Construction on loess soils

Conclusions 1. Inadmissible settlements and tilts of several multistory buildings in Volgodonsk are the result of collapse of the soils under external loads owing to disregard of the requirements for elimination of the collapsibility within the limits of the entire deformable zone under shallow foundations.2. The cause of the possible settlements of structures on pile foundations fully cutting through the collapsible mass lies in development, under soaking from the top, of deformation phenomena with compaction not only of the collapsible layers but also of the underlying non-collapsible soils, which was first mentioned in [9].The concept that the most hazardous situation for a pile foundation, in this regard, occurs when collapse takes place under the weight of the overlying mass with the GWL rising from bottom to top is erroneous and is not confirmed by construction experience.3. In the development of deformation phenomena, it is important to distinguish between the active period and the settlement attenuation period, since differential settlements occur only during the active period for all practical purposes.4. It is possible to eliminate completely the possibility of substantial settlements of structures under severe Type II collapsibility conditions either by construction of deep founations carried to 40–50 m so that they will rest on solid material, or by elimination of the possibility of soaking of the soils. These highly uneconomical solutions can be used only in especially important cases. On the other hand, in the massive construction practice it is justifiable to correctly fulfill the SNiP requirements, taking into account the possible additional settlements caused by compression of the underlying noncollapsible soils.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 24–27, January–February, 1991.     

Experimental confirmation of a criteriong for the bearing capacity of a bed

Conclusions 1. Experiments with full-scale foundations confirm that even after the start of ground bulging, foundation settlements may even continue to stabilize, the average settlements cease to be allowable, and the s-p curve is even simplified, approaching a linear curve, when the pressure beneath the foundation is increased. At the start of bulging, however, settlement nonuniformities of the foundations increase sharply and even become inadmissible.2. The limiting pressures initiating ground bulge correspond to that section of the s-p curve, where its initial segment converts into an inclined section that is close to a straight line. Up to pressures equal to half the limiting pressures and for shallow rigid foundations on sands of average density and dense sands, the s-p curve is close to linear, and the foundation settlements can be calculated in conformity with the recommendations of the Construction Rules and Regulations.3. For foundations on loose sands, the compaction of sand during shear, which may lead to inadmissible settlement nonuniformities even at minimal pressures due to the foundations, are the most dangerous settlements. The possibility of these nonuniformities should either be eliminated by compaction prior to construction, accounted for during design, In predicting settlement nonuniformity, we should proceed from data on plate tests of loose sands with consideration of the recommendations in [5, 6].VNIIOSP. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 23–26, March–April, 1988.     

Full-scale investigations of the static deformations of foundations below 1000-MW turbine units at nuclear power plants under construction

Conclusions 1. Systematic geodesic observations of static deformations should be organized in constructing foundations for turbine units at high-capacity nuclear power plants; the results of these observations will ensure attainment of the required operational control data during construction and operation.2. During the design of these foundations, it is necessary to consider the installation of special surficial and deep marks for the organization of observations on bed settlement, beginning from the moment when the lower concrete slab is poured.3. In placing distributive cushions for the foundations, it is necessary to provide for a high quality of compaction within the bounds of the entire lower surface of the foundation and for careful geotechnical control.4. In designing foundations for turbine units on inhomogeneous beds, we should consider the difference in the rheological properties of the soils, the character and sequence of bed loading, and the variations in its hydrogeologic regime in order to exclude nonuniform settlements during equipment assembly and operation of the machinery.Dniepropetrovsk Civil Engineering Institute. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 8–10, July–August, 1985.     

Investigation of the behavior of brick buildings on inhomogeneous bases

One of the possible approaches to determining differential settlement of buildings on inhomogeneous bases when using shallow foundations is proposed. Numerical methods, particularly the finite-element method, are used for calculating such buildings.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 2–5, January–February, 1992.     

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.     

