Experimental investigation of the effect of the bending stiffness of reinforced-concrete piles under lateral load

Conclusions 1. The stress-strain state of the reinforced-concrete-pile/soil system depends on both the elastoplastic properties of the soil, and the pile material.2. The variation in the bending stiffness of the cross section of a reinforced-concrete pile during loading should be accounted for in calculating the lateral load on these piles. Consideration of this factor will make it possible to determine the stress-strain state of the system under consideration more accurately; this will ensure a saving of concrete and reinforcement.Kharkov Institute of Civil Engineers. Kharkov Scientific-Research Institute for the Design and Planning of Industrial Construction. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 9–11, July–August, 1988.     

Stock test sounding pile

A new design is suggested for a stock sounding pile that makes it possible to separately determine the bearing capacity and deformation characteristics of layers of engineering-geological elements (EGE) on the side surface and tip of the test pile. From these data, any piles sunk into a base with different thicknesses of the EGE can be calculated.Vorkuta Branch of the "Komigrazhdanproekt" Institute. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 15–18, November–December, 1993.     

Analysis of settlements of bored-cast-in-place piles in collapsible soils

Conclusions 1. The proposed method of analysis makes it possible to investigate the behavior of bored-cast-in-place piles interacting with collapsible bases for different complex cases of "soaking" of the soils.2. The sequence in the "soaking" of the soil base and the application of the load to the pile exerts a determining effect on their settlement.3. The loading force of "negative" friction depends on the soil base "soaking" scheme, the "soaked" soil layer thickness, the collapsible soil properties, and other factors.4. The additional pile settlements caused by the "negative" friction forces developed as a result of hanging of the collapsing soil from the pile can be significantly larger than the pile settlements under the load in the absence of collapse.5. "Soaking" of the collapsible soil base from the bottom in parallel layers is more dangerous for bored-cast-in-place piles than "soaking" from the top.Scientific-Research Department of S. Ya. Zhuk Gidroproekt Institute. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 14–17, January–February, 1987.     

Investigation of the operation of pyramidal piles in swelling soils

Patterns of operation of pyramidal piles in swelling soils are given: the dependence of their rise on the taper angle, the length of the pile, and the transmitted load. The authors studied layer-by-layer displacements of soil around the pile and give their dependences on the depth of the layer's location. A formula is presented for determining coordinates of the neutral point, from which the rise of an unloaded pile is found.Scientific Research Institute of Foundations and Underground Structures. Central Scientific Research Institute of Experimental Design of Rural Construction. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 8–11, March–April, 1993.     

Method and results of testing piles tamped into holes drilled in soils classed as type II in terms of proneness to slump-type settlement (in order of discussion)

Conclusions 1. Piles that are tamped into predrilled holes cutting through soils classed as type II in terms of proneness to slump-type settlement, which have expended tips supported on clayey soils and clays that are not prone to slump-type settlement and that are situated above the water table under conditions prevalent in Zaporozhe, have low (with respect to type-I soils), but, in many cases, completely adequate bearing capacity, and can be used to build many structures.2. The load friction in soil classed as type II in terms of proneness to slump-type settlement amounts to 30–35 kN/m² along the lateral surface of a pile in Zaporozhe.3. The allowable design load on a pile in soils classed as type II in terms of proneness to slump-type settlement should be determined, as a rule, from pile tests in an experimental trench where the soil develops slump-type settlement under its own weight.4. A smaller load friction acts on a pile whose lateral surface is covered with three to five layers of elastic sheathing than on the unprotected piles.Scientific-Research Institute of Bases and Underground Structures. Dnepropetrovsk Civil-Engineering Institute. Ukrainian State Design Institute for Special Construction. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 7–10, May–June 1984.     

Determination of the bearing capacity of piles in permafrost by static penetration

Conclusions 1. The tests that we conducted demonstrated the technical feasibility of the static penetration of plastically frozen soils with temperatures of 0 to –0.4°C by series-produced type SP-59 and SP-72 apparatus.2. According to penetration data, computation of the bearing capacity of piles in plastically frozen soils using the method proposed by Ladanyi indicate good convergence with data derived from the field testing of piles.3. Penetration makes it possible to determine the bearing capacity of piles in plastically frozen soils with a temperature above –0.3°C on which there are no data for the computation in SNiP II-18-76, and the increase their bearing capacity by 25–30% as compared with the SNiP for soils with temperatures of –0.3 to 0.4°C.4. Further research on the development of a technology and methodology for static penetration of plastically frozen soils of different lithologic composition and temperature, and also a more precise definition of a number of parameters , n, and m, which are used in computations of pile bearing capacity, are necessary.State Institute for the Design and Planning of Beds and Foundations. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 18–20, March–April, 1986.     

