Geotechnical Engineering Services
PROJECT MANAGEMENT | SITE INVESTIGATION AND TESTING | ENGINEERING SERVICES | ROAD AND PAVEMENT DESIGN | PILE DRIVING ANALYSIS
PROJECT MANAGEMENT
Project Assessment
Often the most important aspect of geotechnical engineering is a clear understanding of the problem. An initial consultation would typically include meeting with the client plus a brief information review or site walkover. This can often help steer the project in the right direction early, before costly design and construction begins. Clearly laying out a path and options at this stage helps the client make informed decisions and better understand their project requirements.
Construction Monitoring
We can provide construction services including Quality Assurance / Quality Control (QA/QC), testing, contract administration, part and full time site monitoring for owners, all levels of government, and contractors.
BCBC Letters of Assurance
“Schedule B / Schedule CB”. We provide Letters of Assurance for geotechnical aspects of the project, as required by municipalities issuing the building permit.
SITE INVESTIGATION AND TESTING
Site Investigation
Site characterization using drilling, testing, and other methods. We have experience using many methods including drilling (Auger, Cone Penetration Testing (CPT), Mud/Air Rotary, Diamond Coring, Sonic), Test Pits, Dynamic Cone Penetrometer. Limited access, marine, heli, tight areas, sensitive/secure locations. We can assist with access planning, coordinating the utility checks, and permitting.
Site Testing
Earthtec is equipped for a wide array of geotechnical testing services: Pile Drive Analysis (PDA), Vibration Monitoring, Plate Load Testing, DCP, Benkelman Beam, Nuclear Densometer, and others.
ENGINEERING SERVICES
Ground Improvement
Ground improvement can be used as a means to construct at sites with difficult ground conditions such as compressible, weak, or liquefiable soils. Earthtec has experience with preloading, rapid impact compaction, and other techniques normally used in the Lower Mainland.
Instrumentation
We work with our drilling subcontractors to design and install geotechnical instrumentation for our projects and clients as needed. This may include standpipe/electric piezometers to measure groundwater levels, slope inclinometers, settlement gauges, thermistors, and other installations.
Foundation Design
Due to the variable ground conditions of the lower mainland, a number of foundation types are regularly used. For more competent bedrock and soils, concrete spread footings are the conventional standard. Many sites with poorer conditions, however, require other solutions including raft (mat) foundations, and deep foundations such as steel, concrete or timber piles which are either driven, drilled, or cast into place as well as other specialized systems. Designs normally must take into account seismic hazards, including assessing liquefaction potential so that structural designers can take into consideration the site’s expected response under an earthquake event.
Retaining Walls and Engineered Slopes
Frequently these are part of construction in this region to increase usable spaces and stabilize slopes. Construction in the Lower Mainland is often in challenging and steep areas, as developable land is limited. Typical retaining solutions include MSE, concrete cantilevers, and gravity systems, and engineered slopes typically consist of controlled fill placed with reinforcement to increase the inclination at which the material can be stable.
Landslide Hazard Assessments
Legislated Landslide Hazard or “Geohazard” Assessments have been a part of the BC Building Code since 2006, introduced to address safety for land development projects such as new subdivisions. These studies help identify natural hazard risks to a property or as a result of new construction. We work with local governments to understand their requirements and acceptable risk levels, to ensure that the owner receives a practical Landslide Hazard Assessment for their project.
Stormwater Management
Infiltration design (i.e. trench drains, rock pits), site grading, reviewing the removal of perimeter drains from design where possible.
Temporary Works
Earthtec can provide cost-effective, safe temporary works design for construction. This can include excavation reviews, excavation support/shoring design, retaining walls, crane foundations, and value engineering to help develop suitable Specifications and testing and monitoring approaches.
