Q&A: What are some major traffic engineering design challenges in the Middle East?

The Middle East’s dependence on private automobiles as the major mode of transportation creates unique challenges for new development projects in the region. Not only does it require an efficient design of roadway infrastructure to process high traffic volumes, but also requires a smart design of space to provide on-site parking spaces. A majority of developments in the Middle East are mixed-use projects that have a wide array of users including residents, professionals, retail customers, restaurant patrons, and hotel guests. The traffic and parking demand generated by this diverse user base varies throughout the day creating challenges for traffic engineers. It is important to design a traffic circulation and parking system that will not consume a lot of space while at the same time is efficient in processing the project’s peak traffic and parking demand. This can be achieved by working closely with the master planners and architects early on in the design process to identify locations for siting connections with surrounding roadway networks and highway ramps, and developing an efficient parking layout and internal site circulation plan.

Four-Seasons-Bahrain-Bay[1]

Langan provided transportation and parking services for the design of the iconic Four Seasons Hotel in Bahrain. (Photo Credit: SOM | © Future Brand)

With the increase in transit infrastructure developments in the Middle East, specifically in Saudi Arabia, it is important to consider the changes in commuting patterns in the future. A shift in commuting from private automobiles to mass transit will result in decreased traffic and parking demand and should be accounted for in future traffic planning estimates. Given that land is at a premium, specifically in large cities like Jeddah and Riyadh, a lower parking demand will consequently require less parking, freeing up space for more financially viable uses. Therefore, as a first step, it is critical to conduct due-diligence to obtain information on infrastructure work as well as potential future development projects for the area.

Like most other urban regions of the world, there is a growing shift in the Middle East to create walkable neighborhoods that serve as cultural hubs — entertainment, dining, and leisure destinations. Many mixed-use projects in the Middle East are now incorporating designs emphasizing safe and efficient walkable environments for the community. Currently, we are working closely with master planners and landscape architects to design an inviting walkable public space for a large-scale confidential mixed-use project in Saudi Arabia. As part of this effort, Langan is assisting the design team in establishing unique pedestrian connections for retail, hospitality, entertainment, and residential uses within the site.  One important aspect of this design process is to strike the right balance between safety and functionality. This is achieved by applying design techniques such as removing excess width from traffic lanes, providing space for pedestrian refuge islands, and adding landscaping in a non-linear pattern to reduce opportunities for speeding and aggressive driving, while at the same time enhancing safety for all users.

About Adnan Pasha, PE
As Director of Transportation and Traffic Engineering at Langan International, Adnan has over 18 years of international experience with transportation, real estate development, site/civil engineering, Transit Oriented Development (TOD), project management, and finance.

 

Q&A: Aren’t sediments just wet soils? Is sand capping appropriate to isolate contaminated sediments?

Sediments are NOT just wet soils.

Sediments deposited underwater in modern geological times are categorically different than wet soils.  Ignoring those differences could lead to major errors in remedial investigations, evaluation of regulatory requirements, and assessment of environmental liabilities.  These differences may include:

  • High susceptibility to water transport (e.g. tides, storm induced flows)
  • Temporal variations existing over hours to decades
  • Large spatial heterogeneities, and
    • Low percent solids
    • High organic carbon
    • Wide range in particle sizes
    • Strong biological influences
    • Debris
  • Contaminant reservoirs in many forms
  • Complex geochemical changes over short (centimeter scale) vertical intervals
  • Ground water and surface water pathways
16 minutes later with 2, 4, and 6-inch sand caps

16 minutes later with 2, 4, and 6-inch sand caps; and sharp interfaces (<2 millimeters)

Soft, fluffy sediment

Soft, fluffy sediment

Sand caps can be utilized to isolate contamination even in very soft “fluffy” sediment.

