ABSTRACT
The soils of the former Texcoco Lake located in the Mexico Basin are structured soft lacustrine sediments, comprising a variable mixture of high plasticity clay minerals and siliceous diatoms. These soils present an unusual combination of high void ratio coupled with high friction angles. Other properties like the ability to sustain large shear deformations without generation of any significant excess pore pressure, thixotropic behaviour and high natural period of vibrations makes it a uniquely challenging material to work with. The properties of this soft lake deposit are a moving target due to ongoing consolidation caused by the groundwater abstraction from the deep aquifer. The former lake is effectively undeveloped, but importantly site investigations including excavation trials were carried out in late 1960 demonstrating the difficulties of working with these materials fifty years ago when ground levels were about 8 to 10 m higher than they are today. As a part of the development of the New International Airport of Mexico City (NAICM), extensive ground investigations were carried out including a largescale trial excavation in 2016. This paper presents the key results from the ground investigation and the detailed calibration work carried out to develop input parameters for the Hardening Soil model with Small Strain stiffness (HSsmall) constitutive model. This paper also shows how the Finite Element analyses were successfully used to reproduce the trial excavation behaviour.