ROAD AND PAVEMENT DESIGN
Development projects large and small typically require roadway design in some capacity. Based on a site investigation our experienced personnel will deliver a design for the road structure based on the existing soil conditions. Depending on the municipality or type of road being built, many factors will need to be considered. Visual pavement condition surveys and Benkelman Beam testing of existing road structures may also be employed in determining roadway repairs.
PILE DRIVING ANALYSIS
Dynamic load testing using Pile Driving Analyser (PDA) equipment is a high-strain non-destructive load test method which can be performed during or after pile installation using conventional pile driving equipment. This test can be applied to steel, timber and concrete piles. The PDA was developed primarily to assist in evaluating the ability of pile-driving equipment to install piles to the desired depth without damage. It measures driving stresses and is therefore useful to prevent pile overstressing. The ability to predict load resistance also can be used to assess variation in pile resistance across a site and hence provide guidance for designers.
PDA equipment calculates the velocity and force signals obtained from accelerometers and strain transducers attached to the pile during driving. This data is analyzed using CAse Pile Wave Analysis Program (CAPWAP) software to calculate the pile capacity. CAPWAP is a signal-matching procedure which, based on pile toe force and velocity measurements during hammer impact, extracts static and dynamic soil resistance parameters for pile shaft and pile toe. PDA testing can be undertaken during initial driving or during re-strike drives after allowing soil set up on the pile for a suitable period of time. PDA testing is undertaken in conformance with current ASTM Standard D4945.
PDA TESTING AND CAPWAP BASICS
There are three basic types of PDA tests on driven piles:
- Testing of a pile during the full installation.
- Testing of a pile at the end of the initial drive (EOID)
- Testing of the pile several days after the initial drive (i.e. “Re-strike”).
Testing during the full drive of a pile will provide a complete record of the pile installation, including the ability to assess initial capacity and pile integrity along the full length of the installed pile. When used in conjunction with the PDA data collection program, iCAP allows for immediate analysis during initial drive conditions. Testing at the end of installation only verifies the EOID resistance. It should be understood that while PDA testing is relatively unobtrusive, some loss of production may be experienced during testing.
In many soil profiles, the pile resistance at EOID is unlikely to be the ultimate capacity for a pile. Some soils will experience a temporary decrease in skin friction due to remoulding of the soil during driving and can produce excess pore pressures around the pile shaft which allows for easier installation. Dissipation of pore water pressures leads to an increase in soil strength resulting an increase in pile resistance. The amount of time required for this resistance gain or soil setup will depend on the type and sensitivity of the soil. Generally, most of the strength will be regained between 2 to 4 weeks after the pile is installed. The setup can be measured by comparing the PDA capacity results from EOID and Re-strike testing. In some soils, the setup can be in the order of 50 to 100 percent.
BENEFITS AND ECONOMICS OF PDA TESTING
Using PDA allows the end user to solve problems early in the testing program which may avoid significant delays and complications. In addition, PDA provides various parameters during pile installation including the ability to detect poor hammer performance by monitoring impact stresses during pile driving which develops better installation procedures. The information that PDA testing can provide includes verification of pile capacity at the time of testing; data for developing termination criteria for design loads; assessment of energy transfer and driving efficiency; measurement of stress levels induced on the pile during driving; and assessment of pile integrity and possible damage.
Current building codes reference pile foundations designed based on the Ultimate Limits State (ULS) methodology. Ultimate geotechnical resistance parameters are factored in using the Geotechnical Resistance Factors (GRF) listed in the National Building Code of Canada. For conventional pile design, a GRF of 0.4 is required, but with PDA testing, the GRF may be increased to 0.5. This means smaller or shorter piles may be used to carry the same loads as conventionally designed piles. This translates into direct savings in the order of 20 percent on pile foundation materials and associated installation costs. Costs may be even greater with the elimination of splices. Ultimately, PDA allows for more piles to be tested versus static load testing alone leading to significant cost savings. Published literature and results of PDA show that significant piling project cost savings can be achieved through the use of a well-planned PDA testing program.