Under-reamed Piles Research Articles

Shrinkage Behaviour of GPA-Reinforced Expansive Clay Beds Subjected to Swell–Shrink Cycles

Expansive soils undergo alternate swelling and shrinkage respectively in rainy seasons when they absorb water and in summers when water evaporates from them. Hence, all types of foundations constructed in expansive soils are also subjected to alternate swelling and shrinkage in rainy and summer seasons. As a result, super-structure members are also affected, undergoing severe distress. Various tension-resistant and innovative foundation techniques such as belled piers and under-reamed piles have been devised for arresting the problems posed by expansive soils. Granular pile-anchor (GPA) is a recent innovative technique suggested for expansive clay beds. GPA is quite effective in controlling heave or swelling. Useful experimental heave data were obtained on laboratory scale and field scale GPAs. However, it is also necessary to study the behaviour of GPA-reinforced expansive clay beds subjected to swelling and shrinkage. This paper presents experimental data on shrinkage of GPA-reinforced expansive clay beds. Laboratory scale GPA-reinforced expansive clay beds were subjected to alternate swell–shrink cycles, each cycle for a duration of 300 days. Each clay bed was subjected to three swell–shrink cycles (N = 1, 2 and 3), each cycle monitoring swelling for 10 days and shrinkage for 90 days. The number of GPAs (n) reinforcing the clay beds was varied as 0, 1, 2 and 3. Shrinkage (mm) of a clay bed, recorded in a given swell–shrink cycle, decreased with increasing number of GPAs (n). Further, shrinkage of a given clay bed decreased significantly with increasing number of swell–shrink cycles (N) also. It was also found that shrinkage (mm) of a particular layer in the clay bed decreased with increasing depth (z) of the layer from the top of the clay bed.

Computerised processing of ground investigation data and use in predicting the load-settlement behaviour of piled foundations

A new computer program “PILESET” is developed for use in predicting the bearing capacity and load-settlement behaviour of axially loaded single piles. The program can analyse almost any soil profile and accommodates (a) displacement piles (b) replacement (c) friction piles, (d) end-bearing piles, (e) under-reamed piles and (f) partially sleeved piles. A variety of soil input data can be used, including: (i) standard penetration tests, (ii) cone/piezo-cone tests, (iii) pressure-meter tests and (iv) laboratory tests. The above data types can be combined, if desired, for pile analysis by PILESET. The program calculates the shaft and base capacities of a pile based on 23 methods published in design guides in over 10 European countries. PILESET also predicts the pile load-settlement curve using five published methods, which include two modified load transfer (t-z) approaches formulated by the author. To demonstrate the capabilities of the program, analysis is carried out for case study involving seven full-scale screw piles formed in sand and tested to failure. In each case, the load-settlement curve computed using the author’s modified method in PILESET is found to be in excellent agreement with the actual pile test results.

Swell–consolidation characteristics of artificial sand clay mixes

Many remedial measures have been devised to lessen the damage caused by expansive soils. Physical alteration, chemical stabilization, innovative foundation techniques like belled piers, drilled piers, under-reamed piles and granular pile anchors are some of these remedial measures. Mixing a non swelling material such as gravel or sand to expansive soil is one of the methods of physical alteration. This paper presents experimental data on artificially prepared sand-clay mixes. Swell and consolidation characteristics of these artificially prepared sand-clay mixes were studied in one dimensional consolidometer. Fine sand content and fines content in the expansive soil were arbitrarily varied in the investigation. The fines content was varied as 425–300 μm and 150–75 μm, separated from the same expansive soil based on the grain size. Swell potential and swelling pressure decreased with increasing fine sand content but increased with increasing fines content. Coefficient of compressibility, coefficient of volume compressibility and compression index of the samples decreased initially up to a sand content of 15% and thereafter increased at higher sand contents.

