Evaluation of life cycle assessment (LCA) use in geotechnical engineering

In recent years, there has been a growing emphasis to incorporate sustainability metrics into geotechnical engineering design decisions, driven by the surging eco-consciousness of industry standards. Consequently, life cycle assessment (LCA) has emerged as a popular method for evaluating the environmental impacts of geotechnical systems or projects. This paper conducts a critical review of 54 publications that apply LCA to various geotechnical systems, including deep foundations, biogeotechnics, dams, ground improvement, earth retaining structures, tunnels, and others. This review assesses the current state of practice for LCA in geotechnical engineering, identifies common barriers to implementation, and provides suggestions for successful execution. While sustainability practices have been more readily adopted by some subdisciplines of civil engineering including structural and transportation, geotechnical engineering faces distinct challenges due to its inherent site-specific nature, characterized by non-homogeneous soils and the necessity for bespoke solutions. Despite the notable increase in geotechnical LCAs, the absence of uniform standards remains a critical issue. Many studies could be improved by enhancing transparency in reporting data and results, clearly justifying input assumptions, and assessing the effects of variable soil conditions. Geotechnical LCA studies often concentrate on highly specialized problems, limiting the relevance of findings to other projects and impeding the development of clear recommendations for industry practitioners. Future research endeavors would benefit from establishment of comprehensive frameworks and multi-indicator models tailored to geotechnical systems to more accurately capture expected environmental impacts and opportunities for their reduction. A standardized approach could reduce redundancy in studies, encourage knowledge transfer, and provide a basis for broader applicability of sustainability practices in the geotechnical engineering profession.


Introduction
The building and construction sector plays a crucial role on global energy consumption and carbon emissions.In 2021, it was responsible for 37% of global energy and process-related carbon dioxide (CO 2 ) emissions.Building operations accounted for 10 GtCO 2 and material production (e.g.concrete, steel, and bricks) contributing an additional 3.6 GtCO 2 (United Nations Environment Programme 2022).
Though civil engineering projects have traditionally been designed with an appropriate priority on safety and serviceability, emerging concerns related to climate change, depletion of natural resources, and environmental hazards have become increasingly significant considerations (Basu et al 2015).Subdisciplines of civil engineering such as structural and transportation engineering have readily implemented sustainability practices.For example, the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED), which provides guidance on selection of structural materials for efficient buildings, has been implemented in more than 185 countries and territories (Weisenberger 2011, Press Room|U.S. Green Building Council 2023).It has also been made mandatory in certain regions, such as California since 2004(California LEED Certified State Buildings 2023).Additionally, in 2013, the national center for sustainable transportation was established to advance sustainable transportation through research, policy engagement, and education with funding from several government agencies, like the U.S Department of Transportation and the California Air Resources Board (National Center for Sustainable Transportation 2023) and the Federal Highway Administration has also released guidelines for the analysis of environmental impacts associated with pavements (Harvey et al 2016).Other sectors, such as geotechnical engineering, however, have been slower to adopt sustainability metrics in project planning due to a variety of unique challenges.
Geotechnical engineering, a critical component of civil infrastructure projects, applies the sciences of soil mechanics, rock mechanics, and engineering geology to construction, environmental preservation, and the extractive industries (e.g.mining) (Giles 2005).Whereas most engineers specify the materials they use, geotechnical engineers must use naturally existing in-situ materials with the occasional aid of prefabricated additives (e.g.concrete and steel) as needed (Eslami et al 2020a).The inherent variability of soils and environmental conditions at a specific project location often result in the development of bespoke geotechnical solutions based on engineering expertise and judgement (Robbins et al 2021).This complex and site-specific nature, along with a risk-averse design mindset, renders it difficult to apply generic sustainability practices to all geotechnical projects, requiring a level of customization that is unique to the industry.
The increased focus on environmental sustainability has led to a surge in studies that conduct systematic environmental impact assessments of geotechnical engineering systems.One framework that can be used to quantify impacts of a product or system over its life cycle is life cycle assessment (LCA) (Muralikrishna and Manickam 2017).LCA is a versatile approach that can be applied to a wide range of projects, providing a framework for evaluating and comparing the tradeoffs of feasible design alternatives for a specific geotechnical application (Raymond et al 2023) Despite the advantages of and growing interest in LCA, various barriers to implementation for geotechnical systems still exist.As such, the goal of this paper is twofold: (a) to understand the current state of practice of and (b) to determine the prevailing limitations to conducting high quality geotechnical LCA studies.
To accomplish this, a critical literature review of existing LCA applications to major geotechnical systems is performed.Synthesis of the commonalities and trends across the various studies reveals the depth of insights and knowledge that can be gained from a rigorous LCA analysis, as well as recurring simplifications and assumptions that can curtail the practical utility and applicability to industry.

Geotechnical engineering primer
Geotechnical engineering includes the analysis, design, and construction of civil infrastructure systems on, in, or with geomaterials (i.e., soil or rock) (Eslami et al 2020a).Nearly all civil engineering projects require geotechnical expertise to address the critical interface between the natural and the built environment (Giles 2005).Consequently, geotechnical engineers work on a wide range of projects, the most common of which are discussed in this section and used to facilitate comparison across literature included in this review.

Deep foundations
Geotechnical engineers are often responsible for foundation design.Foundation elements or systems are structural units that transfer various load combinations from the superstructure (e.g.buildings, bridges, and maritime platforms) to the underlying soil or rock such that safety and serviceability requirements (i.e.allowable settlement) are satisfied (Eslami et al 2020b).For the purposes of this study, deep, as opposed to shallow, foundations are considered.Deep foundations refer to displacement piles, which are generally driven by a hammer to penetrate the ground, and non-displacement piles, which are generally bored.Piles can be further classified by material, shape, end condition, reinforcement, and fabrication (e.g.pre-cast or cast in-situ) (Fleming et al 2009).Piles are generally constructed in groups, with the specific number depending on site stratigraphy, loading conditions, and allowable settlements.As such, the main environmental concern arises from material (i.e.steel or concrete) consumption (Lee and Basu 2022).

Biogeotechnics
Biogeotechnics is an emerging branch of geotechnical engineering that examines bio-mediated and bio-inspired solutions for geotechnical engineering challenges (Liu et al 2023).Some examples of bio-mediate processes include biocementation and enzyme induced cementation for liquefaction mitigation and fugitive dust control.Bio-inspired projects include tree-root inspired foundation systems, snakeskin inspired piles, and burrowing probes (Biogeotechnics Bio mediated Processes and Bio Inspired Ideas for Geotechnical Engineering Innovation|National Academies 2020).Though the scopes of these projects differ widely, for the studies included herein the main contributor to environmental impacts is material processing (e.g.calcium chloride or urea) (Raymond et al 2020, Deng et al 2021).

