What do Geotechnical Forensic Engineers do?

How often do you see news about a structural collapse or massive landslide occurring somewhere in the world? What happens after such an event occurs? Once the situation is stabilized, a selected group of experts may be brought to the site to conduct an investigation and provide opinions on possible causes of failure.

Forensic engineering is the engineering practice which determines the likely cause(s) of the failure of structures. Merriam-Webster dictionary defines a failure as an unforeseen and unplanned event or circumstance. In geotechnical engineering, failures can be related to man-made structures or natural formations. Such failures can result in significant losses that may include environmental damages, economic losses, and societal impacts, among others.

What is it like working on a forensic engineering project? It feels like solving a mystery. It starts with brainstorming about potential causative factors and continues to comprehensive analyses of each contributing mechanism to establish the likely root cause of the failure. Forensic engineers have to rely on available data, new data gathered in the investigation, their background knowledge and experience, as well as industry practices and applicable standards and codes. Often, they have to devise innovative ways to process data or to acquire new information.

By studying failures, geotechnical engineers improve their practices and analysis methodologies. Multiple failures have contributed to such improvements. In 2004, the metro tunnel along Nicoll Highway in Singapore failed. The nature of this failure illustrated the need to use representative soil properties in numerical analysis and to property update analysis based on field observations. The Vajont Dam overtopping in 1963 in Italy was one of the key failures showing the importance of conspiring pore pressures in landslide triggering, and the need for a thorough geotechnical investigation to locate any potential weak failure planes. The landslide that occurred east of Oso, Washington in 2014 showed the importance of a detailed study of site history and monitoring of field condition changes.

Oblique aerial photograph of the 2014 landslide in northwest Washington. Credit: Mark Reid, USGS(Public domain.) Source: https://www.usgs.gov/news/revisiting-oso-landslide

Historic records show that dam failures occur somewhat frequently in the US. There has been an average of 10 dam failures per year since the mid-nineteenth century, many of which are small failures with limited impact to the downstream area. However, some of the largest disasters in the US like South Fork Dam in Pennsylvania (1889), St. Francis Dam Failure in California (1928) and Buffalo Creek dam failure in 1972 each took lives of hundreds of people. Through extensive review of case studies, geotechnical engineers determined that the most frequent causes of dam failures are overtopping and seepage related causes.

Experts in the forensic geotechnical engineering field use advanced geotechnical exploration, laboratory studies, instrumentation and monitoring, and advanced analyses using digital models to understand the sequence of events leading to failure. The conclusions of the investigation are usually summarized in forensic engineering reports, which may include recommendations for remedial measures. Many reports of forensic investigations have become publicly available, and the lessons learned have been very useful to improve design methodologies, construction means and methods, and rules and regulations. 

For example, the now famous case of failed apartment buildings after the Niigata earthquake in Japan in 1964 triggered much focus on geotechnical earthquake engineering. As a result, we now have much more robust methodologies to design against earthquake induced liquefaction. The Oroville spillway dam failure in 2017, triggered substantial discussion on spillway design and general industry practices in the Unites States. California state implemented new laws and regulations for classification of hazard potential of dams and emergency preparedness, which were adopted by the end of the same year.

Oroville Dam (California).
Source: https://damfailures.org/case-study/oroville-dam-california-2017/

What makes forensic geotechnical engineering unique? It is the variety of technical issues that occur under different conditions all over the world. Forensic analyses oftentimes need state-of-the-art methodologies. This is one of the reasons they can push the envelope in improving our current standards. Forensic engineers allow us to gather and share knowledge about reasons of failures and appropriate remedial measures. With the advances in science and technology and utilizing lessons learned from past performances engineers can update standards of practice and be better prepared to face challenges of the future.

Anna Suprunenko earned her Master of Science Degree in Geotechnical Engineering from the University of New Hampshire. She has over six years of experience in slope stability and settlement analysis, interpretation of in-situ measurements, geotechnical and geophysical field testing, foundation design and advanced laboratory testing.She volunteers for the MATHCOUNTS school competition and Mass STEM Hub program to promote engineering as a field of study and profession among middle school students.  She also gives back to her profession by serving on STEM Outreach Task force of ACEC-MA.

References:

Delatte, Norbert J., “Beyond Failure: Forensic Case Studies for Civil Engineers” (2009). Civil and Environmental Engineering Department Books.

https://www.ferc.gov/industries-data/hydropower/dam-safety-and-inspections/oroville-dam-service-spillway-p-2100

https://www.icold-cigb.org/GB/dams/dams_safety.asp

Geotechnical Illustrated: Triaxial Testing in the 21st Century

The triaxial test is arguably the most widely used test method in investigating soils’ stress-strain behavior in geotechnical engineering. Its popularity is partially due to the well-understood state of stress during the test, as well as its versatility. In a triaxial test, the specimen is encased in a membrane with drainage from top and bottom (and sides if filter paper is used). The specimen is confined to specific stress through a pressurized fluid (such as water) inside the test chamber. In many cases, the specimen is backpressure saturated before being consolidated to desired stresses. Pumps or other sources of pressure and volume control can be used to generate confining stress and backpressure. Once the specimen is at the target stresses, deviator stress is gradually applied, usually axially, via a load frame, until the specimen fails, or the desired strain or stress is achieved.

Various types of failure during a Triaxial test

The most common triaxial tests are Consolidated Drained (CD), Consolidated Undrained (CU), and Unconsolidated Undrained (UU) conducted in isotropic condition and with deviator stress applied with a constant rate of axial strain. Using the results of several tests at different confining stresses, one can develop shear strength parameters using a failure criterion like Mohr-Coulomb. Shear strength parameters can then be used in the process of designing geostructures.

Soils are unusual materials in that their engineering properties are stress path-dependent. This means their strength and stiffness depend on past, present, and future stress conditions. For instance, an in-place soil element will have different strength and stiffness if the stresses increase in horizontal direction compared to stresses increased in the vertical direction.