VERTICAL LOAD-DEFLECTION BEHAVIOUR AND EVALUATING THE RESISTANCE OF UNDER-REAMED BORED PILE

The authors carried out “tensile and compressive load tests in the laboratory and fields”, “simulation analysis load-deflection behavior” on cast-in-place under-reamed piles. We obtained below conclusions from the results of these tests and analysis. 1. The (pu)- value decreases with increasing the ratio (D/d). 2. The shape of (p-S)relation curve changes according to the value of (D/d),θ,etc., but [(p/pu)-(S/D)]curve is a fixed curve regardless of these value. [P : load-carrying capacity of under-reamed bulb, p : P/A(A:π (D2-d2)/4 where D and d are under-reamed and stem diameter respectively), S : displacement of under-reamed bulb, θ : tapered angle of the bulb, pu : p-value where (S) reaching to 10% of under-reamed diameter]

Behavior of expansive soils under stabilized fly ash cushions during cyclic wetting and drying

Structures built in expansive clays are likely to be damaged due to the strains caused in them by alternate swelling and shrinkage. Variations in the moisture regime during monsoon and summer are the cause of this alternate swelling and shrinkage. Several innovative foundation techniques have been suggested to overcome the problems associated with expansive soils. Belled pier and under-reamed pile are some of the foundation practices adopted in these soils. Besides, overburden in the form of a sand cushion or a cohesive non-swelling soil (CNS) cushion has also been tried for arresting heave. But, most of them suffer from one shortcoming or the other. In order to overcome the drawbacks of the existing foundation practices, fly ash cushion, stabilized with lime or cement, has been tried by the authors. The principle of this technique is the same as that of a CNS cushion. This proved to be very effective in arresting heave. However, its efficacy over a few cycles of wetting and drying needs to be established since CNS cushion, which was found to be effective in arresting heave during the first cycle of wetting and drying was ineffective during the subsequent cycles. The present study relates to the behavior of expansive clays under lime- or cement-stabilized fly ash cushion subjected to several wetting and drying cycles.

Fly ash columns (FAC) as an innovative foundation technique for expansive clay beds

Various innovative foundation techniques have been in practice to counteract the swell–shrink problems posed by expansive soils. Apart from techniques such as belled piers and under-reamed piles, chemical stabilisation of expansive soils has also met with considerable success. Lime, cement and fly ash are the various additives used in chemical stabilisation. This paper presents an innovative foundation technique in the form of fly ash columns (FAC) for expansive clay beds. Results from a laboratory experimental study on expansive clay beds reinforced with fly ash columns (FAC) are presented. Heave tests and compressive load tests were performed on expansive clay beds into which fly ash was introduced as compacted columns. Heave decreased significantly on reinforcing the clay beds with FACs. Stress-settlement characteristics of expansive clay beds also improved when reinforced by FACs. Curing of FAC-reinforced expansive clay beds improved stress-settlement characteristics.

Investigations on the Static Behavior of Self-Compacting Concrete Under-Reamed Piles

Self-compacting concrete (SCC), a recent development, eliminates the need for internal or external vibration, as it freely flows in and around dense reinforcement and fills the mold completely without any blockages. SCC would be an ideal material for cast in situ piles, where compaction is infeasible. Six double under-reamed piles having a diameter of 250 mm and a length of 4 m, three made of SCC and three of conventionally vibrated cement concrete having similar strengths, were cast and tested to evaluate their static behavior in axial compression and tension (pullout). Later, all the piles were exhumed using suitable machinery to examine whether the pile shaft and bulbs had been well formed. Ultrasonic pulse velocity measurements were also taken on the exhumed piles along the length to evaluate the integrity of the concrete. Concrete cores of 75 mm diameter and 150 mm height taken from the pile shaft were tested for mechanical and durability related properties. The experimental study clearly demonstrated that the SCC in situ piles had better control on geometry when cast against soil form work.

Lateral Load Capacity of Underreamed Piles—An Analytical Approach

Underreamed piles having one or more bulbs at specified locations along their depths have been extensively used in India to support a wide variety of structures in almost all types of soil strata. In many situations, these piles are also required to resist considerable amount of lateral loads besides vertical compressive and uplift loads. However, the behaviour of these piles under lateral loads has not been properly investigated and the present guidelines for their design under lateral loads are mainly empirical. In this paper, an analytical procedure has been suggested to predict the ultimate lateral load capacity of the underreamed piles incorporating the influence of (i) size of bulb, (ii) position of bulbs, (iii) number of bulbs, (iv) length to diameter ratio of piles and (v) type of soil strata. The point of rotation and ultimate lateral resistance of underreamed piles have been computed in terms of passive resistance along the shaft and additional resistance on the surface of bulb(s) as well as bearing on the bottom and uplift resistances on the top of bulb(s). Non-dimensional relationships and design coefficients have been established for the estimation of improvement in lateral load capacity of underreamed piles over straight shafted piles. The limiting lengths of the underreamed piles to decide them as either rigid or flexible under lateral loads have also been brought out. An illustrative example followed by comparison with a few reported field cases demonstrates the effectiveness of the developed approach.

