The deep cement mixing(DCM)is used to improve the capacity and reduce the settlement of the soft ground by forming cemented clay columns.The investigation on the mechanical behaviour of the DCM samples is limited to e...The deep cement mixing(DCM)is used to improve the capacity and reduce the settlement of the soft ground by forming cemented clay columns.The investigation on the mechanical behaviour of the DCM samples is limited to either laboratory-prepared samples or in-situ samples under unconfined compression.In this study,a series of drained and undrained triaxial shearing tests was performed on the in-situ cored DCM samples with high cement content to assess their mechanical behaviours.It is found that the drainage condition affects significantly the stiffness,peak and residual strengths of the DCM samples,which is mainly due to the state of excess pore water pressure at different strain levels,i.e.being positive before the peak deviatoric stress and negative after the peak deviatoric stress,in the undrained tests.The slope of the failure envelope changes obviously with the confining pressures,being steeper at lower stress levels and flatter at higher stress levels.The strength parameters,effective cohesion and friction angle obtained from lower stress levels(c′0 andφ′0)are 400 kPa and 58°,respectively,which are deemed to be true for design in most DCM applications where the in-situ stress levels are normally at lower values of 50-200 kPa.Additionally,the computed tomography(CT)scanning system was adopted to visualize the internal structures of DCM samples.It is found that the clay pockets existing inside the DCM samples due to uneven mixing affect markedly their stress-strain behaviour,which is one of the main reasons for the high variability of the DCM samples.展开更多
The main objective of this research is to study the mechanical behaviour of tropical soils using elasto-plastic constitutive equations in the so-called limit and critical states. Indeed, researchers of the Cambridge U...The main objective of this research is to study the mechanical behaviour of tropical soils using elasto-plastic constitutive equations in the so-called limit and critical states. Indeed, researchers of the Cambridge University had noticed that during their various experiments, the rate of volumetric deformation ( ) of the sample tending to zero every time the rupture of the specimen is reached during a test performed on a clay specimen Roscoe et al., 1958. To better understand and clarify this mechanical behaviour, a description has been proposed in the (e, p, q) representation that means void ratio, volumetric stress (spherical pressure) and deviatoric stress. This frame of theoretical study and apprehension is called: the theory of the Critical State. One of the major problems met at the time of our present research is the non-availability of triaxial apparatus allowing us to achieve some tests on tropical soils (samples from Senegal in West Africa) and to describe the behaviour of these materials easily like the researchers of the university of Cambridge in the theory of the critical state. To by-pass this difficulty, we decided to consider two very classical and simple mechanical tests: shear-box and the oedometer test as well as the interrelationship of the results given by the tests and some theoretical calculations. This is a way to identify an elasto-plastic model (the modified Cam Clay model) without any triaxial experiment. Indeed it supposes the model to be suitable to describe the mechanical behaviour of the considered clays.展开更多
The complex distribution of gas hydrate in sediments makes understanding the mechanical properties of hydrate-bearing sediments a challenging task.The mechanical behaviors of hydrate-bearing interlayered sediments are...The complex distribution of gas hydrate in sediments makes understanding the mechanical properties of hydrate-bearing sediments a challenging task.The mechanical behaviors of hydrate-bearing interlayered sediments are still poorly known.A series of triaxial shearing tests were conducted to investigate the strength parameters and deformation properties of methane hydrate-bearing interlayered sediments at the effective pressure of 1 MPa.The results indicate that the stress-strain curves of hydrate-bearing interlayered sediments are significantly different from that of hydrate-bearing sediments.The peak strength,Young's modulus,initial yielding modulus,and failure mode are deeply affected by the methane hydrate distribution.The failure behaviors and mechanism of strain softening and hardening patterns of the interlayered specimens are more complicated than those of the integrated specimens.This study compares the different mechanical behaviors between integrated and interlayered specimens containing gas hydrate,which can serve as a reference for the prediction and analysis of the deformation behaviors of natural gas hydrate reservoirs.展开更多
基金funded by the Environment and Conservation Fund(Grant Nos.2020-170 and 2021-156)the National Natural Science Foundation of China(Grant No.42102327).
