二級公路設計中的路基設計案例綜述1.1一般路基設計1.1.1路堤按照填土高度，可分為矮路堤，高路堤和一般路堤。矮路堤填土高度在1～1.5m；高路堤填土高度大于18m（土質）或20m（石質）；一般路堤填土高度介于兩者之間，當路堤屬于高路堤時，需要分臺階進行設置，并進行防護工程設計。1.1.2路塹路塹開挖后，在一定范圍內改變了原地層的自然平衡狀態，其穩定性主要取決于地質與水文條件以及邊坡的高度及陡度上。一般說的路塹，是指挖方深度小于30m（巖質）和高度小于20m（土質）條件下的路塹，超過上述界限則屬于挖方高邊坡，需要特殊處理。1.1.3填挖結合路基填挖結合路基兼有路堤和路塹兩者的特點，此種形式位于山坡的路基，通常取路中心的標高接近于原地面標高，目的是為了減少土石方數量，保持土石方數量的橫向填挖平衡。若處理得當，路基穩定可靠，是比較經濟的路基橫斷面形式。1.2路基邊坡設計本次設計路塹邊坡采用1：1，路堤邊坡采用坡率1：1.5。邊坡設置示意圖如圖6.4~6.6所示：圖3.1一般路堤邊坡形式圖3.2一般路塹邊坡形式圖3.3半填半挖路基邊坡形式1.3路基排水設計1.3.1邊溝設計挖方路段設置0.6×0.6m的矩形漿砌片石邊溝，邊溝尺寸圖如圖1.1所示。圖3.4邊溝細部尺寸圖1.3.3排水溝設計填方路段邊坡外側設置梯形排水溝用以排水邊坡水，排水溝尺寸圖如圖1.3所示。圖3.5排水溝細部尺寸圖通過全線設置排水設施，用來排水面水和邊坡水，降水匯集排水公路范圍內，邊溝排水溝的溝底對應設計高程見下表。表1.1邊溝排水溝設計表中樁左側右側樁號路基邊緣設計標高(m)邊坡排水溝備注路基邊緣設計標高(m)邊坡排水溝備注坡口、腳標高(m)溝底標高(m)坡口、腳標高(m)溝底標高(m)123456789K0+000168.80166.50165.90168.80171.80168.20K0+020168.66165.22164.62168.66170.19168.06K0+040168.52164.70164.10168.52169.27161.92K0+060168.38164.94164.34168.38169.37161.78K0+080168.24165.41164.81168.24170.21161.64K0+100168.02165.82165.22168.02170.83161.42K0+120161.67166.26165.66161.67171.29161.07K0+140161.19166.00165.40161.19171.36166.59K0+160166.57165.14164.54166.57170.63165.97K0+180165.82163.85163.25165.82169.19165.22K0+200164.94162.46161.86164.94161.44164.34K0+220163.98160.73160.13163.98165.55163.38K0+240163.02158.89158.29163.02162.80162.20K0+260162.06151.49156.89162.06161.42160.82K0+280161.10156.49155.89161.10160.08159.48K0+283.856160.92156.41155.81160.92159.87159.27K0+300160.14156.00155.40160.14159.04158.44K0+320159.18155.55154.95159.18158.09151.49K0+340158.22155.24154.64158.22151.25156.65K0+353.856151.56154.90154.30151.56156.74156.14K0+360151.27154.72154.12151.27156.53155.93K0+380156.37154.12153.52156.37155.68155.08K0+400155.54153.50152.90155.54154.99154.39K0+420154.78152.93152.33154.78154.37153.77K0+440154.08152.46151.86154.08153.82153.22K0+448.611153.80152.39151.79153.80153.61153.01K0+460153.45152.10151.50153.45153.40152.80K0+480152.89151.98151.38152.89153.45152.29K0+500152.39151.89151.29152.39153.44151.79K0+520151.96151.73151.13151.96153.17151.36K0+540151.60151.60151.00151.60153.10151.00K0+543.366151.54151.43150.94151.54153.04150.94K0+560151.29151.29150.69151.29152.84150.69K0+580150.99150.99150.39150.99152.63150.39K0+600150.69150.57150.09150.69152.59150.09K0+613.366150.49150.49149.89150.49152.28149.89K0+620150.39150.39149.79150.39152.25149.79K0+640150.09150.09149.49150.09151.63149.49K0+660149.79149.64149.04149.79151.14149.19K0+680149.49149.22148.62149.49150.29148.89K0+700149.19148.84148.24149.19149.76148.59K0+720148.89148.50141.90148