| In recent decades,the shallow sea oil and gas resources are gradually exhausted,and the exploration of offshore oil and gas is entering the deep sea.This trend has also led to a shift in the basic form of offshore platforms from structures fixed to the seabed to floating structures attached to the seabed by taut or semi-automatic mooring systems.There are many types of anchors suitable for deep sea environments including suction caissons,drag-installed anchors,suction embedded plate anchors,and gravity installed anchors(GIAs).Among these anchors,GIAs are attractive in terms of cost-effectiveness and time efficiency in the process of dynamic installation.And the OMNI-Max and torpedo anchors as GIAs are widely used in offshore engineering.Compared with torpedo anchor,the capacity to weight ratio of the OMNI-Max anchor is relatively high.Besides,the OMNI-Max anchor can dive into deeper soil when subject loads that exceed the design loads.However,the maximum penetration depth of torpedo anchor is relatively deep since it is subjected to smaller soil resistance during the dynamic penetration.Based on the advantages and limitations of the OMNI-Max and torpedo anchors,an innovative light-weight gravity installed plate anchor(L-GIPLA)was designed which combined the advantages of deep embedment depth,high capacity-to-weight ratio,diving property,and low installation cost was designed.This paper presents a series of 1g dynamic penetration tests to investigate the working efficiency of an innovative light-weight gravity installed plate anchor(L-GIPLA)both in normally consolidated(NC)and lightly over-consolidated(LOC)soils.The parameters studied in this paper include the soil strength characterisation,impact velocity,booster weight,and water entrainment effects.A micro electromechanical systems(MEMS)accelerometer was used to measure the dynamic penetration process of the L-GIPLA in clay.Based on the data obtained from the MEMS accelerometer,the effect of water drag force and water entrained by the penetration of the L-GIPLA were analyzed.The experimental results showed that with the aid of the booster,the penetration depth of the L-GIPLA increases as the impact velocity and mass increase.In the range of impact velocity of 13.3-25 m/s and clay strength of 1.5-4.3 z k Pa,the penetration depth ratio of the light-weight gravity installed plate anchor can reach 2.05-4.97.Besides,in normal consolidated soil and slightly over-consolidated soil,the water entrainment effect on L-GIPLA penetration depth seems to outweigh that from the water drag and buoyancy effect.The second part of the paper proposed two frameworks for predicting the depth of anchor penetration.One is based on the force method of Newton's second law,considering the soil resistance and rate effect of the anchor in the process of penetration.The other one is based on the total energy,considering the influence of soil strength and anchor geometry.The test results show that both frameworks can predict the depth of penetration promptly and accurately.The force method can analyze the influence of each resistance on the depth of penetration.And the energy method is more convenient and more quickly.Finally,the advantages of the proposed L-GIPLA were highlighted by comparasion with other GIAs in terms of penetration depth ratio,ze/ha,and the capacity to weight ratio F_N/W_d.The third part of this thesis studied the change of the excess pore pressure during the process of penetration and the dissipation of the excess pore water pressure after the installation.In the test,the excess pore pressure of different positions in the horizontal direction and the vertical direction was studied with the aid of pore pressure transducers.The results show that the change of the excess pore pressure is related to the position of the anchor during penetration.In the horizontal direction,the farther away the penetration point is from the center axis of the anchor,the smaller the peak pore pressure will be in the process of dynamic penetration.In the vertical direction,the deeper the depth,the greater the peak excess pore water pressure caused by penetration. |
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