In some cases, the underground soil is not isotropically consolidated but is in at-rest (K0) condition. The soil elements change in axial and radial stresses that may be increased or decreased. The geostructure is subjected to axial or radial unloading rather than loading, or there may be a pore-pressure decrease or increase due to the changes in the hydraulic equilibrium and condition of the area such as heavy rain. These complicated stress paths and conditions have traditionally been hard to simulate in the laboratory. For example, to conduct a triaxial test under the K0 condition, one must maintain the radial strain at zero while applying the target axial stress to the specimen by constantly changing the cell pressure. This requires a fast closed-loop controller which renders manual testing impractical.

The introduction of computer-controlled equipment with high-speed closed-loop and adaptive control systems has revolutionized the quality, reliability, and speed at which stress path tests can be conducted. A modern computer-controlled triaxial testing apparatus with advanced adaptive control can:

  • Easily back-pressure saturate specimens, conduct B-checks and move on to the next step automatically when saturation is complete
  • Consolidate the specimen at any stress state (isotropic or anisotropic), automatically
  • Determine the K0 value for the applied axial stress (for K0 tests)
  • Ensure completion of the consolidation before automatically moving on to the next step (after a predefined time or number of log cycles are past the 100% primary consolidation)
  • Easily impose various stress paths on the specimen

Such advanced systems enable engineers and researchers to go beyond standard tests and study the specimen’s behavior in more realistic stress states, however complicated they might be. They can simulate different scenarios or possible failure mechanisms, with a high level of accuracy.

Another benefit of the triaxial test is that it can be fitted with additional measurement sensors to expand the capabilities of this test method further. For example, by adding piezoelectric sensors at the end caps or sides of the specimen, one can determine the S- and P- wave velocities in different directions from which the low-strain shear and P- wave modulus can be measured at any stage of the test. The resulting data can provide valuable insight into the low-strain characteristics of the specimen at any given stress state and be used to investigate possible levels of disturbance in the specimen. End caps can also be retrofitted to measure the electrical resistivity of the specimen or measure and apply matric suction for unsaturated testing.

PnS caps

With the addition of a cyclic loading unit, the cyclic strength, liquefaction susceptibility, cyclic strength, cyclic mobility characteristics, and dynamic properties of soil specimens under triaxial loading conditions can be investigated. More advanced equipment can even apply the actual Cyclic Stress Ratio (CSR) or strain time history of an earthquake or other vibration sources at any given effective stress on the specimen for a more realistic study of its behavior.

Geocomp pioneered the introduction of fully automated testing equipment in production laboratories with the 1985 installation of three fully automated consolidometers in the USACE materials testing facility in Dallas, TX. Since then, it has continuously improved and expanded its line of fully automated geotechnical testing equipment to include triaxial, consolidation, direct shear, direct simple shear, permeability, resilient modulus, resonant column torsional shear, cyclic triaxial, cyclic direct simple shear, and cyclic torsional shear tests. Nowadays, engineers have many affordable options in their tool chests thanks to the technological advances and expanded capabilities of automated testing machines. This is in a sense the golden age of geotechnical engineering. We can put aside conservative approaches and take on data-driven best practices to manage risks and save money and lives at the same time.

Kaveh Zehtab is the Director of Research, Development, and Production at Geocomp. Kaveh has a wide array of experience in investigating soil behavior, experimental geomechanics, and automated testing.

Geotechnical Illustrated: Sulfate Reducing Bacteria (SRB) – What is it?

Microbes live everywhere including the oceans. Sulfate-reducing bacteria (SRB) are considered microbes. SRB is one of many common bacteria species that live throughout our ecosystem. Seawater is a primary source of SRB where a single gallon of seawater has roughly a few billion different kinds of bacteria. While most bacteria are aerobic and require oxygen to survive, SRB is among a group of species that are anaerobic and thrive only in the absence of oxygen. While SRB exist in the wild and does not present a danger to humans or animals, its effects can cause damage to metals and concrete. Offshore structures either resting on the seabed or penetrating through, whether made of concrete or steel are exposed to those attacks by SRB. Offshore structures, such as oil and gas platforms, monopiles foundations and concrete gravity base structures for wind turbines, subsea pipelines, and subsea manifolds are potential targets for those bacteria attacks.

This attack can be described as a phenomenon called Microbiologically Induced (or Influenced) Corrosion (MIC). MIC is the degradation of structures because of the activity of various microorganisms. So, the attack comes in a form of corrosion and can be called, microbial corrosion, bacterial corrosion, biological corrosion, or concrete/metal eating bacteria.

SRB perform anaerobic respiration utilizing sulfate (SO42) as a terminal electron acceptor, reducing it to hydrogen sulfide (H2S), which is a highly corrosive compound to concrete, steel, and other elements such as copper. Another set of microbes turns hydrogen sulfide to sulfuric acid, which can cause pitting of steel or concrete and hence reducing the service life of the structures. In other words, these sulfidogenic microorganisms “breathe” sulfate rather than oxygen and the results are highly corrosive substance.

Cathodic protection (CP) is one of the corrosion control methods mostly used with satisfactory results; however, where the phenomenon is microbiologically influenced corrosion (MIC) related, the efficiency of such control methods decreases significantly, due to several factors, (e.g. MIC may increase the kinetics of the corrosion reactions, which in turn increases the CP current necessary to achieve a given level of polarization.) The microorganism can attack pipeline coating for example, increasing exposed metal surface area and further increasing the CP current required to achieve the desired polarization. Hence, the use of coatings with high resistance in the presence of bacteria is a must.

