=Advantages and Disadvantages.=--The principal advantages claimed for the Austrian method of tunneling are: (1) The excavation being conducted by driving a large number of consecutive small galleries, which are immediately strutted, there is little disturbance of the surrounding material; (2) the polygonal type of strutting adopted is easily erected and of great strength against symmetrical pressures; (3) the masonry, being built from the foundations up, is a single homogeneous structure, and is thus better able to withstand dangerous pressures; (4) the excavation is so conducted that the masons and excavators do not interfere, and both can work at the same time. The disadvantages which the method possesses are: (1) The strutting while very strong under symmetrical pressures, either vertical or lateral, is distorted easily by unsymmetrical vertical or lateral pressures, and by pressure in the direction of the axis of the tunnel; (2) the construction of the invert last exposes the side walls to the danger of being squeezed together, causing a rotation of the arch of the nature discussed in describing the Belgian method of tunneling. CHAPTER XV. SPECIAL TREACHEROUS GROUND METHOD; ITALIAN METHOD; QUICKSAND TUNNELING; PILOT METHOD. ITALIAN METHOD. The Italian method of tunneling was first employed in constructing the Cristina tunnel on the Foggia & Benevento R.R. in Italy. This tunnel penetrated a laminated clay of the most treacherous character, and after various other soft-ground methods of tunneling had been tried and had failed, Mr. Procke, the engineer, devised and used successfully the method which is now known as the Italian or Cristina method. The Italian method is essentially a treacherous soil method. It consists in excavating the bottom half of the section by means of several successive drifts, and building the invert and side walls; the space is then refilled and the upper half of the section is excavated, and the remainder of the side walls and the roof arch are built; finally, the earth filling in the lower half of the section is re-excavated and the tunnel completed. The method is an expensive one, but it has proved remarkably successful in treacherous soils such as those of the Apennine Mountains, in which some of the most notable Italian tunnels are located. It is, moreover, a single-track tunnel method, since any soil which is so treacherous as to warrant its use is too treacherous to permit an opening to be excavated of sufficient size for a double-track railway, except by the use of shields.