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Intro to CPTu: What Can You Learn From Pore Pressure Data?

The most basic CPT tests classify soil based on tip resistance and sleeve friction measurements. In coarse soils and shallow testing depths, this data may be sufficient to accurately characterize the soil behavior. However, most modern CPT cones incorporate a third measurement: pore water pressure. What does this measurement mean and how can it add to our understanding of soil behavior? Pore pressure is simply a measure of the in-situ groundwater pressure, i.e. the water pressure in the “pores” between soil grains. This data is used to determine the compressibility and permeability of the soil, as well as indicating groundwater conditions. It is used to correct or “normalize” the sleeve friction and tip resistance readings in the presence of in-situ moisture and overburden stress. This is especially important in soft, fine-grained soils where in-situ moisture takes longest to dissipate, and in tests at depths greater than 100 feet. A CPT cone that is equipped with one or more pore pressure sensors is called a piezocone, and a CPT test using a piezocone is often indicated with the abbreviation CPTu. Piezocones may have between one and three pore pressure sensors, located on the cone (denoted u1), directly behind the cone (u2), or at the top of the friction sleeve (u3). Most piezocones for everyday applications use one sensor located at u2 (see image below). The pore pressure sensor consists of a porous filter (usually made of plastic resin), a small cavity of incompressible, low-viscosity fluid, and a pressure transducer. The filter and tubing between the filter and transducer must be fully saturated with fluid, usually glycerin or silicon oil, to ensure fast and accurate readings. The filter must be replaced frequently so that it does not become clogged with soil. The procedure for the CPTu test is slightly different than the [...]

By smadi66|December 2nd, 2019|Geotechnical Utah, Geotechnical Tennessee, Geotechnical Vermont, Geotechnical Pennsylvania, Geotechnical Virginia, CPT Data, Geotechnical Washington, Introductory, Cone Penetration, Soil Testing, Geotechnical Rhode Island, Geotechnical South Carolina, Geotechnical South Dakota, Geotechnical Texas|0 Comments

Using CPT Pore Pressure Dissipation Tests to Characterize Groundwater Conditions

In a previous blog, we talked about how pore pressure data is used to correct and adjust soil behavior type characterizations – but this is only one application of this important and revealing information. Pore pressure data can also be used to estimate the depth of the water table and the direction and rate of groundwater flow. This information is useful both for site characterization and for geo-environmental and remediation applications. What is a Pore Pressure Dissipation Test? As a CPT cone is pushed into saturated subsurface soil, it creates a localized increase in pore pressure (denoted excess pore pressure, ui) as groundwater is pushed out of the way of the cone. In a pore pressure dissipation test, the downward movement of the cone is paused and the time it takes for the pore pressure to stabilize is measured. This stable pore pressure is called equilibrium pore pressure, uo. This information allows the user to identify important hydrogeologic features: The water table (or phreatic surface) depth is defined as the distance below the soil surface at which pore pressure is equal to atmospheric pressure. This can be roughly visualized as the level below which subsurface materials are fully saturated with groundwater. Especially in fine-grained soils, estimating the water table can be more complex than simply detecting moisture, since surface tension draws groundwater upwards, creating negative pore pressures. This is effect is called capillary rise. Very low or negative pressures can be difficult to measure precisely with the piezocone, which is primarily designed to measure high pressures below the water table. In this case, the water table depth can be calculated by the following formula: dwater = dcone – hw dwater = water table depth dcone = depth of piezocone hw = water head The water head, hw, is the height [...]

By smadi66|December 1st, 2019|Geotechnical Washington, Geotechnical West Virginia, Introductory, Cone Penetration, Geotechnical Rhode Island, Geotechnical South Carolina, Geotechnical South Dakota, Geotechnical Texas, Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia, Geotechnical Tennessee|0 Comments

