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.     

Bearing capacity of cast-in-place piles on construction sites of the volgodonsk heavy machine-building plant

Conclusions 1. The behavior of large-diameter (a shaft diameter of 1 m, a pedestal diameter of 2.2 m, and a length of up to 25 m) cast-in-place piles subject to an increasing crushing load in a stratum of wetted loess soil is characterized, as with small-diameter piles, by a clear-cut transition from an elastic to a plastic state with small settlements (up to 12 mm).2. Pile settlement owing to compression of the shaft is a significant part (0.6) of the total settlement experienced by the pile within the loading range from 0 to P_ul.3. Computations of the bearing capacities of piles performed in accordance with an approximate solution of the problem of limiting equilibrium [4, 5] are in good agreement with data obtained from static pile tests in all cases under consideration; this made it possible to use them in designing the Nos. 1 and 3 frames of the plant with a savings of 1.5 million rubles.4. Computations of pile bearing capacities, which are performed in accordance with the plan outlined in Chapter II-17-76 of the Construction Norms and Specifications should be defined more precisely.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 13–16, March–April, 1977.     

Stabilization of settlement of base and correction of tilt of a 16-story residential building on pile foundations

Conclusions 1. For insufficient bearing capacity of the pile group and development of significant settlement, a grating was added which substantially improved the bearing capacity of the piles and reduced the settlement of the pile field.2. Modern methods of evaluating the bearing capacity of piles by carrying out static tests made it possible to achieve effective solutions, since the safety factor was low (the removal from service of only two piles from the group of about 30 piles immediately led to development of additional settlement).3. During the carrying out of pile construction work, special attention should be given to the recording, in the pile-driving logbook, of the number of blows of the hammer, the height of fall, and the refusals, since these data may reveal piles with low bearing capacities.4. For construction of tall buildings on weak soils having complex stratification, even on piles, it is necessary to perform observations on the development of settlements during construction and operation.Lenniiproekt. Leningrad Civil Engineering Institute. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 9–11, July–August, 1981.     

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.     

Experimental investigations of pile loads and foundation settlements in tall large-panel buildings

Conclusions 1. During the process of settlement of pile foundations with and without gratings in the nine-story large-panel frameless buildings with transverse and longitudinal bearing walls, the loads were redistributed and equalized, which was a consequence of interaction between the relatively rigid building box and the pliant base of the foundation. 2. Field investigations of the actual pile loads in the foundations of the nine-story large-panel buildings made it possible to establish that the design pile loads exceeded the actual values by 12–16%. 3. The nature of the distribution of the forces in the elements of the pile foundations of the large-panel frameless buildings indicates the need for taking into account the pliancy of the soil base of the pile foundation and its joint operation with the constructional components of the building box for determining the pile loads and for designing the gratings as well as the wall panels with gratingless support. 4. In the pile foundations of the nine-story frameless large-panel buildings with load-bearing, frequently transverse walls of the type of Series 1-464D, with and without gratings on compressible soils, the loads in piles with equal rigidities of the soil bases can be assumed to act as uniformly distributed, as an approximation, in engineering analyses. In the case of different rigidities of the soil bases of the piles, the load on each pile can be determined as a force proportional to the corresponding rigidity. 5. The actual settlement of the pile foundation of the large-panel building on alluvial soils was greater by a factor of 5–6, and for the building on the clay soils of the Ufa floor it was greater by a factor of 15 in comparison with the settlement of a single pile constructed on the basis of the same static test results, under the same soil conditions, and for the same loads. Hence, the coefficient ζ recommended in the SNiP II-17-77 for transfer from settlements of individual piles in static tests to settlements of piles in foundations under long-term loading should be differentiated according to the soil type and state. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 8–10, March–April, 1982.     

Effectiveness of using pile foundations in housing construction in Tyumen

Conclusions 1. Pile foundations of residential buildings in Tyumen under the usual soil conditions with the use of 30×30 cm prismatic piles and low monolithic grillage are, as a rule, ineffective.2. The use of pile foundations with a high grillage does not produce perceptible advantages and their technicoeconomic indices are close to those of foundations with a low grillage.3. The use of grillage-free pile foundations permits obtaining indices comparable with strip foundations at a pile length up to 8 m (working length 6 m).4. The economic effectiveness of pile foundations under conditions of Tyumen can be increased by using short piles of rational designs having an increased bearing capacity under the given soil conditions.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 4–6, May–June, 1977.     