Dams
Geotechnical engineers play a significant role in the design, construction, operation, and maintenance of dams.Geological studies are critical during the early stages of analysis, in which geotechnical engineers plan the site investigation to quantify material properties and quality.At the design stage, geotechnical engineers are responsible for the dam embankment foundation, filter and drains, and slope stability.Geotechnical engineers participate extensively during the construction stage to verify characteristics of materials used and ensure that design specifications are met for aspects such as foundation grouting and zoning compaction (Flores-Berrones et al 2019).Following construction completion, geotechnical engineers continue working with dam owners to ensure structural safety and stability, monitoring aspects such as settlement, seepage, reservoir conditions, response to damaging or emergency events, and in some instances, retrofitting (Fell et al 2015).The construction stage of these projects is typically the most critical to environmental impacts, as large quantities of material and energy are required for installation (Yuguda et al 2020).

Ground improvement
Ground improvement refers to the alteration of soils to improve their engineering properties and meet project specific needs (Raymond et al 2021).The objectives of ground improvement (e.g.bearing capacity or settlement control, excavation support, liquefaction mitigation, seepage control, and slope stability) and employed methods to achieve them (e.g.deep dynamic compaction (DDC), vibro compaction (VC), deep soil mixing (DSM), and compaction grouting (CG)) are site specific, often depending on factors such as performance criteria, soil type, construction feasibility and material availability, timeline, and cost (Schaefer et al 2012, Robbins et al 2021).The main contributors to environmental impacts differ based on the employed methods.For example, the impacts associated with DDC and VC, which employ densification as the improvement method and do not introduce additional materials, are largely from construction activities.Conversely, those associated with DSM and CG, which introduce cementitious materials, are mostly a product of materials processing (Raymond et al 2021) Geotechnical engineers are involved with site investigation, ground improvement design, and quality control during construction.

Earth retaining structures
Earth retaining structures are engineered systems designed to support and retain soil, preventing collapse and erosion.Various types of structures can be used to accomplish this goal, including retaining and mechanically reinforced earth (MSE) walls.Retaining walls come in various designs (e.g., gravity walls, cantilever walls, and piling walls) and are typically rigid structures made from various materials, whereas MSE walls rely on the mechanical interaction between soil and inclusion that act as reinforcements (Berg et al 2009, Rajapakse 2016).Due to their structural nature, new material consumption and construction of the walls are expected to contribute significantly to environmental impacts (Balasbaneh and Marsono 2020) 2.6.Tunnels Geotechnical engineers oversee the site investigation, stability analysis, design, excavation methods, quality control, and maintenance associated with tunnels.Additionally, they may be responsible for risk assessment and mitigation strategies.This can apply to transportation, water, or utility tunnels (Tunnels-WSP USA 2023).Generally, the main source of environmental impacts stems from construction activities, including the use of explosives, diesel, and electricity (Huang et al 2014).

Other
Some studies included in this review did not fall into any one of the categories previously discussed.They are highlighted individually as comparisons across different systems would not be appropriate.This is not to indicate, however, that the systems discussed in this grouping are outliners in the geotechnical engineering profession, but in the realm of geotechnical LCA.For instance, a study by Purdy et al (2022) conducted an LCA of site investigation, which is a principal component of virtually all geotechnical projects, is considered here due to the lack of any other study with this scope.

