Designing Site Investigations

The research addresses the prevalence of gassy soil, containing methane (CH4), within the soil particles of southeast coastal areas of China, such as the Quaternary deposit in the Hangzhou Bay area. This soil exhibits spatial variability in the distribution of gas pressure, posing a potential threat of engineering disasters, including fire outbreaks and blasting, during the construction of underground projects. Consequently, it is crucial to assess the risk state of gas pressure, involving accurate identification and reduction of associated uncertainty, through site investigation. This is indispensable prior to the commencement of underground projects. However, during the site investigation stage, the random field parameters that quantify the spatial variability distribution of gas pressure (e.g., mean value, standard deviations, and scale of fluctuation) are unknown, introducing corresponding statistical uncertainty. Therefore, the most significant consideration for planning site investigation from an engineering perspective involves determining the risk state of gas pressure while considering the statistical uncertainty of these random field parameters. This consideration heavily relies on the engineering experience gained from current site investigation practices. To address this challenge, the study introduces a probabilistic site investigation optimization method designed for planning the site investigation scheme for gassy soils, including determining the number and locations of boreholes. The method is based on the expected state-identification probability, representing the probability of identifying the risk state of gas pressure, and takes into account the statistical uncertainty of random field parameters. The proposed method aims to determine an optimal investigation scheme before conducting the site investigation, leveraging prior knowledge. This optimal scheme is identified using Subset Simulation Optimization (SSO) in the space of candidate site investigations, maximizing the value of the expected state-identification probability at the minimal value point. Finally, the paper illustrates the proposed approach through a case study.

This paper compares results of a deepwater geotechnical investigation using a seafloor drilling system, large-diameter core samples, and cone penetration tests performed from a coring vessel with results of a geotechnical investigation performed from a conventional drillship. The paper reports the first use of a seafloor drilling unit in the Gulf of Mexico to conduct a geotechnical site investigation for the mooring design of a floating platform. Common practice in the Gulf of Mexico for geotechnical investigations of anchor spreads for moored production facilities has been to perform seafloor cone penetration tests and to drill and sample one or more soil borings. "Soil borings" are prescribed but not defined by 30 CFR 250.19 API RP 2SK1 recognizes currently available site investigation tools, such as large-diameter core samples, that could be used in lieu of rotary soil borings; however, some certified verification authorities/agents (CVAs) have been reluctant to accept the use of API-accepted methods of site investigations in the Gulf of Mexico. Seafloor drilling units have been used successfully in various parts of the world, and cone penetration tests from a coring vessel have been performed and studied at numerous sites, both in the Gulf of Mexico and worldwide. This paper demonstrates that a seafloor drilling unit, large-diameter cores, and coring-vessel-deployed cone penetration tests integrated with AUV subbottom profile data can be used in the Gulf of Mexico without reliance on samples obtained from a drillship. Cone penetration resistance is compared using different cone systems and deployment methods at nearby locations. Results are essentially identical. Representative soil sample data are compared, and geotechnical laboratory test results are very similar. The paper confirms that when ASTM standards for cone testing and thin-walled-tube sampling are used, consistent results can be obtained from site investigations performed from seafloor drilling units and coring vessels or purpose-built geotechnical drillships. Integrated site investigation programs using technologies such as seafloor drilling units, large diameter coring, and cone penetration testing from a coring vessel should be acceptable for site investigations without special regulatory approvals beyond those that would apply to a site investigation program performed from a purpose-built geotechnical drillship.

The development of a liquefaction hazard map generally requires field data from site investigations. In this study, a bi-objective optimization framework is proposed for selecting an optimal site investigation program considering both the accuracy of the liquefaction hazard map and the site investigation efforts. To validate the proposed framework, a three-dimensional synthetic soil field with extremely detailed soil properties is generated and the corresponding liquefaction hazard map is used as the benchmark. Both regular and random sampling-based site investigation programs with varying site investigation efforts are considered and are used to infer input parameters of the subsequent random field-based liquefaction hazard mapping. It is found that the random field-based liquefaction hazard maps generally overestimate the hazard when validated against the benchmark liquefaction hazard map. When site investigation efforts (quantified by the number of sounding sites) are the same, regularly spaced site investigation programs yield more accurate hazard maps than those by random sampling-based investigation programs. An optimal site investigation program is recommended for the study site and the proposed framework can be applied to optimize site investigation of other sites.