Corrosion protection of offshore structures according to several organizations such as DNV (a European based advisor for the maritime industry) must include a holistic approach including corrosion allowance, cathodic protection, corrosion protective coatings and use of corrosion resistant materials. Measurement of corrosion rate with techniques such as linear polarization resistance (LPR) may also be very useful especially both for new and old structures.

Although SRB is a very tiny organism we cannot see, it can lead to potentially catastrophic consequences and costly operational shutdowns and should be taken seriously in the design of any offshore structures.

Assem Elsayed is the Vice President and Practice Area Leader of GeoStructural Engineering at Geocomp. Assem has extensive experience with waterfront and marine structures, design of monopiles for wind farms, and support of deep excavation.

How to Assess the Strength of Coal Combustion Residuals

Stability failures of impoundments involving release of Coal Combustion Residuals (CCRs; commonly known as coal ash,) like the one that occurred in Dan River Coal Ash Spill in 2014, have recently highlighted the importance of assessing the stability of CCR impoundments. CCR materials contain pollutants like Mercury, Cadmium and Arsenic. Without proper management, these contaminants can be released, resulting in pollution of waterways, ground water, or drinking water.

Collapsed coal ash impoundment with closed power plant in the background

Failures in CCR slopes can occur suddenly with little time for corrective action to occur. It is hence crucial to assess CCR slop stability with realistic strength properties of the CCR materials to help avoid this undesirable performance.

What are these CCR materials? How are these deposited? And more importantly, how do we determine the strength of these materials to use in calculating the factor of safety for stability?

What are CCRs?

CCRs are produced from burning of coal in coal-fired power plants. They include various by-products such as fly ash, bottom ash, boiler slag or flue gas desulfurization material.

Coal Combustion Residuals:

  • Usually classify as non-plastic or very low plasticity silt, silty sand, or sandy silt
  • Are much lighter than typical soil with a specific gravity as low as 2.0
  • May have water content as low as 20% when dry stacked or as high as 80% when loosely placed

How are CCRs deposited?

CCRs are placed by various methods. The two most common ways are:

  • Ash stacks: CCRs are “dry stacked” and compacted. Dry stacks of CCR are most commonly unsaturated and compacted to some degree.
  • Ash ponds: CCRs are loosely placed by hydraulic sluicing and receive no compaction. These sluiced materials are generally very loose, saturated and therefore susceptible to liquefaction.

CCRs can exhibit considerable variability in deposition over short distances.

Example x-ray: undisturbed tube of ash

How do we determine the strength of CCRs?

Engineers typically perform stability assessments of CCR impoundments which have been in place for some time by assuming they are in a steady state seepage condition. That means they are considering a “drained” failure mode where excess pore water pressures do not develop during shear. Undrained stability with accompanying excess pore pressures generated by shear has generally not been considered a potential failure mode unless the impoundment is still under construction, or some significant alteration to its condition has been recently done.

This common approach for stability assessments overlooks the potential for an undrained failure to be triggered by an event that causes a rapid increase in mobilized shear stress or a rapid decrease in effective stress, such as and earthquake or heavy rainfall. Undrained strength of loose granular materials is less than the drained strength so the undrained failure mode can be more critical. In these instances, if a contractive saturated material (susceptible to liquefaction) is present, an undrained failure can be triggered. An undrained behavior in contractive materials can trigger liquefaction (the CCR material transitions to behave like a viscous fluid) and result in a flow slide. 

Such a failure can be evaluated by means of an undrained stability analysis using undrained shear strengths for the contractile materials. Saturated, contractive CCR materials tend to produce shear strength ratios ranging from 0.12 to 0.35. Common drained strength friction angles for CCR materials range from about 28 to 45 degrees. The associated strength ratios for these friction angles range from 0.53 to 1.00. The difference in strength ratios for an undrained contractive CCR clearly shows the undrained condition to be more concerning.

It is a challenge to obtain a meaningful assessment of the strength of materials like CCRs. They are highly variable and very sensitive to sample disturbance which alters their mechanical properties. In our experience, we find we must use both field and laboratory methods to obtain reliable strength parameters.

Field Testing

These tests require mobilization of drilling equipment to the site and monitoring of the work by trained engineering staff. In addition to the described tests, disturbed and undisturbed samples are generally recovered and returned to a laboratory for further testing. Field tests are accompanied by in-situ measurements of pore pressures in CCR stacks using vibrating wire piezometers that are installed in various depths as well as spatially. We recommend using grouted-in-place pressure transducers with several installed in each borehole to measure total head changes in the vertical and horizontal directions. Flow in most stacks is almost never hydrostatic as assumed by many engineers. Measured pore pressures can help understand the flow regime and the saturation conditions within the deposited CCR.

Standard Penetration Tests (SPTs) are the traditional tool used by geotechnical engineers to characterize granular materials. The so-called “blow count,” for blows per foot required for a 140 lb hammer dropping 30 inches to drive the sampler 12 inches into the soil, gives an indication of the relative density of the penetrated material and returns a disturbed sample. However, as typically performed by drillers, where drilling mud is not used, this measurement can give misleadingly low values. To be meaningful, the hole must be advanced with heavy drilling mud with the mud level always kept above the top of the hole. Otherwise, the SPT value can be quite low and lead to a wrong assessment of the material’s condition. SPT values obtained strictly following ASTM D1586 and D6066 can provide valuable data to help assess the strength behavior of CCR materials.  

Cone Penetration Tests (CPTs) provide the tip resistance, side shear and excess pore pressure developed when pushing a 10 cm2 probe into the material at a constant rate. It can provide lots of data on relative density of the CCR quickly and inexpensively and is a good tool to capture the material variability. However, the measurement is an index test which must be converted to strength through semi-analytical, empirical correlations. Such correlations are reasonably well understood for natural clays and sands, but for CCRs, well established correlation data are limited. Developing an understanding of the strength characteristics of these unique materials requires advanced laboratory testing.