Piles injected into predrilled holes in soils prone to slump-tyre settlement

Conclusions 1. Drill-and-inject piles of increased bearing capacity with a diameter of 250–400 mm and more and a depth of up to 50 m and more, which are embedded into underlying soils not prone to slump-type settlement can be used in loess soils classed as type-II in terms of proneness to slump-type settlement.2. The use of washing mud based on sodium silicate, which eliminates slump-type settlement of the soils during pile fabrication and reduces the friction against their lateral or surface by 10–15% within the limits of the stratum prone to slump-type settlement, lowering the negative loads on the pile, is effective when piles are injected into predrilled holes in soils prone to slump-type settlement.3. Drill-and-inject piles 250–400 mm in diameter and up to 50 m long have a design bearing capacity of from 0.50 to 2.50 MN and can be recommended for the installation of new, and the strengthening of existing foundations for civil and industrial projects in soils prone to slump-type settlement.4. A special set of equipment, which makes it possible to ensure the continuous production of work that includes the drilling of holes, assembly of reinforcing cages, and the filling of the holes with a hardening grout, should be used for the installation of these piles."Soyuzgidrospetsstroi." Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 18–20, January–February, 1988.     

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.     

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.     

Bored/cast-in-place piles employing soil compaction of hole bottom,for the "Atommash" Plant

Conclusions 1. Compaction of the soil at the bottom of deep holes of 1-m diameter as described, raised the bearing capacity of piles at their ends, under the Volga-Don ground conditions, by three to five times.2. In view of the fact that the toe of long (exceeding 15 m) floating bored/cast-in-place piles of usual construction contributed only to a weak extent (up to 10% of the total resistance, under Volga-Don conditions) to the performance of the pile, right up to its failure, it is expedient and economically efficient to install such piles only in holes previously rammed at their ends. Under ground conditions of type II in regard to collapsibility, this measure is particularly important in order to avoid inadmissible pile settlements resulting from negative friction following soil collapse under the weight of its own thickness. Cast-in-place piles placed in prerammed holes were introduced in the construction of Section 5 of the Volga-Don "Atommash" Plant, and are recommended for buildings of a substantial number of stories in Volga-Don.Scientific-Research Institute of Bases and Underground Structures. (NII Osnovanii) Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 10–13, November–December, 1980.     

Results of field tests of piles in permanently frozen ground

Conclusions 1. To estimate the bearing capacity of piles and to determine the deformation characteristics of soils it is necessary to conduct comprehensive pile tests on plots with the same frozen-ground conditions.2. Pile tests should be conducted before the appearance of the second region of continuous deformations. For structures allowing considerable deformations this will permit increasing the bearing capacity, taking it to be equal to the value at which the jog of the soil consolidation under the pile point ends.3. Calculation of pile foundations with respect to the second limiting state permits a substantial increase of the design bearing capacity of piles, which ultimately leads to a reduction of construction costs.4. The use of the accelerated test method with the obtainment of the experimental values of the conversion factor to long-time strength permits a considerable reduction of the test period.5. The data obtained in pile tests permits developing more economical designs.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 35–36, September–October, 1977.     

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.     

Investigation of the effect of a vertical surcharge on horizontal displacements and resistance of pile columns to horizontal loads

Conclusions 1. The principle of independence of the action of forces in the general case is not applicable to calculation of pile columns with relative embedment < 15. A vertical surcharge can somewhat decrease (in weak saturated soils) or increase (in clays of very stiff consistency) the resistance of pile columns to horizontal loads. In the investigated saturated soils, the bearing capacity decreased by no more than 15%, and in very stiff slump-prone soils it increased by a factor of 1.9.2. Under equal conditions, pile columns with cantilevers absorb a 1.3–1.6 times greater horizontal load than prismatic.3. When designing pile columns, the depth of their conditional embedment in the soil should be determined in conformity with the requirements of Instructions [12] and not by Table 12 in SNiP II-B.5-67*, since this leads to uneconomical reinforcement of the pile columns.4. For pile columns of agricultural buildings a permissible crack width of 0.3 mm should be adopted instead of the 0.2 mm according to SNiP II-B.5-67*.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 11–14, January–February, 1978.     

