Are polymer slurries all the same?
BIG-FOOT® is a very high molecular weight synthetic polymer with negative charges on the backbone. Its high molecular weight gives viscosity to water at low concentrations. BIG-FOOT is a higher molecular weight and higher % anionic charge of any other polymer on the market today.
BIG-FOOT® is a dry granular synthetic anionic partially hydrolyzed polyacrylamide, (PHPA). BIG-FOOT is manufactured from co-polymerization of acrylamide and acrylic acid or its inorganic salts. The molecular weight (in the region of several million Daltons) and negative charge density varies (by variation of the ratio of acrylamide and acrylic acid monomer units).
The high molecular weight polymer chains are so long that different parts of individual polymer chains bridge different solid particles. It is this adsorption on surfaces and bridging of solid surfaces that makes this polymer effective in keeping solids consolidated while drilling a foundation caisson hole. In addition, the adsorbed layer of hydrophilic polymer on soil surfaces slows down the diffusion of water into the soil.
How does the BIG-FOOT slurry hold the ground open?
The way the drilling slurry functions is by what is known as the “positive effective stress” principle. Essentially, this means that the drilling slurry produces stress on the sides of the drilled hole due to fluid pressure applied by differential head. This induced stress is produced by maintaining the level of the drilling slurry as high as possible (usually at least 6 feet) above the groundwater level in the drilled hole. In cases where the groundwater level is very close to the ground surface, use of a surface casing is necessary to ensure positive effective stress is developed on the sides of the drilled hole.
BIG-FOOT was developed specifically for the Foundation Drilling Industry and has a higher molecular weight and % anionic charge than other dry PHPA polymers on the market.
Research and development was completed prior to its introduction.
BIG-FOOT mixes easier, reaches higher viscosities, and suspends less sand while reinforcing the excavation.
What is the difference between using hydrant water or river water when mixing slurry?
Hydrant water must be pre-treated with CHLOR-AWAY to neutralize chlorine, then M-BOOSTER. Chlorine breaks down the slurry. River water must be treated with M-BOOSTER only to over-come calcium (hardness) and river water must also be tested for organics prior to being used as mix water.
Adding M-BOOSTER to make up water prior to mixing will precipitate the free calcium ions and therefore will maximize the viscosity of BIG-FOOT
Identifying the contaminants in the water and treating accordingly will save significant time and money. Matrix has a full range of additives to treat make up water prior to mixing BIG-FOOT polymer.
Increasing BIG-FOOT dosage in applications where brackish or seawater may be encountered while drilling, will give the desired viscosity of BIG-FOOT.
What is the difference between mixing in the excavation versus pre-mixing in tanks?
Sufficient water supply of proper quality for slurry makeup shall always be available to support planned operations and unknown contingencies. Plenty of slurry deliverability or creation volume shall be instantly and always available to support planned drilling operations and unexpected events. If the water supply is from a low-rate or irregular source such as a small well, a small diameter supply line, or tanker truck, a tank for storage of water shall be used to guarantee adequate and uninterrupted slurry making capacity.
Pre-Mixing is the recommended method of mixing the BIG-FOOT polymer into slurry as this gives the polymer proper time to mix and allows for better quality control.
Mixing in Vessels or Tanks
When BIG-FOOT polymer is pre-mixed in tanks it shall be added to water that is being passed through a hose, tube or hopper, across a stationary panel or surface, or stirred or otherwise agitated, in a manner which avoids the formation of lumps and results in a uniform mixture of polymer in the makeup water. The polymer slurry shall be agitated until it develops viscosity adequate to be self-suspending (i.e., particles of partially-dissolved polymer do not settle in the fluid). This normally occurs within 15 to 30 minutes. Polymer shall not be mixed in a tank or vessel without adequate agitation. Agitation may be accomplished by use of motorized stirrers, air injection, (as with blowpipes or fixed perforated piping), or other suitable and effective means. Recirculation by a single pump (without other means of agitation) is usually inadequate and shall not be permitted unless the mix tank is small enough that the pump provides adequate agitation of the entire tank.