Evaluation of pile bearing capacity by dynamic tests

Conclusions 1. In determining the bearing capacity of piles, dynamic resistance should be understood to mean that maximum value of soil reaction which is generated during the hammer blow. However, this concept should not be confused with the resistance obtained from the results of dynamic pile tests.2. Upon the delivery of a dynamic blow, as pile penetration proceeds, an increase in soil reaction occurs which reaches the limiting and then the critical load values as obtained from static tests. Therefore, the results of dynamic tests if the latter are correctly performed should coincide with the critical load obtained from static tests. Experience has shown that for this condition to be fulfilled, the total refusal of piles due to a single blow should be not less than 10–15 mm and the residual part of the refusal should be not less than 2 mm.3. The results of the dynamic tests enable the static pile resistance to be determined for the soil condition at the given instant. As is shown by graphs of the dynamic and static tests, the limiting pile resistance depends not on the type of test but on the condition of the soil and the degree of its thixotropic recovery.4. The determination of pile bearing capacity by the dynamic method, taking their "resting" into account, should be based on the results of the initial blows.Scientific-Research Institute of Foundations. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 11–13, March–April, 1975.     

Technicoeconomic basis for selection of pile and pile-foundation designs

Conclusions 1. In addition to the factors enumerated at the outset of this paper, the character of the given external effects should be considered in selecting a pile design.It is expedient to use large-diameter (60–120 cm) predrilled-and-rammed piles in cases where the piles should sustain large (100 kN and greater) horizontal loadings, and driven or predrilled-and-rammed piles with a pedestal where the piles should sustain large vertical loads.2. The advantage of one pile design over another should be weighed from both the cost indicators, and the material-outlay indicators for the pile and pile-foundation design, taking into account the resources of the construction organizations as a basis for a variant design.State Institute for the Design and Planning of Beds and Foundations. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 13–16, January–February, 1976.     

Results of evaluation of the strength of concrete placed in the shafts of cast-in-place piles

Conclusions 1. Application of the method of underwater concreting with the use of a container is inexpedient in connection with the presence of a large number of flaws detected in the shafts of cast-in-place piles formed by this method; concreting of holes by the VAT method is preferable.2. The strength of concrete in the shafts of cast-in-place piles increases, reaching a maximum at a depth of 0.4–0.5 the length of the shaft. Variation in strength along the shaft is explained primarily by the percentage of coarse aggregate contained in the concrete.3. The quality of pile concrete should be monitored during all stages of pile installation, and, primarily during the stage of concreting, i.e., when there is a chance of correcting an observed defect.All-Union Institute for the Design and Planning of Health Resorts. Scientific-Research Institute of Foundations and Underground Structures. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 14–17, September–October, 1976.     

Effect of underreaming on bearing capacity of bored pile

Conclusions 1. From the data for the full-scale static tests of piles 6–22 m long, it was found that as the ratio /d increases, the load transmitted through a pile underreaming having the same size decreases proportionally.2. The limit strength at the foot of piles over 10 m long cannot be determined by means of analytical strengths depending only on the depth h and the liquidity index I_L but which do not depend on the ratio /d.Scientific-Research Institute of Bases and Underground Structures. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 12–14, November–December, 1986.     

Performance characteristics of horizontally loaded piles located near a trench

Conclusions 1. The excavation of a trench (pit) in the vicinity of a pile diminishes its ability to resist horizontal loading. This reduces the depth of pile embedment in the soil and depends on the depth of the trench and its distance from the pile.2. The above-described method of testing piles for horizontal loading with strain gages can be used to determine the design depth of pile embedment in a soil.3. The upper layer of soil of thickness d exerts no significant influence on the performance of horizontally loaded piles due to the formation of a gap between the pile and soil during its backfilling and can therefore be disregarded in their disign.Scientific-Research Institute of Industrial Buildings and Structures. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 13–14, May–June, 1976.     

