LCA and Sustainability Assessment for Selecting Deep Foundation System for High-Rise Buildings

ICSI 2014: Creating Infrastructure for a Sustainable World 621 © ASCE 2014

LCA and Sustainability Assessment for Selecting Deep Foundation System for High-rise Buildings

Rajiv K. Giri1 and Krishna R. Reddy2

1Graduate Research Assistant, University of Illinois at Chicago, Department of Civil & Materials Engineering, 842 West Taylor Street, Chicago, IL 60607; PH (312) 996- 5165; e-mail: [email protected] 2Professor, University of Illinois at Chicago, Department of Civil & Materials Engineering, 842 West Taylor Street, Chicago, IL 60607; PH (312) 996-4755; FAX (312) 996-2426; e-mail: [email protected]

ABSTRACT

This study focuses on selecting the most sustainable foundation system based on life-cycle assessment (LCA) and sustainability assessment of alternate deep foundation systems, specifically piles and caissons, over their design life. Sustainability evaluation of alternate deep foundations is performed using triple bottom line: environmental, economic, and social impacts and by considering various life cycle stages that cover raw material extractions, construction, maintenance, and demolition efforts. For design purposes, subsurface soils, factor of safety against bearing capacity and allowable settlement for both foundations are considered to be the same. Technical designs of both systems are developed based on bearing capacity, both primary and secondary settlements and structural integrity. The LCA is conducted to assess potential environmental impacts, such as global warming, acidification, and smog, associated with the concrete and steel production along with the diesel used for transportation and on-site machinery due to mineral extraction and refining, and required energy inputs for processing. Subsequently, economic evaluation and social impact analyses are performed and the results of analyses are compared. For the site-specific conditions considered, it is concluded that a caisson is more sustainable foundation option than a pile foundation in terms of environmental, economic, and social aspects over its design life.

INTRODUCTION

Deep foundations are invariably recommended for high-rise buildings due to poor subsoil conditions at shallow depth and large column loads. It is common practice to use the two alternative deep foundation systems (caissons and piles) as permanent structures alike. Currently, foundation system decisions are based solely on preference, sound technical design, and cost. The superior solution is not decided on sustainability aspects. Consequently analysis of sustainability is required to ascertain the validity of each individual structure of the two distinct foundation systems. Subjects such as construction, environmental impacts, maintenance and demolition also have to be put under consideration, while keeping in mind the desired ICSI 2014: Creating Infrastructure for a Sustainable World 622 © ASCE 2014

lifecycle of 50 years of the structure installment. The problem resides in designing both deep foundation systems, and evaluating which system is more sustainable. In this study, sustainability assessment was performed for two-alternate deep foundations, namely piles and caissons during various life cycle stages of raw materials excavation, unit manufacturing, transportation emissions, energy needed for foundations, possible in-situ degradation, and recycling of materials. As it is defined, sustainability incorporates the environmental, economic, and social impacts associated with a given geo-structure. But, before any of these can be looked at, deep foundations are to be technically sound and well designed. For comparison purpose, the piles and caisson were subjected to the same conditions. The load applied on both alternative foundations was 1000 Kips, the settlement limit was 1 inch, and the depth at which they were constructed was considered as 55 ft. This was crucial in order to establish the more sustainable option in an unbiased approach.

METHODOLOGY

Subsurface Soil Profile

The project site was considered to be located in General Chicago area. Figure 1 shows the typical subsurface soil profiles found in Chicago region for designing deep foundations.

DEPTH Ground Level 0 ft A Sand = 33° " = 120 pcf B1 7 ft B2 GWT 7.5 ft C Clay c = 1400 psf D1 " = 106 pcf 13 ft D2 Clay c = 900 psf E1 " = 101 pcf 18 ft E2

Clay c = 200 psf " = 106 pcf

F1 48 ft F2 Clay c = 3200 psf G1 " = 126 pcf 53 ft G2 H Clay c = 6100 psf 55 ft " = 138 pcf 62 ft

Figure 1. Typical subsurface soil profile considered for two-alternate deep- foundation systems. ICSI 2014: Creating Infrastructure for a Sustainable World 623 © ASCE 2014

The geotechnical engineering properties of soil layers were determined based on literature and the available site boring samples. These properties included the internal friction angle (), undrained shear strength (c), cohesion factor (), and the unit weight of the dry and moist soils ("). Using these findings, along with the principles for deep foundations design, the pile group and caisson properties were determined.

