GLOSSARY OF GROUND IMPROVEMENT VOCABULARY Accelerator Agitator tank Atterberg limits Batch Blaine fineness Bleed Colonne ballastée Compaction grout Compaction crater Consolidation CPT CUU shear test A substance that accelerates chemical reaction(s) in grout. A tank that contains mixing paddles or blades to maintain the grout in suspension before it is pumped into the ground. A set of laboratory testing methods devised by Atterberg to determine the water content at -> liquid limit and -> plastic limit. Defined amount of gravel or grout handled by the soil improvement method in one increment of the treatment. Measures the specific surface area of a powder such as cement or bentonite. Typically measured in cm 2 /gram. Process when the grout is separating from (bleeding off) excess water. French name for -> Stone Column. Grout with less than 25 mm of slump. Compaction grout shall not infiltrate the soil pores but remain one mass that by it s expansion shears the soil particles against each other and thereby achieves compaction. The imprint on the soil surface after the falling weight hits the soil surface. Surveying of the crater between multiple drops can give indications about the progress of compaction. The portion of the time-settlement of a soil, which is governed by the dissipation of excess pore pressures. Cone Penetration Test, also called "Dutch Cone". A rod with a conical tip is pushed in the ground at a constant speed while its tip and sleeve resistance are recorded. The CPT test gives an indication on soil density and soil type. Consolidated unconfined undrained shear test. Quick and simple test in the lab to determine the ->
undrained shear strength of a clayey soil sample. Differential settlement Settlement difference between two relevant parts of a structure, is often more relevant to prevent damages to structures than total settlement. Displacement factor Stone Column volume in percent of the volume of the - > unit cell.. Usually lies in the range of 5 % to 30 %. DMT Dilatometer Test after Marchetti. A thin blade is pushed into the soil. Then on the side of the blade a pin is pushed into the soil while the pushing force is measured. Drop height In -> Impact Compaction the height that the -> Pounder is falling. Dry bottom feed method A stone column installed in a way that the gravel is transported without the aid of water in a special duct alongside the vibroprobe. Dry top feed method Same as dry bottom feed method, but the gravel is dumped into the open hole while the vibroprobe is fully retracted. This method works only if the hole does not collapse, i.e. in stable soil above ground water. Dynamic Compaction Another name for -> Impact Compaction. Fines content Percentage of the total dry mass of a soil sample that contains grains in the silt and clay range, i.e. particles smaller 0.06mm (US: #200 sieve or 0.074 mm). Hydration The chemical reaction between water and cement. Impact Compaction Soil compaction by a falling weight. The weight hits the soil in one impact and does not vibrate continuously. Technically a continuous vibration loading is called a dynamic loading as opposed to a short impact or transient loading. Surface Impact Compaction is technically a more fitting term than Deep Dynamic Compaction. Liquefaction Phenomenon by which soil looses part or all of its shear strength. Liquefaction is mostly triggered by dynamic shear deformations during an earthquake but can also result from wave loading or dynamic loads on machine foundations.
Liquid limit Mandrel NC OC OCR Plasticity Index Plastic limit PMT Water content wl in percent at which a soil sample is at the border of becoming a liquid. At liquid limit the soil is too soft to be reasonably handled with earthmoving equipment and mostly too soft to drive or walk on. The liquid limit and -> plastic limit were first defined by Atterberg and are therefore also called -> Atterberg limits. Hollow steel profile used by a -> stitcher to push a ->prefabricated vertical drain to depth. Normally consolidated: This soil was never in the past under a higher overburden pressure than today. -> OC, over consolidated Over consolidated: This soil was in the past under a higher overburden stress than today. As a consequence of this, this soil behaves relatively stiffer under a loading until it reaches the value of the maximum past overburden stress. Over consolidation ratio: Factor of how much higher the maximum ever overburden stress on the soil is compared to today's stress level Penetration Phase of lowering the Vibroprobe to the full required depth. Abbreviated as PI or Ip. The difference in percent between the water content at liquid limit and plastic limit. The PI is a measure for the ability of a soil to bind water to its surface. The higher the PI the higher usually the clay content of the sample. Water content wp in percent at which a soil sample is at the border of becoming too dry for kneading it with compaction equipment such as roller compactors. As the name suggests it is the limit water content below which the soil behaves brittle (crumples) and not plastic anymore. The plastic limit is close to the optimal water content for compaction in many soils. Pressuremeter test. Invented by Louis Ménard, who also pioneered the industrial application of -> Impact Compaction.
