Relations of calculated and actual settlement of a thawing foundation bed

Conclusions 1. The dependence of relative compression of thawing soil on pressure is nonlinear, and it is in agreement with views on the nature of deformation of thawing soil. A dominance of natural pressure in the total load on a foundation bed permits one to use the method of unit summation in calculating settlement of nonlinearly deformable soil. Such calculations, as compared with the linear formulas employed in SNiP, give better agreement with actual settlement.2. In calculating settlement of thawing foundation beds, we need differential consideration of soil compressibility with depth, since the combination of genetic features of frozen ground and the increasing natural pressure with depth may create a different inhomogeneity in the foundation bed.Yakutniproalmaz, Mirnyi. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 18–21, January–February, 1975.     

Experimental studies of the long-term deformability of clayey soils

Conclusions 1. Standard methods of determining the strain characteristics of a soil, e.g., GOST 12374-66, do not make it possible to evaluate to the fullest extent their yielding properties, which are governed by the rheological character of the deformation.2. The strain characteristics of soils (overall-compression modulus, stiffness coefficients of the foundation bed), which are determined from soil tests conducted in accordance with GOST 12374-66 may exceed their limiting long-term values obtained with consideration given to rheological properties by several factors (in our case, by a factor of 3.4).The use of stiffness coefficients on the high side for the design of buildings raised on nonuniformly deformable foundation beds (underexcavated sites, soils prone to slump-type settlement) leads to overdesigned structures. For these cases, therefore, it is recommended that the rheological characteristics of the soils be determined experimentally.3. For comparability of the rheological characteristics of soils determined from plate tests and on small specimens, it is necessary to assign consistent criteria for displacement stabilization, e.g., criteria that are interrelated over the depth of an equivalent layer.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 30–33, January–February, 1978.     

Mechanical properties of sandy soil at different depths

Conclusions 1. Loading tests of soil with a plate set at different depths, with measurement of the settlement of the plate itself and of the surrounding ground surface, and with determination of the ratio between total and restorable settlement, permits one to obtain very complete information on the mechanical properties of the soil and to find a basis for selecting the most appropriate model of a foundation bed.2. The characteristics of soil compressibility may be determined from the results of impression of a plate in accordance with the method proposed by N. A. Tsytovich and I. I. Cherkasov.3. The compressibility of the investigated sands depends on the external load on the test plate and the depth of the horizon being tested.4. The coefficient of compressibilitya ₀ of the investigated soils declines with depth and increases with increase in test load on the plate.5. The modulus of general strain E₀ and the modulus of subgrade reaction c_Z of shallow sands increase with depth and decrease with increase in load on the test plate.6. The relation of compressibility of the investigated sands to load varies with depth, changing gradually from a nonlinear law to practically a linear law.7. The most suitable design model of a foundation bed for the investigated conditions is linearly deformable half-space with a strain modulus that increases with depth.Scientific-Research Institute of Foundations and Underground Structures. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 28–31, January–February, 1975.     

Method of accelerated compaction of soils prone to slump-type settlement using jet technology

Conclusions 1. The installation of an anti-seepage curtain around a wetted mass makes it possible to reduce the area being wetted by 4–6 times, decrease the zone of propagation of deformations caused by slump-type settlement by 7–9 times in the direction away from the mass being wetted, accelerate the development of slump-type settlement by a factor 2–3, and lower the consumption of water by 3–6 times.2. The installation of drainage slots in the mass being wetted as compared with wetting from the surface makes it possible to accelerate the processes of soil wetting and development of slump-type settlement by a factor of 2–3.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 15–16, January–February, 1991.     

Experimental investigation of the deformability of thawed clay bases

Conclusions 1. Soil deformations occur predominantly in the vertical soil column whose boundaries pass through the limits of the plate.2. The formation of a soil wedge under the plate has a decisive effect on the development of settlements formed mainly as a consequence of soil compression within the wedge and directly under it.3. Conditions analogous to compression-test compression are created in the wedge. Under the wedge the soil is deformed as a linearly deformable medium. The base can be represented as two-layered.4. An increase of soil compression in the wedge with depth can be explained by an increase of pressure. The pressure distribution reflects the existence and shape of the wedge.Khar'kov State Planning Institute for General-Construction and Sanitary-Engineering Planning of Industrial Establishments. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 15–18, September–October, 1973.     