Settlements of multistory buildings on foundations placed in tamped trenches with an expanded base

Conclusions 1. A compacted zone of soil with a thickness equal to the stratum being compressed, within the limits of the soil loses its slump-type-settlement properties, and the pressure on the lower boundary of the compacted zone does not exceed the structural strength of the uncompacted soil, is created as a result of the tamping of trenches and the embedment of crushed stone.2. Settlements of the bed of foundations in tamped trenches are virtually completed during the building's construction and amount to less than 80% of the final settlement.3. The relative difference in the settlements of foundations in tamped trenches with an expanded base is significantly lower than that established by requirements set forth in the Construction Rules and Regulations; this indicates uniform bed performance after tamping of the trenches and embedment of crushed stone.Tol'yatii Polytechnic Institute. State Trust for Specialized Residential Construction. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 19–21, November–Decber, 1986.     

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.     

A Case History on Underpinning for a Distressed Building on Hard Residual Soil Underneath Non-Uniform Loose Sand

This paper presents a case history on the failure of Suranivet 9, a student dormitory in the campus of Suranaree University of Technology (SUT), Thailand. The dormitory encountered excessive differential settlement due to the variation in soil profile. Part of the building was underlain by very stiff to hard SUT silty clay and part by loose clayey sand. Underpinning to extend the foundations down to stable stratum was employed to strengthen bearing capacity and minimize settlement. The underpinning design and procedure were summarized. In practice, the static formula was used for the preliminary micro-pile design (selection of pile section and length for different loads and soil profiles). The undrained shear strength (S_u) of SUT silty clay was approximated using the Stress History and Normalized Soil Engineering Properties (SHANSEP) technique and standard penetration number (N). The finite element method was employed to predict the load-settlement curve of the micro-pile. Modified cam clay model was proved as a suitable model for this prediction. The measured settlements of the underpinned foundations after one year service were less than 0.5 mm. This small settlement guarantees the stability of the underpinned structure. It is also found that the settlement ratio (ratio of the measured settlement of underpinned foundations to the predicted settlement of single micro-pile) varied from 0.7 to 3.0.     

超深开挖对单桩的竖向荷载传递及沉降的影响机理有限元分析

目前对于超深基础下的桩的设计尚未考虑超深开挖、坑底隆起对桩产生的作用。现场采用静载试验确定单桩承载力时也仍采用常规的地表加载并扣除开挖深度范围内桩侧摩阻力的方法,没有考虑深开挖效应的影响。采用经实际工程算例验证的土参数、桩身材料参数和桩土接触面参数,在均质土中建立了轴对称有限元模型,对三种不同试桩方法进行了模拟。通过开挖模拟,首先揭示了深开挖对桩的影响效应,在此基础上,对超深开挖对桩在开挖后再加载的荷载传递机理和沉降机理进行了研究。与常规试桩法和套管试桩法中的基坑底以下相同桩长的桩相比,超深开挖产生的影响效应使桩的极限承载力降低,竖向刚度减小,相同荷载下沉降加大,且其沉降中桩整体刺入所占的比例显著大于其它两者。桩侧摩阻力完全发挥时需要的桩土滑移量增大。此外,超深开挖可在桩身中产生较大的拉力,桩身中下部钢筋不能随意减少。     

Load–settlement modeling of axially loaded steel driven piles using CPT-based recurrent neural networks

The design of pile foundations requires good estimations of the pile load-carrying capacity and the settlement. Designs for bearing capacity and settlement have been traditionally carried out separately. However, soil resistance and settlement are influenced by each other, and thus, the design of pile foundations should consider the bearing capacity and the settlement together. This requires that the full load–settlement response of the piles be accurately predicted. However, it is well known that the actual load–settlement response of pile foundations can only be obtained through load tests carried out in-situ, which are expensive and time-consuming. In this technical note, recurrent neural networks (RNNs) were used to develop a prediction model that can resemble the load–settlement response of steel driven piles subjected to axial loading. The developed RNN model was calibrated and validated using several in-situ full-scale pile load tests, as well as cone penetration test (CPT) data. The results indicate that the developed RNN model has the ability to reliably predict the load–settlement response of axially loaded steel driven piles, and thus, can be used by geotechnical engineers for routine design practice.     

