GeoCorner

Author: Kirill Goloviznin
Supervisor: Professor Jarkko Niiranen
Advisor: MSc Henry Gustavsson, PhD Summer Shahzad
Collaborative partner/sponsor: Ramboll Finland Oy

Abstract:

A concrete structure that is designed to last for a hundred years must withstand various actions, including temperature gradients which may cause cracking. Although such actions are typically provided in design standards, the Finnish design guidelines do not specify temperature loading for soil-immersed concrete structures like troughs or retaining walls. One of the current engineering approaches is to adopt the loading from the Bridge design guidelines and apply it in the linear elastic finite element analysis which results in excessive reinforcement. The first problem with this method is that the temperature magnitude is too large for soil-immersed structures. And the second problem is that the linear elastic model does not account for stress relaxation due to concrete cracking. The aim of the research is to calculate proper temperature distribution and derive an equivalent temperature loading for crack assessment, applicable in the linear finite element analysis. First, the temperature distribution is calculated with a thermal conduction analysis, based on annual recorded temperatures, thermal insulation surrounding the structure, and the water content of the soil. Then it is applied in the nonlinear analysis to calculate crack width and required reinforcement. Finally, an equivalent temperature for the linear analysis is determined which requires the same amount of reinforcement as predicted by the nonlinear analysis.

Author: Hamza Javed
Supervisor: Professor Jussi Leveinen
Advisor(s):  Dr Mateusz Janiszewski, Dr Tero Hokkanen

Abstract:
 Rock mass characterization is vital for assessing the geotechnical and geomechanical stability of a rock mass which ensures safe tunnel designs and ultimately a sufficient reinforcement design. The validity and reliability of different rating systems is based on the accurate characterization of fracture parameters like orientation, joint set number, spacing etc. A comprehensive study of such fracture parameters will only ensure the correctness of numerical models. In this thesis, a combination of non-invasive techniques for mapping of fracture properties is studied. Photogrammetry uses 3-D digitization technique to generate high resolution models of the rock mass while ground penetrating radar can image the subsurface for fractures in a tunneling environment. The research location is tunnel 3 at the Underground Research Laboratory of Aalto University (URLA). 

The research questions are: What are the limitations imposed by ground penetrating radar in tunnels? How can GPR be used for characterization of fractures within the rock mass? How can photogrammetry be used to evaluate geometrical properties of fractures and digitization of roughness profiles? 

This thesis deals with the characterization of fracture properties like orientation, joint set number, aperture, filling, roughness, spacing and persistence through the use of photogrammetry and GPR. Photogrammetry is carried to reconstruct a 3-D point cloud which is analyzed in a point cloud editing software and discontinuity set extractor for the extraction of joint properties. The test site is divided into two mapping windows. GPR (800 MHz) is used to survey four vertical profiles on the rock mass where photogrammetry is conducted. The four profiles are processed and interpreted showing two to maximum of four fractures. The analysis suggest that the fractures observed with GPR in the test site are all thin bed fractures whose aperture is smaller than the radar range resolution. The floor survey profile by 500 MHz in the same tunnel shows three wide fractures with a mean aperture of 10.3 cm in one of the fractures. 

Sensitivity analysis resulted in three joint sets for mapping window one and four joint sets for mapping window two. The surface analysis concluded in moderate spacing of joint sets ranging between 0.2-0.6 m with undulating rough fracture surfaces as indicated by the manual and digitized joint roughness profiles. GPR studies concluded the wall surveys to have thin-bed subvertical fractures in the subsurface with moderate spacing of 0.2-0.6 m between the individual fractures. 

