Stability analysis of gravity anchor foundation of layered argillaceous sandstone under dry-wet cycles

To investigate the stability of gravity anchors of suspension bridges,in-situ tests of the vertical bearing capacity of the bedrock,shear resistance of the anchor-rock interface,shear resistance of the bedrock were conducted in a suspension bridge project.Under dry-wet cycles,the deterioration law of the mechanical properties of argillaceous sandstone was identified in laboratory tests:the elastic modulus,cohesion and friction of the argillaceous sandstone deteriorated significantly at first few dry-wet cycles and then declined slowly after 10 cycles,ultimately these three mechanical parameters were reduced to about 1/3,1/3,2/3 of the initial value respectively.Moreover,numerical simulation was used to restore in-situ shear tests and a good agreement was obtained.Base on the results of in-situ and laboratory tests,the stability of the gravity anchor foundation under natural conditions and drywet cycles was calculated and its failure modes were analyzed.The results demonstrated that the dry-wet cycles caused uneven settlement of the anchor foundation,resulting in more serious stress concentration in the substrate.The dry-wet cycles remarkably reduced the stability coefficient of the anchor foundation,whose failure mode shifted from overturning failure under natural conditions to sliding failure.When there was weak interlayer in the rock layer,the anti-sliding stability of the anchor foundation was affected drastically.

Feasibility of columnar jointed basalt used for high-arch dam foundation

Columnar jointed basalt, with a lot of small-spacing structural planes and poor integrity, is a kind of fractured rock mass. Through comprehensive study of columnar joints shape, roughness of fracture surface and chemical composition of basalt, it is known that columnar joints of Baihetan dam area were formed as a result of cooling and shrinkage effects of magma. The columnar jointed basalt is mainly formed through chemical reaction of chlorite, kaolinite, epidote and tremolite, and the columnar joints mainly consist of chlorite according to slice identification and chemical analysis. Test results show that the columnar jointed basalt has high uniaxial compressive strength, low friction coefficient, and high cohesion, shear strength and deformation index. Meanwhile, the columnar jointed basalt is closely locked, and joint surfaces are well closed. The permeability of the rock is quite weak, and the P-wave velocity in the rock could get up to 5 000 m/s. All these show good rock properties. The columnar joints develop regularly, different from the general fractured rock masses. In summary, the columnar jointed basalt can be used directly as a foundation of dam.

Bearing capacity and mechanical behavior of CFG pile composite foundation

CFG pile (i.e., pile constructed by granular materials of cement, fly-ash and gravel) composite foundation is applied in subsoil treatment widely and successfully. In order to have a further study of this kind of subsoil treatment technology, the influencing factors and calculation methods of the vertical bearing capacity of single CFG pile and the CFG pile composite foundation were discussed respectively. And based on the obtained solutions, effects by the cushion and measurements to reduce negative friction area were analyzed. Moreover, the developing law of settlement and bearing capacity eigenvalue controlled by the material strength with the increase of load were given for the CFG composite foundation. The in-situ static load test was tested for CFG pile. The results of test show that the maximum test load or half of the ultimate load is used from all the points of test, the average bearing capacity eigenvalue of single pile is 390 kN, and slightly greater than the design value of bearing capacity. The bearing capacity eigenvalues of composite foundation for 3 piles are greater than 300 kPa, and the mechanical properties of CFG pile composite foundation are almost identical in the case of the same load and cushion thickness. The pile-soil stress ratio and the load-sharing ratio can be adjusted through setting up cushion thickness.

就地固化联合复合地基对堆载邻近桩基的影响

路桥并线路基修筑引起既有桥桩产生挠曲、侧向位移,严重时可能会造成重大坍塌事故的发生。结合工程现场试验,针对道路施工对邻近桥桩影响问题提出就地固化联合复合地基加固新方法,联合数值模型分析就地固化深度、固化土弹性模量和复合地基相关因素对邻近桩基的保护效果。研究结果表明:搅拌桩加固影响深度为1.5倍桩长左右,素混凝土桩施工会对被动桩在0.75倍桩长左右处产生最大水平位移。就地固化(2.0 m)+水泥搅拌桩法(1.8 m)可极大减小被动桩浅层水平位移,保护桥桩的安全。当固化土水泥掺量为5%~7%、水泥搅拌桩水泥掺量为12%~18%时,提高水泥掺量对减小被动桩水平位移有着明显的作用。同时,将普通褥垫层水泥搅拌桩替换为就地固化+水泥搅拌桩复合地基,桩身最大负弯矩减小近16.6%。