The key to designing and constructing sand caps on top of very soft sediment is to use fine sands to minimize initial density differences and to add the sand very gently.  Soft sediment is easily disturbed and can be displaced in mud “waves” when sand is introduced quickly in large volumes or clumps.  These clumps impact the soft sediment as large single “stones” instead of a gentle rain of small particles.  The following figures illustrate the very sharp interface (<2 millimeters) that can occur between a sand cap and very soft sediment using a well-designed and engineered approach to sand placement.

About Rick Beach
Rick Beach brings nearly 45 years of experience with sediment projects and programs where he has managed, directed, and implemented site investigations, data gap evaluations, feasibility studies, remedial designs, remediation services, project optimizations, third-party reviews, potentially responsible party (PRP) identification, litigation support, and expert testimony.

Q&A: Langan has provided geotechnical services on a number of projects in the Mission Bay neighborhood of San Francisco; what makes The Exchange project different?

The Exchange, Mission Bay, San Francisco

The Exchange, Mission Bay, San Francisco

Mission Bay is a reclaimed area of San Francisco that was previously a shallow bay. The site was reclaimed in the late 1880s and early 1900s using a variety of soil materials and debris, including debris from the 1906 San Francisco earthquake. The fill was not properly placed and is typically potentially liquefiable. Underneath this fill is weak, compressible marine clay known as Bay Mud.

The Exchange project is different because we used an alternative foundation type that had never been used in Mission Bay. Strong foundations are particularly important in this neighborhood because of its poor soil conditions.

With these poor soil conditions, most buildings in Mission Bay are being supported on deep foundations that gain capacity in either a dense sand layer, which is present in part of the area, or in bedrock.

Driven piles have typically been the most economical foundation type to support the buildings in Mission Bay. However, driven piles could not be used for The Exchange project because of concerns of noise and vibrations during installation that would impact the nearby UCSF Medical Center.

Langan worked closely with the owner, structural engineer, and general contractor to evaluate alternative pile types. The team asked us to participate in foundation subcontractor interviews so that we could provide input on the different proposals and ask pertinent questions.

Malcolm Drilling proposed a foundation type that had never been used in Mission Bay: rock socketed drilled shafts. With shallow groundwater, poor fill, and weak clay, drilled shafts were not typically feasible in this neighborhood; however, The Exchange site is near the shoreline of the original bay, and bedrock becomes shallower and Bay Mud becomes thinner toward the bay margin.

To evaluate the constructability of the drilled shafts and determine their capacity, Langan drilled the test location, including 30 feet of rock coring. With information we gathered from the test location, the team asked Malcolm to design a test pile, including Osterberg load cells for load testing.

The drilled shaft was successfully installed and the load test provided data for design of the foundation — which resulted in cost savings to the owner. The key to moving forward with this foundation type was good communication, strong relationships, and productive meetings among the design and construction teams.

Answer provided by Lori Simpson, PE, GE, Principal
Lori Simpson has over 26 years of experience in providing geotechnical investigation, design, consultation, and construction observation services for a variety of geotechnical engineering projects, especially sites with reclaimed land. Her projects include commercial and residential buildings, high-rises, infrastructure improvement for new developments, sports facilities, and investigations for seismic upgrades.

 

Q&A: Why is groundwater a major issue in the Middle East, despite many projects being located in desert environments?

Langan provided dewatering services for the Four Seasons tower on Al Maryah Island in the UAE.

Langan provided dewatering services for the Four Seasons tower on Al Maryah Island in the UAE.

Dewatering the Desert 
Despite being in a climactic environment where summer temperatures can reach in excess of 120 degrees, groundwater is generally very close to the surface in many developed cities throughout the Middle East (Dubai, Abu Dhabi, Bahrain, Doha, and Jeddah, in particular).  The nature of the relatively high permeability, near surface geology in these areas means that up to five kilometers from the coast, there is a often direct hydraulic connection between groundwater and the adjacent sea. Typically in these areas, groundwater is within two meters of the surface.  This means that almost every basement excavation and a large percentage of excavations for utility lines require some form of temporary dewatering to allow for construction in a dry environment.  For shallow excavations in sand (up to around four meters below the water table), we typically utilize drilled or jetted wellpoint systems.  For deeper excavations, a combination of staged wellpoint systems, or deep wells, are utilized, to draw the groundwater down anywhere from five to 25 meters.