Cross-Hole Seismic Tests can provide a profile of shear wave velocity measurements throughout the CCRs, providing information on the variability within the deposition of the CCRs and the low strain stiffness. Shear wave velocity measured in the field when compared with the corresponding laboratory shear wave velocity measurements can help with assessing the sample disturbance and guide targeted laboratory testing to determine the strength of the CCRs.

Advanced Laboratory Testing

Since disturbance alters the properties of CCR materials, laboratory tests to measure mechanical properties are generally performed on undisturbed samples recovered from the field investigation. Since no sample obtained in the field can be truly undisturbed, testing technique and test interpretation must seek to minimize the effects of sample disturbance on the test results. The advanced tests should be accompanied by index tests (e.g., material classification, moisture content, Atterberg limits, specific gravity) from the same sampling tube to support the knowledge of the tested material and interpretation of the test results.

Laboratory Shear Wave Velocity Measurements is a very useful and quick test to determine the level of sample disturbance and whether the test specimen is representative of field conditions. Piezo-ceramic plates also known as bender elements can be embedded in any type of strength test apparatus and used to measure the shear wave velocity of the specimen at stress levels similar to the in-situ stress conditions. Shear wave velocity gives an indication of the relative density of the test specimen.

Direct Simple Shear Test (DSS) measures the strength of a test specimen in a simple shear mode (distorting the specimen similar to shifting a rectangular cross section to a parallelogram).  A few advantages of DSS are:

  • It is an undrained test
  • The shearing in DSS is closer to the mode of shearing for global stability under CCR embankments which is different from the mode of shearing induced in triaxial loading
  • The size of the specimen is short (1” in height) allowing many more tests from a sampling tube
  • The total duration of the test is much shorter since there is no saturation phase for the specimen and the duration of the consolidation phase is reduced with the short height of the specimen

Closure

Dealing with unique materials like coal combustion residuals may require using a series of field and laboratory techniques to assess both their strength and variability. The combination of an appropriate field and laboratory testing program can help reduce unnecessary conservatism and accurately evaluate the stability of a CCR embankment. Actual field pore pressures are also important as they directly affect the effective stresses within the impoundment barrier which in turn directly affect the material strength.  We strongly recommend measuring actual pore pressures in the field at multiple locations vertically and horizontally rather than assume certain flow conditions.

Our practice is to use the most appropriate tools and methods for both field and laboratory testing to obtain a reliable picture of how the CCR material is likely to behave for all the potential failure modes of an impoundment. This comprehensive approach helps us avoid the unnecessary conservatism used when data quality for CCR strength are incomplete or unreliable. This approach takes more engineering effort up front, but it usually pays for itself many times over by avoiding unnecessary conservatism in the stability assessment, reducing, or removing the need for expensive corrective actions, and providing a firm basis to help manage risk.

Seda Gokyer Erbis is a Project Engineer/Assistant Project Manager for Geocomp’s Massachusetts Consulting Group. She has been with Geocomp for six years, holding a doctoral degree in Geotechnical Engineering. She has been leading the project management and technical efforts for one of Geocomp’s largest consulting projects on seismic assessment of coal ash impoundments. She has over seven years of experience in geotechnical earthquake engineering especially in advanced laboratory testing. She has authored and co-authored several publications in peer reviewed ASCE and ASTM journals and conference proceedings.

The Value of Numerical Modeling for Geo-Structural Engineering

Numerical modeling uses complex computer programs to build a digital model of a site from which to calculate how a design will perform for various loading conditions. These methods avoid some of the simplifying and conservative assumptions that get made in simpler approaches. They help improve the efficiency of a design, predict how a design is likely to perform, show how a structure’s foundation and the groundwater will interact as a unit, and provide insight into the important mechanisms controlling how the design will perform. Improved predictions, better understanding of complex behavior, and optimized designs with minimal assumptions help reduce risks and costs for many projects. 

What is Numerical Modeling? Numerical modeling uses digital computer models to analyze stress, strain, and deformations in a project with complicated soil, water and structural geometries and materials. Numerical modeling methods include the finite element method (FEM), the finite difference method (FDM), the boundary element method (BEM), and the discrete element method (DEM). Nonlinear material properties can be considered which allow designs to be optimized with some degree of non-linear behavior and yielding which results in less conservatism and less cost. Numerical modeling can be used to analyze almost any type of geostructural problem in two or three dimensions.

When is Numerical Modeling Needed? Numerical modeling is used when the structure/soil/water geometry and materials are too complicated to solve with closed-form analytical equations. The methods rely on breaking the complex geometry into smaller pieces. The behavior of each small piece is described with a stress-strain model that represents the basic understanding of each material’s behavior (bending of a beam, stress/strain behavior of a soil cube, flow of water through soil, etc.). The numerical model combines engineering mechanics equations for force equilibrium, conservation of mass, kinematic continuity, and stress-strain-strength behavior of each piece into a large set of equations describing how the pieces interact.  Matrix algebra is used to combine the pieces and equations to create the digital model that gives stresses, strains, and displacements throughout the geometry for each specific load case. Examples of different types of problems addressed with a numerical model are described herein.

Evaluating Potential to Create a Seepage Barrier with Ground Freezing

The first example shown in Figure 1 is for a client that was designing a groundwater cutoff in an area with flowing groundwater. Flowing groundwater makes it difficult to freeze the ground (a construction technique used to provide temporary earth support and groundwater control). The left figure in Figure 1 shows a plan view (looking down from the top) of frozen soil in blue around the freeze pipe shown in white. The right three figures in Figure 1 show the frozen soil (in blue) for conditions of increasing velocities of groundwater flow. The flow direction is from the bottom to the top in the figure. Numerical modeling demonstrates to the client that flowing groundwater must be taken into account in the design of the frozen groundwater cutoff. Numerical modeling of the effects of groundwater flow saved the client millions of dollars in delays and redesign.