Elastoplastic analysis of the nonlinear stage of behavior of a soil base

Conclusions 1. In an elastoplastic calculation of a base, it is expedient to use the Coulomb—Mohr criterion as the condition of plastic flow for upward yielding zones and the Tresca—Hill criterion for the core under the plate and deep zone.2. Calculation of soil bases in the nonlinear stage of their behavior should be done with consideration of the process of localization of shear strain of the soil.3. Reflection of the unstable character of deformation with a decrease of soil strength in the shear band is an important factor in determining the bearing capacity of dense sand bases.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 4–7, November–December, 1991.     

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.     

Effect of lateral earth pressure on the limit load and settlement of the sand base of a plate

The results of a model experiment on loading the sand base of a plate with preassignment of various lateral earth pressures are examined. An increase of lateral earth pressure reduces the limit load on the base and under loads exceeding the initial critical load causes an increase of settlement of the plate. The reliability of the result obtained in the experiment is proved by a numerical analysis of the limit stress state at a point.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 8–10, May–June, 1992.     

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.     

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.     

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.     

Stress State of Soil Subjected to a Periodic System of Strip Loads

Finite formulas are obtained for the stresses in a linearly deformable half plane subject to a periodic system of loads (concentrated and uniformly distributed); the stress distribution is investigated, and it is demonstrated that stresses level-off with depth. It is possible to use the results to determine the stresses in a soil under the action of a large number similar structures (strip foundations, piles, etc.), and to verify finite-element programs.__________Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 2–6, March–April, 2005.     

Strip foundations with intermediate earth-pile pads

Conclusions 1. It was found that an intermediate pad of variable rigidity (in the form of earth piles) improves the operation of the soil base and of the foundation itself.2. When use is made of an intermediate pad of variable rigidity under the center of a foundation, a region of increased compaction of the soil is formed which is less deformable in comparison with the surrounding soil.3. When a pad is constructed redistribution of the pressure occurs — under the foundation center it increases by 25–40% and under the edges it decreases by 30%. The effect of the pad on the stress conditions of the soil base decreases with depth and is limited to a depth equal to 1.5 b.4. As a result of use of an intermediate pad in the form of earth piles, the bending moment in the design section of the foundation is reduced, which yields a saving of 25–27%.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 12–14, November–December, 1991.     

Structure settlements at the Atommash plant as a result of prolonged soil wetting

Conclusions 1. In the 14 years that have elapsed since the start of construction on the Atommash plant, deformation phenomena, which have not, however, lowered the strength of the structure in the production buildings, have developed as a result of nonobservance of waterproofing requirements at the site in areas where surface-water domes that had developed as a result of prolonged wetting of the stratum from above have been detected. The design solutions for these foundations have ensured reliable operation under a rising GWT. The absolute settlements, exceeding those permitted by the Construction Rules and Regulations, affect less than 1% of the total number of columns in the buildings at the Atommash plant, while the relative settlements are within allowable limits. Cracks have formed in some auxiliary buildings primarily because their superstructures were built disregarding possible nonuniform foundation settlements.2. The causes of pile-foundation settlements that had exceeded the standard values with respect to absolute magnitude are not associated with their bearing capacity, but are the result of deformations of the underlying soil layers that are not prone to slump-type settlement and to the development of deformation phenomena. This hypothesis explains the development of additional deformations in the stratum due to the compression of soils beneath the surface-water dome.3. The deformation phenomena that develop at the site of the Atommash plant as a result of the wetting of the soil stratum from above do not affect the foundation settlements induced by live loads, and should be accounted for in design as a possible displacement of the area. It is possible to eliminate the effect of probable relative settlements on a structure by taking structural measures and observing waterproofing measures.4. Under conditions favorable to the development of the deformation phenomenon, it is recommended to predict possible compressive deformations in a portion of the stratum underlying the stratum prone to slump-type settlement within the limits of the layers with a relative compression of more than 3% under a pressure equal to the natural pressure in compression devices.5. Studies directed toward the nature of the processes explaining the development of the deformation phenomenon must be continued.All-Union Scientific-Research Institute of Bases and Underground Structures. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 12–15, July–August, 1988.     