Specific issues arise when we attempt to dewater areas where solution features exist, which is particularly problematic in certain parts of Abu Dhabi where layers of karstic gypsum exist.  These solution features are irregularly distributed and flow rates can be extremely high, requiring large scale pumping to allow sufficient groundwater drawdown.  In many cases, long term pumping can actually exacerbate the groundwater flows. Increased flows gradually increase groundwater velocities which causes further erosion of the gypsum karst, until the flow volumes effectively become unmanageable without resorting to ground treatment (i.e. grouting) to reduce flows to manageable levels.  Cut-off walls are often ineffective in reducing flow volumes as flow is effectively vertical (rather than horizontal) through the base of the excavation.

The most notorious area in the Middle East with respect to groundwater issues is Jeddah, particularly along the ‘Corniche’ north of the city.  A combination of proximity to the Red Sea and the presence of highly permeable porous coralline limestone at relatively shallow depth causes major issues when trying to control groundwater flows into a typical basement excavation.  For example, it is common in Jeddah for a 50 x 50 meter footprint site with three basement levels to have groundwater flows as high as 5,000m3 per hour (1.1 million gallons per hour) without some form of grout-based ground treatment (again cut-off walls are largely ineffective as most flow is vertical rather than lateral).  Even if pumping capacity is available, there are major issues associated with both water treatment and discharge of such large volumes of water.  These issues among many others, certainly make life as a geotechnical engineer interesting in the Middle East.

About Paul Gildea
Paul  is a geotechnical specialist with 27 years of experience as both a specialist contractor and consultant in the UK, Ireland, Hong Kong, China, Australia and throughout the Middle East. He currently manages international projects for Langan, primarily in the Middle East, Asia, and Africa with specific expertise in the design and construction aspects of foundations for high-rise structures and deep basements.

Q&A: How did the integration of the site/civil, geotechnical, and environmental engineering bring added value to the Bayshore Technology Park project?

About the Project
Bayshore Technology Park was built in the late 1990s on an 85-acre waterfront property that was a former landfill from the 1940s to 1970s. Located in Redwood Shores, the Park contains 20 office buildings that are supported on deep foundations, which extend through the landfill and into bay mud (thick deposits of soft, unconsolidated silty clay).

Bayshore Technology Park, Redwood City, CA

Bayshore Technology Park, Redwood City, CA

The original design anticipated future settlement of the site due to the degradation of landfill waste and the consolidation of the bay mud. Our services address American with Disabilities Act (ADA) compliance to resolve differential settlement between the building structures and walkways leading to the buildings.

Solutions to Challenges
The integration of our site/civil, geotechnical, and environmental disciplines is key to addressing the main challenges facing the site in an efficient and cost-effective manner. Surface slopes and utilities (site/civil), excavation and grading (geotechnical), and clay cap and landfill gas building protection systems (environmental) are all intertwined issues that demand a collaborative design approach.

Our multidisciplinary engineering team delivers constant responsiveness to clients, as all three disciplines are communicated via a single point of contact: our multi-disciplined project manager. Client communication during the design process is critical — especially on projects such Bayshore Technology Park, where the final product needs to be functional, cost-effective, and aesthetically pleasing. The multi-disciplinary team works together closely on each improvement project to develop new designs to address varying situations.

On several projects, our team designed and implemented a unique “floating” footing for the new ADA stairs and ramps. Through ongoing monitoring and maintenance, this footing will prolong the life of the improvements by separating the structure from site settlement. Also, the removal and replacement of existing soil with lightweight fill on many projects reduces the surface weight over the landfill and subsequently reduces future site settlement.

