Jean-Louis Briaud

Using the pressuremeter curve to design laterally loaded piles

The P-y curve is a soil model used in the design of laterally loaded piles. A method is presented to obtain the P-y curve from the pressuremeter curve. This method distinguishes between the friction model and the front resistance model. Using this approach, comparisons are made between the predicted and measured behavior of two laterally loaded piles; one in a soft clay and one in a medium to dense sand. The comparisons show very good agreement and point out that a distinction may have to be made between displacement piles and non displacement piles.

Statistical, Risk, and Reliability Analyses of Bridge Scour

Bridge scour is the loss of soil by erosion because of water flowing around bridge supports. Scour has been the number one cause of bridge failure in the United States with an average annual rate of 22 bridges collapsing or being closed owing to severe deformation. This paper addresses three topics related to bridge scour. First, a set of databases was used to quantify the statistical parameters associated with the scatter between the predicted and measured pier scour depth, as well as the probability that a deterministically predicted pier scour depth will be exceeded. These databases also were used to provide the bias factors in current predictions. Secondly, these statistical parameters were used to develop a reliability-based load and resistance factor design for shallow and deep foundations subjected to scour. The goal was to provide a design procedure where the reliability of the foundation is the same with or without scour. Reliability only addresses the probability of success and, therefore, of failure. Finally, the discussion was broadened by using the concept of risk defined as the probability of failure times the value of the consequences. In this third part, the risk associated with bridge scour was quantified and compared to risks associated with other engineering structures. Target values of acceptable risk were recommended as part of the conclusions.

Probability of scour depth exceedance owing to hydrologic uncertainty

The average risk of a bridge over water in the USA collapsing from scour during its 75 years design life is estimated at 3.7×10−3. This risk makes scour of foundations the number one cause of bridge collapse and 3 times larger than the next cause of bridge collapse, which is collisions. The current paper presents a site specific method to estimate the probability that a certain scour depth will be exceeded during the life of a bridge. The methodology is limited to some uncertainties associated with the randomness of hydrologic conditions. It does not include uncertainties associated with other input parameters, such as geometry and soil erodibility or uncertainties associated with the scour prediction model. The SRICOS–EFA method is used as the reference method to predict the scour depth. This method requires three inputs: the hydraulic parameters (e.g. velocity hydrograph), the geometry parameters (e.g. pier size) and the soil erodibility parameters (e.g. erosion function). The input is used together with the program to generate the scour depth versus time over the period of interest. The final scour depth is that reached at the end of the specified period. This paper proposes a probabilistic framework to present the final scour depth as a cumulative density function. The cumulative density function of the flow is sampled randomly to give a future hydrograph, which has the same mean and standard deviation as the original hydrograph. For this synthetic hydrograph a final scour depth is obtained by using SRICOS–EFA. Thousands of equally likely hydrographs are generated and the corresponding final scour depths are organized in a distribution. That final scour depth distribution gives the probability that a chosen scour depth will be exceeded.

Analysis of downdrag on pile groups by the finite element method

Abstract The downdrag on friction and endbearing pile groups was investigated, based on a numerical analysis. The emphasis was on quantifying the reduction of downdrag on pile groups, with a flexible pile cap, due to group effect. The case of a single pile and, subsequently, the response of groups were analyzed by developing interaction factors obtained from a three-dimensional nonlinear finite element study. Based on a limited parametric study, it is shown that the downdrag on piles in a group is much less than the downdrag on a single pile and is highly influenced by the group spacing, total number of piles, and the relative position of the piles in a group. In light of all these influencing parameters, a simple method is recommended for square groups of 9–25 piles with spacing-to-diameter ratios of 2.5 and 5.0 for downdrag loads.

Coupled Water Content Method for Shrink and Swell Predictions

Lane/shoulder drop-off or heave due to expansive soils beneath is a common distress in both concrete and asphalt pavements, resulting in substantial discomfort, safety hazard and vehicle damage. The situation becomes worse when exposed to moisture changes, particularly in Texas, Colorado, Arizona, California, etc. where many soils are expansive soils. Therefore, expansive soils pose great challenges for the design of pavements and foundations. One of the most difficult issues for designing pavements and foundations on expansive soils is to predict the volume change of the soils. In this study, current methods for movement predictions are summarised and their relationships and shortcomings are discussed. It is found that all these methods have the same theoretical basis. Based on the theory of unsaturated soil mechanics, it is found that the water content and the mechanical stress can be used to determine the soil status. Hence, a void ratio versus mechanical stress and water content surface is constructed, which coupled both mechanical stress and suctions influences on volume change of expansive soils. The new surface is developed into a coupled water content method that can be used to predict the potential vertical swell and the potential vertical shrink simultaneously, while all the existing methods can only predict the potential vertical rise. The method is used to analyse the data collected from a construction site at Arlington, Texas. The predicted movements match the measured data reasonably well. The method is simple and overcomes the shortcomings existing in the current movement prediction methods for expansive soils.