LCA of geotechnical systems
LCA is a systematic analytical framework used to characterize, quantify, and interpret a product or system's environmental impacts over its entire life cycle (ISO 2006a).In the LCA context, environmental impacts refer to adverse effects to ecosystems, human health, and natural resources, which are typically referred to as areas of protection (Dewulf et al 2015).LCA methods have been standardized by the International Organization for Standardization (ISO) in ISO 14040:2006 (principles andframework) andISO 14044:2006 (requirements andguidelines).These standards discretize LCA into four phases: goal and scope definition, life cycle inventory (LCI), life cycle impact assessment (LCIA), and interpretation (ISO 2006a(ISO , 2006b)).
In the goal and scope definition stage, the purpose, target audience, functional unit, and system boundary are identified.The functional unit is a quantified description of the function that a product or system serves and is used as the reference basis for impact assessment calculations (Arzoumanidis et al 2020).Definition of the system boundary, which describes the life cycle stages and unit processes included and excluded from the scope, is also important to ensure accuracy of data collection and LCA results.Ideally, the system boundary would comprehensively consider all inputs and outputs associated with a product or system's entire life cycle.However, data and resource constraints often hinder the ability to conduct such an exhaustive study, forcing analysts to determine appropriate boundaries (Li et al 2014).In geotechnical engineering, system boundaries are especially unique to each project, as the extent of operations depend heavily on site-specific conditions.Practitioners typically consider activities in terms of raw material acquisition, material processing, transportation, manufacturing or construction, use and operation and maintenance (O&M), and end of life, which can be described as follows: • Raw material acquisition: includes the processes (e.g.mining, drilling, or harvesting) required to extract raw materials (e.g.aggregate, iron ore, coal, crude oil) from the environment.• Material processing: includes industrial processes that transform raw materials into desired products.
• Transportation: includes material transportation and equipment mobilization to project site.
• Manufacturing or construction: includes onsite activities specific to the project (e.g.drilling hole or driving piles for deep foundations, compaction or grouting for ground improvement, and application of enzymeinduced carbonate precipitation for bio-geotechnics).• Use and O&M: includes utilization of product and maintenance as needed (e.g.riprap repair and crosssection reinforcement of dams, replacement of tunnel linings, and aesthetic aspects of retaining walls).This stage is often excluded from many models because subsurface structures (e.g.foundations and ground improvement techniques) have no upkeep post completion.• End of life: includes processes after service life of the system has been exhausted, including demolition and waste management.This stage is also often excluded from many models because many geotechnical systems remain in place indefinitely.
The LCI phase follows goal and scope definition.An LCI quantifies the relevant environmental flows associated with inputs (e.g.raw materials and energy resources) and outputs (e.g.emissions to air, water, and land and waste generation) of the system.A LCI requires two kinds of data, the first defines the foreground system (the system directly being studied), and the second defines the background systems, namely the supply chains and infrastructure on which the system depends.Data may be gathered from multiple sources, including established databases (e.g.EcoInvent, GaBi, and the Life Cycle Assessment Society of Japan (JLCA)), primary data, published literature, and expert opinion.Data quality concerns can arise regarding geographical applicability, uncertainty, and temporal representation (Bicalho et al 2017).The variability between methods of data acquisition should be considered to ensure accuracy in system modeling, and LCIs are often designed to allow for sensitivity analyses in the LCIA phase.
In the LCIA phase, environmental flows contained in the LCI are translated into indicators of impacts to the environment and human health.LCIA methods, such as CML, TRACI, and RECIPE (European Commission-Joint Research Centre-Institute for Environment and Sustainability 2011), use a specific set of indicators for the impact categories they consider.Common impact categories included are global warming potential (GWP), acidification potential (AP), eutrophication potential (EP), ozone formation potential, ozone depletion potential, primary energy consumption, human toxicity potential (HTP), and ecotoxicity potential (European Commission-Joint Research Centre-Institute for Environment and Sustainabilit 2011).
Some practitioners may also choose to incorporate optional steps like normalization and weighting of impacts.The ISO 14044 standards define normalization as 'calculating the magnitude of category indicator results relative to reference information' and weighting as 'converting and possibly aggregating indicator results across impact categories using numerical factors based on value choices' (ISO 2006b).Normalization and weighting are commonly done to identify important impact categories, understand the significance of outcomes by comparing them to established benchmarks, and solving tradeoffs between results.Though frequently used, these approaches are subject to criticism due to potential bias and lack of scientific validity (Pizzol et al 2017).
A LCI and LCIA can be compiled in a spreadsheet or dedicated LCA software, such as SimaPro (PRe Sustainability 2022), openLCA (Green Delta 2022), and GaBi (Sphera 2021).Several tools geared toward other civil engineering disciplines, like structural engineering and building operations, also exist (e.g.EC3 (Building Transparency 2023) and eTool (Cerclos 2023)).To date, the only tool specifically designed to model geotechnical systems is the EFFC-DFI Carbon Calculator (Carbone 4 2020).Though this tool assists in the assessment of deep foundation and ground improvement techniques, its sole outputs is GWP, limiting its utility to a carbon footprint rather than LCA.Although these tools can facilitate comprehensive LCAs, their value and accuracy depend on the input quality.As a result, practitioners must be cautious when using these tools and ensure that embedded assumptions are well understood.
The final phase of the procedure is interpretation, in which the results of the LCI and LCIA are analyzed for conclusions or recommendations to decision-making in accordance with the defined goal and scope (ISO 2006a).This phase often involves determination of data sensitivity and uncertainty.
LCA, which only considers environmental impacts, can also be broadened to include life cycle costing (LCC), which is a sum of costs to the manufacturer, user, and society (Asiedu and Gu 1998).One way to quantify the imposed burden to society is through the social cost of carbon (SC-CO 2 ), which provides an estimate of the monetized damages associated with annual incremental increases in CO 2 emissions (Environmental Protection Agency 2016).Federal agencies, such as the Environmental Protection Agency, sometimes use estimates of the social cost of methane (CH 4 ) and nitrous oxide (N 2 O) in addition to SC-CO 2 (Marten et al 2015).

Methods
This review was conducted using web-based and journal database searches (i.e.Elsevier, SpringerLink, Taylor and Francis, ASCE Library, Canadian Science Publishing, and ICE Virtual Library) with the following combination of keywords: 'life cycle assessment' and/or 'environmental analysis' and/or 'geotechnical engineering' and/or 'civil engineering' .Studies were excluded based on relevance to LCA of geotechnical engineering through analysis of the title, keywords, and abstract.In addition to publications identified with these methods, sources included in reference lists of the identified articles and previous literature reviews (i.e.Raymond et al 2017) were also analyzed.This review considers 54 studies, available as journal articles, conference papers, reports, and theses, conducted between 2008 and 2023 which have evaluated the environmental sustainability of alternative designs for geotechnical systems.For ease of comparability and thoroughness of systematic review, they were grouped based on the application studied.
The results were parametrically analyzed based on goal and scope definition, reported LCI (tracked flows), and reported LCIA (reported impact categories) to evaluate the quality of LCAs conducted.In the field of geotechnical engineering, there is a prevalent focus on carbon emissions and GWP, resulting in the execution of carbon footprint analyses (CFA).To gauge the frequency of such analyses, a distinction was made between reported impact categories, specifically GWP and others.To assess the completeness of each LCA study and to identify overarching trends within categories, several components were considered, including defining the functional unit, providing LCI data, and reporting multiple impact categories.Additionally, studies which only accounted for carbon emissions are further demarcated.The inclusion of non-environmental impacts (e.g.LCC), uncertainty analysis, and interpretation within categories are also discussed.The completeness and transparency of the studies, including data presentation and reported conclusions, were qualitatively assessed.

Results
Table 1 presents the results of the systematic review of studies based on inclusion of several factors, such as functional units, life cycle stages, inventory data, and impact categories.Within each geotechnical subcategory, the results of studies are discussed and compared where appropriate.It is important to note that many studies under the same broad category assess different systems (e.g., the use of biogeotechnics for slope stabilization versus fugitive dust mitigation), making it impractical to derive overarching trends regarding environmental impacts.Consequently, the primary emphasis is on evaluating the quality of the LCA rather than the specific results from each study using the components previously discussed.Additionally, within each geotechnical system, overall trends of LCA modeling are discussed.