Investigation of the bearing capacity of piles driven in plastic frozen soil

Conclusions The bearing capacity of a pile lowered into a borehole whose cross section exceeds the cross section of the pile for the possibility of filling in with slurry (frozen-in, friction, bored-sunk piles) is close to the calculated, but has a greater settlement under a standard load in comparison with a bored-drive pile.The bearing capacity of piles driven by the VMS-1 vibratory hammer into plastic frozen soil (bored-drive piles) is on the average 1.6 times greater than the calculated. Such an excess of the bearing capacity of the piles can be explained by the formation of a new structure and frost texture of the soil within 30–50 mm around the pile skin. A characteristic feature of the newly formed zone of soil is a considerably greater homogeneity and density of the soil than under natural conditions and absence of ice lenses and interlayers directly contacting the pile.The settlements of the pile tested under a standard load were less than the allowable deformations for the bases of the majority of buildings and structures.The cross-sectional area of the pilot hole should be equal to 0.65–0.75 of the pile section in the case of driving it at the time of the maximum depth of thawing of the soil and 0.95 at the time of seasonal freezing of the soil.Restoration of the contact bonds between the soil and pile during its freezing-in after driving into soil with a temperature of -0.5°C and higher can continue for several months.Deceased.Central Scientific-Research Institute of Transport Construction (TsNIIS). Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 19–20, January–February, 1979.     

Interaction of cast-in-place piles with soil under type II collapsibility conditions

Conclusions 1. Under the given and similar hydrogeologic conditions, the settlements of piles fully cutting through the collapsible mass and sunk 2–12 m into the noncollapsible soils, when the pile bearing capacity under the external load is satisfied, are practically equal to the ground surface settlements in the pile site.2. For long-term soaking of the soils from the top, the low position of the depth at which soil compression starts under the action of the dead weight of the mass (it is in the range 14–16 m), and the development of compression deformations in the noncollapsible layers, which prevents detachment of the upper soil zone from the piles, are essential under the given conditions.3. For increase in the pile length from 24 to 31 m and support on denser soil layers (alluvial clays), the soil base resistance and the additional load caused by the soil mass action increase correspondingly, but the pile settlements remain practically unchanged.For substantial reduction of the possible absolute pile settlements with prolonged soaking of the soils under the given hydrogeologic conditions, the pile length should be increased by about 20 m. However, for establishment of the foundation dimensions it is extremely important to compare the allowable and possible differential settlements of adjacent foundations, which are comparatively small under the given conditions.Scientific-Research Institute of Bases and Underground Structures. TISI. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 14–17, March–April, 1986.     

Experimental investigation of the distribution of stresses in large bored situ-cast piles

Conclusions 1. Diagrams were obtained of the distribution of specific skin friction of bored situ-cast piles with a diameter of about 1 m and length of 18 m and of their transformation as a result of flooding the soils and successive loading of the pile with gradual involvement of shearing resistance forces in a downward direction.2. Before the long bored situ-cast piles broke loose, the specific skin friction in homogeneous soil is practically constant over the length of the pile, which confirms the correctness of the concept used in [3].3. On flooding soils at the base of the piles, when the external load is equal to zero and there is still no slumping of the soil layers under their own weight, substantial normal stresses occur in the cross sections of long bored situ-cast piles, as a result of which they are additionally loaded by the soil hanging on them.4. The foot of long bored situ-cast piles penetrating loose layers of loam soils and supported on a layer of loam with =0.662 carried no more than 10% of the total load applied to the pile prior to breaking loose. Thus it behaves as a friction pile before breaking loose.5. After the pile breaks loose, the normal contact stresses on its foot increase in direct proportion to settlement. It follows from this that to increase the point resistance before breaking loose it is necessary to preliminarily compact the bottom of the hole of the bored situ-cast pile.Scientific-Research Institute of Bases and Underground Structures (NII Osnovanii). Research Department, All-Union Planning, Surveying, and Scientific-Research Institute (Gidroproekt). Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 11–13, May–June, 1980.     

Investigations of the distribution of contact pressures in a short bored pile with a radial enlarged toe

Conclusions 1. The outlines of the diagrams of the normal contact pressures in the case of separate vertical and horizontal loads permit determining the character of redistribution of pressures in the soil-pile contact zone during an increase of loads applied to the pile head.2. The results of investigations can be used for studying the mechanisms of distribution of loads between elements of a short bored pile with a radial enlarged toe and for developing practical methods of calculating its bed with respect to bearing capacity and deformations.A. I. Mikoyan Kuibyshev Civil Engineering Institute. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 18–19, May–June, 1975.     

