ASTM'ye göre şişme deneyleri
Test methods for swell according to ASTM
- Tez No: 46371
- Danışmanlar: PROF.DR. ERGÜN TOĞROL
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 44
Özet
ÖZET Düşük su muhtevalı şişebilen zeminlerin su alması veya zemin üzerindeki basıncın herhangi bir nedenle azalması sonucu oluşan büyük hacim değişiklikleri zeminin şişme özelliğidir. Bu hacim değişikliği sonucu oluşan basınç üst yapıya büyük çapta zarar verebilir. Şişme basıncının önceden belirlenmesi halinde gerekli mühendislik önlemleri alınabilmekte ve böylece üst yapıda oluşabilecek hasarlar minimuma indirilebilmektedir. Şişen zeminlerin şişme potansiyeli ve şişme basıncı değerlerinin belirlenmesi için bir çok deney tekniği geliştirilmiştir. Bu çalışmada ASTM'de verilen üç alternatif şişme deneyi ele alınmış ve bu standarta aynen uyulmaya çalışılmıştır. Üç yöntem birbiriyle karşılaştırılmış ve hangi yöntemin daha sağlıklı sonuç verdiği tartışılmıştır. Elde edilen deney verileri incelenerek varılan sonuçlar açıklanmıştır.
Özet (Çeviri)
SUMMARY TEST METHODS FOR SWELL ACCORDING TO ASTM Expansive soil has been responsible for many structural damages that result in great financial losses in many part of the world. In recent years, considerable progress has been made in clarifying the mechanism of swelling in soils, in understanding the behavior of expansive soils, and in developing technigues for handling swelling soils in engineering practice. Expansiveness of soil is related to the clay mineral type of soil, amount of clay, structure of soil, dry density of soil, water content of soil, availability of water and surcharge pressure of soil. The plasticity index and the Liquid Limit are usefull indices for determining the swelling characteristics of most clays. The swell potential is presumed to be related to the opposite property of shrinkage measured in a very simple test. Many empirical methods have been proposed to correlate the swelling potential to soil properties. These relationships are useful for identifying the swelling potential of soil. The grain size and the and the amount of clay content have a bearing on the swelling potential of expansive soils. The clay content as well as the Atterberg Limits should be included in the routine laboratory investigation on expansive soils. The swelling characteristics of soil can be explained percent swell and swell pressure. Percent swell can describe the increase in the ratio of the change in vertical height to the original height of a column of in situ soil. ASTM defines swelling pressure as the pressure which prevents the specimen from swelling or that pressure which is required to return the specimen back to its original state ( void ratio, height ) after swelling. The main factors effecting volume change are : * Soil Type * Structure * Dry Density* Moisture Content * Permeability * Thickness of Soil Straum * Insitu Stress Condition * Externally Applied Loads * Method of Compaction for Remolded Samples * Degree of Saturation * Time Required for the Test If potential of swelling and pressure of swelling of clay soils can be forecasted in advance, some collapes and failures can be avoided. A large number of techniques and apparati have been developed for expansive soil testing. In this study, according to ASTM, test methods for swell have been investigated. These test methods cover three alternative laboratory methods for determining the magnitude of swell or settlement of relatively undisturbed or compacted cohesive soil. The following three alternative test methods require that a soil specimen be restrained laterally and loadded axially in a consolidometer with access to free water. Method A : After the initial deformation reading at the seating pressure is recorded, inundate the specimen and record deformations after various elapsed times. Readings at 0.1, 0.2, 0.5, 1.0, 2.0, 4.0, 8.0, 15.0, and 30.0 min. and 1, 2, 4, 8, 24, 48, and 72 h are usually satisfactory. Continue reading until primary swell is complete. After completion of swell, apply a vertical pressure of approximately 5, 10, 20, 40, 80, etc. kPa with each pressure maintained constant. Maintain pressure until the specimen is recompressed to its initial void ratio/height. The duration of each load increment shall be equal and of a duration which assures 100 % primary consolidation. Method A may be modified to place an initial vertical stress, au on the specimen equivalent to the estimated vertical pressure on the in situ soil within 5 min of placing the seating pressure and securing the zero deformation reading. Read the deformation within 5 min and remove the vertical stress, excep for seating pressure. Record the deformation within5 min after removal of d inundate the specimen. Continue readings until primary swell is complete. After completion of swell, apply a vertical pressure. This modification provides a correction to the initial deformation reading at o*» in an effort to more closely duplicate the in situ void ratio of the soil. Method B : Apply a vertical pressure exceding the seating pressure within 5 min of placing the seating pressure. Read the deformation within 5 min of placing the vertical pressure. The specimen is inundated immediately after the deformation is read and deformation recorded after elapsed times similar to Method A until primary swell is complete. Continue the test as Method A. Method C: Apply an initial stress, ot, equivalent to the estimated vertical in situ pressure or swell pressure within 5 min after placement of the seating pressure. Read the deformation within 5 min after placing oi, and immediately inundate the specimen with water. Apply increments of vertical stress as needded to prevent swell. Variations from the deformation reading at the time the specimen is inundated at stress cti shall be kept preferably within 0.005 mm and not more than 0.010 mm. Load the specimen no furter tendecy to swell (usually overnight ). Load increments shall be sufficient to define the maximum point of curvature on the consolidation curve and to determine the slope of the virgin compression curve. Duration of rebound load decrements shall be in accordance with 1 0.6 of Test Method D-2435. The relative swell potential of soil determined from these test methods can be used to develop estimates of heave for given final moisture and loading conditions. The initial water content and void ratio sould be representative of the in situ soil immediately prior to construction. Selection of test method, loading, and inundation sequences sould, as closely as possible, simulate any construction and post-construction wetting and drying effects and changes in loading conditions. Laboratory-prepared test specimens should duplicate the in situ soil or field-compacted soil conditions as closely as possible because relatively small variations in unit weight and water content can significantly alter the measured heave and swell pressure. Differences in soil fabric of the compacted specimens, such as obtained by kneading or static compaction, could also have a significant impact on the swell behavior of cohesive soils. XISoils containing montmorillonites are iikeiy to have a significant potential for swell and are commonly tested by these test methods. These test metods are applicable to undisturbed test or remolded specimens.or as folows. Method A : This test method measures, ( a ) The free swell ( b ) Percent heave for vertical confining pressure up to the swell pressure ( c ) The swell pressure Method B : This test method measures, ( a ) The percent heave or settlement for vertical pressure usually equivalent to the estimated in situ vertical overburden and other vertical pressure ( b ) The swell pressure Method C : This test methods measures, ( a ) The swell pressure ( b ) Preconsolidation pressure ( c ) Percent heave or settlement within the range of applied vertical pressures. In this investigation, soil sample which show high swelling, have been tested with three alternative laboratory methods. The clay used in laboratory test was brought to the laboratory from a construction area in İ.T.Ü. Ayazağa. The properties of the sample such as the atterberg limits, dry density and optimum water content were obtained by utilizing routine laboratory tests. The sample which were used in the consolidometer swelling test have been prapered by standart compaction mold. The swelling pressure of all samples which were at optimum water content were obtained. Three alternative laboratory test methods were compared each others. Methods A and C have produced estimates of have consittent with observed heave. Method B may lead to estimates of heave less than observed heave. Method A has not been recomended for evalution of xnswell pressure and consolidation parameters for settlement estimates because sorption of water under practically no restraint may disturb the soil structure. xm
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