The paper makes a review of important contributions from the geotechnical profession to offshore development, from the early piled and gravity base foundations to the new lightweight skirted foundation concepts. Geotechnical breakthroughs have enabled new and daring constructions offshore and opened the way to cost-effective solutions. At the same time, the requirements and conditions imposed by the offshore industry also greatly contributed to an improved understanding of the behavior of soils under new loading conditions. The paper looks into the development of enhanced site investigations and soil characterization, model testing, improved design methods and new foundation solutions. Joint-industry sponsored research proves to be a necessary contributor for developing new, safer and more cost-effective solutions. The paper outlines the challenges facing the profession when entering the new millennium and the steps needed to meet these challenges. Introduction The OTRC Honors Lecture series covers a wide array of contributions from different fields of offshore engineering. Bramlette McClelland's overview in 1991 on the frontiers in geotechnical engineering, Ben Gerwick's research promises for concrete sturctures and Don Murff's position paper on the use of centrifuge were the predecessors of the present paper. Odd Faltinsen on sea loads on floating systems and Leon Borgman on directional wave polyspectra presented views from hydrodynamics. Patrick Dunne and Mamdouh Salama outlined the structural challenges and innovations associated with resource exploitation in deep water, and Allin Cornell reported on the contributions of structural reliability to offshore engineering. This paper gives a personal view of major geotechnical achievements that have contributed to the progress of the offshore industry. The ideas presented are favorably biased towards geotechnics. The author is of the opinion that geotechnical progress has enabled the offshore industry to move towards increasingly optimum solutions. Perhaps these contributions do not receive today the recognition they deserve. On the other hand, the needs and requirements of the offshore industry have contributed significantly to the advancement of geotechnical knowledge and this should also be recognized. Achievements and Challenges Over the past 25 years, geotechnical practice has greatly evolved and improved, at times with giant leaps, because of the needs of the offshore industry. The following takes a brief look at the progress made in site investigations, testing for soil characterization and evaluation of soil models, improved foundation design methods and the development of new foundation solutions. The OTRC session presents companion papers on specific achievements within seismics, skirted foundations, pile design and seafloor instability. This overview mentions the main areas where significant advances have been made, and where needs are judged to be the greatest. The reader should consult the other papers for specific recent advances. Site and Soil Investigations. For adequate design of foundations, soil parameters need to be determined through a combination of interpretation of the local geology, in situ testing and laboratory testing. The impetus of offshore work had led to rapid developments in both in situ and laboratory testing. Equipment, testing methods, methods of interpretation and parameter determination are some of the aspects that have greatly benefited from enhanced research and attention. In Situ Testing. In particular, the developments around the piezocone penetration test and new sampling devices to be used at increasingly greater depths have been noteworthy

3 - Site investigation

Comparing classifications of death in the Mode Selection Trial: Agreement and disagreement among site investigators and a clinical events committee

Offshore site investigation is time-consuming and relatively expensive compared to onshore site investigation, because it is affected by severe weather conditions and has low accessibility from the land. Due to these economic and spatial-temporal constraints, it is essential to integrate the available site investigation information for the planning and design of offshore infrastructures. In this study, a GIS-based system was developed to manage and utilize the offshore site investigation data using opensource software. The system mainly performs the function of modeling the geo-information in three dimensions based on the offshore site investigation database. Through the input module, borehole data, geophysical survey data and numerical terrain information are standardized and stored in the database. The three-dimensional spatial modeling module performs outlier analysis of borehole data, subsurface geo-layer stratification, and interpolation of geotechnical properties. For the geo-layer stratification, the geostatistical integration method of borehole and geophysical datasets is adopted as well as conventional geostatistical methods. The optimization method of the results from geostatistical conditional simulation can be used for three-dimensional modeling of geotechnical property. The geoinformation predicted by the analysis module is inserted back into the database. Although this system is designed for offshore site investigation information, it can be used to manage inland and onshore site investigation information. Three-dimensional spatial modeling of site investigation information of an expressway construction site in South Korea was carried out using the developed system and its applicability was verified.