Technical Design

Technical designs were carried out based on load transfer mechanism by evaluating side frictional resistance and end bearing capacity. Assumptions were made in order to normalize the comparison between the two foundation options. The factor of safety (FS) for both structures was given a value of three. This value is the lowest of the design allowable ranges in order to avoid a conservative design. The same factor of safety was assigned to both alternatives to prevent bringing any discrepancies, therefore increasing quality of the comparison. A dead load of 600 kips and a live load of 400 kips were applied on both alternatives. The idea was to see the behavior and performance for both foundations under especially high loading cases so that the comparison would provide better results. Also, it was assumed that the loading is purely concentric meaning that there will be no moment applied. Therefore eccentricity for both cases was given a value of zero. The total capacity of piles and the caisson was as a result of skin friction and the toe bearing resistant. Since the coefficients of friction are the same for steel and for concrete, and both foundations are to be the same depth, the size was a key factor for the resistance. A detail step by step procedure of the calculation of the foundation skin friction and tore bearing resistance for both alternatives was based on Coduto (2001). The final design of the piles was a group of 14 pipe piles with an outside diameter of 20 inches and a wall thickness of 0.375 inches. The caisson’s final design was a 3 foot diameter shaft with a 4 foot high bell and an 8 foot diameter at the bottom. Both the piles and the caisson had a length of 55 feet. Similarly, the total capacity of 1040 kips and 1020 kips, respectively, was obtained for pile groups and the caisson system. In addition, both foundation alternatives resulted in settlements below one inch, therefore they are satisfactory. No excavation or ground improvement was allowed for this study. This is kept similar to avoid any further confusions and discrepancies. Once the technical design proved to be satisfactory, calculations to determine the amount of materials required were performed (Table 1).

Table 1. Material Assemblies for Foundation Systems in SimaPro. Foundation Weight Distance Diesel Fuel Electricity Type (tons) (miles) (Gallons) (MJ) Assembly 180 4 Piles 27.6 210 Recycle 269 Assembly 22.1 4 Caisson 33.2 30 Recycle 57.7

ICSI 2014: Creating Infrastructure for a Sustainable World 624 © ASCE 2014

For the piles, on the steel for the actual piles was taken into consideration, therefore ignoring the materials required to build the pile cap. For the caisson, concrete and integral reinforcement was taken into consideration. This included the longitudinal and spiral reinforcement to increase the accuracy of the results. A total volume of 124 ft3 of steel was used for piles construction while the caisson required about 7.8 ft3 of steel and 462 ft3 of concrete.

Sustainability Assessment

Sustainability assessment is based on the widely used triple bottom line: environment, economic and social dimensions. When designing any system, any structure or product, careful attention should be given to each step of the design process since each decision made will always have an impact to the environment, economy and the society as well. The main idea is to conduct an assessment on each of the two foundation designs previously mentioned. The environmental impacts of these two designs were studied using SimaPro 8.0.1. The two different scenarios were compared knowing the quantities of materials, energy required for each process and the equipment necessary to complete each mission. SimaPro encompasses various methods to evaluate environmental impacts of a given system; out of which, three methods: TRACI, Eco-Indicator-99, and BEES are commonly used. In this study, the impact assessment was performed using Eco-Indicator-99 method which revolves around environmental damages of three categories: Human Health, Ecosystem Quality, and Resources. Each damage category consists of a number of impact subcategories all measured in kPt (kilo points). This structure facilitates interpretation of the results, allowing analysis of the data separately for each damage category without applying any subjective weighting. Once the life cycle assessment is determined, economic evaluation of each foundation is carried out using overall system costs (e.g. material & excavation cost, transportation cost, costs associated with drilling/driving, splicing and foundation placing). Thereafter, social aspects regarding both foundation systems were evaluated. In order to achieve this, it was necessary to analyze how both design alternatives would interact with the people and its surroundings. Three main issues were discussed, health and safety, well-being, and satisfaction. For this specific study, only actual foundation was taken into consideration ignoring any building that could be supported by the foundations.

