This paper discusses the design, the installation, and the experimental and numerical evaluation of the effectiveness of a stiff wave barrier in the soil as a mitigation measure for railway induced vibrations. A full scale in situ experiment has been conducted at a site in El Realengo (Spain), where a barrier consisting of overlapping jet grout columns has been installed along a railway track. This barrier is stiff compared to the soil and has a depth of 7.5 m, a width of 1 m, and a length of 55 m. Geophysical tests have been performed prior to the installation of the barrier for the determination of the dynamic soil characteristics. Extensive measurements have been carried out before and after installation of the barrier, including free field vibrations during train passages, transfer functions between the track and the free field, and the track receptance. Measurements have also been performed at a reference section adjacent to the test section in order to verify the effect of changing train, track, and soil conditions over time. The in situ measurements show that the barrier is very effective: during train passages, a reduction of vibration levels by 5 dB is already obtained from 8 Hz upwards, while a peak reduction of about 12 dB is observed near 30 Hz immediately behind the barrier. The performance decreases further away from the jet grouting wall, but remains significant. The experimental results are also compared to numerical simulations based on a coupled finite elementboundary element methodology. A reasonable agreement between experiments and predictions is found, largely confirming the initially predicted reduction. This in situ test hence serves as a 'proof of concept', demonstrating that stiff wave barriers are capable of significantly reducing vibration levels, provided that they are properly designed.

Ground-penetrating radar (GPR), as a high-resolution geophysical prospecting method, has proved to be a very useful tool in archaeological site investigations, especially in the detection and identification of tunnels and galleries. This work shows seven selected profiles collected at four different archaeological sites in Spain and Mexico, with a wide variety of targets, not only in terms of their size (from 1 ð 1 m to 3 ð 4 m) but also in their depth (from 0.5 to 7 m). In all, 14 galleries and/or tunnels were detected. The approach to these studies was organized in two ways: firstly the presence of a known subsoil was used to compare the response of different antennae looking for these kinds of targets; secondly, GPR was used to find unknown historical galleries before any excavation took place. The equipment used in these studies were the SIR-8, with 120 and 500 MHz monostatic antennae, and PulseEkko IV, with 100 MHz bistatic antennae.

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A gravimetric survey, covering a site 200 m square, was carried out in order to locate karstic cavities. After eliminating the regional trend using a polynomial fit, the residual is modelled by least-squares prediction. Correlated signals for several wavelengths are detected. The inversion of these anomalies is performed by a global 3D adjustment using spherical bodies as models. The adjustment is repeated in order to obtain a stable configuration. The results show the probable presence of a system of cavities and galleries. Data collected from boreholes and the subsequent appearance of sink-holes are consistent with the results. lntroductionThe interpretation of an anomalous gravity field consists of finding a geologically plausible density distribution whose computed gravity anomalies fit the observed values. The non-uniqueness of this problem is well known. Some interesting solutions can be obtained, including a limited hypothesis about the geometry, homogeneity, depth, mean density contrast, etc. Other conclusions can be obtained by setting bounds on density and depth (Parker 1974).Two types of method can be considered: the space-domain approach and the frequency-domain or spectral approach.The widespread use of spectral analysis (Fourier methods) has been recognized in several publications (e.g. Sybert 1972;Bhattacharyya and Leu 1977). The FFT algorithms allow fast computation using a digital computer. Nevertheless, as discussed by Oldenburg (1974), one of the major drawbacks of the Fourier inversion methods is an instability due to explicit downward continuation, which makes regularization filters necessary.