深基坑基底注浆加固效果数值模拟分析

采用高压旋喷注浆工艺对软土地区的基坑底部土体进行加固是保证深基坑施工安全与工程稳定常采用的方法。基于某地铁站监测数据,利用PLAXIS 2D软件建立了其数值计算模型并进行模型校核,对加固和未加固两种工况进行了数值模拟,对比分析了地连墙的位移和弯矩、地表沉降等开挖响应。研究表明,对软土地区基坑进行基底注浆加固,能有效减小地连墙的侧向变形和地表沉降。并针对加固区厚度、地连墙嵌入深度及刚度、软土层厚度4个参数进行了分析与讨论,优化了加固区的合理厚度、地连墙的合理嵌入深度,研究了基坑变形受地连墙刚度和软土层厚度影响的敏感性。     

Deformations of buildings on loess soils

The writer describes the deformations of a building in connection with its upward (convex) bend and determines their causes. From data from observations on opening of cracks, the process of occurrence of settlement of the base with time is reproduced, and its attenuation is established. The differences in the settlements of adjacent blocks of the deformed building are determined. From the maximum linear settlement the writer establishes mean values of the modulus of deformation which confirm low quality of soil compaction in the base. Some practical recommendations are given.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 19–22, January–February, 1992.     

地基沉降计算的困难与突破

太沙基(Terzaghi)创立土力学理论已近百年,但土力学的两个最基本的问题也是工程设计应用最广的内容:地基沉降计算和承载力合理确定还没有很好的解决,以致土力学被称为是一门半理论半经验的"艺术"科学。问题的根源是什么?如何突破?能使理论更接近实际一点吗?这里介绍我们所做的一些工作和思考,就是分析沉降计算不准的原因是由于室内土样试验获得的参数与现场原位土试验获得的参数差异大,同时通常的沉降计算方法难以考虑土体应力水平产生的侧向变形引起的非线性沉降。建议对硬土地基采用原位压板试验建立的切线模量法计算地基的沉降,可以解决原位土参数和应力非线性的问题,对软土主要是解决应力非线性问题。对合理确定地基承载力,应该计算实际基础的荷载沉降曲线,由基础的荷载沉降曲线,用强度和变形双控的方法,才能合理的确定地基的承载力。希望抛砖引玉,共同努力,推进学科发展。     

既有建筑地基承载力时间效应评价的试验研究

通过大比尺室内模型试验,对既有建筑地基承载力随时间变化的规律进行了分析研究。试验中分别对模型进行持载3d、7d、14d、28d、35d、49d的载荷试验,选定以持载后继续加载产生的附加沉降占加载前总沉降的3％、5％、10％为允许变形控制指标,结合p-s曲线数据得到了在不同的允许变形控制指标下地基承载力随持载时间增长的提高数值,地基承载力在模型持载一周时间内提高的幅度较大,土体的压密效应效果显著。在实际工程中应根据工程允许的沉降变形与载荷板试验的沉降变形的对应关系,通过现场足尺的载荷板持载试验,选择适当的允许变形控制指标来确定地基承载力。通过双曲线拟合进一步得到了既有建筑地基承载力与时间的变化规律,提出了不同允许变形控制指标下的地基承载力提高的极限值。     

Design of a sandy foundation bed by means of physically and mathematically nonlinear equations

Conclusions 1. In calculating the stress-strain state of a sandy foundation bed beneath a rigid strip test plate, and also in determining the stresses in the plate itself, one should consider not only the physical but also the geometric nonlinearity of deformation of soil in the foundation bed.2. Consideration of the geometric nonlinearity of deformation in the foundation bed is especially important in the comparatively narrow vertical zones adjacent to the edges of the plate and at loads near their limit values (p 0.7p_lim).The problem of the effect of geometric nonlinearity in other relations (bending moment, the axisymmetry problem, and others) should be studied further.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 30–32, January–February, 1977.     

Numerical simulations of rock mass damage induced by underground explosion

The damage prediction of rock mass under blast loads induced by accidental explosions, rock bursts or weapon attacks is crucial in rock engineering. In this paper, parametric studies are conducted to evaluate the effect of loading density, rock mass rating (RMR) and weight of charge on the rock mass damage induced by underground explosions. The numerical simulations are carried out based on the transient dynamic finite element program ANSYS-LSDYNA. The numerical model was calibrated against the data obtained from a field blast test. A fully coupled numerical analysis, incorporating the explosion process, has been performed, where the large deformation zone near the charge is solved by the Arbitrary Lagrange–Euler (ALE) method. The deformable modulus and compressive strength of rock mass of granite are estimated by the RMR system. The peak particle velocity (PPV) damage criterion and the plastic strain criterion were adopted to study the damage zone around the charge hole, and an empirical formula considering the effects of loading density, RMR and weight of charge was obtained to estimate the damage zone in granite based on the numerical results.