RESULT AND DISCUSSION

Sustainability Assessment

Environmental Sustainability

As mentioned, Eco-Indicator 99 was used to assess the environmental impacts of both foundation systems. Figure 2 shows the environment impact assessment due to various impact categories using Eco-Indicator 99 V2.08 method for both foundation systems. Higher percentage represents more adverse environmental ICSI 2014: Creating Infrastructure for a Sustainable World 625 © ASCE 2014

impacts. Based on the Fig.2, it can be seen that how the piles-model is, for the most of the aspects, almost twice as likely to have a negative impact on the environment as the caisson-design. For example, if we look at global warming, we realize that there is a 90% higher damage potential associated with piles as compared to the caissons.

Figure 2. Impact characterization of different variables for selected foundation systems, Eco Indicator

Figure 3 shows the damage potential in three different sections: Human Health, Ecosystem Quality and Resources. It is implied from the result that pile group has a higher damage potential all across the board. For instance, looking closely at the human health section of the graph, we can appreciate that the piles have 5.25 points where as the caissons gets 3.2 points; the higher the points the higher the damage potential. The damage potential for the piles was 40% more than the caisson.

Figure 3. Damage assessment for different foundation systems using Eco- Indicator 99 Method

ICSI 2014: Creating Infrastructure for a Sustainable World 626 © ASCE 2014

Similarly, Figure 4 shows the actual energy demand for different foundation systems obtained using Eco-indicator method. It is noted that the energy demand is mainly derived from various environmental impact categories (Fig. 2), such as, climate change, ozone layer, eco-toxicity, acidification and fossil fuels, human health, ecosystem quality and resources. Based on the results, it is cleared that fossil fuel contributed the most to energy demand for both foundations and piles require more energy than the caisson. In addition, it is important to remember that manufacturing steel requires a great deal of energy. Furthermore, shaping the steel piles takes even more mechanical work. As a summary, for the Caisson, about 80 gallons of fuel are needed where as for the Piles about 480 gallons are needed.

Figure 4. Energy requirements for different foundation systems using Eco-Indicator 99 Method

Figure 5 shows the single score results for two foundation systems as a result of different environmental impact classes. Caisson system scores a value of 1.4 kilo point (kpt) while the piles model scores 4.8 kpt. It is implied that the Caisson system has about a 60% less damage potential than the Piles model. Therefore, we can easily conclude that the Caisson model is definitely a better choice as supposed to the Piles- model if we are concerned with the damage potential to human health, ecosystem quality, and natural resources. Moreover, caisson is more environmentally sustainable than piles. ICSI 2014: Creating Infrastructure for a Sustainable World 627 © ASCE 2014

Figure 5. Environmental impact (single score) for different foundation systems

Social Sustainability

First, the issues of health and safety were evaluated using streamlined life cycle assessment (SLCA) health & safety matrix as shown in Figure 6. This evaluates the concerns of physical, chemical, shock, ergonomic, and noise hazards over the entire life cycle of both design alternatives. The life cycle consisted in raw materials excavation, product manufacture, product delivery, construction, field service and disposal of the foundation. Each element of the matrix received a rating ranging from 0 to 4 along with its assigned color code. In other words, the higher the rating, the higher the safety of the design. Due to the fact that there are no clear defined limits on the boundaries of the scale, these assessments were subjective and were based on our own engineering judgment. For example, there is no defined limit between what would be undesirable hazard and tolerable. Comparing the matrixes for each design alternative, it was determined that the caisson produced better results scoring an 82.5% unlike the pile which only scored an 80.3%. The two following tables show the actual matrixes along with its scoring system. Thereafter, the comfort and well-being was examined. For this the working conditions were considered for both alternatives separately as shown in Figure 7. Another set of matrices were assembled evaluating the diversity, work unions, safety, child labor, community involvement, accessibility, time invested and wages over the life stages of material excavation, product manufacture, construction and disposal. Again, analyzing results showed that the caisson obtained a higher score of 69% unlike the piles which only scored a 65.6% showing that the caisson is a better design alternative.

Figure 6. SLCA and Safety Matrix for two-alternate deep foundation systems

Finally, once both design alternatives are implemented, an evaluation of the satisfaction would be the next step. One last matrix was assembled for both design alternatives, which is shown in Table 2. For this, there was a focus on the functionality, maintenance, space occupied, architectural, and service life for both designs. Both designs obtained favorable results in all categories, except piles in the space occupied and architectural issues. This is because the number of piles is too high that it requires a large pile cap to properly transfer the load from the column to the piles. In this case it requires a pile cap of 16.5 ft X 14.66 ft rectangle. With such relative size, it could interfere with the accommodation of other structural members in the building, such as neighboring columns, requiring a modification in the building layout. Therefore, the caisson obtained a higher score in satisfaction.

