Wave-induced Soils Failure Of Subaqueous Hard Crust On Delta Of Yellow River, China

The dissertation is relied on the project of National Science Foundation Project "Formation and Failure of Hard Crust on the Subaqueous Delta of Yellow River" (Contract No. 141720888), and objective to research wave-induced soils failure of Subaqueous Delta of Yellow River.As the foundation of the oil extraction platform and oil pipe of ShengLi oil Field, hard crust of the subaqueous Delta of Yellow River always have enough strength statically. While during of the process of the construction of the overseas structures, especially during of the process of storm tide, there often be unexpected engineering geological happenings and usually causes magnitude loses. So it means very much to know the soils' failure process under wave action. Hard crust of the subaqueous Delta of Yellow River is mainly made up of silt soil. Silt soil have many especial geological features, and have very complicated response manners under wave action. Up to now, there have many researchers studied the response manners of sand sea-bed and clay sea-bed to wave actions, while there very few studied the response manners of silt sea-bed to wave actions systemly. This dissertation will do some research on this fresh question.The dissertation is made up of 7 chapters. The 1st chapter discusses the significance and actuality of this field, and based on this give the research steps. The 2nd chapter describes the features of the hard crust of the Subaqueous Delta of Yellow River. From 3rd to 6th chapter, physical simulation, in-situ simulation, dynamic triaxial test and numerical simulation researches are used to study the process of failure of the hard crust. The 7th chapter gives the main conclusions.In order to understand the failure process of silt sea-bed under wave action, the works we have done are listed as follows: 1. Around Delta of Yellow River, we selectedseveral positions to do some tests using portable cone penetration, shallow drilling, and picked several original state samples. Back to the lab, we performed conventional tests and micro-structure tests using the original state soil samples get from the field. 2. We design a physical stimulation experiment in the lab to study the response manners of the silt soil to the wave actions. 3. Performing concussion tests in the filed, test the changing of pore pressure and CPT of the silt sea-bed. 4. Performing soil dynamic trial test in the lab, test the soil samples' trial strain and horizontal strain and the changing pore pressure under different dynamic stress. Based on the results get from the soil dynamic trial test, we calculated the dynamic elastic modulus and the dynamic damping ratio and analyzed these changing riles. 5.Taking into account the excess pore pressure accumulated and the transient strain changing caused by the waves actions, we establish a numerical model to study the stability problems caused by the changing wave height and wave length and the sea-bed parameters.According to the studies we have done, we get several main conclusions as follows:1. The drain velocity of the silt sea-bed which was quickly deposited will accelerated under the wave actions, and will forming a hard crust, which geological properties are very uniformly, of certain thickness; Under unexpected large wave actions, the silt sea-bed will be destroyed and arises "water sprinkle and sands emits ",and the hard crust will become very asymmetric.2. Under concussion vibrations, CPT of the silt sea-bed will falls, pore pressures in the soils appears ascend and large fluctuations; There are more concussion energies the influence depth will be more deep, and at certain depth the excess pore pressure will exceeds the soils' available stress and forming "water bursa"3.From the dynamic axial test, we gets that different loading sequences affects the silt sea-bed's response manners obviously. When the load thrown gradually up, the silt soils dynamic damping ratio will hoist suddenly and then gradually descend; When the load thrown gradually down, the silt soils dynamic damping ratio will graduall...