軸部を細くした場所打ちコンクリート杭の耐震性能

The cast-in-place-concrete piles can be slimmed by the construction method of the under-reamed pile. However, the seismic shear stress increases because the area of the pile head decreases. In this paper, first, the specification of such piles and the result of frame analysis which consists of building and foundation are shown as the background data. Secondly, the earthquake-resistant properties of reinforced concrete piles with the normal-strength transverse reinforcement(350MPa) or the high-strength transverse reinforcement(1300MPa) are experimentally considered. Six-teen specimens were tested; two with the diameter of 450mm, twelve with the diameter of 350mm, and two with the diameter of 300mm. The specimens with the diameter of 450mm are models of standard cast-in-place-conerete piles, and the specimens with the diameter of 350mm or 300mm are models of under-reamed piles. Experimental results show that, when properly reinforced with the transverse reinforcement, slim reinforced concrete piles can exhibit stable hysteretic behavior and significant ductility.

Experience with construction of long underreamed piles in collapsible soils : Soil Mech Found Engng V27, N4, July–Aug 1990, P135–141

Experience with construction of long underreamed piles in collapsible soils : Soil Mech Found Engng V27, N4, July–Aug 1990, P135–141

Experience with construction on long underreamed piles in collapsible soils

1. The noneffectiveness of construction of underreamings in long piles resting on insufficiently dense soils is due to high resistance on their lateral surfaces and small settlements until rupture occurs, as a result of which the tip resistance is not realized.

Performance of instrumented underreamed pile foundation supporting a single storey structure in expansive soil : Indian Geotech J V18, N4, Oct 1988, P340-355

Performance of instrumented underreamed pile foundation supporting a single storey structure in expansive soil : Indian Geotech J V18, N4, Oct 1988, P340-355

Pile testing using raked under-reamed piles : Mohan, D; Jain, G S; Gupta, S P Ground Engng, V12, N3, April 1979, P47–52

A simple set-up for conducting high capacity pile load tests, using raker under-reamed piles as anchors, is described. The technique requires little space and eliminates the need for heavy joists and kentledge in addition to giving safety benefits and effecting savings in cost and time. The paper also highlights the load-carrying capacity of multi-under-reamed piles in compression and as anchors. /Author/

Vertical shifting of underreamed piles in swelling clay soils (in Russian) : Boiko, N V; Piven, V G; Kudriashov, V P Osnov Fundam, V10, 1977, P9–12

Vertical shifting of underreamed piles in swelling clay soils (in Russian) : Boiko, N V; Piven, V G; Kudriashov, V P Osnov Fundam, V10, 1977, P9–12

Bored Pile Groups under Vertical Load in Sand

The results of field tests of bored underreamed pile groups under sustained vertical loads are presented, along with an empirical approach for estimating group efficiencies and load-displacement characteristics of pile groups from the known behaviour of single piles. The effectiveness of available methods for estimating group settlements are compared, resulting in a conservative estimate.

Design of underreamed piles. 4F, 1T, 8R : Vovk, AA Mikhailyuk, AV Gundarev, KA Soil Mech. Found. Engng, V11, N5, Sept–Oct. 1974, P290–295

Design of underreamed piles. 4F, 1T, 8R : Vovk, AA Mikhailyuk, AV Gundarev, KA Soil Mech. Found. Engng, V11, N5, Sept–Oct. 1974, P290–295

Design of underreamed piles

In the construction of underreamed piles, maximum development of radial cracks should be aimed at when forming the lower cavities by the blasting method. This can be achieved both by using special high explosives (pentaerythritol tetranitrate, hexogen, trotyl, etc.) and by reducing the plastic properties of the soil mass (reduction of its water content and other measures). In the latter case the useful effect from the utilization of the free space in the radial cracks can be significantly enhanced, for further increase of the economy in construction work.

Experience in sinking bored, underreamed piles in the Ukraine

Experience in sinking bored, underreamed piles in the Ukraine