Value of information analysis of site investigation program for slope design

Gassy soils are distributed in relatively shallow layers the Quaternary deposit in Hangzhou Bay area. The shallow gassy soils significantly affect the construction of underground projects. Proper characterization of spatial distribution of shallow gassy soils is indispensable prior to construction of underground projects in the area. Due to the costly conditions required in the site investigation for gassy soils, only a limited number of gas pressure data can be obtained in engineering practice, which leads to the uncertainty in characterizing spatial distribution of gassy soils. Determining the number of boreholes for investigating gassy soils and their corresponding locations is pivotal to reducing construction risk induced by gassy soils. However, this primarily relies on the engineering experience in the current site investigation practice. This study develops a probabilistic site investigation optimization method for planning investigation schemes (including the number and locations of boreholes) of gassy soils based on the conditional random field and Monte Carlo simulation. The proposed method aims to provide an optimal investigation scheme before the site investigation based on prior knowledge. Finally, the proposed approach is illustrated using a case study.

The Birrimian rocks are structurally complex and extensively weathered in most places. The transition from rock to soil in the formation is often rather imperceptible. With just the basic site investigation equipment available in the country, site investigation in the residuals of the Birrimian rocks could be challenging. The only way to avoid over-designing is patient and systematic analysis of investigation data based on full understanding of the geology of the material at every site. This paper analyzes the problems associated with the Birrimian residuals encountered during site investigation at over sixty sites within the Birrimian, highlights solutions prescribed, and shows how a judicious combination of rock and soil mechanics principles could lead to reasonable solution of site investigation problems in soils with predominant structural features.

The purpose of this investigation was to gain a better understanding of drying shrinkage of slabs on ground. There were four components to this work: - background research; - a site investigation at the Capral Aluminium Warehouse site in Dinmore, in conjunction with Readymix; - a laboratory investigation at the University of Queensland concrete laboratory, in conjunction with Readymix; and - the application of codified shrinkage models and their comparison with laboratory results. The background research involved the consideration of concrete shrinkage. It was seen that good design and construction practices were the most effective way of controlling shrinkage. The site investigation was carried out at the Capral site and involved documentation of the placement of seven slabs, as well as the general monitoring of other slabs. This site was chosen as there was a high chance that significant cracking would occur, due to its location and the time of year during which pouring began. However, significant cracking did not occur, and may be attributed to the successful design, specification, supply, and construction of the concrete. The laboratory investigation involved the testing of three standard Readymix concretes. Mix A was the standard Capral Aluminium mix, Mix B was a high shrinkage mix, and Mix C was a low shrinkage mix. Standard specimen tests were carried out at the University of Queensland. The placement and monitoring of a slab and free shrinkage box for each mix was undertaken in attempt to model in situ slabs, and to better understand the effect of restraint on the shrinkage of members. Mix C was disregarded from analysis as test results were inconsistent with design specifications. The effect of base restraint on shrinkage of slabs was clearly identified when comparing the slabs to the free shrinkage boxes. Restraint of the slabs was seen to hide some of the early age shrinkage effects that were observed in the free shrinkage boxes. Three codified models for shrinkage were considered: AS 3600-2001, AS 3600 revised, and ACI. The variations between the parameters of each model were discussed, and their comparative performance analysed. It was seen that the ACI model performed best, followed by the AS 3600 revised, followed by the AS 3600-2001.

Site investigation data can play an important role in not only site characterization but also the improvement of engineering design. It is tempting to predict the potential benefit of a site investigation before it is actually conducted. In this study, a Bayesian framework to assess the effectiveness of a site investigation program is proposed. The expected reduced variance (ERV) is employed to measure the uncertainty reduction owing to site investigation data. The uncertain outcomes of all possible site investigation data are considered through their probabilistic distributions. Then a framework to calculate the ERV is established. Monte Carlo simulation is adopted and the statistical uncertainty can be analyzed through the bootstrap method. Two examples of a shallow foundation on sand and an undrained slope are illustrated in this paper. Based on the examples studied, the optimal sampling layout is also discussed. The proposed method is promising to be applied in optimization of the sampling layout for various geotechnical practices.