Figure 1: Numerical modeling of the effects of groundwater flow on growth of a freeze wall

Underground Storage of Compressed Gas

In the US, compressed natural gas has been stored in solution mined caverns in salt domes since the 1960’s. Salt creep is a major factor which needs to be considered in the design and stability analysis of these underground openings. Numerical modeling is used to evaluate the stresses around the opening and predict the deformation of rock salt with use and time. When the gas pressure is cycled in an underground cavern, there are changes in temperature and stress that influence the creep rate. Under these conditions numerical modeling is the only method available to calculate the closure rates in the cavern walls. Numerical modeling provides the client with minimum and maximum cavern operating pressures and design parameters for spacing between multiple caverns. This benefits the project designers by allowing them to develop an optimized storage design based on site specific geotechnical engineering analysis and operational needs. 

Figure 2: Numerical model of a deep cavern in salt for compressed air energy storage

Helping Design for a Complex Use Case

In the final example shown in Figure 3, a client wanted to develop design charts to promote the use of a proprietary retaining wall system comprised of steel soldier beams with soil mix lagging spanning between the beams. Traditional design methods for lagging are mostly empirical built up from experience. Numerical modeling provided the client with a parametric design chart used to promote the use of composite soil mix retaining wall structures. The numerical models also helped show that part of the load of the final structure could be supported by these retaining walls resulting in further efficiency of the design.

Figure 3: 3D numerical analysis of horizontal deformations in a composite soil mix retaining wall

In summary, numerical modeling is an important tool for analyzing complex geo-structural cases. It eliminates some of the conservatism used in regular design, reduces risk, and saves the client money. When analytical methods are not available, numerical modeling offers a great alternative to help develop safe designs without unnecessary conservatism.

Martin Hawkes is a Senior Geotechnical Engineer with a master’s degree in Geotechnical Engineering from MIT. Mr. Hawkes has been with Geocomp for 27 years, involved with developing the early versions if iSiteCentral, developing the laboratory information  database management system (LIMS) for GeoTesting Express, installing instrumentation, and geotechnical consulting. Martin provides a key role in numerical modeling with a unique skillset as a mentor for younger engineers.

Geotechnical Illustrated: Good Vibrations or Not?

Heavy construction in densely populated cities can be conducted near neighboring buildings. Vibrations induced by such heavy construction are one of the most claimed causes of adjacent building damage. These vibrations can be generated by multiple types of equipment such as pavement breakers, excavators, or pile drivers. Such activities can generate short term vibrations or contribute to longer periods of increased vibration levels.

Property owners experiencing construction-induced vibrations may file claims for nuisance or cosmetic/architectural and structural damages. Since the vibration threshold for nuisance is typically lower than the threshold to cause any damage, property owners may express concerns about vibrations that are not substantial enough to damage their property. During the COVID-19 era, more residents stay and work from home, giving a rise to construction-induced vibration claims.

Construction activities cause vibrations of various amplitudes and frequencies that propagate within the subsoils. The waves propagated through the soils typically attenuate with distance. Wave attenuation is caused by geometric and material damping. Geometric damping is caused by the spreading of the wave front over an increasing area. Material damping is caused by energy converted to thermal energy within the subsoils. The attenuation of vibrations with distance is typically estimated by a straight line in a double logarithmic plot of peak particle velocity (PPV) versus distance.

Construction vibrations are typically a nuisance to residents; however, many times they can contribute to property damage. Ground vibrations may be of sufficient magnitude to cause direct damage to structures. The magnitude of vibrations that causes damage varies with the type and the vibration response of the structure. For example, generally historic buildings are more sensitive to vibrations compared to modern residential or commercial buildings. Vibration damage can vary from threshold damage such as paint loosening, or minor damage such as masonry cracks to major damage that can cause structural weakening and distress. Various levels of threshold PPVs have been evaluated in the industry for different structures and damage levels. For example, Caltrans (2004) has proposed threshold PPVs as low as 0.12 inches per second for extremely fragile historic buildings to 2 inches per second for modern industrial buildings.

Vibrations can also cause indirect damage. For example, they can cause densification of loose soils beneath buildings, resulting in differential settlements. Vibrations can also cause partial loss of strength of loose saturated subgrade soils and hence contribute to loss of bearing capacity. Both for densification and for partial loss of strength to occur, a sufficient shear strain within the subsoils should be triggered (i.e., threshold shear strain) and enough vibration cycles should occur.

Vibration levels can be measured by geophones (i.e., velocimeters) or accelerometers. Geophones have been traditionally used in construction and is a proven technology. Accelerometers historically were less effective for the lower frequencies of construction vibrations, however modern accelerometers may be competitive with geophones. Such devices can relate to data collection systems, which automatically stream data to interfaces such as Geocomp’s iSiteCentral® portal. Such systems can also automatically provide text or email alerts to all involved stakeholders.

The vibration data measured at a site can be compiled, and over-laid with a series of other data such as aerial imagery, property parcels, tax assessor information, city maps, surface elevations or others. These publicly available geospatial data and project specific data, including damage claim data, can be combined within GIS software to create an incredibly robust tool to efficiently perform sophisticated analyses of damage claims. Once the data are input in a GIS system, the user can create graphics and statistics that allow for analysis of the specific issues of each property. Moreover, the graphics produced can become very compelling exhibits in a dispute (e.g., court exhibits). 