Prefab. vertical drain A cardboard or plastic core enveloped in a filter cloth or paper filter. Water flows from soil through the filter into the core of the drain and from there upwards to the soil surface. Pounder Another name for the falling weight in -> Impact Compaction. Pulling criteria Rule to operate a Vibroprobe when installing a Vibro Compaction. Usually a threshold amperage and time, whichever comes first, for which the Vibroprobe is pulled again 0.5 m upwards. RDV German abbreviation for -> Vibro Compaction (Rütteldruckverdichtung) RSV German abbreviation for -> Vibro Replacement and/or -> Stone Column (Rüttelstopfverdichtung) Re penetration During installation of Stone Columns, when the Vibroprobe is lowered back into the gravel to enlarge the column diameter to the desired value. Replacement factor Volume of washed-out soil which was later replaced by gravel, given in percent of the total volume of a -> unit cell see also -> displacement factor Safety factor A dimensionless number. Typically in foundation engineering the safety factor is the quotient of actual shear stress over shear stress at failure. In liquefaction analysis the safety factor is actual cyclic stress ratio (CSR) over maximum resistance cyclic stress ratio (CRR). Self-feeding The phenomenon that granular in-situ soil flows towards the Vibroprobe in a way that makes feeding from the top obsolete. Sensitivity Quotient of initial (maximum) shear strength over residual (minimal) shear strength. Non sensitive soils have a sensitivity of around 2, while very sensitive soils can have sensitivities over 20. Scandinavian marine clays are known to have high sensitivities (so called quick clays ), i.e. they are very prone to sudden failure if shear deformations are applied to them.
Vibratory methods or other methods (impact compaction, driven piles, compaction grouting, etc.) that unduly shear the in-situ soil shall not be applied in very sensitive soils. SPT Standard Penetration Test. A very widely used sounding device, measuring the number of blows necessary to drive a split barrel sampler 1 ft ( 30 cm) into the soil. Mostly done from the bottom of a borehole. Stitcher A rig that installs -> prefabricated vertical drains. Name also used for a rig that installs -> dry bottom feed stone columns using an excavator. Stone Column Column of granular material, mostly gravel, installed for drainage and/or load bearing in cohesive noncompactable soil. Top feeding Feeding granular material with a loader to the compaction point from the top of the hole, compare -> self-feeding. Undrained shear strength Strength of a soil sample against fast (=undrained) shearing. Soil mechanical engineers only use undrained shear strength if they do not know the water pressures during shear. This is unfortunately very often the case. The undrained shear strength concept ignores all effects caused by water pressures, hence the concept is useless in all analyses where pore water pressure dissipation or long term strength needs to be studied. It is also useless in all silts and sands where drainage is too fast to assume they would behave undrained in any case, even short term. In summary: The concept of undrained shear strength is limited to short term behavior of clays. Unit cell Zone of soil around a stone column that can be attributed as belonging to that column. (In an infinite stone column mesh with equal soil conditions and equal loading conditions, at the border between two unit cells, the horizontal deformations in the soil are
zero.) Vane shear test A test in which a rod with wings (vanes) at its end is pushed in soft soil and then rotated. The force needed for rotation is proportional to the -> undrained shear strength of the soil. The test records the beginning strength and the residual strength after several roatations. The quotient initial over residual strength is called ->Sensitivity VCC Vibro Concrete Column. A column installed using a Vibroprobe and pumpable concrete. Vibro Compaction Procedure to compact granular soil by vibration using a Vibroprobe. Vibroflotation Procedure name as well as a company name. As a procedure name it is equivalent to ->Vibro Compaction. The term describes the fact that all granular soils first have to float before they can move in a denser state. The floating state is achieved by Vibration. Vibro Displacement Name for a procedure of installing "Stone Columns", expressing that most of the soil is displaced laterally by the stone column and not washed out. This is often the case for the -> dry bottom feed method and the -> dry top feed method. Vibroprobe Torpedo shaped vibratory probe with rotating eccentric weights for Vibro Compaction and Vibro Replacement Vibro Replacement Name for a procedure of installing "Stone Columns". The term replacement is expressing that the soil is more replaced than displaced. This is often the case for the -> wet top feed method. VSS German Abbreviation for Vibro Mortar Columns (Vermörtelte Stopfsäule Wet top feed method Installation method where the gravel is added from the top of the hole using flushing water to keep open an annular space around the vibroprobe. Wet bottom feed method Installation method as -> dry bottom feed method but using water for penetration to depth.
Wick drain Another name for -> prefabricated vertical drain (PVD)