GEOPHYSICAL INVESTIGATIONS

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SEISMIC REFRACTION

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Seismic refraction techniques are used to optimize residential and commercial construction projects by assessing subsurface conditions with precision. This geophysical method measures the travel time of seismic waves through different soil and rock layers, providing valuable data on the composition, density, and depth of subsurface materials. By identifying potential issues such as rock depth, soil stability, and the presence of voids or fractures, Vann Engineering can inform foundation design, mitigate risks, and ensure compliance with structural and safety standards. This approach enhances project efficiency, reduces unexpected costs, and is a non-destructive testing technique.

 

SURFACE WAVE ANALYSES (PASSIVE AND ACTIVE)

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Passive and active surface wave analyses are advanced geophysical techniques used to determine the shear wave velocity (Vs) profile of subsurface materials, a critical factor in identifying the IBC (International Building Code) seismic site class. Passive surface wave analysis captures ambient seismic noise generated by natural or human activities, while active surface wave analysis involves creating controlled vibrations at the surface. These methods are used to calculate Vs values across various depths, enabling us to characterize soil and rock stiffness accurately. By integrating these analyses, project teams can classify the site per IBC standards, from soft soil (Site Class E) to hard rock (Site Class A). This classification helps optimize structural design for seismic safety, ensuring buildings can withstand site-specific earthquake forces effectively while complying with regulatory requirements.

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GROUND PENETRATING RADAR

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Ground-penetrating radar (GPR) is a non-invasive geophysical technology that uses electromagnetic waves to image subsurface features. The system transmits high-frequency radio waves into the ground, and these waves reflect back to the surface when they encounter materials with differing electrical properties, such as soil, rock, water, or buried objects. A receiving antenna records the reflected signals, and specialized software processes the data to generate two-dimensional maps of the subsurface. The depth and resolution of the GPR survey depend on the frequency of the radar waves, with higher frequencies providing greater detail at shallower depths and lower frequencies penetrating deeper with less resolution. This technology is widely used in construction, archaeology, utility detection, and environmental studies to identify underground utilities, voids, and changes in material composition without the need for excavation.

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SONIC ECHO

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Sonic echo testing is a non-destructive method used to evaluate the integrity and length of deep foundation elements, such as piles and drilled shafts. This technology involves generating low-frequency stress waves by striking the top of the foundation with a hammer or similar device. The waves travel down the foundation and reflect back when encountering changes in material properties, such as the pile toe, defects, or voids. A sensor, typically an accelerometer or geophone, records the returning echoes, which are analyzed to identify irregularities or confirm the foundation's length. Sonic echo testing is especially valuable for quality assurance in new construction and for assessing the condition of aging foundations, providing a cost-effective and reliable means to ensure structural stability and compliance with engineering standards.

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FIELD RESISTIVITY

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Field resistivity testing is a geophysical technique that measures the electrical resistivity of subsurface materials to characterize soil, rock, and groundwater conditions. The method involves placing electrodes in the ground in a specific configuration and passing a controlled electrical current between them. As the current flows through the subsurface, the voltage differences are measured and used to calculate resistivity, which varies depending on factors such as soil composition, moisture content, and the presence of voids or fractures.

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