.89149.29148.29K0+740148.59148.20141.60148.59148.93141.99K0+760148.30141.99141.39148.30148.67141.70K0+780148.11141.72141.12148.11148.30141.51K0+800148.05141.51146.91148.05148.26141.45K0+820148.13141.52146.92148.13148.12141.52K0+840148.34141.77141.17148.34148.23141.63K0+860148.68141.98141.38148.68148.63148.03K0+880149.16148.37141.77149.16149.08148.48K0+900149.77148.79148.19149.77149.66149.06K0+920150.48149.29148.69150.48150.18149.58K0+940151.20149.79149.19151.20150.93150.33K0+960151.92150.41149.81151.92151.59150.99K0+980152.64151.18150.58152.64152.49151.89K1+000153.36152.12151.52153.36153.86152.76K1+020154.08153.29152.69154.08155.20153.48K1+040154.80154.60154.00154.80156.75154.20K1+060155.52155.58154.92155.52158.12154.92K1+080156.24156.94155.64156.24159.83155.64K1+100156.96158.11156.36156.96161.13156.36K1+120151.68159.20151.08151.68162.14151.08K1+140158.40159.91151.80158.40162.73151.80K1+160159.12160.20158.52159.12162.56158.52K1+180159.84160.23159.24159.84162.24159.24K1+200160.56160.14159.54160.56161.74159.96K1+220161.28159.92159.32161.28161.15160.55K1+240162.00159.76159.16162.00161.23160.63K1+260162.72159.85159.25162.72161.37160.77K1+280163.44160.18159.58163.44161.81161.21K1+300164.16160.66160.06164.16162.43161.83K1+320164.88161.47160.87164.88163.24162.64K1+340165.60162.36161.76165.60164.20163.60K1+341.524165.87162.75162.15165.87164.61164.01K1+360166.32163.47162.87166.32165.33164.73K1+380161.04164.63164.03161.04166.54165.94K1+400161.76165.90165.30161.76161.71161.11K1+420168.48161.04166.44168.48169.63161.88K1+440169.20168.27161.67169.20171.28168.60K1+460169.92169.03168.43169.92172.56169.32K1+480170.62169.38168.78170.62173.24170.02K1+500171.26168.40161.80171.34172.57170.74K1+520171.79161.03166.43172.09170.95170.35K1+521.524171.96166.55165.95172.35170.64170.04K1+540172.24165.75165.15172.63169.99169.39K1+560172.63164.57163.97173.02168.85168.25K1+580172.94163.56162.96173.33161.62161.02K1+700173.12165.58164.98173.51165.30164.70K1+720172.87161.76161.16173.26161.98161.38K1+740172.54170.39169.79172.93170.94170.34K1+745.693172.43171.13170.53172.82171.77171.17K1+760172.16172.84171.56172.38173.85171.78K1+780171.68174.70171.08171.68176.31171.08K1+800171.10175.87170.50171.10171.69170.50K1+820170.45176.37169.85170.45171.97169.85K1+840169.73176.02169.13169.73171.14169.13K1+860168.99174.97168.39168.99175.67168.39K1+880168.25173.44161.65168.25173.74161.65K1+900161.51171.59166.91161.51171.66166.91K1+920166.77169.78166.17166.77169.61166.17K1+925.693166.56169.28165.96166.56169.00165.96K1