Figure 7. Working condition matrix for two-alternate deep foundation systems ICSI 2014: Creating Infrastructure for a Sustainable World 629 © ASCE 2014

Table 2. Design Satisfaction for Piles & Caisson Caisson Piles Functionality 4 4 Maintenance 4 4 Space Occupied 4 2 Architectural Aesthetic 4 2 Service Life 4 4 20/20 16/20 Column Score 100 % 80 %

Economic Sustainability

The economic aspects of the two evaluated alternatives included the purchase, transportation, and construction costs. The rates of these were found at several online suppliers and construction databases. The driving of the piles; and the drilling of the caisson, were given at a rate per vertical linear foot (VLF). For the splicing of the piles; and excavating the bell shape at the bottom of the caisson, the rate was listed for each unit. The piles were driven at a depth of 55 feet. Since the PP 20” x .375” came at a maximum length of 50 feet, splicing was required for all 14 piles. The total construction cost was calculated to be $43,461 at $50.0/VLF. To purchase the units, the rate of $595/metric-ton was multiplied by the weight of steel. The volume and weight were related by the density of steel. The price of 14 piles was $16,410. The caisson was also driven at a depth of 55 feet and required reinforcement and special excavation of the bottom bell. The price to drill the bell shaped shaft and fill it with concrete was calculated to be $10,221 at $158.62/VLF. The price to purchase the concrete and rebar was $4,208. After estimating the purchase and construction costs, it is noticeable that the piles costs stand out with four times those of the caisson; this is due to the fact that there are 14 individual piles with a splice for each. The caisson was much cheaper because it is a single unit. In addition, the transportation costs were assumed to be part of the purchase cost since it was nearly impossible to get an accurate estimate; and to avoid any possible discrepancies in the side-by-side comparison of these alternatives.

CONCLUSION

In this study, two commonly used deep foundation systems were assessed based on the three pillars of sustainability: environmental, economic and social aspects. Piles and Caisson were selected for sustainability evaluation based on site- specific data pertaining to General Chicago area over their entire design life period. SimaPro was used to perform life-cycle assessment of two alternate deep foundations and based on the results, it was concluded that caisson system would be more environmentally sustainable than piles. The piles were the leading contributor to the negative impact on every category for the Eco Indicator 99 method causing 60% more damage to the environment. The amount of steel in the piles required high ICSI 2014: Creating Infrastructure for a Sustainable World 630 © ASCE 2014

energies to extract, mil, and form. Furthermore, the 14 piles required high energy to construct compared to the single drilling and placing for the caisson. Similarly, both economic evaluation and social impact assessment proved caisson foundation to be more sustainable, since, costs associated with the purchase, transportation and driving of caisson are around 4.2 times cheaper than that of piles. This was because the number of pipe piles required to achieve the desired capacity was far too many and that drove the high costs. However, social sustainability can be subjective and vary from one project site to another. Overall, this study shows the approach that can be followed for the design of sustainable foundation systems, or in general built infrastructure systems, in civil engineering practice.

REFERENCES

Coduto, D. P. (2001). Foundation design principles and practices 2nd Ed., Prentice- Hall, New Jersey. B2-Consultants LLC. (2014). “Free Construction Cost Data.” http://www.allcostdata.info/detail.html/023664700/Pile,-steel,-pipe,-splices,- not-in-leads-18%22-dia (March 4, 2014). B2-Consultants LLC. (2014). “Free Construction Cost Data.” http://www.allcostdata.info/detail.html/023664100/Pile,-steel,-pipe,-50'-L- 18%22-dia,-59-lb/LF,-no-conc (March 4, 2014). ICSI 2014

CREATING INFRASTRUCTURE FOR A SUSTAINABLE WORLD

PROCEEDINGS OF THE 2014 INTERNATIONAL CONFERENCE ON SUSTAINABLE INFRASTRUCTURE

November 6-8, 2014 Long Beach, California

SPONSORED BY Committee on Sustainability of the American Society of Civil Engineers

EDITED BY John Crittenden Chris Hendrickson Bill Wallace

RESTON, VIRGINIA