Research On Polyurethane Curing Improvement Methods And Physical Mechanics Characteristics Of Calcareous Sand

With the proposal of "One Belt,One Road",the construction of islands and reefs in the South China Sea is in the ascendant.There is a large amount of calcareous sand around the Nansha Islands,and the calcareous sand is used as the backfill material for the foundation soil,which can reduce the cost of the project and shorten the construction period.However,calcareous sand has the characteristics of high compressibility and brittleness,and it is easy to cause problems such as collapse,cracks and insufficient bearing capacity of pile foundations in practical engineering.Therefore,it is necessary to study the physical and mechanical properties and reinforcement methods of calcareous sand.Therefore,this paper proposes to use polyurethane to reinforce calcareous sand,and studies the physical and mechanical properties of calcareous sand before and after reinforcement.The main research contents and conclusions are as follows:(1)Particle analysis,specific gravity and maximum and minimum dry density tests were carried out on the calcareous sand of Baa Atoll in Maldives,and the calcareous sand Cu(inhomogeneous coefficient)and Cc(curvature coefficient)were 0.57,which belonged to the graded poor soil,with a specific gravity of 2.72,the maximum dry density was 1.487 kg/m3,and the minimum dry density was 1.304 kg/m3.A preparation method of polyurethane cured calcareous sand is proposed,and the cured substance prepared can be used for indoor dynamic and permeability test research through manual mixing and layered compaction.(2)In order to study the static strength of polyurethane calcareous sand,the unconfined compressive strength test was taken,and the optimal gel time of polyurethane-cured calcareous sand was obtained as 6.5h;The cohesion of 5%,8%,and 10% calcareous sand is 1.4,1.9,3.4,and 4.3 times that of calcareous sand,respectively,and the internal friction angle is between 38.1°and 38.9°.The functional relationship between failure strength and polyurethane content and confining pressure was established.When the content and confining pressure increased,the failure strength was improved.The projection of the fitting curve on the failure strength-content plane was approximately parallel.(3)Cyclic triaxial tests were carried out to study the dynamic stress-strain relationship of polyurethane calcareous sand under different dosages(0～10%)and confining pressures(50～200k Pa),and established dosages,confining pressures and initial dynamic shear A function of shear modulus and maximum damping ratio.Under low confining pressure(50 k Pa),the initial dynamic shear modulus values of 2%,5%,8%,and 10% of the calcareous sand were increased by 4.69,18.14,49.19,and 67.33 MPa,respectively.The maximum damping The ratios are 82.9%,77.3%,59.8%,and 40% of calcareous sand,respectively.Under high confining pressure(200k Pa),the dynamic shear modulus increased by 6.89,35.69,79.57,and 109.51 MPa,respectively,and the maximum damping ratio was 79.6%,65%,51%,and 35% of that of calcareous sand,respectively.(4)The permeability coefficient index of polyurethane calcareous sand was studied by permeability test.The order of magnitude of the permeability coefficient of calcareous sand is10-6,and the order of magnitude of the permeability coefficient drops to 10-8～10-7 after adding2%,5%,8%,and 10% of polyurethane,which proves that polyurethane is effective for calcareous sand.The effect is better.The functional relationship between the dosage,confining pressure and permeability coefficient is established.In the permeability coefficient-concentration plane of0～70 k Pa,the slope of the curve of dosage and permeability decreases gradually,and when the confining pressure reaches 70 k Pa,the slope decreases.is-3.05 and remains largely unchanged.(5)In order to study the adaptability of polyurethane in the construction of island and reef projects in the South China Sea,a static triaxial test after seawater conservation was carried out,and the static properties of polyurethane calcare sand under seawater conservation were obtained.Compared with the conservation of freshwater environments,polyurethane-doped calcareous sand can still maintain a high strength in seawater environments.