A. Viana da Fonseca

Numerical Methodology to Minimize Resolution and Sensitivity Effects in P-Wave Measurements

This paper presents a new numerical methodology aiming at facilitating the identification of seismic wave’s propagation time, using a time domain approach. The solution uses first- and second-order differential computing, namely divided differences methods. Results of extensive laboratory seismic wave tests over aggregate–cement mixtures with different voids ratios (densities) and cement contents (1 %, 2 %, 3 %, 4 %, and 5 %) are discussed. The results indicated relevant differences in values of longitudinal modulus (or P-wave modulus) derived with and without this methodology. This was considered especially important in stiff specimens with high-seismic wave velocities and low-energy input signals.

Characterization of Highly Variable Rock Weathering by Using DPR

The highly variable nature of the deeply weathered Porto granite has been posing significant challenges in the geotechnical design and some problems in the execution of foundations, deep excavations and tunneling, due to the nature of the rock mass which is extremely difficult to differentiate between the several class qualities. The identification of geotechnical patterns in weathered rock profiles from conventional borehole investigations is common and ideal, but rather time consuming. Drilling Parameter Recording (DPR) has been pointed out as a complementary alternative to this site investigation. A series of boreholes where both classical exploration techniques (including standard penetration tests on soil masses with sampling to allow some lab tests and rock quality monitoring by the analysis of coring, as well as some geophysics in both ambient) and drilling with recording systems, have been used to develop protocols between indices coming out from this most practical and efficient technique. This paper presents the preliminary results of the study developed in this geological and geotechnical ambient, by comparing the drilling parameters – both individual and compound, which may magnify specific contributions – with the conventional site investigation measurements This research, in a joint venture with the industry, aims to potentate this technique in order to become a reliable complementary alternative in mapping and characterizing these weathering profiles.

Factors Affecting Steady State Locus in Triaxial Tests

Models based on critical state soil mechanics (“CSSM”) require careful calibration of laboratory parameters in order to ensure accurate prediction of the behavior of soil under in situ conditions. This paper presented research on the testing of two distinct materials, a silt and a silty sand. Several triaxial tests were conducted under drained and undrained conditions, with low to very high confining pressures. Distinct mechanical responses were observed: some samples liquefied, some softened, and others hardened when loaded under undrained conditions. The degree of saturation, the induced anisotropy and the induced stress-path were found to influence the state limits between these distinct behaviors. This affected the steady state line (“SSL”) position defined by specimens showing strain softening in the experiment. Furthermore, the “critical state line” was only achieved when the specimens experienced strain hardening despite the stress-path during shear and the initial state conditions. Therefore, as these factors can impact the steady state line (SSL) position, it is essential when assessing the geomechanical behavior of the soil that these factors are monitored and controlled under laboratory conditions according to the in situ state condition and stress-path during shear. In the future, constitutive models have therefore to be adapted in order to determine the influence of these conditioning factors in the ultimate CSSM reference lines positions.

Ground Reinforcement and Rehabilitation of Foundations Systems for Their Reuse

The reuse of foundations for a second superstructure is technically feasible and is increasingly becoming part of standard practice. For refurbishment projects, reuse of old foundations and structures is the norm. For foundation reuse to be viable, the following conditions need to be satisfied: (i) there should be compatibility between the locations of the applied loads and the existing foundations, which should have sufficient bearing capacity to carry the new loads; (ii) sufficient verification should be carried out so that the old foundations are shown to be as reliable as new ones; (iii) there should be an expectation that the foundation performance over the range of expected loads will be acceptable, and that they will fulfil those functions reliably over the planned design life of the building; (iv) the project team needs to agree that all parties accept the risks associated with foundation reuse; (v) adequate insurance cover is available for the design team and client; (vi) regulatory approval is possible from the necessary authorities. Currently old foundations tend only be reused in a redevelopment, if there is a particular constraint that acts as a driver: (i) the ground beneath the building has already been filled; (ii) there are archaeological remains that can be preserved by foundation reuse. One of the main inhibitors to foundation reuse is uncertainty: unless records have been kept that indicate the foundation locations, sizes and capacities with a high degree of reliability, it can be difficult to reuse them reliably or efficiently. Therefore one important issue to maximize the future ability to reuse foundations is the collection and safe preservation of construction and maintenance records. When the risk to full trust on the original foundations is high, ground improvement techniques are advisable, mainly versatile and small diameter drilling techniques as jet grouting and micropiles.