筒桩桩承式加筋路堤现场试验研究

为了进一步明确筒桩桩承式加筋路堤的工作机制,在广州绕城高速公路九江—小塘段进行现场试验。试验结果证明,筒桩单桩竖向承载力大,均以刺入方式破坏,并且筒桩单桩复合地基承载力大,沉降小。筒桩桩承式加筋路堤荷载传递机制主要受"土拱效应"和"拉膜效应"控制,桩土应力比随路堤荷载以及桩顶与桩间土之间沉降差的变化而变化。路堤荷载下筒桩复合地基,总沉降小,桩帽上和桩间土上的土体存在沉降差,沉降差的发展可以反映土拱效应的发挥程度。另外,路堤荷载在地基土中产生的超孔隙水压力很小,且随深度迅速减小,地下6.0m处超孔压已接近0。路堤侧向变形小且随深度迅速减小,最大侧向变形发生在地下3.0～4.5m处。     

Improved methods of testing piles in frozen soils

Conclusions 1. The approach adopted in this article for analysis of pile test data based on the above relations made it possible to work out three accelerated testing methods — stepped with equal-duration steps; dynamometric; and stepped-dynamometric.2. The results of the performed tests are characterized by an increased information content, which makes it possible to design the piles for two groups of limit states and to take into account the pile load variation.3. The reliability of the proposed testing and design methods is confirmed by comparison with experimental data.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 14–18, July–August, 1990.     

Actual and calculated loads on piles and results of observing settlements of a large-panel building

Conclusions 1. During the construction period the loads on extreme piles along the axes of transverse bearing walls are considerably greater than on the middle ones.2. Under the effect of rigidity of the building a redistribution of the loads on the piles during its operation occurs even in the absence of a grillage, i.e., the more loaded piles are unloaded and the less loaded ones are additionally loaded.3. The actual loads on the piles in the operating period are considerably less than the calculated, which indicates the need to refine the recommendations of SNiP II-6-74 for the purpose of taking into account the useful loads in calculating the foundations of residential buildings.4. The factor =0.2, concerning conversion from settlements of single piles in static tests to settlements of piles in foundations under long-term load, given in the draft of the new edition of SNiP II-17-77, is acceptable.5. To accumulate data on the actual loads on pile foundations it is necessary to continue their measurements under various soil conditions.Deceased.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 17–19, May–June, 1977.     

Performance of vertically loaded combined pile foundations

Conclusions 1. Bending moments, which increase in proportion to the settlement and the angle of incline of the piles, develop in inclined piles as the CPF settle under load. The possibility of their determination in accordance with the method outlined in [4] has been substantiated experimentally.2. Proceeding from conditions of the optimal performance of inclined piles and conditions under which their strength is ensured, it is established that it is expedient to adopt an angle of incline within the range of 5–6° for the piles.3. A method of calculating the bearing capacity of CPF from static-penetrometer data, proceeding from the hypothesis of the possibility of determining the strength of CPF as the sum of the strengths of its component elements with allowance for strength assurance in the material of the inclined piles, is proposed. The discrepancy between computed and experimental data was 16–32% as a factor of safety.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 15–18, November–December, 1991.     

Investigations of negative skin friction on piles and suggestions on its calculation

Conclusions The investigations showed that negative frictional forces appear at the time of occurrence of continuous settlement of the soil relative to the pile, but for their maximum development this settlement should be relatively large, of the order of 5 cm and more. In addition, it was established that the negative frictional forces act only during active displacement of the soil surrounding the pile as a result of its consolidation or other causes. After this displacement stops the negative frictional forces practically disappear.The established physical characteristics of the effect of negative frictional forces permitted taking the presence of an excess of the rate of soil settlement over the rate of pile settlement as the criterion of their occurrence. The suggestions on calculating piles worked out with consideration of this criterion allows in a number of cases disregarding the negative frictional forces in the effective design load or taking them to be considerably less than by the previously known calculation methods.Scientific-Research Institute of Bases and Underground Structures. State Planning Institute for General Construction and Sanitary-Engineering Planning of Industrial Establishments, Kiev. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 11–15, July–August, 1974.     

Reduction of additional loads on piles due to loading-friction forces using antifriction coatings

Conclusions 1. The use of low-strength (sand-clay, lime-clay, etc.) grouts for filling the gap between piles and the walls of leader holes having a diameter of no less than the diagonal of the cross section of the pile and a depth equal to the stratum prone to slump-type settlements is one of the most effective measures for reducing additional loads on precast piles due to loading-friction forces in soils classed as type-II in terms of proneness to slumptype settlement.2. Use of jackets formed from polyethylene film on cast-in-place piles ensures significant reduction in additional load due to loading-friction forces. In this case, however, it is necessary to adopt measures to ensure the film's longevity over the entire period during which the building or structure is occupied.3. Considering the extremely high efficiency of anti-friction coatings on piles in soils classed as type-II in terms of proneness to slump-type settlement, it is necessary to continue and expand research in this direction.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 18–20, September–October, 1989.