Deep foundations
Eight studies included in this review used process-based LCA to analyze deep foundations, many of which compared the environmental impacts of drilled shaft, driven piles, or caissons with one another (Misra 2010, Misra and Basu 2011, Lee and Basu 2018), though the assumed site conditions and system boundaries differed among studies.Some studies (Lee andBasu 2016, 2022) considered several subsurface profiles and design methods under a constant axial load, and others (Misra 2010, Misra and Basu 2011) maintained one  Table 1.Life cycle stages included, tracked flows, and reported impact categories for studies analyzed by category.subsurface profile but considered various load cases.Uniquely, Pujadas-Gispert et al (2021) performed a study to optimize a conventional foundation by studying the prefabrication extent of piles, concrete strength of cast in situ piles, pile type, and number of piles per ground beam.All of the studies omitted stages beyond construction, citing the long service life and minimal maintenance requirement of most deep foundation systems (Lee and Basu 2018).Though Giri and Reddy (2014) qualitatively evaluated the maintenance of piles and caissons, insufficient detail was provided regarding methodology and assumptions.Six of the eight studies clearly defined a functional unit, with the majority reporting results in terms of a single pile.The two studies which did not define a functional unit (Giri andReddy 2014, Pujadas-Gispert et al 2021) presented results of the total system specific to the study, rendering them non-transferrable to other designs.Uniquely, Lee and Basu (2022) defined their functional unit as the 'mass (in kg) of drilled shaft required to support the applied load in a given subsurface profile without bearing capacity failure (assuming factor of safety between 2 and 3) and settlement exceeding 30 mm' .Relative to the other studies, this choice most accurately adheres to the purpose of a functional unit.Seven studies reported results for at least one impact category in addition to GWP, and two published the results of their complete LCI (Misra 2010, Chau et al 2012).Two studies built upon traditional environmental impacts by developing a multi-criteria decision analysis framework for pile foundations, resulting in a sustainability index that considered resource use, environmental impact, and socio-economic indicators (Misra 2010, Misra andBasu 2011).Additionally, Giri and Reddy (2014) used streamlined LCA to evaluate the concerns of health and safety, working conditions, and design satisfaction.These impacts were qualitatively determined and given a numerical score associated with acceptability based on the authors' engineering judgement.Misra (2010) implemented a multi-criteria analysis (MCA) that considered different weights for resource consumption, environmental impact, and socio-economic impact; under this methodology it was determined that for clayey soils, driven piles are less environmentally sustainable than drilled shafts due to greater steel consumption, but the opposite is true for sandy soils.This conclusion was supported by HTP, AP, and GWP associated with each installation type for the two soil types, demonstrating the importance of considering design in multiple soil profiles as well as the incorporation of different impact categories.Misra also considered resource consumption of land, cement, and soil and socio-economic benefits associated with a cost benefit analysis.The weights of these factors were arbitrarily selected, which could alter the results if changed.Misra and Basu (2011) used a similar approach and found that drilled shafts consumed more resources in terms of cement and land than driven piles, but driven piles consumed more embodied energy.Ultimately, it was determined that driven piles were a more sustainable option for clayey soils.The discrepancies in these findings may be due to the assigned weights for each impact category and the fact that the 2011 study considered diesel consumption, but the 2010 study did not.These studies demonstrate the importance of scope definition and transparency in documentation; without a proper understanding of methods and results, these contradictory findings would not have been well understood.Lee andBasu (2016, 2018) also considered drilled and driven piles and found that drilled shafts had fewer variations in environmental impacts and embodied energy than driven piles for the same subsurface profile and applied load.However, driven pile designs required less materials and energy, resulting in less environmental impacts than drilled shafts and emphasizing that decisions made during the design process can affect environmental impacts.

Life cycle stages included in scope
Two studies extended the scope of their research to develop innovative relationships and optimization functions in the context of LCA.Pujadas-Gispert et al (2021) performed a Pareto front optimization to assess the ideal foundation system based on costs and 'eco-costs' , a metric used to monetarily express the environmental burden of a product or service.This analysis showed that piles with the least amount of concrete and steel were the most favorable.Lee and Basu (2022) considered multiple single and group pile configurations with a particular focus on GWP and established general relationships to be used as initial impact estimates for drilled shafts in similar environments and system boundaries (e.g.GWP as a function of pile diameter, reinforcement volume, applied load, pile spacing, and pile cap thickness).This study reported a comprehensive set of flows and impact categories and transparently published the LCI results for each life cycle phase, facilitating the application of the results to other studies.

Ground improvement
Eleven studies examined ground improvement techniques (i.e.DSM, vibro replacement, VC, DDC, earthquake drains, and CG) using comparative LCAs (Egan and Slocombe 2010, Pinske 2011, Spaulding et al 2012, Shillaber et al 2016, 2017, Raymond et al 2017, 2021, Ashfaq et al 2021, Ghadir et al 2021).Except for Shillaber et al (2017), who conducted a hybrid LCA, the studies used process-based LCA.Of the eleven studies, seven defined a functional unit and provided LCI data, while only five tracked and reported environmental flows and impact categories beyond GWP.Due to the variety of systems studies, the functional units also differed greatly, highlighting the specifity of the results from each LCA.Many excluded the stages beyond construction either to reduce uncertainty or due to negligible impacts (Raymond et al 2021).Shillaber et al (2017) specifically argue that the primary material in ground improvement is the existing soil itself, making it irrelevant to extend the boundaries to include demolition, disposal, and recycling.
Some studies evaluated the cost of ground improvement works (Egan and Slocombe 2010, Shillaber et al 2017, Purdy et al 2022, Raymond et al 2021), including the economic pillar of sustainability.Several of these studies did not fulfill the full scope of an LCSA as the social impacts or benefits of ground improvement were not quantitively evaluated.Raymond et al (2017), however, did calculate the social cost of carbon (SCC) associated with alternative ground improvement scenarios.In a later study, Raymond et al (2021) developed a qualitative approach to assess the impacts of construction activities on soil quality based on prioritization and weighting of several considerations (e.g. the ability to provide erosion resistance or enable mechanical filtration) followed by comparison of methods with each of the identified priorities.This study included an extensive evaluation of multiple impact categories (commonly omitted by others), including environmental, soil quality, cost, and social indicators.Sánchez-Garrido et al (2022) incorporated a hierarchical structure to assess economic (e.g.construction and service life), environmental (e.g., midpoint and endpoint indicators), and social dimensions (e.g. generation of local employment, user health and safety, and occupational health and safety) of sustainability.
Three studies found that DSM had the largest environmental and economic impacts, largely due to material processing (Pinske 2011, Raymond et al 2017, 2021).Spaulding et al (2012), who analyzed three case studies that compared alternatives to traditional ground improvement methods, found materials to be a large driver in carbon emissions, suggesting that less carbon intensive materials (i.e.soil bentonite and fly ash based cement mixtures) should be used when possible.Other studies also emphasized the potential benefits of alternative ground improvement materials.Ghadir et al (2021) evaluated the feasibility of using volcanic ash based geopolymer instead of cement as a soil stabilizer by comparing mechanical properties and environmental impacts.This study presented LCI data and associated assumptions for only the production phase.Although the LCA results estimated similar impacts for the two technologies, the authors highlighted the importance of specific boundary conditions on results.Ashfaq et al (2021) also performed a CFA for the construction phase to evaluate the impacts of non-traditional soil stabilization techniques, namely ground-granulated blast-furnace slag and lime stabilization, in borehole and ponding methods.Though not technically an LCA, the results highlighted the importance of vehicle selection and transport distance for material transportation, as these decisions resulted in emissions increasing by more than 100 times.
Shillaber et al (2016) evaluated three alternative ground improvement options-DSM for support of an earthen embankment, prefabricated vertical drains (PVDs) to increase the rate of primary consolidation in the foundation soils, and piled-supported reinforced-concrete T-wall-for levee stabilization as a case study to illustrate the use of a streamlined energy and emissions assessment model (SEEAM).It was determined that PVD design had the lowest embodied energy (EE) and CO 2 emissions, while concrete T-walls had the greatest.Despite being the most environmentally sustainable, the PVD design was not viable due to time constraints needed for flood protection, emphasizing the precedence that performance criteria can take.In an accompanying publication, Shillaber et al (2017) applied the SEEAM method and Monte Carlo simulation to generate data sets of EE and CO 2 emissions based on variability of impact coefficients and subsurface conditions for competing ground improvement methods.This approach can determine whether alternative methods differ significantly in terms of EE and emissions, assisting in decision-making while considering project uncertainties.As an example, this was applied for PVD and DSM in the aforementioned case study.After considering 1000 values in simulated data sets of emissions, it was determined that PVDs resulted in less EE and emissions than DSM, corroborating previous results and validating the methodology.

