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Video illustrating liquefaction at the site Video play at ½ the speed that is was captured at. In areas were liquefaction took place there were mounds of sediment.
Project Examined Sedimentology and stratigraphy identified as quicksand. Site located south of the turtle mountains in Bottineau county indicated by the blue dot. The red dot is an aprox. Location of Minot. The Turtle mountains come down from Canada and strattle botno and rolette counties Project examined whether the liquefaction is the result of local geological features
The quicksand site is aprox. 3.8km east of botno and 2km south of the turtle mtns. The county is underlain by Pleistocene Coleharbor Group consisting of glacialy derived sediments. In the western part of the county the Pleistocene coleharbor group ranges in thickness from 61-76m, in the central part of the county it ranges in thickness from 15-30m thick, and in the NE part of the county where the turtle mountains are it ranges in thickness of 61-92m but in places 122-152m thick in the turtle mtns.
This is an areal view of the quicksand site along highway 5
The top left image is a personal photo taken facing N. towards the turtle mtns. Note the gradual upwards slope. The bottom right image is a personal photo taken facing E. near the center of the site. Note the sign indicating quicksand.
Botno county is dominately glacieated plains. The central part of the county was once under glacial lake souris during the last glacial period. The western part of the county has low relief collapsed glacial topography. The northeastern part of the county has high relief collapsed glacial and ice thrust topography.
Liquefaction is the process by which saturated, unconsolidated sediments are transformed into a substance that acts like a liquid. The image on the left illustrates the liquefaction process. Under normal conditions the grains are in contact with eachother and the pore spaces in between are filled with water. During liquefacation energy waves moving though the material increase the pore pressure causing the grains to separate, lose cohesiveness, and strength. Image to the right is a car buried during liq. Generated during an earth quake in new Zealand.
Now moving on to field methods.
The image on the left is the hand auger unit used to extract samples from the subsurface. The image on the right is an example of a sample we extracted.
These are the core locations with B1 and B4 being the cores that we did lab analysis on. B1-3.6m B2and B4 2.7m B3-1.5m
During field sampling we identified 2 strat units. The lower most unit, strat unit I was massive, overcompacted, very dense, and had obvious joints or fractures with discontinuous sand lenses. Strat unit II was stratified, less dense, and lacked joints.
Strat unit I was interpreted to be a lodgement till deposited beneath a glacier. Strat unit II was interpreted to be a supra-glacial melt out till, which is sediment on the surface of the glacier that collapses as the ice melts. There maybe younger slopewash material within strat unit II.
These images illustrate the 2 types of till from exposures in Iowa. Note the supra-glacial till on the left is stratified. While the sub-glacial till is massive. In addition supra-glacial till tends to be less dense then subglacial till.
Wells were installed in 4 core locations, in 2 well nests. Each consisting of a shallow and a deep well. B1 being the deepest well at 3.6m, B2 & B4 at 2.7m, and B3 at 1.5m.
The installed wells consisted of 1.5in. PVC. The lower 25cm had perforations to allow water into the well. The PVC was lowered in to the hole and the bottom 30cm was filled in with sand, then 20cm of clay was added to act as a plug, then the rest of the hole was backfilled with dirt.
This represents the stratigraphy of the site based on field observations. Strat unit I, a lodgement till is over lain by strat unit II a supra-glacial till. Both wells B1 and B2 were extended into strat unit I. while B4 extended into the upper part of strat unit I. while B3 extended into strat unit II.
This is an image of the pocket penetrometer we used to take density readings. Readings are read in kg/cm2. it is a measure of compressive strength. As you push the small piston in to the sample the large handle moves downward moving the white ring and a reading is obtained from the lower side of the ring closer to the tip of the instrument.
Particle size analysis consisted of gravel separation that removed the greater then 2mm size fraction, followed by the bouycous hydrometer method which seperates the less then 2mm size fraction into relative percentages of sands, silts, and clays within a sample.
Gravel separation started by taking aprox. 60g. Of sample and soaking it in water for 24hrs. The sample was then placed on a magnetic stir plate for 5min. The contents was then poured though the 2mm size sieve. The contents that was captured on the sieve was dried, weighed and recorded. The contents that made it though the sieve was captured in a beaker and 100mL of 50g/L sodium hexametaphosphate was added to defloculate the clays.