Compiled publicly available geospatial data and project specific data, along with any pre and post construction surveys of any adjacent buildings are efficiently analyzed to answer both simple and more complicated questions such as:

  1. Are construction activities sufficiently close to cause damage to the subject property? An overlay of construction drawings, field records, along with aerial photos allows for estimation of the distance of the subject property and the limits of various construction activities such as pavement removal, excavations, and pavement compaction with private buildings and improvements.
  2. Can construction-induced vibrations contribute to the claimed conditions? A geospatial overlay of the measured peak vibration levels can indicate whether significant vibrations occurred within a construction period and at what distances from the subject properties.
  3. Are there any effects of non-construction activities that need to be considered? For example, has the damaged property ever been flooded from a large flooding event? A simple overlay of the property and an inundation map could show if that ever occurred. Can vegetation affect the measured cracking within a building? An overlay of a city-wide tree map and aerial imagery can show whether any trees exist that can contribute to this damage mechanism. 

Fortunately, many effects of construction vibrations can be mitigated. If damage in a building is claimed due to construction vibrations, then the above mechanisms can be investigated to demonstrate cause-and-effect.

Antonios Vytiniotis is the Director/Group Lead of the Massachusetts Consulting Group at Geocomp. Antonios has wide experience in evaluating and mitigating damages from machine and construction vibrations.

Geotechnical Illustrated: What is your CPT Test Really Telling You?

In many cases with offshore filling construction, such as building and forming artificial islands in the middle of a body of water, borrow areas of suitable seabed materials must be first identified. A comprehensive soil investigation will subsequently help assess the suitability of the potential seabed borrow material to be dredged and used for engineering purposes.  Some of the seabed in areas around the world consist of carbonate sand that may have shell fragments within its matrix composition. Shell fragments contribute to carbonate content that may be in the order of 90% or more. This specific soil composition can influence the measurements obtained by in-situ soil testing techniques.

One of the most commonly used in-situ techniques to assess soil strength, especially in offshore applications, is cone penetration tests (CPT). The most important measurement obtained from CPT is the cone penetration resistance, which is the force required to push the tip of the cone through the soil of interest and is defined in ASTM D: 5778.  However, most of the standardized in-situ testing techniques, such as CPT, have been commonly calibrated to interpret soil properties for soils found onshore, such as silica sands.

  • Ariel view of The Palm on Dubai’s man-made Palm Jumeirah artificial island; REUTERS, August 31, 2011

After reclamation of an artificial island using carbonate sands, CPT can be used to assess its strength to carry loads for engineering purposes. However, a correction factor is required to adjust the measured tip resistance so that correlations developed for silica sands can be used for the carbonate deposits. This correction factor is called the Shell Correction Factor (F shell) and has been extensively studied by researchers around the world.  The Shell Correction Factor is the ratio between cone tip resistance of silica sand to cone tip resistance of carbonate sand. F shell commonly varies from 1.2 to 1.6 depending on the relative density of the sand.

So, don’t just pick up some standard correlations to interpret your CPT results. Make sure you understand the soil’s composition and its effects on engineering properties. 

Assem Elsayed is the Vice President and Practice Area Leader of GeoStructural Engineering at Geocomp. Assem has extensive experience with waterfront and marine structures, design of monopiles for wind farms, and support of deep excavation.

Geotechnical Illustrated: Risks of Spudcan Punch-through

Jack up rigs are used widely in offshore drilling and for offshore wind turbine installation. Such rigs can be often times supported by spudcan footings such as the ones shown below. However, there are multiple challenges in evaluating the capacity of such footings.

Punch-through of spudcan legs for offshore barges is defined as rapid uncontrolled barge leg penetration into the seabed.  Such an event could result in catastrophic damage and even loss of lives such as the one shown in the figure below. 

Accident Aboard Pemex Jack-Up, Bay of Campeche, Mexico, Picture Credit: Reuters, May 5, 2015

Spudcan legs jacked against seabed that is made of interbedded soil layers creates a recipe for potential punch-through.  In addition, the presence of a strong soil layer on top of a weak layer can contribute to sometimes unaccounted for punch-through.  These risks can be quantified using a probabilistic approach as a decision-making tool.

Barges are typically proof-loaded by vertical preloading through water ballasting prior to being operational, in order to obtain a safety margin against extreme storm design events.  It is a common practice to assess the potential for barge leg penetration into the seabed using both lower and upper bound soil parameters. This analysis requires engineering judgment to choose the right soil parameters based on the available soil information using a deterministic approach.  A more informative methodology is to perform a quantitative probabilistic study taking into account all possible variable soil data as well as other uncertainties. Insurance companies may be more willing to insure a project once the risks of failure are properly quantified.

A probabilistic analysis can be performed easily when the variability of soil properties or other input parameters is known. The most common approach is to assume that a normal distribution with a specified mean value and a standard deviation of a parameter, based on the available geotechnical information, can accurately represent the “randomness” of such input parameters. The parameters can be soil properties such as undrained shear strength and friction angle, or geometry parameters (e.g., soil layer thickness).

Such analyses can be commonly performed with simple random number generator tools, two way data tables (What-if Analysis) in tools like Excel. A common way to incorporate probabilistic data from multiple variables is a Monte Carlo simulation. Via this simulation, a cumulative probability distribution function of the spudcan footing’s factor of safety can be determined. An example of such a cumulative probability curve is shown in the figure below. An engineer, a project owner, or an insurance agent can then be able to better represent the uncertainty in the factor of safety calculation. For example, in the schematic below, there is only a 20% probability for the factor of safety to be less than 2, and a 90% probability that the factor of safety is less than 3.

This simple probabilistic approach can be applied to any engineering equation to quantify the associated results in a simple risk language.  

Assem Elsayed is the Vice President and Practice Area Leader of GeoStructural Engineering at Geocomp. Assem has extensive experience with waterfront and marine structures, design of monopiles for wind farms, and support of deep excavation.

How to Prevent Ransomware Attacks on Your Business

If you haven’t recently heard, cybercrime and ransomware are at an all-time high across all industries. With business after business getting hacked, it is more important than ever to tighten up your security.

When it comes to cyber-attacks, it is not a question of if, rather of when.

To begin, let us cover the basics…

What is Cybercrime?