Earth retaining structures
Seventeen studies compared multiple types of retaining walls or MSE walls.Of these studies, 14 defined a functional unit.Leal et al (2018) was the only study that selected a functional unit in terms of the ability of a earth retaining structure to stabilize failed slopes, while the others selected purely geometric components (e.g., 1 m length or width of retaining wall).Five studies considered stages beyond construction (Rafalko et al 2010, Giri and Reddy 2015, Pons et al 2018, Balasbaneh and Marsono 2020, Speranza et al 2022).Damians et al (2017) conducted a sensitivity analysis which indicated that maintenance and post-construction electricity and diesel use had negligible environmental impacts, justifying their omission.Pons et al (2018) considered carbonation of concrete during the structure service and end of life, as well as concrete crushing for its recycling process.Because maintenance activities were excluded from the scope, the CO 2 uptake from carbonation resulted in negative impacts.It is important to note that these negative values do not retrospectively negate the emissions associated with the process, but rather present the possibility of reusing concrete as a carbon sink.Speranza et al (2022) also calculated environmental impacts associated with end of life (i.e., demolition and disposal/recycling), and noted that calculated impacts were significant, especially if assuming material disposal.Balasbaneh and Marsono (2020) extended the study scope to include retaining wall demolition.Though Giri and Reddy (2015) considered both phases, insufficient information was reported to allow for detailed review.Three studies also considered the impacts of soil stabilization using lime or cement (Ashfaq et al 2021, Samuelsson et al 2022, von der Tann et al 2022).Ashfaq et al (2021) determined that lime stabilization of embankment soils substantially affected CO 2 emissions and reported that a 3% addition of lime doubled the overall CO 2 emissions for the project.von der Tann et al (2022) corroborated this result, reporting that lime stabilization contributes between 15% to 45% of GWP.Samuelsson et al (2022) compared the use of crushed rock fill and cement-stabilized sandy till (using Portland cement, Portland cement with 30% blast furnace slag, and Portland cement with 64% blast furnace slag) as two embankment fill methods.For the crushed rock method, results varied based on transport distance; a 20 km increase in haulage distance resulted in a 25% increase in GWP.For the stabilization method, however, cement accounts for 84% (64% blast furnace slag) to 95% (no blast furnace slag) of total climate impact.These results could be referenced by practitioners seeking to decrease impacts of similar designs.
Of the 17 studies included in this category, 13 reported on impact categories other than GWP.In addition to environmental impact categories, some studies incorporated economic and social assessments.Balasbaneh and Marsono (2020) adopted a multi-criteria decision method to select the best design choice considering LCA, social LCA, and LCC results.The social-LCA was conducted based on questionnaires distributed to 40 individuals, including engineers, experts, and stakeholders.The methodology adopted provided insight on how to assess the most sustainable system while considering multiple complex criteria.Similarly, Lee and Basu (2015) integrated a MCA to evaluate design alternatives based on resource consumption, environmental impact, and socio-economic benefit.In this case, as well as the study by Giri and Reddy (2015), the weights assigned to each attribute were defined qualitatively, so it is not clear how sensitive the rankings may be to the assigned weights.Economic assessments implemented in several studies (Rafalko et al 2010, Giri and Reddy 2015, Damians et al 2017) indicate that material consumption is largely responsible for costs.Samuelsson et al (2022) considered the level of contamination of waste products for stabilized till and reported that this degree most heavily influenced the life cycle cost.Leal et al (2020) reported that material haulage accounted for more than 50% of GWP.Seol et al (2021) also applied the environmental costs per unit of pollutants for each reported impact categories.
Several studies considered the effects of recycled materials on environmental impacts.Ongpeng and Ginga (2022) investigated the use of concrete with natural aggregates and recycled aggregates from construction and demolition wastes (CDWs) in a reconstruction of earth retaining structures and highlighted that using recycled aggregates from CDW can decrease impacts by 50%.Phillips et al (2016) applied the SEEAM method to determine the EE and CO 2 emissions associated with two culvert bridge design alternatives.The results indicated that a geosynthetic reinforced soil bridge system was more sustainable than a piled abutment system, largely due to reduced material and waste haul distances for select backfill, once again emphasizing the importance of material selection.Chau et al (2012) also determined that recycled steel wall systems consumed less EE and emitted less CO 2 than other concrete wall systems.Additionally, there was a significant difference in impacts when recycled versus virgin steel was used, further highlighting that use of recycled materials can reduce impacts.This was corroborated by Inui et al (2011), who found that use of recycled steel reduces the overall EE of four different retaining walls for a railway embankment.Kumar and Parihar (2023) conducted a comparison between a retaining wall filled with natural sand and used foundry sand (UFS), a byproduct of the foundry industry.Their analysis considered energy consumption, human health impact, ecosystem quality, and resource surplus.Findings revealed that the use of UFS reduced these impacts by 82.6%, 87.6%, 90%, and 86.8%, respectively.