Introduction of rectangular pyramidal piles in Belorussia

Conclusions 1. The investigations corroborate the results of well-known theoretical and practical studies on the effect of the geometric shape of piles on their bearing capacity. A computational analysis and model and full-scale pile tests established some quantitative relationships between the bearing capacity and shape of driven piles currently being used in construction.2. Investigations and construction experience indicate that there is no "universal" pile which is optimal for all structures and all types of soil conditions. According to the results of investigations of short driven piles, and from design and construction experience, it can be concluded that for loose and medium-density, homogeneous sands and clay soils having a consistency ranging from semistiff to soft/plastic, it is expedient to adopt rectangular pyramidal piles for large-scale construction in the conditions in Belorussia, instead of the prismatic type, as they have shown that, under the above conditions, the volume of pile work is reduced 1.6 times, and labor consumption and costs are reduced commensurately.Belorussian Polytechnical Institute (BPI). All-Union State Trust of Enterprises for Manufacture of Construction Machinery (Stroimekhanizatsiya). Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 8–10, January–February, 1980.     

Testing buildings for strength and stability

Conclusions 1. The proposed method makes it possible to realize safe controllable deformation of a subgrade, given a "building-bed" system of various shapes and values of settlements recorded with time. It shortens the time required for experimental operations from 6–10 months (for measurement of field settlements) to several days.2. The method can be used in conducting field experiments; the leveling and occupacy of buildings on platforms are not associated with the expectancy of deformation effects due to slump-type settlement or undermining.Scientific-Research Institute of Structural Parts, Zaporozhe Division of the Scientific-Research Institute of Structural Parts. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 7–8, July–August, 1980.     

Possibility of reducing the duration of static pile tests

Conclusions 1. The experiments, carried out under different conditions, did not show substantial differences in the limit strengths of prismatic piles tested at the standazd loading rate and by the accelerated method when it is considered that attenuation of the settlement has been reached when it has a rate of 0.1 mm in 15 min. The tests performed by continuous increase in the load over a period of 10–15 min led to overestimation of the limit strengths by 20–30%.2. Under conditions in which the settlements are not the object of special studies, accelerated pile tests (with a settlement stabilization criterion of 0.1 mm in 15 min), in place of standard prismatic piles applicable under the most widespread soil soil conditions (for example, in alluvial, deluvial, and similar deposits). In this case, it is advisable to use the pile limit strength for settlements which are smaller by a factor of two than for the standard tests.NIIpromstroi Institute. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 9–12, January–February, 1987.     

大型土与结构相互作用恒刚度直剪试验装置研究

已有的土与结构接触面室内剪切试验多集中在恒荷载和恒位移加载条件下接触面力学特性的研究,而预制桩基础沉桩过程中桩土界面受力条件与恒刚度加载类似,即桩土界面法向应力随桩周土体法向位移是动态变化的。针对目前黏性土中桩土界面大型恒刚度的试验手段比较缺乏,自主设计研制了一种大型恒刚度直剪仪用于桩土界面力学特性的测试。该直剪仪考虑了桩周土体变形特点,剪切过程中桩土界面接触面面积始终保持不变,能够准确模拟桩土界面剪切试验;采用弹簧组加载系统和数控电机控制系统,法向可提供恒刚度边界条件,水平切向可按位移控制,能够实现桩土界面上直线和循环剪切的加载路径。试验结果表明:该直剪仪能够很好地再现黏性土中桩土界面在恒刚度加载条件下直线剪切的力学响应,为静压桩沉桩过程的桩土界面力学特性的研究提供了基础。     

Reliability analysis of laterally loaded piles using response surface methods

Response surface methods have been applied to the reliability analysis of laterally loaded piles. Beam elements and a series of discrete springs are used to model the pile–soil system. The pile head displacement and the maximum bending moment in the piles are used as the performance criteria in this study. It is shown in the illustrative example that the CDF and PDF curves of the pile head displacement and the maximum bending moment in the pile obtained from the proposed methods are in good agreement with Monte Carlo simulation. The failure probabilities of the pile under specified performance criteria, the probabilistic responses of the pile-soil system, and the effect of pile-soil parameters to the failure probability of the pile are also studied.