Additionally, the cone tip resistance is correlated much more precisely with su data obtained from torvane test than that of unconsolidated undrained (UU) triaxial test. The EPR-based models offer a considerable improvement in estimating su based on cone penetration test data and can predict su with minimum error in comparison with other theoretical and empirical models. The models are also verified successfully by the data obtained from another survey area, outside the main survey area which has been used to develop the models.

Uncertainty analysis on remoulded undrained shear strength of marine clay

Remoulded undrained shear strength s u−r is a soil property associated with disturbed clay. This parameter is used to indicate the evolution of the post-failure behaviour of seafloor soil, estimate the rheological properties of debris flows and the drag forces on seafloor structures exerted by a submarine slide, and calculate the penetration resistance of skirt walls. This work discusses the influence of uncertainty on the estimate of empirical relationships between s u−r and liquidity index I L as a potential predictor of the remoulded soil strength. Special emphasis is made on assessing the uncertainty inherent to s u−r , when the definition of the empirical models is updated from a global to a local (regional) data set. For this purpose two approaches are compared: a parameterisation in the ‘log space’ (Log-Linear Model, LLM) by transforming least square exponential fitting to log-linear expression, and a parameterisation in the ‘physical space’ using Bayesian Non-Linear Regression (BNLR). The updating of the trend models conditioned on the two available data sets is performed using simple Bayesian principles. Results show similar trend models obtained by the two approaches, and the standard deviation of the trend indicates different values. A thorough discussion is included based on the different hypothesis considered for the estimate of each model.