## 4 Discussion
### Effect of Ground-Borne Vibrations on the Building
For vibrations generated by the operation of soil compactors and buildings class II, in which the building should be included, the standard indicates two threshold values above which building damage may occur: PPV = 7.6 mm/s (band 10-30 Hz) and PPV = 7.6-12.7 mm/s (30-60 Hz) [27]. The standard DIN 4150-3 [23] introduces one type of threshold values for short-term vibration and another for long-term vibration, dividing buildings into three groups (1, 2, and 3; where type 2--refers to dwellings and buildings of similar design and/or occupancy) and three frequency bands (1-10 Hz, 10-50 Hz and 50-100 Hz). In the case of short-term vibrations and a building classified as type 2, the recommended maximum absolute value of the velocity signals for the three components (so called \"guideline values\"), recorded on the building foundation, below which there should be no damage to the building, are respectively [23]: PPVx,y,z = 5 mm/s (1-10 Hz), 5-15 mm/s (10-50 Hz) and 15-20 mm/s (50-100 Hz) and regardless of the frequency PPVx,y = 15 mm/s in the case of vibrations recorded in the horizontal plane on the top floor of the building. In a situation when dealing with long-lasting vibrations threshold values (so called \"guideline values\") recorded on the top floor of the building should not exceed 5 mm/s [23]. A much higher level of acceptable peak component particle velocities is recommended by the BS 7385-2 standard [25], which introduces a division of buildings into 2 types (1--reinforced or framed structures, industrial, and heavy commercial buildings, 2--unreinforced or light-framed structures, residential, or light commercial type buildings). According to the guidelines, minor damage in the type 2 building will not appear if the peak component particle velocities of transient vibration registered on the foundation of the building will not exceed the value of PPVi = 15 mm/s at 4 Hz--increasing to 20 mm/s at 15 Hz or 20 mm/s at 15 Hz--increasing to 50 mm/s at 40 Hz and above. In the case of continuous vibrations, which can cause resonance, the above values should be reduced by 50%--to the values accordingly: PPV = 7.5 mm/s at 4 Hz--increasing to 10 mm/s at 15 Hz or 10 mm/s at 15 Hz--increasing to 25 mm/s at 40 Hz and above [25]. The British standard BS 5228-4 [26] is more stringent, when it comes to vibration thresholds that can cause cosmetic damage to buildings. It represents a much more conservative approach and it meets the needs of owners and users of buildings exposed to excessive vibrations generated during construction works involving piling works, and which can also be used for assessing the probability of occurrence of structural damages arising from vibrations associated with construction. The standard introduces the division into four types of buildings, and makes the threshold values dependent on the duration of vibrations (intermittent vibrations and continuous vibrations). In residential buildings \"in generally good repair\" [26], recommended vibration limits, regardless of dominating frequencies, are PPV = 10 mm/s--in the case of intermittent vibration, and PPV = 5 mm/s--in the case of continuous vibrations. Residential buildings where preliminary survey reveals significant defects, PPV values shown above should be decreased by 50%, to a level equal to: PPV = 5 mm/s and 2.5 mm/s [26]. Analyzing the above, it should be assumed that cosmetic damage to a residential building (such as surface cracks in plaster or brickwork) in accordance with the most stringent standards [26] can occur when the level of vibrations recorded on the foundation or foundation wall of a building in any direction exceeds the level of 5 mm/s, in the case of a building in good technical condition, or 2.5 mm/s in the case of a building in poor technical condition.