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.     

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.     

浅谈混凝土灌注桩的施工质量控制

随着我国基建事业的迅速发展,工业与民用建筑、桥梁、港口码头等高重建筑物也开始增多。混凝土灌注桩作为桩基础,能适应与不同地质条件,具有承载力大、建筑费用低等优点,应用越来越广泛。混凝土灌注桩能很好的将上部的荷载传到深层稳定的岩土层上,从而减少基础的沉降和建筑物的不均匀沉降。近年来,被广泛用于高层建筑和重型厂房等工程中。以下,本文主要从灌注桩的质量控制方面对其进行简单的探讨和分析。     

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.     

桥梁逆作承台–群桩复合基础应用与现场实测研究

为进一步研究逆作复合基础在桥梁工程中的适用性,开展了桥梁逆作承台–群桩复合基础的实桥应用研究,针对有水和无水的施工环境,分别提出了桩与承台间预留孔采用带剪力连接键的钢护筒和收口网模板的构造设计与连接施工工艺,并通过12组接头承载性能试验验证了工艺方案的可靠性。通过现场实测,揭示了桥梁逆作承台–群桩复合基础受力机理,测试结果表明:采用逆作方案,先施工桩基和预留桩孔的承台,待盖梁施工完成后再封桩,使桩与承台形成整体共同参与受力,能够使封桩前承台底土承担上部荷载,有效发挥浅层地基土的承载能力;封桩后,基础沉降增量和承台底土压力增量均明显减缓,继续增加的上部荷载主要由桩基承担,能够有效控制封桩后桥梁沉降。     

钻孔灌注桩后注浆技术在某桥梁基础施工的应用研究

本文在介绍灌注桩后注浆技术作用机理基础上,以某桥梁桩基础项目为背景,介绍了后压浆工艺施工流程,并通过与未注浆灌注桩的承载力和地基沉降量进行对比,确定钻孔灌注桩采用后压浆技术后其沉降量更小、承载能力更高。     

地面水对黄土地区桥梁桩基承载力影响试验研究

黄土因其特有的工程性质,使位于黄土地区的桥梁桩基础在桩周土受地面水浸湿后产生湿陷变形,该变形引起桩的负摩阻力,降低了桩的承载力。通过陕西芝川河特大桥桩周浸水前、后的荷载试验,对黄土区域桩基浸水前、后的承载性状进行了分析研究,揭示了地面水对黄土区域桥梁桩基承载力性状具有较大的影响;分析了桩及桩周土浸水期间的沉降变化规律。研究成果对黄土区域公路桥梁桩基础的设计与施工具有重要理论价值与指导意义。     

Model test of the group piles foundation of a high-speed railway bridge in mined-out area

The research on the mechanism of pile-soil-cap-goaf interaction and settlement of high-speed railway bridge located in mined-out area is still relatively rare. By taking the pile group of Guanshandi bridge foundation in Hefei- Fuzhou high-speed railway as the prototype, a model test is carried out. According to the similarity theory, the similar constant is derived and the similar model material is determined. Meanwhile, three types of data including the bearing behavior of piles, and the settlement law, and soil among piles are investigated. It can be found that: the influence of goaf on the bearing capacity of pile is inversely to the loading degree, the larger of loading degree, the smaller impact of goaf on the bearing capacity. There is no negative side friction can been found in pile body and the degree of downward tendency for the barycenter of side friction layout is obvious for piles in goaf. Although the bearing ratio of soil resistance under cap is relatively large, the cap effect is suggested be ignored considering the characteristic of goaf. There is a maximum critical value for the uneven settlement of pile group in goaf, and when the value is reached, the uneven settlement stop growing anymore. In addition, the formula for calculating bearing capacity and settlement of pile group in goaf based on test results, theory analysis and related standard is established.     

Performance of driven reinforced-concrete piles in a pile grillage subject to lateral loading

Conclusions 1. The proposed method of testing single piles with simulated fixity of the heads in a grillage slab can be used to determine the bearing capacity of grillages subject to lateral loading when designing pile foundations, particularly for large-scale construction.2. The resultant data on the variation of the fixed-end moments in the heads of piles can be employed to confirm and evaluate different computational methods and models that require load-displacement curves as initial data to obtain parameters.3. The resistance of grouped piles to lateral loading significantly exceeds the resistance of piles with an unrestricted head deflection. This occurs owing to the fixity of the pile heads in the slab.4. Pile interaction in a single-row group, and also the presence of slab deflection were reflected slightly in the resistance of laterally loaded piles.Khar'kov Scientific-Research Institute for the Design and Planning of Industrial Construction. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 17–20, March–April, 1977.     

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.     