Mixing BIG-FOOT Polymer Directly In The Excavation
When mixing directly in the excavation it is important to have a steady stream of water or recycled fluid that is positioned to provide a point of rapid and wide water flow for introduction of the polymer by sprinkling or sifting. Mixing of fresh polymer shall be completed by sprinkling or sifting the polymer carefully onto a flowing stream of water or fluid from a pressurized source directed into the excavation, such that the flowing fluid catches, wets and separates the polymer grains so that they disperse and hydrate as individual particles, avoiding the forming of lumps or balls of un-mixed polymer. Dry polymer shall not be added directly onto the fluid in the excavation (as opposed to being added on a flowing stream) because this normally produces lumps or “fisheyes.” Adding MO’S-MUD will create instant viscosity with-out having to shear.
Mixing directly in the excavation uses more BIG-FOOT than pre-mixing as the polymer does not hydrate and is removed when the drilling tool plunges into the slurry filled excavation. This is necessary only when the project is in a remote location such as for Cell Towers or projects that have logistic challenges and limited space.
What is the effect of slurry on soil and rock skin friction and end bearing?
The BIG-FOOT slurry does not form a filter cake that interferes with the integrity of the drilled shafts axial capacity.
It is not recommended to ream out the sidewalls inside of the borehole. This removes the only support in place exposing the fresh soil to water which causes softening. This practice is not necessary with the polymer BIG-FOOT when made into a slurry, as the slurry does not form a filter cake that interferes with the integrity of the drilled shaft. The high molecular weight polymer chains are so long that different parts of individual polymer chains bridge different solid particles. It is this adsorption on surfaces and bridging of solid surfaces that makes this polymer effective in keeping solids consolidated while drilling a foundation caisson hole. In addition, the adsorbed layer of hydrophilic polymer on soil surfaces slows down the diffusion of water into the soil.
During construction of the borehole the BIG-FOOT slurry is used to hold the excavation open, and to facilitate the removal of spoils. When the bottom tip point is reached the excavation is cleaned and the rebar cage is set. Next concrete is poured through a tremie pipe placed into the hole just off the bottom. As the concrete fills the borehole the lighter BIG-FOOT slurry weighing 8.4 lb/gal is displaced and pushed up and out of the hole. Any remaining residual BIG-FOOT slurry clinging to the rebar or the sidewalls of the borehole is physically displaced by the rising column of dense concrete, and secondly chemically destroyed by the alkalinity (pH-13) of the concrete as it fills the hole.
What is the settling time for sand?
Because the primary polymers of the standard BIG-FOOT® system add no significant weight to slurry, measurement of slurry specific weight is a direct indicator of the soil solids content (sand, silt, clay) of the slurry. Sand content is dealt with by a sand specification. Sand tends to settle to the bottom of the excavation because the BIG-FOOT polymer slurry has no tendency to gel, so temporary or transient elevated sand content is not a problem during the excavation process. Aside from sand present in the slurry, the remainder of the slurry’s specific weight above the specific weight of water (1.00 kilogram per liter or 62.4 lbs. per cubic ft.) comes from soil fines dispersed in the slurry. Consequently, the slurry specific weight specification is in effect a limiting factor on the amount of fines that are acceptable in the slurry. High fines content can cause problems if the fines are not held in stable suspension. The slowly-settling fines can create a bed of sediment on the bottom of the excavation after a period of time. The maximum allowable final specific weight for synthetic polymer slurries, according to the present specification, is listed in the specification table.
What is the effect of BIG-FOOT slurry on rebar and concrete?
The BIG-FOOT polymer slurry exerts increased pressure per unit of fluid column height to maintain excavation openness. Testing has proven that the polymer slurry coming in contact with the steel rebar cage within the excavation has no effect on skin friction and end bearing integrity. The residual polymer slurry coating the steel is scraped off and dissolved off from the steel by the rising column of concrete. The alkalinity pH=13 of the concrete assures a clean homogeneous concrete placement.
BIG-FOOT slurry cohesively binds excavated soil solids together, facilitating their removal from the excavation and preventing them from dispersing into the slurry. BIG-FOOT maximizes spoil loading on augers increasing excavation rates. BIG-FOOT makes it possible to drill with augers, even in sand and gravel, eliminating the need to use a bucket necessary with mineral slurry and full length casing. This feature can reduce slurry wastage.
What is Proper Procedure to Tremie Pouring Concrete under BIG-FOOT SLURRY?
