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APPLICATION OF DIGITAL PHOTOGRAMMETRY IN GEOTECHNICS 
R. Roncella?, M. Scaioni^, G. Forlani® 
* DICATA, Dept. of Civil Engineering, Parma University, Parma, 43100, Italy - (rroncell, gianfranco.forlani)@unipr.it 
? DIIAR, Politecnico of Milan, Milan, 20133, Italy - marco.scaioni@polimi.it 
Commission V, WG 1 
KEY WORDS: Geology, Engineering, Close Range, Digital, Photogrammetry 
ABSTRACT: 
Acquiring geometric data, such as coordinates, displacements or deformations, has always been a way to verify mathematical 
modelling in civil engineering. The introduction of finite elements methods further reinforced this trend. This paper reports on two 
applications of photogrammetry to soil and rock mechanics in order to provide an accurate and dense description of the deformation 
fields of sand specimens in different loading conditions. In the first case, the displacements induced by a foundation under load in 
sand layers are traced until the collapse of the terrain with accuracies in the order of about 20 micrometers in object space. In the 
latter, the trajectories of particles, tied to a sloping sand specimen that slides along a plane, are determined with an accuracy of about 
3 mm at a rate of 22 fps. In both examples, the measurement runs automatically, the only interaction required being the test setup. 
1. INTRODUCTION 
There is a wide range of tasks in university laboratories where 
digital photogrammetry is proving to be an ideal measurement 
tool, from tracing the slow progress of deformations of a 
specimen in a loading machine to particle tracking in fluids. 
Requirements in terms of accuracy, measurement rate, number 
of targets to be tracked and object size are very specific to the 
applications, so design and setup must be tailored to the 
specifications of each experiment. Besides often representing 
interesting tasks in themselves, they also offer the opportunity 
for interdisciplinary cooperation among different fields, leading 
to a larger acceptance of photogrammetry within academia. 
This paper reports on two such experiences, jointly held at the 
Politecnico of Milan and at the University of Parma, where 
photogrammetry has been used to support research activities in 
soil mechanics. 
The first had the objective of determining the deformation field 
induced by the foundations of buildings or bridges in sand 
layers. This should ultimately lead to improved design 
techniques of foundations, thanks to the deeper understanding 
of their interaction with sand. The movement of the sand 
particles under test were in the order of 100 micrometers at each 
loading step, so the key point was to follow accurately a very 
small and slow movement. 
In a second application, the goal was to track the movement of 
the superficial layer of a terrain slope sliding over a 
discontinuity plane (reproducing at a smaller scale an 
artificially induced landslide of incoherent soil); again this was 
meant to verify the prediction of the movement by a 
mathematical model. In this case, the accuracy requirements 
were less demanding in absolute terms (1-2 mm) but the 
dynamics of the movement was significant and the 
displacement field 3D. 
2. MEASUREMENT OF DISPLACEMENTS INDUCED 
BY FOUNDATIONS ON SAND 
2.4 Background 
Evaluation of the tensile strenght of a sandy terrain subject to 
different loading conditions relied so far on methods based on 
the elastic model. In reality, this assumption is not completely 
satisfied, also when dealing with reduced load and small 
deformations. Since a more accurate knowledge of the 
maximum load sustainable by a terrain would result in the 
optimization of foundations design, several experimental tests 
have been set up at the Dept. of Structural Engineering (D.I.S.) 
of the Politecnico of Milan to assess the dependency of the 
mechanical behaviour of the terrain on frequency and 
magnitude of load cycles as well as on foundation stress. 
Results of this study will help to prevent situation of risk in case 
of structures stressed by earthquakes, winds and waves, such as 
those experienced in off-shore platforms and structures for sea- 
side protection built over incoherent sand. 
2.2 Experimental setup 
At the Dept. of Structural Engineering, a testing device 
designed and built to execute load tests on sand specimens has 
been in use for the last 15 years with several kind of materials 
and loading configurations (Montrasio & Nova, 1989). As 
shown in Figure 1, the device is a box (with dimensions 
890x20x385 mm) made up of two tempered glass walls, 
reinforced by steel bars, and two lateral wooden walls. The sand 
specimen is deposited in the box through a specially designed 
sieve, so that the stratification and density of real terrain can be 
reproduced. The scale model of foundation press the sand, just 
fitting the size of the device but without direct contact with the 
lateral glass walls, to avoid friction. Thanks to a pair of oleo- 
dynamic actuators, loads in horizontal and vertical direction 
may be applied, while two strain-gauges along the same 
directions perform a continuous measurement of displacements. 
Cyclic loading is possible as well. The typical outcome from 
this instrument is the diagram load-displacement for the point 
located just below the foundation centre. Until photogrammetry