就地固化表层地基承载特性现场试验研究

以浙江省31省道北延线绍兴市区路段地基处理为例,研究两种原位固化地基处理方式(ALLu强力搅拌头搅拌法和国产自制设备与ALLu强力搅拌头联合应用)的适用性及其处理效果,针对两种地基处理方式进行现场平板载荷试验、无侧限抗压强度试验、标准贯入试验和静力触探试验。为得到就地固化处理后地基应力和地基变形的规律,在地基处理路段布置土压力盒和沉降板进行现场监测试验。试验结果表明:与传统的换填法相比,就地固化处理后的地基承载力提高至少30%;固化养护龄期28 d时,原位固化土的无侧限抗压强度与室内无侧限抗压强度之比在0.35~0.65之间;标准贯入试验和静力触探试验均表明原位固化处理后地基土的强度提高,且计算的地基承载力与平板载荷试验实测结果相差不大,均可以作为就地浅层固化地基处理技术的检测指标;对两组路段的应力和附加应力系数进行分析发现,经原位固化形成的人工硬壳层具有较好的扩散应力作用。

Non-contact and full-field online monitoring of curing temperature during the in-situ heating process based on deep learning

Online monitoring of the curing temperature field is essential to improving the quality and efficiency of the manufacturing process of composite parts.Traditional embedded sensor-based technologies have difficulty monitoring the full temperature field or have to introduce heterogeneous items that could have an undesired impact on the part.In this paper,a non-contact,full-field monitoring method based on deep learning that predicts the internal temperature field of composite parts in real time using surface temperature measurements of auxiliary materials is proposed.Using the proposed method,an average temperature monitoring accuracy of 97%is achieved in various heating patterns.In addition,this method also demonstrates satisfying feasibility when a stronger thermal barrier covers the part.This method was experimentally validated during the self-resistance electric heating process,in which the monitoring accuracy reached 93.1%.This method can potentially be applied to automated manufacturing and process control in the composites industry.

普通蒸养配制高性能材料在桩基防护层中的应用探索

跨河桥梁墩柱桩基因需要防止河水及其漂浮物的冲击磨蚀,需要设置防护层。受作业面、运输条件等现场实际情况限制,部分墩柱桩基保护层难以预制或者现场高温蒸养。对采用现场普通养护方式制备超高性能混凝土制作墩柱防护层的工艺进行了探索,并对现场制备的试验组进行了力学性能测试。试验结果表明,制备的试件力学性能基本满足设计要求,该探索结果可为类似墩柱耐磨层防护施作提供技术参考。

淤泥质软土地基固化处理技术

经过大量试验表明淤泥软土地基其结构受外力影响变化较大,在经过一段时间沉降后其结构可慢慢复原,由于淤泥软土地基产生的沉降为不均匀沉降,会导致建筑主体产生倾斜、结构破坏,所以淤泥软土地基不适合作天然地基。将淤泥软土地基作为工程主体的基础时必须进行处置,常见的有强夯挤压、加压密实、砂井排水、淤泥固结等施工处置措施。在实际工程施工中如何处理好现有地基减少换填量,在保证工程质量的情况下,降本增效是一个值得我们技术人员思考的问题。

基于固废物的土壤固化剂加固软土应用研究

通过利用矿渣、粉煤灰、脱硫石膏等工业废料制备了一种固化效果优异、成本低的新型固化剂。研究表明:新型固化剂的水泥、矿渣、脱硫石膏、粉煤灰的最佳配比为30∶40∶16∶14;添加新型固化剂可以加速软土固化,与普通硅酸盐水泥固化剂相比,同等掺量下强度对比增长113%。此外,还可明显改善传统水泥固化土早期强度不足的问题,在相同固化剂掺量下,早期强度增长101%,可迅速满足工程需求。由此可见,该新型固化剂可以替代水泥等传统土壤固化剂,在工程应用中具有良好的前景。