Tunnels
Two studies that analyzed tunnels were included in this review; one performed an LCA of a standard road tunnel (Huang et al 2014), while the other performed an LCA on the construction process of a sewage treatment tunnel (Arena 2019).The difference in project scope translated to the defined system boundaries, resulting in the inclusion and exclusion of certain life cycle phases.Neither study considered tunnel demolition, citing that no tunnels had been demolished regionally to date (Huang et al 2014).However, Huang et al (2014) included the disposal of blasted rock, electricity consumption for lighting and ventilation for operation, and pavement replacement and tunnel lining changes for maintenance.Arena (2019) only accounted for tunnel construction and excluded transport of materials to the site, energy associated with concrete production, and O&M.Results for this study were reported for the entire construction phase, whereas Huang et al (2014) defined a functional unit of 1 m standard Norwegian road tunel with a 100 year lifetime.Arena (2019) quantified endpoint indicators, whereas Huang et al (2014) neglected to.In addition to reporting various impact categories, both authors made recommendations for actions that could be taken to minimize environmental impacts, which included onsite construction optimization, material durability and energy efficiency improvement, and environmentally conscious policy promotion.Arena (2019) showed that increasing ground granulated blast-surface slag used in concrete lining from 36%-65% to 66%-80% reduced the contribution to climate change, human health, and resources by 39, 12%, and 16%, respectively.The results from this study indicate that steel reinforcement and fuel used for operation contribute significantly to environmental impacts, and increasing recycled steel content or decreasing the total steel quantity reduces the impacts.Huang et al (2014) determined that the construction stage contributed most to GWP, ozone depletion, terrestrial acidification, and photochemical oxidant formation, mainly due to the consumption of concrete and explosives.The maintenance stage generated over half of the particulate matter formation due to use of aggregates and bitumen, and the operation stage was the main contributor to human toxicity, ionizing radiation, and terrestrial ecotoxicity due to electricity usage.Huang et al (2014) transparently included inventory data sources, assumptions, and allocation procedures for the foreground system, reported an extensive list of impact categories, and conducted sensitivity analysis to assess effect of data quality.
Ultimately, the authors recommend that onsite construction should be optimized by improving material durability, energy efficiency of ventilation systems, and upstream supply chain impacts.Both authors suggest further collaboration with stakeholders to identify decisions early in the project process that could reduce overall impacts throughout the lifetime of tunnels.

Dams
Although the studies broadly focused on dams, they each evaluated a specific, different aspect associated with these facilities.Consequently, the selected goals, scopes, and functional units varied considerably.Liu et al (2013) conducted the only study assessing the life cycle environmental impacts of constructing a new dam, with a functional unit per unit of cast concrete.Yuguda et al (2020) compared the life cycle impacts and costs of alternative methods of retrofitting an existing dam to generate hydroelectricity based on 1 MWh of energy generated.Noh et al (2018) proposed a method for evaluating the life cycle CO 2 emissions associated with fill dams in terms of typical construction and repair activities.Additionally, each study adopted a different service life based on project scope; Noh et al (2018) assumed a time span of 100 years, while Liu et al (2013) and Yuguda et al (2020) assumed a time span of 50 years.
The studies consistently considered the life cycle phases from material processing through use, and justified the omission of end of life, as large-scale dams are rarely demolished and often remain in place indefinitely.The selection of life cycle phases also influenced the flows tracked in each LCI analysis, the results of which were reported by Liu et al (2013) and Yuguda et al (2020).Authors were bound by the scope of study when determining impact categories.For example, Noh et al (2018) only reported CO 2 emissions, as this was the focus of the project, while Yuguda et al (2020) expanded results to include acidification, human-, and eco-toxicity potential to present a more holistic analysis.Noh et al (2018) was the only study to analyze the impacts of common repair activities.Noh et al (2018) determined that CO 2 emissions increase over the lifetime of dams, particularly when repair activities are conducted, stressing the need for careful consideration of construction materials and repair methods to reduce associated emissions.The study conducted by Yuguda et al (2020) emphasized the importance of life safety, noting that though some retrofitting options were more sustainable, they were not adequate in terms of reducing risk.Liu et al (2013) showed that using rock-filled concrete instead of conventional concrete reduced total life cycle GHG emissions and energy used by 64% and 55%, respectively.The main contributor to GHG emissions for conventional concrete dams was materials production, due to the large quantities of cement required; this was still the main source for rock-filled concrete dams, though the total impact was lower.This study explicitly reported detailed inventory of raw material production, transportation distances, and equipment used studies such as this can aid early decision-making regarding improving the sustainability of construction methods and materials for dams.

Bio-geotechnics
There are fewer LCAs in biogeotechnics, as this field is younger.Of the seven studies included in this review, six of them clearly defined a functional unit, two published LCI data, and seven reported multiple impact categories.Most publications reviewed focused on ground improvement techniques, including enzyme induced carbonate precipitation (EICP), microbially induced carbonate precipitation (MICP) and bio-grouting (Suer et al 2009, Martin et al 2020, Alotaibi et al 2021, Deng et al 2021).Though Raymond et al (2020) also studied EICP, they did so in the context of fugitive dust control.Storesund et al (2012) uniquely compared concrete retaining walls to bioengineering slopes.Deng et al (2021) analyzed the energy consumption and carbon emissions of MICP technology and compared results to other soil stabilization methods (e.g.lime mortar and cement).This analysis was performed using an environmental impact potential value, which is a comprehensive index of total emissions of various pollutants for an entire product system.Huntoon et al (2023) compared root-inspired and conventional straight-shaft ground anchors, reporting that the former led to a 25% reduction in GWP.Due to the various systems studies, a wide range of functional units were selected to best address the goal of the system being modelled.None of the studies considered end-of-life, presumably because bio-geotechnical systems often work in conjunction with the surrounding environments, and thus will not often be disposed of.Suer et al (2009), however, did consider spoil disposal (i.e., cement used for jet grouting and calcite used for bio-grouting), as is customary of projects requiring these services.Storesund et al (2012) did account for the O&M of the aforementioned design options but focused on the preservation of aesthetic value (i.e.removal of graffiti and landscaping) rather than engineering metrics to estimate the use-phase requirements and environmental impacts.
Three of the studies compared bio-geotechnical alternatives with their business as usual counterparts (Suer et al 2009, Raymond et al 2020, Alotaibi et al 2021, Huntoon et al 2023), while the others reported results of a single technology (Martin et al 2020).Alotaibi et al (2021) and Raymond et al (2020) established that although bio-geotechnical solutions can be more sustainable in some respects, they can also be more environmentally intensive in others, highlighting the tradeoff between applied methods.Storesund et al (2012), conversely, found that bioengineered solutions for slope stabilization had less impact on the environment than conventional retaining walls in all measured environmental aspects.The study by Martin et al (2020) emphasized methods for reducing impacts associated with EICP, demonstrating how LCA can be utilized to improve standalone technologies in addition to conducting comparisons across alternatives.
Raymond et al (2021) developed a robust framework for assessing environmental impacts.Not only do the authors provide a thorough explanation of the modeling processes and report the LCI datasets and results, but they also detail the environmental impacts of each life cycle stage for multiple flows.Additionally, the study includes two sensitivity analyses that assess the accuracy of the baseline results.

