Table of Contents
Introduction
The underground or sub-soil strata/classification within the project site varies and is uncertain. This may result in insufficient bearing capacity of constructed bored piles based on the designed length of the pile. Clay pocket at the designed pile toe level is a main problem causing inadequate end bearing capacity.
Bored piling records and confirmation of soil classification by visual inspection is important during the drilling process for each pile. As it will determine if such pile will be constructed typically or need to be base grout. Where constructed bored piles are proven to be disastrous, without sound toe and proper seat into the virgin ground based on bored piling and soil sampling records, base grouting techniques are to be used to rectify the soft toe or clay pocket problem of bored piles as jointly agreed upon by the Contractor, Consultants, and the Employer.
Today we’ll discuss the tube-a-manchette technique for grouting the base after the completion of the pile.
Scope
The work shall consist of preparing grout holes, check holes, pressure testing, pressure washing, and injecting suspension grout under pressure. It shall include furnishing all materials, labor, and equipment as described and specified for the tube-a-manchette method.
Materials for Pile Base Grouting
Portland Cement:
Portland cement shall conform to the requirements for the specified type. The cement contains lumps or foreign material which would clog the grouting equipment or interfere with grout injection. So the Contractor should screen it through a 100-mesh screen before using.
Water:
Water used shall be clean and free from harmful amounts of oil, acid, organic matter, or other toxic substances.
Bulk Fillers:
Bentonite or polymer shall be of the type and quality specified in the project specification as Bulk fillers. Bulk fillers in the mix shall be measured in cubic-meter boxes. Or by dry unit weight with correction for moisture content, if applicable.
Admixtures:
Admixtures shall be the type and quality specified in the project specification.
Storage and Supply:
A sufficient quantity of all materials shall be on hand to ensure that grouting operations will be completed on time. Materials shall be stored and protected at all times and all locations. So that the quality of the materials is maintained.
Equipment for Pile Base Grouting
All drilling and grouting equipment shall be of a type and capacity and in condition to perform the work described:
Delivery Pipe:
For the “tube-a-manchettes” method, the delivery pipe shall be 25 mm(min.) diameter HDPE pipe or 56 mm.(min.) diameter steel pipe which is prepared while the reinforcing cage is installed. The pipe casing shall be installed along the bore pile , and the pipe size shall conform to the packer to use depending on the “tube-a-manchettes” inner diameter.Grouting Equipment:
The equipment shall be capable of mixing and pumping grout having a mix ratio. By volume, of one part water, one part cement, and two parts bulk filler, such as bentonite or fly ash.
Mixers:
Unless otherwise specified, mixers shall be high-speed colloidal and capable of thoroughly mixing water, cement, and bulk fillers. It must produce a uniform texture and consistency grout. Mixers shall match the capacity of the pumping plant.
Holdover Tank:
The Contractor shall furnish a holdover tank if they use a single-compartment mixer. It shall be equipped with mechanical agitators to prevent segregation of the grout. It should have sufficient capacity to store the grout and thus provide a continuous supply temporarily. The outflow shall pass through a No. 16 wire with its proper flow into the voids it intends to fill.
Pumps:
Grout pumps shall be of the long stroke, multiple pistons, or helical screw type. The capacity shall be at least 0.085 cubic meters per minute at 1,380 kPa. For this, the maximum grout mix will be of 1:1:2 (w:c: bf) by volume.
Cement and Fly Ash-Handling Equipment:
Suppose the Contractor uses bulk cement or fly ash. In that case, they shall store it in weather-tight bins or silos equipped and arranged to discharge directly into a weighing hopper and hence, directly into the grout mixer without spillage and intermediate handling.
Air Supply:
The air supply shall meet the requirement of the pumps. It shall be at least 5.7 cubic meters per minute per plant.
Water Meter:
Each mixer shall use one water meter of the reset type, graduated in tenths of 1 cubic meter.
Pressure Gauges:
One pressure gauge shall be installed at the pump and one at the collar of the hole. Gauges shall be of the non-clogging type or shall be prevented from clogging by using gauge savers or grease. Spare gauges shall be available at the plant at all times.