Cybercrime is criminal activity that either targets an individual computer or a network to perform activity that causes serious disruptions to the end user or business. There are quite a few types of cybercrime. To name a few:

  • Email and internet fraud (phishing)
  • Identity fraud (personal information is stolen and used)
  • Ransomware attacks (demanding money)
  • RDP compromise
  • Vulnerability exploit (scanning of networks to identify weak systems and taking control)
  • Account takeover or identity theft.

In 2020, the most common type of cybercrime as reported to the U.S. Internet Crime Complaint Center was phishing and similar fraud, with 241,342 complaints. In addition, 43,330 cases of online identity theft were reported to the IC3 that year.

Cybercrime takes many forms, and not all of them are something new, it just got easier and more widespread with new technologies. It is very important that we, both in our personal life and in our professional one, are mindful of these and other cybercrimes and keep an eye open, especially in a time of crisis (such as the COVID-19 global pandemic) when wrongdoers proliferate.

What Harm Does Cybercrime do to Firms?

Cybercrime leads to several negative effects on your business including:

  • Reputation loss
  • Financial loss
  • Intellectual property loss
  • Loss of customer confidence
  • Legal implications
  • Loss of goodwill

Report Cybercrime to Appropriate Agency

If you are the victim of online or internet-enabled crime, file a report as soon as possible. Crime reports are used for investigative and intelligence purposes. Rapid reporting can also help support the recovery of lost funds.

HOW TO RECOGNIZE & PREVENT CYBERCRIME

Be Smart.

Be Aware.

Be Responsible.

The Stop. Think. Connect™ campaign encourages all Americans to recognize these three common cybercrimes and to follow simple steps to protect yourself.

Identity theft is the illegal use of someone else’s personal information in order to obtain money or credit. How will you know if you’ve been a victim of identity theft? You might get bills for products or services you did not purchase. Your bank account might have withdrawals you didn’t expect or unauthorized charges.

Phishing attacks use email to collect personal and financial information or infect your machine with malware and viruses. Cybercriminals use legitimate-looking emails that encourage people to click on a link or open an attachment. The email they send can look like it is from an authentic financial institution, e-commerce site, government agency, or any other service or business.

Imposter scams happen when you receive an email or call seemingly from a government official, family member, or friend requesting that you wire them money to pay taxes or fees, or to help someone you care about. Cybercriminals use legitimate looking emails that encourage people to send them money or personal information.

SIMPLE TIPS

  • Keep a clean machine. Update the security software and operating system on your computer and mobile devices often. Keeping the software on your devices up to date will prevent attackers from taking advantage of known vulnerabilities.
  • When in doubt, do not click. Stop and think before you open attachments or click links in emails. Links in email, instant message, and online posts are often the way cybercriminals compromise your computer. If it looks suspicious, it is best to delete it.
  • Use stronger authentication. Always opt to enable stronger authentication when available, especially for accounts with sensitive information including your email or bank accounts. A stronger authentication helps verify a user has authorized access to an online account. Visit www.lockdownyourlogin.com for more information on stronger authentication.
  • Consider sharing less online. Including information like your birthdate and the city where you live on your social media profiles can give criminals a more complete picture and make it easier for them to steal your identity.
  • Take advantage of security settings. On your smartphone, tablet, or computer – use PINs or passcodes to protect someone from easily accessing all your information. For social media websites and apps, be aware of your privacy settings and change them to your comfort level so only the people you want to see information can see it.

The best advice an IT professional can give is as follows:

  1. Educate users periodically and keep them informed frequently of cyber activity on the net.
  2. Create a strong password. Passwords should be at least eight characters long, including at least one numerical value and a symbol. You should most definitely avoid common words and never disclose a password to anyone.
  3. Here’s a tough one – never select the “Remember My Password” option. It can be hard to remember a million passwords for various accounts and saving passwords can be super convenient, but you have to be cautious.
  4. Never click on a link from an untrusted source. At Geocomp, we test our employees routinely through Mimecast to see if they can tell if a linked source is secure or not.
  5. Of course, any device should have an antivirus software installed and is important to make sure it’s updated regularly.
  6. Unless you are expecting an attachment in an email, refrain from opening it! Ransomware activity via email phishing using Microsoft Office document attachments is very common.

IT Responsibilities

Information is so accessible these days, that it is becoming easier for hackers to get access and harder for us to prevent. In order to protect your company, you need to do the following:

  • Deploy an IP auto shun device
  • Install a corporate high availability firewall
  • Install a content filtering Barracuda appliance
  • Use SSL certificates to internet facing websites
  • Restrict access to confidential information (Accounting, Finance, Pay roll and HR)
  • Implement Antivirus and Antispam software on end points
  • Backup business data. Most importantly test the backup jobs by performing a restore operation.
  • Identify critical data and ensure data is off network for a defined period.
  • Define recovery point (RPO) and recovery time (RTO) objectives
  • Replicate certain critical systems to ensure business continuity
  • Have a standby generator to supply power in the event of extended period of loss of power from utility
  • Explore cloud providers and costs associated with such providers.

Janakirama (Ramu) Bollapragada is the Senior IT Manager at Geocomp and has been with the company for almost 16 years. He is a certified Microsoft Systems Engineer and Information Technology Information Library (ITIL) foundation certificate holder with several years of experience in all aspects of IT management, especially in corporate infrastructure that streamlines system operations and optimizes productivity.

The Top Three Project Plan Documents to Drive Success

What to do when you have no time to plan!

The importance of project planning cannot be overstated. The Planning Phase offers the most significant opportunity to save time, resources, and money. 

The main purpose of developing a Project Management Plan (PMP) is to break down the broad goals of the contract into manageable tasks that can be understood by team members, sponsors, and clients.  A well-constructed PMP also provides the project manager and sponsor with an accurate means of measuring job progress and an early warning of possible problems and delays.  When completed, it becomes the “road map” for the project to be distributed, followed, referred to, and updated as required.