软土地区竹节桩复合地基承载特性试验研究

结合东钱湖车辆基地软基处理工程,开展了桩间距分别为1.8 m、2.0 m和2.2 m,桩长20 m、22 m和24 m,正方形布置(4×4)的竹节桩复合地基承载变形特性试验研究。对3个试验工况的竹节桩复合地基进行了单桩、单桩复合地基静载荷试验,测定了桩土应力比及群桩复合地基的沉降,结果表明:本场地3个工况竹节复合地基的单桩抗压承载力和复合地基承载力均满足120 kPa的设计要求;各工况单桩静载试验测试的桩土应力比主要分布在4.0~6.0间,群桩静载试验测试的桩土应力比差异较大,随桩间距的增大而减小。竹节桩复合地基在宁波软土地区具有较好的适用性。     

两种静载试验确定大直径扩底桩竖向承载力

工程上通常用一种静载试验确定扩底桩的竖向承载力 ,而本文用两种静载试验方法 (即直接试验法和间接试验法 )确定扩底桩的承载力 ,据此对端承于粗砂层的埋深 1 4.5m左右的扩底桩竖向承载性状进行了分析。结果表明 ,两种试验方法得到的SD1、SD2桩的极限承载力值分别相差 5 %和 1 0 %。扩底直径为 3.40m的SD1桩的极限承载力为 960 0kN ,端阻力达86% ;扩底直径为 3.0 0m的SD2桩的极限承载力为 685 0kN ,端阻力占 81 %。当桩顶沉降 1 8.72mm左右时 ,SD1、SD2桩摩阻力已充分发挥 ;而端阻力充分发挥时 ,SD1、SD2桩顶沉降分别达 31 .85 5mm和 2 9.34mm。直径相同时 ,扩底桩的竖向承载力远大于纯摩擦桩和直身墩     

竖向荷载下变刚度群桩变形性状研究

在试验室进行了一系列变刚度群桩和均布群桩基础的静载荷物理模型试验,并对试验结果进行了分析对比。结果表明,变刚度群桩的位移分布方式是边桩大于中心桩,正好和一般均匀布桩的沉降分布形式相反。其总沉降略有增加,但差异沉降显著减少。变桩长与均布群桩相比,增加中心桩桩长,还能提高桩基的极限承载力和承台下地基土的承载能力,说明均布群桩中边桩的承载能力还有富余。群桩中基桩的侧摩阻力表现与单桩不同,侧摩阻力的发挥是自桩身下部某点向上逐步发挥。桩距越小,这种趋向越明显。     

复杂地质复合桩基施工

结合具体工程实例,根据工程地质特点、难点,提出了复杂地质复合桩基施工方案,并进行了方案论证,详细介绍了钻孔灌注桩和管桩施工的主要技术措施,得出了该桩基工程符合设计承载力和沉降量要求的结论。     

异形灰土井桩承载特性的实测结果

灰土井桩是一种柔性桩,在陕甘地区的多层建筑基础中已体现出较明显的有效性和经济性,其实用价值已得到证实,灰土井桩作为受力桩,其桩型一直采用大孔径的圆柱形.但实践证明这种桩形在灰土井桩基础中较为突出的问题是其承载力偏低、沉降值偏大.针对这一问题,本文提出了异形灰土井桩概念,介绍了柔性桩的现场静力测试方法,和二种异形桩与常规形灰土井桩承载性能的对比试验结果.     

Effect of boring method on bearing capacity of short cast-in-place piles

Conclusions 1. Bored-hole/cast-in-place piles 4–10 m long tend to retain a constant value of the unit bearing capacity, irrespective of soil moisture. Driven piles, and piles cast in punched holes, undergo a loss unit bearing capacity (up to 20%) as their length is increased.2. With the saturation of high-porosity collapsible soils, the unit bearing capacity of bored-hole/cast-in-situ piles up to 10 m long diminishes two to three times, on average. For cast-in-place piles installed in a punched hole, and for driven piles, this reduction ranges up to only 30%. This trend is characteristic of soil layers whose collapsibility properties diminish with depth, from 2–3% to 1–1.5%.3. The unit bearing capacity of cast-in-place piles installed in punched holes is equal to that of driven piles, both for saturated and dry soil conditions.4. Following soil compaction, the unit bearing capacity of concrete cast-in-place piles installed in punched holes is higher than for bored-hole/cast-in-place piles, in the ratio of up to 2 for slightly moistened soils and 3–3.5 for saturated soils.5. All other conditions being equal, the unit bearing capacity is greater for driven piles, and somewhat smaller (by 10–15%) for piles cast in punched holes. The smallest unit bearing capacity is observed in bored-hole/cast-in-place piles (1.5–2 times less than for driven piles).Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 14–15, July–August, 1979.     

塑料套管混凝土桩承载试验及沉降计算方法研究

塑料套管混凝土桩(TC桩)是由预先打设在地基中的塑料套管内浇注混凝土组成的,适用于软土地基处理工程中,具有承载力高、施工速度快和成桩质量可靠等优点。通过TC桩承载力的模型和现场试验,研究了TC桩的工作性状,并考虑到路堤柔性荷载下刚性桩复合地基桩土存在沉降差,分别采用Mindlin应力解计算塑料套管桩群在复合地基中产生的附加应力,采用Boussinesq解计算地基土荷载产生的附加应力,叠加塑料套管桩群桩和地基土产生的附加应力,采用分层总和法计算复合地基沉降量。研究结果表明:TC桩承载力具有明显的时效性,其不同间歇期的承载特性有显著差别;所建立的TC桩沉降计算方法的计算值与实测值相一致。     

桩侧后注浆在厦门怡山商业中心工程中的应用

桩侧后注浆能有效提高桩基承载力和减少桩基沉降量。厦门怡山商业中心工程地质条件复杂,桩端持力层承载力较低,33根抗拔桩均应用桩侧后注浆技术。结合工程实际,介绍了桩侧后注浆的特点、工作机理、施工工艺及质量控制措施等。抗拔试验结果证明桩侧后注浆可明显提高桩基承载力,取得良好的经济效益。     

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.