Hoses, Valves, and Fittings:
Hoses, valves, and fittings shall be compatible with the maximum pressures specified. The hose from the pump to the grout header and return shall not be smaller than 38 mm (ID), and the pipe between the header and packer shall not be smaller than 19 mm (ID). Double or single packers may be required for grouting and pressure testing. Packers shall fit tightly in the holes at all testing and grouting pressures.
Arrangement of Equipment for Pile Base Grouting:
The arrangement of grouting equipment shall provide a return line from the header back to the mixer or holdover tank, permitting continuous circulation of the grout. The grout pressure shall be controlled at the header or the return line’s end. The hose between the take-off at the grout supply line and the hole header shall be at most 4.5 meters. Grouting several holes simultaneously from the same grout pump (multiple header arrangement) will not be permitted.
Each hole shall be equipped with a shutoff valve below the hand coupling union. It will permit shutoff at refusal pressure and removing the header to another hole while maintaining pressure in the completed hole.
The header arrangement shall include a blow-off valve and a control valve to be used to check hole back pressure before header removal, and a return line valve. The header shall be connected to the supply line by means of a U-shaped pipe arrangement or other fashion which prevents fallout of solids into the hole from the bypassing grout during low rates of grout acceptance.
Grout Mixtures
Composition:
Grout shall consist of a mixture of Portland cement, water, bulk filler, and additives, as specified. Grout mixes and sequences of mix ratio or composition changes shall be as specified in the project specification.
Mix Ratios:
Grout mix ratios will be the water-cement ratio should be 0.5 – 0.6 by weight, and a little bentonite should be mixed and try to set the optimum mixture by trial mix before starting the operation. The mix ratios will be expressed in cubic meters of water to a bag of cement. Bulk fillers will be expressed in cubic meters to a bag of cement. Other additives will be expressed in percent to a bag of cement and measured in kilograms, or liters.
Manchette Tubes:This method consists of 2 (nos.) Manchette tubes as a U-shape and connected to HDPE at each side. The HDPE pipe shall have a minimum of 25 mm diameter (ID) and shall be attached to a reinforcing cage along the pile length up to the top of the pile. The Manchette tubes are the perforated steel pipe with rubber sleeves for control of the grouting flow out as a non-return valve and shall be set 50 – 100 mm. above the bottom of the pile tip.
Pressure Testing:
In holes to be pressure tested (water cracking) by clean water at 20 bars pressure after the concreting 12 – 24 hours, to cleaning and run in the Manchette tube, pressures exceeding the specified design pressures shall not be applied unless specifically authorized by the Engineer.
The pressure test equipment shall be calibrated at the site to determine the pressure loss in the equipment at various flow rates and test depths.
Pressure tests and calibration of pressure test equipment shall be performed in the presence of the Employer/Employer’s Representative.
Grout Injection:
The pumping rate shall be at most 1 cubic meter per minute unless otherwise approved by the Employer/Employer’s Representative. The grout injection shall be operated after concreting around 7 – 10 days, and grout pressures shall be as specified as 20 – 60 bars and the grout mixture volume as 0.5 – 1 m3, or specified by the Employer/Employer’s Representative.
The quantity of grout prepared in advance shall be kept to a minimum. Grout, which has remained in the mixer or holdover tank with or without agitation for over one (1) hour, shall be discarded.
Grout temperatures shall be not lower than 10oC. The grouted soil, rock, or concrete shall be not colder than 4oC when the grout is injected and for at least 48 hours after that.
Insulation or heat shall be applied to the surface for 24 hours before and 48 hours after grouting if required to keep the soil, rock, or concrete above the minimum required temperature. When the hole shows signs of refusal, a thinner mix shall be used to prevent or remove clogging.
A hole shall be considered grouted when the grout taken at the design pressure is less than 0.03 cu.m. of grout in 10 minutes.
Grouting Procedure for Pile Base Grouting:
The procedures and grout mixes described below are general guidelines. The Employer/Employer’s Representative may alter them in the field to suit the conditions encountered and meet the design objectives.
Unless on-the-site experience indicates otherwise and instead of pressure testing, each stage or lift of a hole to be grouted shall be started with about 0.5 cu.m. of water: cement mix to be no thinner than 5:6 (w:c) by weight unless otherwise specified in the project specification.
Cleanup:
After grouting is completed, the Contractor shall remove the grouting plant and all related parts, equipment, and supplies from the site, including unused materials and waste.