Given how important planning appears to be and it’s direct connection to project success1, it’s a given that project managers take the time to create complete plans for every project, right?

In reality, PMs are frequently tasked with managing multiple high-profile projects simultaneously, some of which they inherited part way through, jumping from meeting to meeting while balancing deliverable development, procurement, invoicing, and employee training. Many PMs are also technical leads for their projects and balance these two roles concurrently. With all these competing responsibilities and the perpetual needs in the present, it can be a great challenge finding the time to flesh out a Project Management Plan. Most unfortunate is that this problem can feed upon itself, creating a negative feedback loop that I refer to as, “The Leakage Spiral.” 

In essence, a lack of planning leads to leakage (inefficiencies, rework, or unpaid out of scope work). Leakage in turn leads to project delays and unhappy clients, which leads to increased resource needs and stress, finally leading to no time to properly close out the project, perform lessons learned, or properly plan the next project. And on and on it goes, always working behind the 8-ball.

So how do we course correct? Like anything else, it presents a great challenge when you have to pull out of a rut. How can you imagine doing a split when you can’t even touch your toes?  A complete Project Management Plan can easily consist of 10+ subdocuments, each detailing different aspects of the project. This may prove too daunting a challenge if you find yourself stuck in one of these downward spirals and time is too difficult to come by. In this instance, I recommend you take all the time you can muster, enlist the help of other managers, your project team, sponsors, executives, and your Project Management Office, and start with a basic Project Management Plan. Prioritize the following three documents to make the most profound and lasting impact on the health of the project, and ultimately to save yourself time in the long run.

These are my top three project plan documents to drive project success:

Risk Register

The Risk Register2 is arguably the most important component of any functioning PMP. Sometimes referred to as a risk log, the register is a document that allows the PM to identify, catalogue, quantify, respond to, and track risks to your project. Industry metrics indicate that as many as 90% of project threats that are identified and managed through the Risk Management process can be eliminated3. This is incredibly significant and can in and of itself make or break a project.  Moreover, if you’ve gone through this exercise and a risk you’ve identified actually occurs, you already have a plan, an approach, and you know how to deal with it. This saves you and your team from unnecessary stress and lost time. 

Communication Plan

During the execution phase of a project, when the deliverables are actually getting produced and most of the project work is occurring, a PM spends 75 – 90% of their time communicating4. This can be a particular challenge when the PM is also a technical lead on a project. It can be a real struggle to wear both hats, but if you’re a PM, you need to be able to perform your PM responsibilities, no matter what the technical challenges. 

The Communication Plan is essentially a “who, what, when, how, why” document, dedicated entirely to project communications. Beyond simply documenting, “The team will have a project meeting once a week,” a well-developed Communication Plan gives comfort to both project managers and important stakeholders alike. When crafting the Communication Plan, a PM should ask stakeholders what their communication requirements are and subsequently have the stakeholders review and approve the plan. Over the course of the project, if the Communication Plan is adhered to, a PM will not have to field unnecessary questions from stakeholders or sponsors, and stakeholders in turn will not feel anxious about silence from the PM – everyone has an understanding of when and how information will be communicated. In the long run, a Communication Plan saves time, money, and headaches.

Project Charter

The Charter is the front page of the Project Plan. It summarizes all the information from the different plan documents you’ve created (the scope, schedule, budget, assumptions, notable stakeholders, and high level risks). In broad strokes, it spells out not just the project’s scope, but also the company’s goals and objectives for the project (which can vary from the scope itself). 

So if all this information exists elsewhere, why bother creating the Charter at all?  Aren’t we just regurgitating information? Simply stated, by laying out the project goals and objectives in a prominent (front page) manner, the Charter can and should act as a guiding document for the PM and the team. 

It can actually be surprisingly difficult to summarize the scope of a complex project into only a few sentences, but there’s value in the exercise.  If a project gets too far afield or if the project team or manager gets tunnel vision and scope creep starts to develop, reviewing the charter can bring the project back into focus quickly.  The defining characteristic of a Project Charter is that it is distributed to each team member and a hard copy is signed by everyone.  A little cheesy, maybe, but by having each team member sign their name, it is expected people will more fully commit to their role on the project and the project’s success.

So when you’re pressed for time and battling a constant barrage of problems, setbacks, and roadblocks, how do you reorient yourself? As best you can, squeeze out enough time to develop these three simple documents.  More than any other project plan component, the Risk Register, Communication Plan, and Project Charter provide the most universal and lasting impact. If developed and implemented consistently, they will protect you from unnecessary stress, save you time, and they will drive project success.  

David Whall is Geocomp’s Project Management Office Manager, having joined Geocomp in 2012.  As a Registered Project Management Professional (PMP), he leads the development and implementation of new Project Management processes, designed to increase Geocomp’s efficiency, profitability, and enhance the value we provide to our clients.

[1] Serrador, P. (2012). The importance of the planning phase to project success. Paper presented at PMI® Global Congress 2012—North America, Vancouver, British Columbia, Canada. Newtown Square, PA: Project Management Institute. <https://www.pmi.org/learning/library/importance-planning-phase-project-success-6021&gt;.

[2] Ray, S. (2017). Guide to Using a Risk Register. <https://www.projectmanager.com/blog/guide-using-risk-register&gt;.

[3] Dinu, C. (2011). Risk governance: creating a risk superstructure for projects. Paper presented at PMI® Global Congress 2011—EMEA, Dublin, Leinster, Ireland. Newtown Square, PA: Project Management Institute. <https://www.pmi.org/learning/library/risk-management-project-life-cycle-6274&gt;.

[4] Fontein, D. (2020). Building Effective Communication Skills: A Guide for Project Managers. <https://unito.io/blog/communication-skills-for-project-managers/&gt;.