文摘The deep cement mixing(DCM)is used to improve the capacity and reduce the settlement of the soft ground by forming cemented clay columns.The investigation on the mechanical behaviour of the DCM samples is limited to either laboratory-prepared samples or in-situ samples under unconfined compression.In this study,a series of drained and undrained triaxial shearing tests was performed on the in-situ cored DCM samples with high cement content to assess their mechanical behaviours.It is found that the drainage condition affects significantly the stiffness,peak and residual strengths of the DCM samples,which is mainly due to the state of excess pore water pressure at different strain levels,i.e.being positive before the peak deviatoric stress and negative after the peak deviatoric stress,in the undrained tests.The slope of the failure envelope changes obviously with the confining pressures,being steeper at lower stress levels and flatter at higher stress levels.The strength parameters,effective cohesion and friction angle obtained from lower stress levels(c′0 andφ′0)are 400 kPa and 58°,respectively,which are deemed to be true for design in most DCM applications where the in-situ stress levels are normally at lower values of 50-200 kPa.Additionally,the computed tomography(CT)scanning system was adopted to visualize the internal structures of DCM samples.It is found that the clay pockets existing inside the DCM samples due to uneven mixing affect markedly their stress-strain behaviour,which is one of the main reasons for the high variability of the DCM samples.
文摘The main objective of this research is to study the mechanical behaviour of tropical soils using elasto-plastic constitutive equations in the so-called limit and critical states. Indeed, researchers of the Cambridge University had noticed that during their various experiments, the rate of volumetric deformation ( ) of the sample tending to zero every time the rupture of the specimen is reached during a test performed on a clay specimen Roscoe et al., 1958. To better understand and clarify this mechanical behaviour, a description has been proposed in the (e, p, q) representation that means void ratio, volumetric stress (spherical pressure) and deviatoric stress. This frame of theoretical study and apprehension is called: the theory of the Critical State. One of the major problems met at the time of our present research is the non-availability of triaxial apparatus allowing us to achieve some tests on tropical soils (samples from Senegal in West Africa) and to describe the behaviour of these materials easily like the researchers of the university of Cambridge in the theory of the critical state. To by-pass this difficulty, we decided to consider two very classical and simple mechanical tests: shear-box and the oedometer test as well as the interrelationship of the results given by the tests and some theoretical calculations. This is a way to identify an elasto-plastic model (the modified Cam Clay model) without any triaxial experiment. Indeed it supposes the model to be suitable to describe the mechanical behaviour of the considered clays.
基金supported by the National Natural Science Foundation of China (No. 41976074)National Key Research and Development Plan (No. 2017YFC030 7600)+2 种基金the Taishan Scholar Special Experts Project (No. ts201712079)Qingdao National Laboratory for Marine Science and Technology (No. QNLM2016ORP0207)the Graduate School Innovation Program of China University of Petroleum (East China) (No. YCX2019020)
文摘The complex distribution of gas hydrate in sediments makes understanding the mechanical properties of hydrate-bearing sediments a challenging task.The mechanical behaviors of hydrate-bearing interlayered sediments are still poorly known.A series of triaxial shearing tests were conducted to investigate the strength parameters and deformation properties of methane hydrate-bearing interlayered sediments at the effective pressure of 1 MPa.The results indicate that the stress-strain curves of hydrate-bearing interlayered sediments are significantly different from that of hydrate-bearing sediments.The peak strength,Young's modulus,initial yielding modulus,and failure mode are deeply affected by the methane hydrate distribution.The failure behaviors and mechanism of strain softening and hardening patterns of the interlayered specimens are more complicated than those of the integrated specimens.This study compares the different mechanical behaviors between integrated and interlayered specimens containing gas hydrate,which can serve as a reference for the prediction and analysis of the deformation behaviors of natural gas hydrate reservoirs.