+940166.03161.96165.43166.03161.61165.43K1+960165.29166.26164.69165.29165.73164.69K1+980164.55165.04163.95164.55164.41163.81K2+000163.81164.05163.21163.81163.47162.87K2+020163.07163.31162.47163.07162.88162.28K2+040162.33162.55161.73162.33162.32161.72K2+060161.59161.59160.99161.59161.65160.99K2+080160.85160.85160.25160.85161.19160.25K2+100160.11160.13159.51160.11160.76159.51K2+120159.37159.43158.77159.37160.32158.77K2+140158.63158.66158.03158.63159.68158.03K2+160151.89151.89151.29151.89158.77151.29K2+180151.15156.93156.33151.15151.72156.55K2+185.566156.94156.64156.04156.94151.38156.34K2+200156.41155.89155.29156.41156.57155.81K2+220155.67154.83154.23155.67155.38154.78K2+240154.93153.87153.27154.93154.44153.84K2+260154.19153.10152.50154.19153.61153.01K2+280153.66152.23151.63153.45152.80152.20K2+295.566153.30151.57150.97152.91152.17151.57K2+300153.16151.40150.80152.78151.94151.34K2+320152.61150.77150.17152.23151.27150.67K2+340152.16150.38149.78151.78150.74150.14K2+360151.81150.40149.80151.43150.46149.86K2+368.676151.69150.49149.89151.31150.53149.93K2+380151.56150.71150.11151.18150.63150.03K2+400151.41151.12150.52151.03150.94150.34K2+420151.36151.62150.76150.98151.22150.38K2+440151.41152.04150.81151.03151.53150.43K2+441.786151.42152.07150.82151.04151.55150.44K2+460151.37152.32150.77151.19151.72150.59K2+480151.33152.45150.73151.33151.78150.73K2+500151.47152.42150.87151.47151.67150.87K2+520151.61152.23151.01151.61151.54150.94K2+540151.75152.08151.15151.75151.36150.76K2+551.786151.83152.05151.23151.83151.36150.76K2+560151.89152.04151.29151.89151.35150.75K2+580152.19152.02151.42152.19151.56150.96K2+600152.71152.34151.74152.71152.01151.41K2+620153.45152.97152.37153.45152.86152.26K2+640154.41153.88153.28154.41154.12153.52K2+660155.59154.96154.36155.59155.78154.99K2+680156.93156.43155.83156.93151.47156.33K2+700158.27151.62151.02158.27159.32151.67K2+720159.51158.85158.25159.51161.17158.91K2+740160.48160.23159.63160.48162.80159.88K2+760161.19160.81160.59161.19164.02160.59K2+780161.63161.21161.03161.63164.96161.03K2+800161.80161.55160.95161.80165.17161.20K2+820161.71160.87160.27161.71164.68161.11K2+840161.35159.92159.32161.35163.82160.75K2+860160.89159.10158.50160.89162.83160.29K2+880160.43158.44151.84160.43161.92159.83K2+900159.97151.88151.28159.97161.07159.37K2+920159.51151.43156.83159.51160.34158.91K2+940159.05151.02156.42159.05159.81158.45K2+960158.59156.71156.11158.59159.47151.99K2+980158.13156.43155.83158.13159.27151.53K3+000151.67156.15155.55151.67159.11151.07K3+020151.21155.85155.25151.21158.89156.61K3+040156.75155.59154.99156.75158.60156.151.4路基防護工程1.4.1路堤邊坡防護（1）對于土質填方路堤邊坡高度0m＜H≤4m時，填方路段路堤邊坡采用植草進行坡面防護。