Other systems
Several studies analyzed unique geotechnical systems that did not fit into any one category.Though comparison of these with one another is limited, it should be noted that five of the six studies defined a functional unit and that all six studies included in this group evaluated multiple impact categories.None of them, however, published LCI data.In a study by Frischknecht et al (2013), geosynthetic filters were compared to mineral filter layers used in road construction.In addition to inventory data, information for this study was collected from the participating companies through a series of questionnaires.This study also included the land occupied by the factory producing materials as a direct burden.Results indicated that implementing a geosynthetic layer in filters reduces all measured indicators by more than 85%, which could be beneficial for practitioners in the design process.
Harbottle et al (2007) compared aspects of the technical sustainability of in situ stabilization/ solidification in landfilling to remediate contaminated land.The authors used both MCA and LCA to study a set of sustainability criteria developed for the project, including risk to human health and safety, local/global environment, and third-party concern.These criteria were weighted based on importance, with human health and safety being of primary concern, and local issues taking precedence over global environmental effects.It is mentioned that in the absence of data, predictions of impacts were made, but little clarification was provided regarding the methodology used, making it challenging to review.Goldenberg and Reddy (2017) evaluated the sustainability of conventional and alternate landfill cover systems, stating that although cost is typically the driver between the two, there are environmental factors to consider.One of the main aspects studied was the distance between the project site and the clay/evapotranspiration (ET) cover system borrow source; it was determined that if the soil required for an ET cover needs to be transported, the impacts associated with the design will be substantially higher, potentially resulting in greater impacts than the conventional systems.
da Rocha et al (2016) assessed the environmental impacts of lime dosages required to achieve target strength and stiffness in clayey soils.An experimental program evaluated the properties of clayey soil with various amounts of lime blends, which then served as the basis of an LCA to understand the environmental impacts of design alternatives.The authors justified excluding the use, maintenance, and disposal phases from this study since the clay-lime blends may be applied for different purposes with varying performance and service lives.To compare the impacts of dosage levels, the impacts in each category were assigned a value based on overall contribution.Results from this study indicate that dosages with lower lime-binder and higher density have lower impacts than those with higher lime-binder and lower density.Further, lime production was estimated to account for over 75% of GWP, photochemical oxidation, and embodied energy impacts.Saldanha et al (2021) expanded this research and assessed the sustainability of eggshell limes compared to conventional limes used for soil stabilization using both midpoint and endpoint indicators.Eggshell quicklime and hydrated lime had lower environmental impacts for all mid-point categories and for ecosystem quality and human health than their conventional lime counterparts.Climate change and resource impacts for eggshell and conventional lime were similar.Damage to ecosystem quality was reduced by 65% and 50% with the incorporation of eggshell quicklime and hydrated lime, respectively.Lubrecht (2012) considered the potential sustainability benefits of employing horizontal directional drilling (HDD) over traditional vertical drilling.Although various air emission values are reported showing that HDD is less impactful than auger drilling the methods behind the calculations are not available.The same applies for claims made regarding qualitative social, economic, and environmental advantages associated with HDD, which were anecdotally recounted.The author does disclose a competing financial interest, as they are employed by a HDD company and published the study with the intention of raising awareness of the benefits of HDD, making it tricky to assess the authenticity of the claims.
A study by Purdy et al (2021) evaluated the impacts of several site characterization methods (e.g., cone penetrometer test, standard penetration test, Shelby tube, sonic drilling, vane shear test, and drill-assisted vane shear test), in three different scenarios.These scenarios considered various sampling intervals and a representative investigation was used to facilitate comparison between approaches.On a per linear meter of profiling, the CPT was shown to be least impactful.Further, it was shown that the major contributor to primary energy, smog formation potential, and AP was mobilization, while that to EP and particulate potential was grouting.Mobilization and grouting almost equally contributed to GWP.Using 100% bentonite grout resulted in a 45% reduction in GWP and reducing mobilizations to one vehicle per workday reduced GWP between 7% and 12%.To date, this is the only study that quantifies the impacts of conventional site characterization methods.The methods discussed in this study are commonly used and thus highly standardized, and the authors consider effects of site stratigraphy by denoting three different site scenarios with varying site investigation programs and of equipment remobilization, grouting material, and investigation type by further parametrically studying four alternatives regarding mobilization distances and materials (e.g., Portland cement, bentonite, or combination).The various conditions and their associated results allow these findings to be implemented across a wide spectrum of projects.

Discussion
There has been a significant increase in consideration and quantification of environmental sustainability of geotechnical systems, with 26 of the 54 studies conducted within the past five years.This increase in studies has also been accompanied by an improvement in rigor, as authors conduct more comprehensive implementations of LCA, as evidenced by the inclusion of thorough social-LCA, endpoint impact categories, and ingenuity in analysis.Nonetheless, there remains variations in content, scope, and conclusions across studies.

Goal and scope
The absence of a universal approach grants researchers liberties in almost every stage of LCA, resulting in discrepancies between studies, including those that assess the same system.This is exacerbated by the reality that geotechnical design is highly site specific, a characteristic of the profession that will require evaluation methods to incorporate site specific details.For example, most studies considered in this review had limited or incomplete foreground systems.In fact, 74.1% and 87% omitted the use and maintenance O&M and end-of-life phases, respectively.For some categories, such as deep foundations, biogeotechnics, and ground improvement, this exclusion is appropriate, as these systems often serve a passive function and are left in place permanently.Accordingly, none of the studies in these categories included impacts from end-of-life.Other systems, like earth retaining structures, require more regular maintenance and repairs, indicating that these activities are not negligible in an LCA and should be considered (Pan 2008, Bernhardt-Barry 2019).However, only 17.6% of studies in this category incorporated impacts from the use and O&M life cycle phase, indicating a gap for consideration in future studies.Notably, all of the studies that analyzed dams included the use and O&M phase in their respective scopes.Though some authors justified the decision to include or exclude certain life cycle phases, many did not, making it difficult to assess the validity of the choices and, ultimately, the results.Another area in which LCA of geotechnical systems can be improved is in the definition of a functional unit.Twenty-five percent of studies included in this review presented results as a cumulative output for the entire system rather than specifying a quantified description of its performance.This lack of a standardized functional unit restricts the comparability between various systems and their alternatives, leading to potentially misleading assessments.It is crucial for future studies to emphasize the inclusion of a well-defined functional unit, enabling more accurate and insightful comparisons between different systems.

