Método MASW na análise do melhoramento de solos com a técnica CPR Grouting

Abstract

Studies that enable civil construction in areas characterized by soft clayey soils have been increasingly frequent and necessary due to urban expansion. The use of techniques for soil conditioning is, many times, indispensable for the accomplishment of constructions in certain areas.In the midst of these new technologies, the Radial Deep Consolidation, known as CPR Grouting, stands out, a technique of stiffening of soft soils defined by the driving of vertical geodrains and subsequent creation of bulbs sequentially expanded from bottom to top in the soil layer, with the purpose of providing the consolidation.The evaluation of the degree of improvement of geohardened soils with conventional tests is a challenge, since the technique promotes the creation of a homogeneous soil reinforced by discontinuous rigid inclusions, making it difficult to carry out invasive tests. In this context, geophysics can provide a flexible tool for the macroscale evaluation of grouting efficiency, relating the increase in shear wave velocity with the increase in soil stiffness.The dispersive nature of surface waves can be explored using various techniques to obtain a model of shear wave velocity distribution as a function of depth. One of these techniques is Multichannel Analysis of Surface Wave (MASW), commercially called Seismic Tomography by Image. The present work has as objective the analysis of three Works that present a program of field tests composed by borings, pressure tests and seismic tests. An attempt was made to evaluate the ability of seismic tomography to detect the level of improvement in soft soils treated with the CPR Grouting technique, associating correlations between seismic tomography and traditional field tests such as pressuremetric tests and borings, in addition to the composition of the degradation curve for the researched soils. Soil classification information, shear wave velocity (Vs), undrained strength (Su) and soundings were collected at the three study sites. The gathering of all data allowed the establishment of correlations between Vs x NSPT and Vs x Su values. The proposals were evaluated and showed a high coefficient of correlation and agreement with international studies. The analysis between Vs and (effective limit pressure) pl’ e did not show good results. The evaluation of strength gain was positive in all cases which were analyzed, demonstrating the good performance of the soil improvement technique and showing an average strength gain of around 70%. A faithful comparison between the locations was not possible due to the different configurations of application of the technique, such as spacing between bulbs and meshes. Even so, it can be inferred that the places that showed better performance, greater gain in undrained resistance, were those where the mesh was configured with a shorter distance between the drains and smaller spacing between bulbs. It is concluded the variables make it impossible to establish a categorical value for the strength gain promoted by the application of the CPR Grouting technique, but that the seismic tests are able to capture the degree of improvement of the local soil taking into account its specific characteristics.