A site investigation by wash boring method was carried out in the compound of the Engineering Campus, Universiti Sains Malaysia, in Northwest Peninsular Malaysia. The subsurface soils of the region are known to be comprised of quaternary deposits including the prominent marine clays of the Gula formation. The conventional Standard Penetration Test, or SPT, was carried out for every 1.5m depth. The 18 disturbed samples collected were tested for grain size distribution, Atterberg limits, and specific gravity; and categorized according to the unified soil classification system. The results indicate low SPT numbers, or SPTN, i.e. SPTN 8 for depths deeper than 12m. Samples from shallower than 12m were mostly classified as low plasticity clay, or CL, which represents the soft marine clay while the underlying materials were mostly sands, namely poorly graded sand, or SP, silty sand, or SM, clayey sand, or SC, and well graded sand, or SW. Another site investigation by the CPTU method was also carried out 5m from the wash boring position, penetrating the entire soft clay stratum, thus giving another marine clay characterization in addition to the one given by the first method. The CPTU results generally gave SPTN≤2 for depths lesser than 8m, 2≤;SPTN≤4 for depths between 8 and 12m, and SPTN=23 at 12.5m, where the CPTU test terminated. The CPTU method classified the soft materials as sensitive fine grains, clays, and clayey silts to silty clays. Thus the CPTU results did not agree very well with the conventional wash boring SPT results in terms of the SPTN obtained. Nevertheless both methods equally identified the prominent presence of the soft marine clay stratum in the top 12.5m and the underlying strong sandy bed with higher bearing capacity values.A site investigation by wash boring method was carried out in the compound of the Engineering Campus, Universiti Sains Malaysia, in Northwest Peninsular Malaysia. The subsurface soils of the region are known to be comprised of quaternary deposits including the prominent marine clays of the Gula formation. The conventional Standard Penetration Test, or SPT, was carried out for every 1.5m depth. The 18 disturbed samples collected were tested for grain size distribution, Atterberg limits, and specific gravity; and categorized according to the unified soil classification system. The results indicate low SPT numbers, or SPTN, i.e. SPTN 8 for depths deeper than 12m. Samples from shallower than 12m were mostly classified as low plasticity clay, or CL, which represents the soft marine clay while the underlying materials were mostly sands, namely poorly graded sand, or SP, silty sand, or SM,...

When designing pile foundations, it is normal practice to perform a site investigation in order to quantify the physical and engineering properties of the ground. Often, the scope of the site investigation is dictated by construction time lines and budgetary constraints, rather than on the variability of the ground. It has been shown by a number of authors that as little as 0.04% – 0.3% of the total construction budget is spent on geotechnical investigations. Limited site investigations have the potential to impact significantly on the success or otherwise of the completed project. These include cost over-runs, construction delays, foundation failure and over-design. It has been suggested that “You pay for a site investigation whether you have one or not.”

Dikes and levees play a crucial role in flood protection in deltaic areas such as the Netherlands. Internal erosion piping or under-seepage is a major cause of levee failures and a main contributor to the probability of failure of river levees due to the large (mostly geotechnical) uncertainties. The present thesis investigates how geotechnical uncertainties can be reduced and how we can provide input for rational investment decisions for uncertainty reduction measures such as monitoring or site investigation. The general trade-off is between investing in uncertain reduction and realizing cost reductions of retrofitting measures necessary to achieve the required reliability target. The key ingredients of the approach are Bayesian posterior and decision analysis. Posterior analysis allows us to update the piping reliability with new information; Bayesian decision analysis enables us to estimate the consequences and costs of the considered decision options. The goal of the decision analysis is to identify the strategy with the least expected cost which meets the reliability target as set by the safety standard. The essential strategy options are (a) investing in uncertainty reduction and (b) retrofitting (i.e., taking physical measures to increase the structural reliability). Within each strategy we optimize the design parameters such as the site investigation density or the width of piping berms. Several sources of information are investigated in this thesis, the first being field performance observations made during substantial loading conditions such as seepage or sand boils. Whereas earlier studies only considered survival information (in Dutch: bewezen sterkte), the proposed approach allows to incorporate much more detailed performance observations indicating good or poor performance of the levee. The case study results suggest that the probability of piping failure can decrease or increase roughly one order of magnitude depending on the prior uncertainties and the observation made. Another source of information is monitoring the response of the hydraulic head in the aquifer, which can have a considerable effect on the piping reliability, because it provides information on the geo-hydrological properties in the foundation of the levee. The same holds for site investigation such as soundings, which allow us to map the stratification including the thickness of the blanket layer, which is very important for the sub-mechanisms uplift and heave. Pre-posterior decision analysis enables us to determine the optimal monitoring configuration or site investigation density such that the sum of investigation cost and expected retrofitting cost is minimized. The application examples elaborated in this thesis suggest that investments in back-analysis of historical observations, monitoring and site investigation can be very cost-effective. The results also show that a framework which does not consider the benefits of risk reduction beyond meeting the reliability target is sub-optimal in an overall risk sense.