LCI and LCIA
The lack of consistency in methods also permeates to data collected and used, potentially creating further uncertainty between results.Researchers make crucial decisions regarding data use, including what actions to take in the absence of geographically appropriate data or in the presence of conflicting sources.Data used to model background systems were largely acquired from commercially available LCI databases or published studies.For some studies, survey and questionnaire responses were used to model specific processes or quantities, the results of which were not published.Of the studies considered in this review, only 25% reported the results of their LCIs, making it difficult to understand the methodology behind calculations and to apply results to other designs.The majority of publications reported outcomes as either impact category indicators or graphically.Additionally, there is no guidance on which impact categories to consider, and approximately 20% of studies only reported GWP or carbon emissions, resulting in the inability to understand potential trade-offs between impacts.

Interpretation
To understand the sources of uncertainty, including those related to data usage, 42% of studies evaluated the sensitivity of important variables and selected parameters.Some studies analyzed the effects of data quality (Inui et (Lee and Basu 2016, 2022, Purdy et al 2022, Speranza et al 2022).Though not a sensitivity study, Seol et al (2021) embedded varying soil conditions and properties in their study.Sánchez-Garrido et al (2022) validated results by implementing different multi-criteria decision-making procedures.Furthermore, because the weighting of environmental impacts was dependent on expert opinions, an additional sensitivity study was performed to examine how fluctuation in the given weights may affect results.Though nearly half of the studies conducted sensitivity studies, several authors did not justify the selection of sensitivity variables, making it difficult to assess the relative significance of one variable over another in the context of the selected scope.The inconsistencies in sensitivity variables between LCAs of similar systems also limit the ability to determine the confidence of observed trends.

Knowledge gaps
There are several geotechnical applications that have not been explored in the context of LCA and environmental impacts.These include shallow foundations and offshore foundations (though pile foundations have been examined).Studies are also lacking in the areas of slope stabilization, mining geotechnics, and hydraulic containment structures (i.e.levees and dikes).While adequate performance and safety are paramount, these expansive systems generate significant impacts; therefore, even a small reduction in impacts per unit length/volume could aggregate to substantial sustainability gains across systems and over time.
Though LCA is becoming more commonplace, there remains a gap in methods used with respect to scope specifications, data quality and acquisition, and uncertainty quantification.In addition, the lack of transparency is an added obstacle in evaluating LCA projects.These present barriers to extendibility of findings to other projects, making some LCAs obsolete and inapplicable beyond the studied project.Historically, geotechnical LCAs have not considered the performance of systems under low-probability, high-consequence events (e.g.landslides, severe seismic activity).Geotechnical systems support complex infrastructure that provides shelter and mobility, and failures can have widespread ramifications to the health, safety, and economy of communities.As such, it may be of interest to expand the scope of LCA studies beyond the direct activities within geotechnical systems to evaluate effects on broader systems.

Recommendations and needs in LCA implementation
LCA is a useful tool that can assist in making environmentally conscious design decisions.However, several barriers to effective implementation of LCA of geotechnical systems remain, including: • Development of a comprehensive framework tailored to geotechnical systems.
• Definition of appropriate functional unit and explanation of scope selection.
• Transparency in reported LCI data, sources, and results along with LCIA methods and results to aid in reproducibility and extendibility to other projects.• Clear definition of how uncertain variables were determined, including justification of assumptions made and specification of variability to enable sensitivity studies.• Development of multi-indicator models that can assess trade-offs between impact categories (i.e., not limited to GWP) and determine which decisions require the least change in geotechnical practice while yielding the most significant improvements in environmental impacts.• Consideration of the variation between design (i.e., idealized desk study) and actual construction (i.e., realized projects).• Assessment of the effect of variable soil properties and stratigraphy on the engineering design required to satisfy safety and serviceability, and consequently on LCA results.

Conclusions
This paper has reviewed existing literature that applies LCA methods to geotechnical systems to (a) provide an updated assessment of LCA utilization within geotechnical engineering and (b) to identify gaps in research and application in real-life projects.As sustainability remains at the forefront of concerns facing the civil engineering profession, there has been an increase in research and development related to LCA of geotechnical systems.Nonetheless, many of these assessments are limited in scope, tracked environmental indicators, and reported impact categories and differ in methodology.The absence of uniform standards across studies extends even to those examining similar systems, resulting in highly specialized and niche findings with limited generalizability to other projects and, consequently, duplication in efforts and resources.Though the bespoke nature of geotechnical engineering must and will continue to be considered in environmental impact analysis, it is imperative that steps be taken to enhance the incorporation of life cycle sustainability principles into design.As such, several key suggestions merit consideration: • When possible, take LCA into account during the initial stages of project planning and design to identify potential impact hotspots and how they may be mitigated prior to commencement of construction activities.• Collect reliable and comprehensive data on materials, energy, transportation, and construction activities for the entire project life cycle to ensure accurate impact calculations.• Involve all pertinent stakeholders (i.e., contractors, clients, and designers) to ensure comprehensive life cycle modeling.• Explicitly report data, sources, and assumptions to increase reproducibility and applicability to other projects.Conduct uncertainty analysis where appropriate, especially when assumptions are prescribed in lieu of documented data and where soil variability alters the results.• Assess a variety of impact categories to provide a holistic LCA framework rather than presenting a footprint analysis.
The field of geotechnical engineering has been gradually considering the immediate and long-term environmental impacts of projects in a more robust manner.Continued progress requires that steps be taken to overcome the obstacles associated with LCA of geotechnical systems to make the evaluation outcomes more rigorous and specific, which will enable more sustainable geotechnical practice.Perhaps, if concentrated efforts are directed towards enhancing transparency of data, selection of design parameters, and choice of environmental impact indicators, comprehensive LCA frameworks could become an integral part of project planning and design decisions in the geotechnical practice, ultimately contributing to the sustainable development of civil infrastructure.

Table 1 .
al 2011, Chau et al 2012, Huang et al 2014, Alotaibi et al 2021, Sánchez-Garrido et al 2022); others focused on material selection and consumption rates (Pinske 2011, Phillips et al 2016, Damians et al 2017, Raymond et al 2017, 2020, Arena 2019, Yuguda et al 2020, Ashfaq et al 2021, Kumar and Parihar 2023); and some considered variability of transport and mobilization distances (Pinske 2011, Liu et al 2013, Phillips et al 2016, Raymond et al 2017, Goldenberg and Reddy 2017, Leal et al 2020, Purdy et al 2021).Although several studies assumed unsubstantiated soil properties, only four analyzed the potential sensitivity of environmental performance based on variability of subsurface conditions