Experience with construction and operation of "Dinamo" stadium on fill soils in Minsk

Conclusions 1. During the preceding period (17 years) the fills were self-compacted until they attained the state of medium-density soils.2. The main operation shortcoming of the structure was the intense formation of cracks in the walls, owing primarily to improper construction of the contraction joints. However, the cracks have not affected the operating adequacy of the structure, although they have made it necessary to repair systematically the weakened masonry and stucco. Some of the cracks are to be converted into regular contraction joints.3. The major repair of the waterproofing coatings was dictated not only by their low quality but also, predominantly, by the differential settlement of the foundation beds. Obviously, the waterproofing elements are the weakest spot in structures built on heavily compressible soils; this fact should be taken into consideration in the projects.4. The adopted construction measures for preventing large and differential settlements of the fills, namely, limitation of the pressure on the soil to 1.25–1.5 kg/cm², application of additional compaction on the fills, and use of sand layers; intercrossed cast-in-place foundations, space-rigid superstructures, and contraction joints, were basically justified.Minsk. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 13–14, March–April, 1973.     

Complex dynamic investigations of foundations for low-speed turbine units at nuclear power plants

Conclusions 1. Dynamic tests indicated that the dynamic flexibility of both types of foundations diminishes on the whole as the equipment is assembled.2. During the startup and output adjustment of a turbine unit on both a foundation with lateral condensors and a foundation with basement condensors, the TFB system will itself be at relative rest. Acute resonance peaks are not observed and the vibration levels of the foundations do not exceed allowable values.Dniepropetrovsk Civil Engineering Institute. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 11–14, July–August, 1985.     

粉土中吸力式桶形基础沉贯及抗拔特性试验研究

吸力式桶形基础的负压沉贯控制和抗拔承载力确定是海洋钻井平台和海上风电机组多桶基础以及深海吸力锚基础设计和施工中的关键问题。通过室内大比例模型试验研究了吸力式桶形基础在饱和粉土中的负压沉贯及抗拔特性。负压沉贯试验结果表明负压并不能明显减小吸力式桶形基础在粉土中的沉贯阻力,基于CPT试验结果可较为准确地预估沉贯施工所需负压,从而确保沉贯的顺利实施和防止沉贯过程中地基发生管涌破坏。不同加载速率下的上拔试验结果表明存在一临界加载速率,当实际加载速率超过该临界值后,加载速率对吸力式桶形基础的抗拔特性影响较小。结合桶体及桶外土体的变形,提出了粉土地基中不同受力状况下吸力式桶形基础的抗拔承载力计算方法。     

Experimental studies of slotted foundations for the supports of high-voltage lines

Conclusions The results of the tests that we conducted on full-scale prismatic foundations and their model with the proposed graph of curves in relative values revealed the variability of the limiting pullout forces at different angles that deviate from the vertical, for different sand densities, surface roughness, and ratios of foundation dimensions.Slovak Higher Technical School, Bratislava, Czechoslovak Socialist Republic. Bulgarian People's Republic. Translated from Osnovaniay, Fundamenty i Mekhanika Gruntov, No. 4, pp. 25–27, July–August, 1988.     

Interaction between shallow foundations and slightly heaving bed soil

Conclusions 1. When foundations ascend as a result of frost heaving, normal heaving forces are reduced. Measures directed not toward overcoming heaving forces, but toward reducing the deformations caused by these forces to limiting allowable values could therefore be considered in designing shallow foundations.2. The pressure transmitted to the soil exerts a greater influence on foundation heaving than does the lower-surface area of the foundation.3. The optimum shape of the lower surface of a columnar foundation on heaving soils is square.4. The cost of 1 m² of the overall area of a building is reduced by 10 rubles on average due to use of shallow foundations.General Scientific-Research Institute of Experimental Planning. Scientific-Research Institute of Bases and Underground Structures. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 21–23, July–August 1984.     