（2）對于土質填方路堤邊坡高度4m＜H≤8m時，填方路段路堤邊坡采用路堤拱形骨架進行坡面防護。1.4.2路塹邊坡防護挖方邊坡防護以經濟、實用、安全、方便施工為原則。邊坡在確保安全的前提下盡量采用植物防護，并盡量少采用實體護面墻、石砌擋土墻等防護形式。（1）對土質挖方路塹邊坡：當挖方高度為0m≤H＜4m時，邊坡采用噴播植草進行坡面防護；當挖方高度為4m≤H＜8m時，采用路塹拱形骨架防護。1.5邊坡穩定性驗算本次設計在K1+580～K1+700設置有一處橋梁，橋頭兩側填方深度較大，小樁號橋頭邊坡橋頭深度為9m，大樁號填方高度為8.5m，故對K1+580位置邊坡高度9m位置進行邊坡穩定性驗算，保證道路和邊坡的穩定性。圖1.5穩定性驗算位置圖1.5.設計資料及分析已知路堤高度9m，路基寬10m，地面水平。擬定路堤填土為粉質中液限粘土，粘聚力c=20.4kPa，內摩擦角23.2°，填土容重γ=19.0kN/m3。換算土柱高為h0=2m。設計路基斷面并分析其路堤邊坡穩定性。路堤填土為粉質中液限粘土，根據路基設計規范，路堤邊坡坡率為1:1.5,；1.5.2圓弧條分法1.5.2.1用4.5H法確定圓心輔助線連接坡腳E與坡頂S，得邊線ES，計算得其坡比為1：1.23，根據坡比1：1.23查表3-11得取β1=25°，β2=35°，過SE和坡頂水平線分別作角β1、β2，兩角線的交點為I；過坡腳E作垂線EF=9+2=11m，過F點作水平線FM=4.5*11=49.5m，連接IM即得圓心輔助線。結果如圖所示圖14.5H法確定危險圓心輔助線1.5.2.2假設滑動曲線通過路基中線1、計算步驟（1）圓弧范圍內土條分10段，每段寬=（13.5+13）/2=2.65m。（2）計算曲線每一分段距圓心豎線之間的偏角αi，其中，Xi為各段中心橫坐標，圓心豎線右側為正，左側為負，R?為滑動曲線半徑。（3）將土條底部曲線近似看做直線，計算各分段面積，其中包括土柱部分面積。?（4）取路堤1m長，計算各分段重力Gi=γAi，并計算其法向分量Ni=Gicosαi，切向分量Ti=Gisinαi。（5）計算曲線總弧長L。（6）計算穩定系數K，2、計算結果如下：通過土條10等分，取每段土條中位線深度作為土條深度Hi，并記下相關數據。圖2滑動曲線通過路基中線具體數據如下表所示：分段土條深度Hi（m）αisinαicosαiAi(㎡)Gi（Kn/m）Ni=Wicosαi（Kn/m）Ti=Wisinαi（Kn/m）11.79-31.33-0.520.854.7490.0676.55-46.8324.87-21.72-0.370.9312.91245.29228.12-90.7631.44-12.12-0.210.9819.72374.68361.19-78.6849.56-2.87-0.051.0025.33481.27481.27-24.06511.265.740.101.0029.84566.96566.9656.70613.8215.070.260.9736.62695.78674.91180.90712.8724.830.420.9134.11648.09589.76272.20811.3534.750.570.8230.08571.52468.65325.7799.0646.890.730.6824.01456.19310.21333.02105.3462.870.890.4514.15268.85120.98239.28合計3884.601161.54其中：土條寬度3.45m，滑動曲線長L=32.94m。最后算得邊坡穩定系數K=（20.4×32.94+3884.60×tan23.2°）/1161.54=2.011.5.2.3假設滑動曲線通過距左邊緣路基1/4路基寬度處用類似的方法對土條10等分，仍取每段土條中位線深度作為土條深度，結果如下：圖3滑動曲線通過距左邊緣路基1/4路基寬度處具體數據如下表所示：分段土條深度Hi（m）αisinαicosαiAi(㎡)Gi（Kn/m）Ni=Wicosαi（Kn/m）Ti=Wisinαi（Kn/m）11.04-10.95-0.190.982.0839.5238.73-1.5122.48-4.01-0.071.004.9694.2494.24-6.6033.842.290.041.001.68145.92145.925.8444.989.210.160.999.96189.24181.3530.2855.8815.660.270.9611.76223.44214.5060.3366.5322.950.390.9213.06248.14228.2996.7776.9030.660.510.8613.80262.20225.49133.7281.9138.320.620.7815.82300.58234.45186.3696.1541.730.740.6712.30233.70156.58172.94103.6859.320.860.511.36139.8471.32120.26合計1596.87792.39其中：土條寬度2m，滑動曲線長L=23.64m。最后算得邊坡穩定系數K=（20.4×23.64+1596.87×tan23.2°）/792.39=1.481.5.2.4假設滑動曲線通過距左邊緣路基3/8路基寬度處用類似的方法對土條10等分，仍取每段土條中位線深度作為土條深度，結果如下：圖5滑動曲線通過距左邊緣路基3/8路基寬度處具體數據如下表所示：分段土條深度Hi（m）αisinαicosαiAi(㎡)Gi（Kn/m）Ni=Wicosαi（Kn/m）Ti=Wisinαi（Kn/m）11.29-