After 24hrs the samples were then placed into a commercial drink mixing machine for 5min. After 5min. The sample was placed into a hydrometer jar, the rest of the jar was filled with distilled water to 1000mL. The hydrometer jar had a rubber stopper placed ontop and was rotated 180degrees for 1min. It was then placed into a hydrometer bath set at 20 C. at 6hrs 52mins. A hydrometer was placed into the hydrometer jar and reading was taken in g/L. at 6hrs 52mins. Only the clays are left in suspension.
The hydrometer jar contents was then poured though a NO.230 Sieve. Capturing all the sand sized particles. The silts and clays washed though the sieve. The contents captured in the sieve were placed in a beaker, which was placed in an oven at 80 C for 12hrs to dry. After 12hrs the beakers were placed in a desiccator to cool once cool they were weighed and recorded. The clay percentage was obtained from the hydrometer reading and the sand percentage was obtained from the weight of the sand captured on the No.230 sieve. The silt percentage was obtained by subtracting out the sand and clay percentage from 100.
Results are going to cover penetrometer readings, site hydrology, and particle size analysis.
This slide shows vertical distributions of penetrometer readings from cores B1 and B4 read in kg/cm2. Boxes represent stratigraphic boundaries observed in the field.
This slide shows water level readings. We were limited to the amount of data obtained due to our wells freezing early and are sill frozen. Note that B3, the shallowest well has one reading which is above 0 which means it had water above the ground surface.
This slide shows vertical distribution of sand, silt, and clay percentages of cores B1 and B4. Note the particle size variability in strat unit II core B4. that variability was lacking in core B1 possibly due to the 20cm sampling interval. Which could have masked some of the variability observed in the field within strat unit II. In core B4 the interval between 120-160 shows a steep increase in silt, these laminated silts may represent deposition within a pond or glacial lake souris.
This map represents the distribution of glacial ice 12,500yr. Ago. This is when we believe strat unit I was deposited beneath the ice.
This map shows the receding of the glacier around 11,000yr ago. The site location is within stagnate ice were supraglacial meltout till representing strat unit II would have been deposited.
This image shows elevation changes along the yellow line. At the bottom left of the line is where our site is located and at the top right of the yellow line is in the turtle mtns.
The blue line on this image is the water table obtained from the NDSWC. Ground water usually follows the topography of the land surface.
This is a diagram of our current working hypothesis. Precipitation infiltrates vertically until it encounters the low permeability strat unit I. the water then flows laterally though the more permeable strat unit II away from the turtle mtns. Towards the quicksand site. At various locations at the site this water encounters a wall of low permeable sediment of strat unit I, in an area were strat unit I has moved upward along a joint or fracture. Water will take the path of least resistance which in this case is to move upwards though strat unit II and towards the surface. Which causes the mounding of sediment and liquefaction.
ND state water commission, Drillers Logs, Check other sites for same,
Potentials for GPR, Also Core more, install more wells.
10g sample in crucible placed in oven at 105C 24hrs,
0-20cm percent silt, trend downwards
140-160cm silt spike
MCF no big changes, had been drying for 2-3 months
Note B4 0-20cm and 140-160cm
Ternary diagrams created from particle size analysis Good indication of homogenized sediment in B1 good characteristic of deformation tills B4 bit more sandy
Geologic Controls on Liquefaction Processes at the Bottineau
GEOLOGIC CONTROLS ON
LIQUEFACTION PROCESSES AT
THE BOTTINEAU QUICKSAND
BRODY B. AWALT
DEPT. OF GEOSCIENCES
MINOT STATE UNIVERSITY
• EXAMINED SEDIMENTOLOGY AND STRATIGRAPHY
Photo of the Turtle Mountains
from the Bottineau Quicksand
Site. View is to the north-
northeast. Note the salt
accumulation at the surface.
Ground level photo of the
Bottineau Quicksand site. View
is toward the east.
Strat Unit II
Strat Unit I
• Less dense
• Lacks Joints
• Over compacted/Dense
• Discontinuous sand lenses
DEPOSITIONAL SETTINGS FOR
VARIOUS TYPES OF TILL
SUPRA-GLACIAL TILL SUB-GLACIAL TILL