桩基施工泥浆固化处理新技术的应用研究

桩基工程施工废弃泥浆直接排放的污染风险较大,需要对其进行处理。因此,以某桩基工程施工废弃泥浆经过絮凝和脱水处理后的絮凝体为研究对象,开展了泥浆固化处理实验研究,以固结体的无侧限抗压强度为评价指标,主要考察了固化剂类型、固化剂掺量、泥浆絮凝体含水量、养护温度和养护时间等因素对固化处理效果的影响。结果表明:不同类型固化剂的加入均能提高固结体的无侧限抗压强度,其中新型复合固化剂GT-2的固化处理效果最好。当实验用泥浆絮凝体的含水量固定在40%时,目标桩基施工废弃泥浆固化处理的最佳实验参数为:选择固化剂类型为新型复合固化剂GT-2,固化剂的掺量为6%,养护温度为35℃,养护时间为28 d。在此实验条件下泥浆固结体的无侧限抗压强度值可以达到0.631 MPa,达到了良好的固化处理效果。现场应用结果表明,新型复合固化剂GT-2的加入能够对现场桩基施工废弃泥浆起到较好的固化效果,并且处理成本较低,具有良好的环境、经济和社会效益。

粉煤灰固化施工在地基加固处理中的应用

为探究粉煤灰固化施工在地基加固处理中的高效应用方法,分别将普通石灰、石膏、水玻璃溶液作为固化剂,制备不同灰水比的测试浆液。以某路面工程项目中的一小段废弃路段为试验路段,利用测试浆液实施地基加固处理施工,使用大型切割机将施工结果切割,作为试验试块,测试试块性能。结果表明:使用石膏作固化剂时固化粉煤灰浆液的初凝、终凝时间最短;以石膏为固化剂的固化粉煤灰浆液的地基加固方格试块的压实系数最大、无侧限抗压强度最高、低温强度最高,三者数值达到最高时的灰水体积比分别为15:10、15:10、13:10。以石膏为固化剂时,固化粉煤灰浆液的地基加固方格试块的性能表现最佳。

就地固化设计参数对软土地基承载特性影响的现场试验研究

为深入研究就地固化技术设计参数对软基加固效果的影响,开展固化剂掺量和养护龄期对加固后软土地基承载特性影响的现场试验研究。试验区1(固化剂掺量)划分为100 kg/m^(3)、120 kg/m^(3)、130 kg/m^(3)、140 kg/m^(3)和160 kg/m^(3)等5个试验区,处理深度为2.5 m,待养护7 d进行载荷试验;试验区2(养护龄期)采用固化剂掺量160 kg/m^(3),处理厚度2 m的方案,分别在养护14 d和28 d后进行载荷试验。通过研究得到以下主要结论:固化后软土地基的承载力随固化剂掺量增加而提高。就地固化加固软土地基存在130 kg/m^(3)的临界固化剂掺量。当固化剂掺量小于临界掺量,载荷试验时地基发生隆起破坏,变形模量很小;当固化剂掺量超过临界掺量,载荷试验时地基承载力增加且不会发生破坏,变形模量随固化剂掺量增加而提高。就地固化后软土地基的承载能力和变形模量随养护龄期的增加而提高。

狭小场地条件下深基坑建筑废弃泥浆固化回填施工技术

针对狭小场地条件下,施工场地受限,传统土方回填的施工难点,通过对比传统土方回填技术与深基坑建筑废弃泥浆固化回填施工技术的优缺点,确定采用深基坑建筑废弃泥浆固化回填施工技术。该技术解决了狭小场地内深基坑肥槽回填无法采用传统回填土的施工难题,确保了狭小空间回填的施工质量,避免了传统回填的质量通病,保证地铁隧道及支护体系的安全。实践证明,该技术工艺简单,施工速度快,充填肥槽后能解决地下室漏水、回填区域下沉等问题,适用于狭小场地、狭小或异形空间、环保要求高的深基坑基槽、房心、管沟等回填工程,同时也适用于矿山采空区、地面塌陷孔洞、废弃地下空间、溶洞等充填施工工程及软基换填、低洼场地填筑等工程施工领域。