Answer provided by DJ Hodson, PE, LEED AP, California Site/Civil Practice Leader
DJ Hodson is a principal in Langan’s San Francisco office and has over 20 years of national and international site/civil engineering experience. He provides expertise in master-plan engineering, site analysis and design, utility assessment and design, hydrologic and hyrdraulic analysis and design, stormwater-management analysis and design, streetscape, waterfront and redevelopment site projects, as well as geotechnical, traffic, and environmental engineering and permitting.

Q&A: Langan designs foundations for some of the tallest towers around the world. How does the firm provide its expertise in so many locations?

Kingdom Tower, Jeddah, KSA

Kingdom Tower, Jeddah, KSA

Langan’s core values of technical excellence, practical experience, and client responsiveness are desirable qualities that export well around the world. The technical excellence starts with a roster of geotechnical engineers that are trained at world class universities. This deep knowledge of soil mechanics, engineering geology, and foundation design allows us to apply fundamental and advanced engineering principles in any type of geology.

As for practical experience, it is essential when adapting to local construction equipment, workmanship, and materials. Many times, foundation options available in North America are not economically feasible in emerging economies.  We find that labor is less expensive compared to construction materials, where the opposite is often true in the U.S.

Last is client responsiveness. We find, especially in emerging markets, that few design teams can outpace Western project teams from concept design all the way through contract documents. Our international clients welcome this accelerated pace of work, because no matter where you are, time is money.

About Alan Poeppel, PE
Alan has over 20 years of diversified experience in geotechnical engineering projects involving the management, investigation, instrumentation, design, and construction of projects in the United States and overseas. He has spearheaded  a number of high-rise “super” towers projects in India and the Middle East including Kuala Lumpur City Center and the 1,000-meter-tall super structure, Kingdom Tower, in Saudi Arabia.

Q&A: What are the design considerations for landfill gas mitigation during site redevelopment?

Over the past two decades, the United States has seen a substantial increase in development on closed municipal-waste landfills. The construction value of these projects could be substantial in addition to the numerous end-use benefits such as tax revenues and new jobs. Redeveloping landfills is particularly challenging not only because of the issues associated with cleanup, but also because of the environmental and geotechnical issues of building on refuse. Landfill gas containing elevated levels of methane poses a significant risk of fire and explosion. Other landfill gases such as sulfur-based corrosives like hydrogen sulfide and volatile organic compound vapors pose significant exposure risks to human health, safety and the environment. Hydrogen sulfide can also cause significant odor issues.

Langan performed all aspects of monitoring, remedial planning, and landfill closure for this Contra Costa Waster Service NPL site.

Langan performs all aspects of monitoring, remedial planning, and landfill closure for various landfill sites.

To be effective, design strategies for mitigating landfill gas, must incorporate the site’s architectural, structural, and geotechnical features. Applying pilot testing and pneumatic air-flow computational modeling tools is good engineering practice to determine key parameters, including air intrinsic permeability of the refuse, radius of influence, well network, desired air-flow rates, vacuum propagation, and pore-air volume exchanges, for cost-effective designs and more reliable predictions of the mitigation system performance. Detailed evaluation of long-term remedial benefits, potential refuse settlement, seismic hazards, fire and explosion hazards, odor problems, and corrosive-gas impacts on the system constructability and performance should also be performed during the design phase.

Although redevelopment of landfills holds great potential, the means and methods used to design and implement gas mitigation systems are such that human health, safety and the environment are protected for the life of the project. Our ability to effectively remediate such sites means that redeveloping closed landfills for sanctioned use will continue for years to come.

About Omer Uppal, PE 
Omer has more than 15 years of experience in the environmental remediation and consulting industry. As Senior Project Engineer at Langan, he is responsible for soil, sediment, and groundwater investigations, field pilot testing, groundwater flow and contaminant transport modeling, risk-based closure and remedial strategy development, and full-scale engineering design. He is experienced in various remedial technologies including in-situ bioremediation, soil vapor extraction (SVE), multi-phase extraction (MPE), air sparging, chemical oxidation, treatment barriers, vapor intrusion, mitigation, and landfill gas mitigation systems.