Keywords Photogrammetry, Ground penetrating radar, fracture properties, thin bed fractures, joint roughnes

Author: Achintha Rathnayaka
Supervisor: Professor Mikael Rinne
Advisor(s): MSc Oskar van der Weij
Funding: Partly funded by  Kalliosuunnittelu Oy Rockplan Ltd. (Finnmap-Infra oy)

Abstract:

Megacities are growing faster than ever before where the demand for adequate parking spaces is continuing to rise while diminishing the free buildable space. Underground parking facilities offer a way around this problem. Building underground can be done in two major ways, either a parking facility in a tunnel or as an open pit version. In countries where the bed rock is at a shallow depth, underground excavation would need to carry out in hard rock in both variants

Giving the impact a large excavation would have on nearby existing structures especially considering the highly disruptive nature of rock excavation techniques it is important to assess the rock mechanical feasibility of the two options when selecting the appropriate method. Further, it is also vital to assess the environmental impacts and overall costs to identify the most favorable approach.

This thesis explored a case study from Meilahti hospital area where an Open-pit parking facility was proposed. A hypothetical underground tunnel version of the parking facility was developed to assess its rock mechanical viability using 3DEC numerical modelling software and compared the results with the open-pit version. Further, total CO2 emissions were computed using One click LCA software and also, the expected theoretical costs of both options were calculated and compared.  

It was observed that the tunnel version would result in minimal displacements at surrounding structures, ranging from 2….3 mm. But, in open pit version the displacements are rather high even more than 10mm at some locations.  Higher displacements could result in severe fractures in the existing tunnel's shotcrete layer, as well as foundation settlement in surrounding structures, causing shear cracks in the walls.

In terms of CO2 output, both variants emit same level of CO2 with a slightly low percentage difference in the tunnel version. Further, there was a considerable difference with the total rock construction related cost where open pit version would cost nearly 1.5 times as much as the tunnel version.

Keywords:  Parking facility, Tunnel, 3DEC, Hard rock modelling, CO2 eq.,  

Author: Sofia Kiikkerä
Supervisor: Sanandam Bordoloi
Advisors: Juha Auvinen
Funding: City of Helsinki

Electro-osmosis is a dewatering method best suitable for cohesive soils, whereby a direct current is applied to the soil by electrodes. The application of current causes a flow of water towards the cathode where it can be removed. This results in consolidation of the soil.

A laboratory study was designed to investigate the feasibility of electro-osmosis in Finnish clay. Undisturbed samples from Malmi field were collected and tested under three different voltages to evaluate the effectiveness of the method. In some tests, electro-osmosis was applied together with incremental loading to gain knowledge of the combined effects. 

The coefficient of electro-osmotic permeability was evaluated from the test data. Corrosion of the electrodes, pH changes and the negative porewater pressure developed were also calculated. These results can be used to design field tests in the future.

Author: Naum Shpata
Supervisor: Professor Wojciech Sołowski
Advisor(s): Piotr Kanty (Menard)
Funding: DeMiCo project

Simulation of the vibration caused by dynamic compaction is complicated, and more research needs to be done on it. The complexity of the problems varies over many factors, including lack of valuable data, different soil properties and behaviour. The main reason is that the willingness to simulate the vibration has been low because the method has usually been applied in remote areas. However, the soil improvement method is considered a small carbon emission method and must be utilised in urban areas where nearby structures are vulnerable to vibrations. This study presents a comprehensive overview of wave propagation, introduces a constitutive model, and replicates the vibration caused by dynamic compaction on a study case within the Finite Element Framework. The model contains two input parameters: shear modulus and Poisson's ratio. The model considers a nonlinear stress-strain relationship at small strains based on a constant reference stiffness degradation curve. 

The model's capabilities were demonstrated in a confirmed case of dynamic compaction, specifically in Gdańsk, as conducted by the Menard Group. The study implemented two falling heights, 5 and 10 m, in a sand soil area. The model can achieve high accuracy when calibrated correctly, providing a reliable tool for predicting wave vibrations. However, it is essential to note that the maximum shear modulus can significantly influence the result, and the dynamic properties of the soil are a crucial factor. The need for an accurate estimation of the damping ratio is evident. While the model can be applied in practice, paying attention to the importance of input parameters from the field is crucial, as they play a significant role in the model's performance and the accuracy of its predictions. 

Keywords dynamic analysis, FEM modelling, dynamic compaction, vibrations, small strain non-linear constitutive mode