自由落体球形贯入仪水下贯入软土过程分析

Analysis of Underwater Penetration into Soft Soil of Free Fall Sphere Projectile

自由落体贯入仪(Free-Fall Penetrometer, FFP)已经广泛应用于海洋原位勘察中。近些年,发展出了一款无轴杆的自由落体球形贯入仪,理想球形外观使其相较于其他形状的贯入仪在强度测试方面更具优势。由于贯入仪是依靠在水中自由下落获得的动能贯入土体,所以需要足够的初始贯入速度来保证其在软土中能够达到预期的贯入深度。基于牛顿第二定律来建立球体在水中和土中的运动方程,将在球体水中由静止自由下落和贯入软土过程看作初值问题,给出了求解下落位移、速度和线性加速度的算法;分析了球体直径和密度对其在水中极限速度和土中贯入深度的影响;根据现场水深条件和海床强度测试深度要求,可以利用给出的模型和算法快速地对所需要的贯入仪直径和密度进行预设计。

Free-fall penetrometers have been widely used in offshore in-situ investigations.Recently, a free fall sphere projectile with no shaft has been devised, whose purely spherical shape make it have merits in determining the undrained shear strength of soil from measured inertia data, compared with penetrometers of other shapes.Because the projectile penetrates into soil by its kinetic energy obtained from free fall in the water, it needs enough impact velocity to ensure that it can reach the expected penetration depth in the soft soil.Newton′s second law of motion has been adopted to formulate the governing equation of penetration of a projectile in water.By treating the penetration process as an initial value problem, an algorithm is proposed for computing the displacement, velocity, and linear acceleration of penetration.The effects of sphere diameter and density on its terminal velocity and penetration depth are analyzed.In addition, according to the site water depth conditions and the requirement of measurement depth, the diameter and density of the sphere projectile required for the field test can be designed quickly by using the given program.