CPT Dictionary: Soil Liquefaction

In our last blog, we discussed using the CPT to estimate the shear strength of soil, which helps gauge how soil will behave during changes in stress. One important application of this capability is the estimation of soil liquefaction potential, meaning the potential of soil to dramatically lose strength when subjected to changes in stress. Liquefaction is of particular concern in sandy, saturated soils. Shaking due to an earthquake or other sudden force causes the grains of loosely packed, sandy soils to settle into a denser configuration. If the soil is saturated and the loading is rapid, pore water does not have time to move out of the way of settling soil: pore water pressure rises, effectively pushing the soil grains apart and allowing them to move more freely relative to each other. At this point, the soil can shift and flow like a liquid—hence the name liquefaction. This dramatic reduction of soil stiffness and strength causes soil to shift under pre-existing forces—say, the pressure of a building’s foundation or the pull of gravity on a slope. The increased pore pressure also increases the force of the soil on in-ground structures such as retaining walls, dams, and bridge abutments. How can the potential for these effects be evaluated using the CPT? The subject is complex, as the wealth of research on the subject over several decades shows! Many approaches for determining cyclic liquefaction potential rely on the cyclic stress ratio (CSR), which requires a seismic analysis of the site. It expresses the ratio of the average cyclic shear stress in an earthquake of a given magnitude and the effective vertical overburden stress at the test site. CSR = 0.65(MWF)(amax/g)(σvo/σ′vo)rd Where: MWF = Magnitude Weighting Factor = (Magnitude)2.56/173 amax = maximum ground surface acceleration g = acceleration of gravity, 9.81m/s2 σvo [...]

By smadi66|November 29th, 2019|Soil Testing, Experienced, Geotechnical South Dakota, Geotechnical Texas, Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia, Geotechnical Tennessee, Geotechnical Washington, Geotechnical Wisconsin, Geotechnical Wyoming, Geotechnical West Virginia, CPT Dictionary, Cone Penetration|0 Comments

Seismic Averaging in SCPTu testing

Did you know that our CPTSND Data Acquisition program can average repeat seismic strikes? Once you have a strike on the screen, simply accept (retain) the strike and then add another strike of the same type ( A strike for example). This second strike will display below the first strike and when the second strike is accepted (retained) it will be averaged with the first strike and only the averaged strike will remain on the screen. If a third strike is added and then accepted (retained) it will be averaged with the result of the first two. (NOTE: Our software does not retain all the individual strikes- once they are averaged only the average is on file) Averaging strikes is recommended by some of the top GeoTechs in the nation!

By smadi66|November 29th, 2019|Geotechnical North Carolina, Geotechnical North Dakota, Geotechnical Oklahoma, Geotechnical Oregon, Geotechnical Rhode Island, Geotechnical South Carolina, Geotechnical South Dakota, Uncategorized, Geotechnical Tennessee, Geotechnical Ohio, Geotechnical Pennsylvania|0 Comments

Upcoming Tunneling Projects – Tunnel

2/10/2016 Upcoming Tunneling Projects CALIFORNIA Laguna Beach Tunnel Stabilization and Sewer Pipeline Replacement Approved by the South Coast Water District Board of Directors in 2010 and the City of Laguna Beach in late 2013, the Tunnel Stabilization & Sewer Pipeline Replacement Project (Tunnel Project) is a 100-year solution to protect the environment, local economies and neighboring communities. The project comprises two key components: Tunnel Stabilization: The District will enlarge the size of the tunnel from an average of 6 to 9 ft. This will ensure safer working conditions and greater access for future pipeline maintenance and repair. Permanent shotcrete lining and steel supports will be installed at several locations where required, replacing rotten timber supports and removal of loose rock that currently exist. Pipeline Replacement: The District will install a new 24-in. pipeline throughout the tunnel. The current pipeline – also 24 in. in diameter – will be encased in concrete, but preserved for redundancy and emergency use. The cost to repair the tunnel is estimated at approximately $90 million and will be funded through low-interest state loans, grants and the District’s general fund. Shortlisted tunnel contractors announcement was anticipated for 2014-2015 with request for bids expected in 2015 and NTP in 2015-2016. Los Angeles The North East Interceptor Sewer (NEIS) Phase 2A The North East Interceptor Sewer (NEIS) Phase 2A project is currently the northern extension of the NEIS Phase 1 project. The project will construct approximately 3.03 miles of 8-ft diameter sewer in tunnel and associated structures. The sewer will be constructed from the Division St. Shaft site, near the intersection of San Fernando Road and Cazador Street and terminate at the northern overflow parking lot for the Pony and Train Rides in Griffith Park, just north of the I-5 Griffith Park On/Off Ramps (I-5 Shaft Site) east [...]