Observation Method for Estimating Future Scour Depth at Existing Bridges

AbstractBridge scour can cause damage to bridge foundations and abutments. Bridges with foundations that are unstable for calculated and/or observed scour conditions are termed scour-critical bridges. There are approximately 17,000 scour-critical bridges in the United States. This designation comes in part from the use of overly conservative methods that predict excessive scour depths in erosion-resistant materials. Other methods capable of overcoming this overconservatism are relatively uneconomical because they require site-specific erosion testing. This paper proposes a new bridge scour assessment method. The new method, termed the observation method for scour (OMS), was developed for the Texas Department of Transportation’s statewide bridge scour assessment program. The proposed method does not require site-specific erosion testing and accounts for time-dependent scour in erosion-resistant materials. OMS was developed for use as a first-order assessment in combination with a routine bridge inspection ...

Simplified Method for Estimating Scour at Bridges

This research proposes a new method to assess a bridge for scour. It is made up of three levels of assessments. The first level is termed Bridge Scour Assessment 1 (BSA 1). The second and third levels are termed BSA 2 and BSA 3, respectively. BSA 1 overcomes the qualitative nature of current initial evaluation procedures by extrapolating present scour measurements to obtain the scour depth corresponding to a specified future flood event. It utilizes computer-generated extrapolation charts based on a large combination of hypothetical bridges, which relate the future scour depth/maximum observed scour depth ratio to the future flood velocity/maximum observed flood velocity ratio. BSA 2 has to be carried out if BSA 1 does not conclude with a specific plan of action for the bridge. BSA 2 determines the maximum scour depth. Though conservative, BSA 2 was introduced due to its simplicity. BSA 3 has to be carried out if BSA 2 does not conclude with a specific plan of action. BSA 3 involves the calculation of time-dependent scour depth rather than simply using the maximum scour depth. BSA 3 is valuable in the case of highly erosion-resistant materials that do not achieve the maximum scour depth within the lifetime of a bridge. Both BSA 2 and BSA 3 utilize erosion classification charts that replace site-specific erosion testing for preliminary evaluations. The scour vulnerability depends on the comparison of the predicted scour depth and the allowable scour depth of the foundation. Hydrologic and hydraulic computer programs were developed to obtain the flow parameters. These programs generate maps of the maximum previous flood recurrence interval experienced by a specified bridge in Texas and converts flow into flow velocities. The 11 case histories used as validation showed good agreement between predicted and measured values. BSA 1 was then applied to 16 bridges. In this process, 6 out of 10 scour-critical bridges were found to be stable in terms of scour. The proposed bridge scour assessment procedure allows for the economical and relatively simple evaluation of scour-critical bridges. It also overcomes the over-conservatism in current methods.

Electrical Resistivity and Induced Polarization Imaging for Unknown Bridge Foundations

AbstractScour is the removal of soil around bridge supports due to water flow during floods. One of the major problems with scour is in the case of unknown bridge foundations. Bridges with unknown foundations are listed in the National Bridge Inventory as having insufficient data for scour evaluation, particularly regarding foundation depth. Knowing the foundation depth is a critical component of scour risk assessment. Multiple nondestructive testing methods are currently used to determine the depth of unknown bridge foundations; however, many methods are hindered by the type of substructure. An advantage of using near-surface geophysical methods, specifically electrical resistivity (ER) and induced polarization (IP) imaging, is that the inversion processes yield subsurface images, thereby allowing the depth and, to a lesser extent, the foundation type to be seen. Unlike a majority of existing testing methods, ER and IP imaging do not physically use the structure so they are applicable to simple and compl...

Sensitivity analysis for multi-attribute system selection problems in onshore Environmentally Friendly Drilling (EFD)

Input data used in Multi-Attribute Decision Making (MADM) problems are often perceived to be imprecise by decision-makers because they are based on expert assessments. As a result, an important step in many applications of MADM is to perform a sensitivity analysis on the input data to help decision-makers understand how in which regions of the input data space they can be most confident in the recommended decisions and where improved input information is most needed. This paper describes sensitivity analysis procedures which will help decision-makers examine the robustness of the optimal solution to changes in input parameters in system selection decisions, where the system is made up of components (drilling technologies) that can be combined in many different ways. This paper presents two different sensitivity analysis methodologies. One is a sensitivity analysis for weighting factors of each attribute, and the other is a sensitivity analysis for uncertainty of overall attribute inputs. An application case study of the proposed approach is described to select optimal onshore Environmentally Friendly Drilling (EFD) systems at Green Lake near McFaddin, TX.

The SRICOS-EFA Method

The SRICOS-EFA method is used to predict the scour depth versus time curve for complex pier and contraction scour in soils including sands, silts, clays, and soft rock. It consists of taking soil samples at the site, testing them in the EFA (Erosion Function Apparatus), and using the results as input to the SRICOS computer program. A hand calculation version of the method for preliminary design purposes also exists. The method is presented and comparisons between predictions and measurements at full scale are shown. A new approach to predict future hydrographs and perform risk evaluation is included.