地铁施工方案对邻近桥基的沉降影响优化分析

针对国贸站西北和东北风道施工对近邻桥基沉降影响这一实际工程问题。运用ABAQUS软件，建立了两个风道施工过程中桩-土相互作用模型，在对施工过程进行动态模拟的同时，重点分析了不同施工方案对桥基绝对沉降和差异沉降的影响程度，并提出了优化的施工方案。研究表明，东北风道和西北风道不同的施工路径对桥基的沉降值影响不明显。但对桥基的差异沉降影响较为显著，从而表明，施工方案的优化是非常必要的。对该工程施工过程中为保障近邻桥基的安全提供了依据和指导作用。     

Experimental checking of stability of underground pedestrian crossings on heaving soils

Conclusions 1. Underground crossing structures on natural soil bases may be used also for heaving soils provided their strength and rigidity are increased, taking into account the nonuniform deformations. It is recommended that a value of 0.0015 be used for the limiting allowable coefficient of relative deformation nonuniformity of tunnels.2. If the tunnel is considered as a reinforced concrete underground frame buried in the soil, then for strength, crack-resistance, and deflection design under the normal frost heave force, this force should be assumed to be equal to the soil reaction in the tunnel base under all the permanent and short-duration loads, taken in accordance with SNiP II-D.7-62; also, account must be taken of the friction force caused by the backfill sand on the tunnel lateral surface.3. For freezing and thawing of the soils in the bases of underground crossings, the plastic deformations are insignificant, i.e., the frost heave is practically equal to the settlement under thawing.4. The weak correlation between the coefficient K_n and the heave indicates that measures intended to reduce the depth of freezing (heave) by heating the bottom or by partially replacing the heaving soils by nonheaving under deep seasonal freezing cannot, per se, ensure crack resistance of the crossing structures.5. During freezing of soils in the bases of crossings, processes of heaving and shrink-age occur. For hard and medium hard consistency, with W_PL, the shrinkage may be greater than the heaving, which should be taken into account for determining the depth of the foundations under deep seasonal freezing conditions.Omskgrazhdanproekt. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 10–12, May–June, 1981.     

Bed strength of T-section foundation blocks under inclined loads

Conclusions 1. The displacements of driven blocks can be determined from a bed model characterized by a coefficient of subgrade reaction that increases linearly with depth using proportionality coefficients from [3].2. Driven T-section blocks ensure that the computed loads are taken up at the design depth, and can be used as foundations for agricultural buildings with three-hinge frames with a span to 21 m, and a frame spacing of up to 6 m at sites with gentle relief, preferentially in regions with deep frost to 1.5 m.Central Scientific-Research Institute of Experimental Design and Planning for Agricultural Construction VNIIOSP. Moscow State Scientific-Research Institute for Agricultural Construction. Translated from Osnovania, Fundamenty i Mekhanika Gruntov, No. 3, pp. 16–18, May–June, 1988.     

无反力条件下锚杆静压桩的设计与施工

锚杆静压桩是一项成熟的基础加固托换技术,在狭小空间内更显其长,但它往往受到基础反力的局限,若没有被加固基础提供反力,就无法进行压桩施工。本文结合广东某综合性大学二级学院学生宿舍楼不均匀沉降加固实例,对锚杆静压桩的工作原理及沉桩机理进行了分析,探讨了锚杆静压桩设计参数的计算和取值原则,详细介绍了无反力条件下锚杆静压桩的设计与施工技术。沉降观测结果表明,加固方案对控制基础不均匀沉降起到了良好作用,为类似工程问题提供了参考经验。     

Performance of piles cast in predrilled holes and consolidated masses during slump-type settlements of soils surrounding them due to their own weight

Conclusions 1. Considerable additional loads are transmitted during slump-type settlement of surrounding undisturbed soils due to their own weight as a result of impendence and the development of negative friction along the lateral surface on piles that are cast in predrilled holes. In this case, the tangential stresses developed over the lateral surfaces of a pile reach 0.043 MPa.2. As a result of interaction between consolidated masses and undisturbed loess soil surrounding them, impendence of the loess soil on the consolidated masses takes place during slump-type settlement of the former. As a result of this, the undisturbed loess soil is partially unloaded, its slump-type settlement is reduced, and the consolidated masses receive an additional loading, which results in compression of the lower portion of the consolidated mass and underlying layers.3. The bearing capacity of piles and consolidated masses at sites having soil conditions classed as type II with respect to tendency to slump-type settlement should be determined with consideration given to the impendence of the surrounding undisturbed soils on them during slump-type settlement of the latter due to their own weight, which results in the development of negative-friction forces along the lateral surface of the pile and consolidated masses.NIISK Gosstroya. Ukrvostokgiintiz, Zaporozh'e. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 22–24, March–April, 1976.