World Tunnelling News

Jan 05, 2016 - Helsinki-Tallinn fixed link seems feasible Yle Uutiset Jan 04, 2016 - India awards large $1.5 billion road link contract India Times Jan 01, 2016 - Bangladesh to improve infrastructure BD News 24 Dec 30, 2015 - India's longest road link to open in July NDTV Dec 29, 2015 - India envisages first underwater link India Times - India Today Dec 29, 2015 - China opens longest lake crossing GB Times Dec 28, 2015 - Japanese court ruling on fatal ceiling collapse The Yomiuri Shimbun - Japan News Dec 28, 2015 - Shanghai completes 13th river link Shanghai Daily Dec 26, 2015 - Bids placed for Istanbul mega-project Daily Sabah Dec 25, 2015 - Complex Singapore road link delayed Straits Times Dec 25, 2015 - Ottawa LRT enters final phase Ottawa Sun Dec 22, 2015 - Rio Metro Line 4 needs more funding The Rio Times Dec 20, 2015 - Work starts on Auckland's City Rail Link Stuff.co.nz Dec 18, 2015 - Study looks at replacing old Baltimore rail link The Baltimore Sun Dec 14, 2015 - US transportation bill boosts Hudson rail project New York Times Dec 14, 2015 - Cost of Mumbai Metro Line 3 underestimated The Indian Express Dec 14, 2015 - Cologne LRT opens phase III Railway Gazette Dec 14, 2015 - Qatar progresses with rail infrastructure Doha News Dec 10, 2015 - Tunnelling to start on Shinkansen maglev line The Asahi Shimbun Dec 09, 2015 - Sweden opens its longest rail tunnel International Railway Journal Dec 04, 2015 - Barge launches Thames Tideway construction Tideway news release Dec 03, 2015 - Memorial ceremony for Sasago tunnel collapse Japan Today Dec 02, 2015 - TT2 recognised for work with the disabled Shield's Gazette Nov 30, 2015 - Group to lobby for Malta-Gozo fixed [...]

By smadi66|January 17th, 2016|Tunneling, Geotechnical Kentucky, Geotechnical Tennessee, Geotechnical Ohio, Geotechnical Illinois, Geotechnical Michigan, Geotechnical Missouri, St. Louis, Geotechnical Indiana|0 Comments

California highway landslide leaves vehicles buried – video

Aerial footage shows work crews clearing mud and debris following flash floods that left nearly 200 vehicles stuck in up to 5ft (1.5 metres) of mud. The Leona Valley, about 20 miles north of Los Angeles, saw extensive downpours on Thursday, with 3.58 inches (9 cm) of rainfall during a 30 minute period. Elsewhere in southern California, several roads were washed out and there were reports of motorists having to be rescued from torrential flooding

By smadi66|October 19th, 2015|Greenfield, Bloomington, Mishawaka, Terre Haute, Greenwood, Calumet, Shelbyville, Vincennes, Highland, Columbus, Portage, Hammond, Landslides, La Porte, Evansville, Louisville, Gary, Geotechnical Engineer Indiana, Lebanon, Fort Wayne, Geotechnical Kentucky, Carmel, Geotechnical Engineer Indianapolis, New Albany, Kokomo, Geotechnical Tennessee, Fishers, Geotechnical Indiana, Noblesville, Lafayette, Geotechnical Ohio, Brownsburg, Soil Testing, Plainfield, Michigan City, Geotechnical Illinois, Crawfordsville, Drilling, Seymour, Muncie, Geotechnical Michigan, Elkhart, Indianapolis, Westfield, Richmond, Geotechnical Missouri, Goshen, Anderson, West Lafayette, South Bend|Comments Off

Interstate 10 in California closed east of Coachella after bridge collapse

A 30-foot section of a bridge on the 10 Freeway in Desert Center east of Coachella co A 30-foot section of a bridge on the 10 Freeway in Desert Center east of Coachella collapsed Sunday, closing Interstate 10 indefinitely. The 10 Freeway was shut down from Desert Center to the Arizona state line as a result of the bridge collapse and heavy flooding, authorities said. llapsed Sunday, closing Interstate 10 indefinitely.Source: Interstate 10 closed east of Coachella after bridge collapse

By smadi66|July 22nd, 2015|Pile Foundation, Geotechnical Indiana, Construction Inspection Indiana, Geotechnical Kentucky, Geotechnical Tennessee, Geotechnical Ohio, Geotechnical Illinois|0 Comments

Sinkhole increases to 40 feet in Tennessee

Construction crews were trying to fill a massive sinkhole that began at 3 feet by 5 feet at Austin Peay State University’s Governors Stadium in Tennessee. Construction crews were trying to fill a massive sinkhole that began at 3 feet by 5 feet at Austin Peay State University’s Governors Stadium in Tennessee. The hole was first discovered near the football field’s end zone, where it meets the track, during a renovation project to replace the main stadium building about a month ago. The workers have since had to dig a larger hole, about 40 feet deep and 40 feet wide, to find stable bedrock. “We’re not going to skip any steps,” Mike Jenkins, the superintendent for Nashville-based Bell & Associates Construction,

By smadi66|May 2nd, 2015|Geotechnical Tennessee, Sinkholes|Comments Off