A. Maintain slurry in the pile hole as necessary to prevent caving and bottom-of-hole instability.
B. Prior to placing reinforcing steel and concrete in the pile hole, clean the bottom of the hole of all loose material using appropriate means such as a cleanout bucket or air lift. No more than 6 inches of loose or disturbed material shall remain. Inspect the hole to determine that this requirement and depth have been achieved. Reinforcement shall be free of rust and mud.
C. Place concrete as soon as possible after completion of pile hole drilling, inspection of the hole, placement of the reinforcing steel, and access tubes. Holes shall not be left open longer than 16 hours after drilling is completed at any stage of excavation.
D. Place concrete by tremie method, in such a manner that the concrete displaces the slurry progressing from the bottom and rising uniformly level to the ground surface. Concrete placement shall continue in one operation to the top of the drill-hole and the elapsed time from the beginning of concrete placement in the pile hole to the completion of the placement shall not exceed two hours. Admixtures in the concrete mix shall be adjusted for the conditions encountered on the job so that concrete remains in a workable plastic state throughout the two-hour placement. Before concrete placement, test results of both a trial mix and a slump loss test using approved methods shall be submitted to demonstrate the concrete meets this two-hour requirement. The test shall be conducted using concrete and ambient temperatures appropriate for site conditions.
E. When placing concrete underwater by pumping, the tremie shall have a hopper at the top that empties into a watertight tube at least 4 inches in diameter. The hopper shall have a capacity at least equal to that of the pipe it feeds. At all times, a sufficient quantity of concrete shall be maintained within the pipe to ensure that the pressure from the concrete exceeds that from the water or drilling fluid.
F. The hopper and pipe of the tremie shall be clean and watertight throughout. The discharge end of the pipe shall include a device to seal out water while the tube is first filled with concrete. The tremie shall be initially positioned at the bottom of the hole prior to placing concrete. Throughout the underwater concrete placement operation, the discharge end of the tube shall remain submerged in the concrete at least 5 feet and always contain enough concrete to prevent water from entering.
G. If concrete placement is halted for any reason in a manner that could lead to defective concrete, the pile shall be dewatered and the top surface of the tremie concrete cut back to sound concrete and cleaned of all laitance and weak concrete. The remainder of the pile shall either be cast by tremie or in the dry. Where concrete is placed in the dry, the concrete shall be placed by tremie and the free fall of the concrete from the bottom of the tube shall not exceed 1.5 times the diameter of the pile.
H. Casing shall be extracted while the concrete within remains sufficiently workable to ensure that the concrete is not lifted. When the casing is withdrawn as concreting proceeds, a sufficient head of concrete shall be maintained to prevent the entry of groundwater that may cause reduction of cross-section of the pile.
A. Perform necessary checks and measurements as drilling progresses. Immediately inform Engineer of over-excavation, obstructions such as a boulder, or boring that is out of tolerance.
B. Use appropriate inspection devices before tremie concreting, to demonstrate that the pile hole bottom has been properly cleaned and excavated to the specified diameter, depth, verticality, and that the requisite overlap of piles will be attained.
- Check slurry properties are as required prior to placing concrete.
D. Check concrete properties are as required prior to placing. Closely monitor concrete placement and chart actual volume of concrete placed versus theoretical volume required.
E. Maintain pile construction log.
Is it True That BIG-FOOT Slurry Has Improved Skin Friction?
BIG-FOOT polymer slurry offers many distinct advantages when compared with Bentonite mineral slurry. Some of the more important advantages would include the following
Greater skin-friction load carrying capacity for the side-walls of the drilled shaft, thus increasing the total working load capacity of the pier.
The elimination of the de-sanding operation, as is necessary with Bentonite mineral slurry. Bentonite slurry suspends sand and polymer slurry does not suspend sand. During the excavation of the shaft under a head of polymer slurry, all the sand drops to the bottom of the shaft as drilling proceeds.
Provides cleaner, harder top surfaces on concrete at the top (cut-off) of drilled shafts; reduces or eliminates cleaning, chipping and dressing at cold joints.
BIG-FOOT polymer slurry is non-toxic and non-hazardous. When ready for disposal, it is chemically broken down with the product NEUTRALIZER to break-down to environmentally safe and clean water and by-products.
BIG-FOOT is considerably cleaner and more manageable than Bentonite. The residual spoil is drier and firmer, and can be used for fill.
BIG-FOOT polymer slurry replaces mineral slurry at ratios ranging between 1 to 50 and 1 to 200 in typical applications. When using salt water as the mix water only a special mineral called Attapulgite or Sepiolite can be used, these ratios mean that 20 pounds of BIG-FOOT can replace 4 tons of mineral slurry.