泡沫轻质土路基施工技术

对于陡坡路堤或桥头、涵台背难以压实的填方路堤段,采用泡沫轻质土路基的施工工艺作为施工质量的技术保证。基础采用C25混凝土浇筑;上下相邻浇筑层变形缝交错布置;浇筑至设计高程后,及时养护。执行泡沫轻质土路基标准工艺流程,验证了施工技术的可行性,节省工期的同时确保发泡剂性能检验基础要求、泡沫轻质土技术指标、密度实时控制允许误差均满足泡沫轻质土路基验收标准,在满足设计要求的同时提高了特殊路基的施工技术标准。

土壤固化剂在沿海滩涂地质地基固化处理中的应用研究

建设过程中难免遇到软土地基难题,如果施工过程中对地基处理不当,易造成严重的工程质量问题。文章依托江苏省某厂房工程沿海滩涂淤泥地基土固化案例,通过对土壤固化剂掺量及施工中的关键技术参数等进行分析,根据试验结果,确定此工程中土壤固化剂掺量为80 kg/m3;通过对固化地基进行动力触探检测,得出固化地基无侧限抗压强度不小于100 kPa,满足设计要求。

水泥土搅拌桩室内配合比试验研究

通过对室内水泥土配合比试验成果数据的分析发现,随着水泥掺入比的增大,水泥土强度先增大而后出现降低;随着养护期的增长,水泥土强度增大,但不同水泥掺入比在同一养护期段强度增大速度不同。设计施工时可根据工程实际情况及工期要求参考室内水泥土配合比试验结论及规律选择合适的水泥掺入比。

大体积混凝土基础动态养护控制因素分析

动态养护技术是大体积混凝土基础施工期养护的有效措施,可有效动态控制基础内外温差及温降速率,降低早期开裂风险。系统开展了蓄水外保温及水管内冷却两类动态养护技术的控制因素分析,明确了各控制因素对基础内部温度峰值、内外温差的作用效应,并相应提出大体积混凝土早期温控施工建议。分析结果表明:蓄水水温和降温速度是蓄水外保温措施的重要温控指标,而开始蓄水时间影响较小;水管内冷却措施关键控制因素有水管间距、开始通水时间、通水水温和持续通水天数,通水流量影响较小。研究成果可为制定大体积混凝土基础动态养护方案提供理论支持。

高性能固化剂在天津软弱地基加固的应用

通过对高性能 (AS系列 )固化剂与水泥的对比试验 ,研究其在天津软弱地基加固中适用性和优越性 。

天津地区软土固化及承载特性试验研究

固化技术是一种常用的软土地基处理方法,已普遍用于工程建设,但由于各地软土存在差异,其固化材料的种类、配比及加固后的承载特性有较大区别。以天津滨海新区吹填软土为研究对象,运用室内试验对固化剂种类、配比及地基承载特性进行研究。通过对不同含水率及养护龄期下不同水泥掺量的固化土进行单轴压缩试验,确定最优水泥掺量,并进一步添加矿粉进行双掺试验及水泥、矿粉、粉煤灰的多固化剂正交试验,从而探究天津地区吹填土固化剂最佳配比;通过在不同荷载宽度、固化强度、固化土层厚度下的固化软土地基进行正交试验,分析了三种因素对结构荷载值的影响程度,为工程设计提供参考。

夯实水泥土强度影响因素的试验研究

为了找出影响夯实水泥土强度的几个主要因素最合理配比值,针对洛阳地区黄土性粉质粘土的土质情况,通过对108组水泥土试块无侧限抗压强度的试验研究,定量地分析了夯实水泥土桩的最优含水量、合理的水泥掺量和最佳的养护龄期。结果表明:夯实水泥土抗压强度值随着水泥掺量的增大而逐渐增大,水泥掺加一定量后其强度提高的趋势将变缓,较为经济合理的水泥掺量应在10%～15%之间;最佳养护龄期为前28天,这是水泥土强度增加的关键阶段。该结论对土建工程设计及施工单位寻求更加经济、合理的施工配合比和参数提供了理论和试验依据。