How often do you test the BIG-FOOT slurry and what are the target ranges of pH, sand content, viscosity and density?
The point of reference for selection and maintenance of slurry level shall always be the water table (piezometric level). This applies even in situations where casing or other protective sleeve has been placed to a depth at or below the water table. The presence of casing does not remove the requirement to keep the slurry level above the water table. Attempts to excavate or hold open an excavation in saturated or unstable soils with inadequate slurry head pressure; even with casing extended into the water table, can be expected to result in soil collapse below the casing.
SAMPLING AND TESTING
Premix BIG-FOOT slurry with a Venturi type mixer and allow two hours of hydration prior to drilling. Samples of the slurry shall be taken from the slurry supply tanks and tested prior to pumping to excavation and once again at excavation prior to drilling. Final sampling and testing of the slurry will take place just off the bottom of the shaft after final cleaning with muck out bucket has taken place, and prior to start of cage splicing over excavation. In instances where sand content cannot meet the <1% requirement, RAPID-DROP or FAST-FLOC may be used to flocculate suspended particles in order to obtain passing test results.
When operating conditions make it prudent to sample and test more frequently, sampling and testing shall be done in accordance with schedule recommended by the Manufacturer or the contractor and approved by the Engineer. It will also be necessary to test slurry in instances where a notice of extreme fluids loss occurs, sudden drops in viscosity, and when other unexpected encounters arise.
Samples shall be collected with a suitable device (Slurry Sampler) that captures representative samples of sufficient volume (≥ 1.8 liters or 2 quarts) to perform required testing of the slurry. Samples collected as described above shall be tested for Marsh Funnel Viscosity, pH and specific weight. A written record shall be maintained, showing viscosities, pH values, specific weights, dates, times, excavation identifiers, depths or locations from which samples were taken (excavation, supply tank, mix tank) and other pertinent information. Testing of specific weight and sand content is required before placement of reinforcing steel cage and concrete. SEE BIG-FOOT MIXING INSTRUCTIONS for more detailed information.
What remains after the BIG-FOOT slurry is broken down by NEUTRALIZER?
Synthetic polymers are not readily biodegradable. Biodegradable means that a slurry made from a biodegradable polymer will be subject to spoilage with breakdown of the slurry. Polymer slurry is not subject to spoilage. BIG-FOOT slurry is chemically degradable. Chemically degradability relates to chemical oxygen demand, or COD, and is the degrading of the polymer through interaction with another non-living substance. BIG-FOOT slurry is chemically degradable on demand by treatment with the chemical oxidizing agent NEUTRALIZER.
The BIG-FOOT polymer slurry contacts the surrounding soil and groundwater during construction of cast-in-drilled-hole piling and has minimal movement into the surrounding soil of the excavation due to a gel membrane that forms along the sidewalls of the borehole. This membrane cohesively binds the soils together forming a temporary glue, which seals off the vertical liquid slurry column.
BREAK-DOWN OF THE BIG-FOOT POLYMER SLURRY
At the end of the project there is usually a need to dispose of a quantity of polymer slurry which remains from the last borehole or excavation. The BIG-FOOT slurry is degraded by a variety of mechanisms. The slurry is broken down or removed during use in drilling or excavating. The mechanisms which cause this include adsorption (bonding) onto earth soils and chemical reaction with alkali’s and contaminates such as calcium in the slurry, the make-up water or the groundwater.
BIG-FOOT slurry fluids are non-toxic and are readily degradable upon completion of a slurry job to facilitate disposal. Upon completion of the project, any remaining BIG-FOOT is broken down with the chemical oxidizer (NEUTRALIZER) the most common oxidizer for this purpose.
The NEUTRALIZER is added to the BIG-FOOT slurry at a rate of 6-lbs. per (3,000 gallons) of slurry to be treated. After the NEUTRALIZER breaker is added, the slurry is circulated using the pumps on-site to ensure complete oxidation of the polymer molecules. This is accomplished by pumping it back into a holding tank.
The NEUTRALIZER destroys the active ingredients within the slurry and at the same time breaks the polymer, reverting it back to basic water. The end result is BIG-FOOT decomposing after its encounter with (NEUTRALIZER) and it is not a harmful substance.